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LTC3546 Dual Synchronous, 3A/1A or 2A/2A Configurable Step-Down DC/DC Regulator FEATURES
n n n n n n n n n n n n n n n
DESCRIPTION
The LTC(R)3546 is a dual, constant-frequency, synchronous step down DC/DC converter for medium power applications. The design consists of 2A and 1A primary output switches. In addition to the 2A/1A capability, a 1A dependant output switch can be externally connected to either of the primary outputs to produce 3A/1A dual regulator or 2A/2A dual regulator configurations. Supply operation is from 2.25V to 5.5V. The switching frequency can be set to 2.25MHz, adjustable 0.75MHz to 4MHz, or synchronized to an external clock. Each output is adjustable from 0.6V to 5V and has output tracking on power-up. Internal synchronous low RDS(ON) power switches provide high efficiency without external Schottky diodes. User-selectable modes (Burst Mode(R) operation, pulse skipping and forced continuous) allow trade-off between ripple noise and power efficiency. Burst Mode operation provides high efficiency at light loads. Pulse-skipping mode provides low ripple noise at light loads. The device is capable of low dropout configurations and both channels can operate at 100% duty cycle. In shutdown, the device draws <1A.
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents, including 5481178, 6611131, 6304066, 6498466, 6580258.
VIN Range: 2.25V to 5.5V VOUT Range: 0.6V to 5V Programmable Frequency Operation; 2.25MHz, or Adjustable Between 0.75MHz to 4MHz Low RDS(ON) Internal Switches High Efficiency: Up to 96% No Schottky Diodes Required Short-Circuit Protected Current Mode Operation for Excellent Line and Load Transient Response Low Ripple Burst Mode Operation (30mVP-P), IQ = 160A Ultralow Shutdown Current: IQ < 1A Low Dropout Operation: 100% Duty Cycle Power Good Output For Each Channel Externally or Internally Programmable Burst Level External or Internal Soft-Start or Supply Tracking Available in Thermally Enhanced 28-Lead (4mm x 5mm) QFN and TSSOP Packages
APPLICATIONS
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Netbooks/Ultra-Mobile PCs PC Cards Wireless and DSL Modems Point of Load DC/DC Conversion
TYPICAL APPLICATION
VIN 2.25V TO 5.5V CIN 22F 0.56H 100pF VIN 95.3k 30.1k VIN VIN1 VCCA VCCD VIN2 SYNC/MODE VOUT2 2.5V, 3A PGOOD2 SW2A SW2B SW1D RUN2 VFB2 BMC2 TRACK/SS2 PHASE ITH2 10pF 13k 1000pF EXPOSED PAD PGND2 GNDA LTC3546 RUN1 VFB1 BMC1 TRACK/SS1 FREQ ITH1 PGND1 13k 1000pF
3546 TA01a
VOUT2 Efficiency (Burst Mode Operation)
100 1.22H 100pF VIN 30.1k 30.1k EFFICIENCY (%) VOUT1 1.2V, 1A SW1D CONNECTED TO SW2 VIN = 3.6V 95 VOUT = 2.5V 90 85 80 POWER LOSS 75 10pF 70 0.001 0.001 0.0001 EFFICIENCY 100 10 POWER LOSS (W) 1 0.1 0.01
PGOOD1 SW1
68F
22F
VIN
0.01 0.1 1 LOAD CURRENT (A)
10
3546 TA01b
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LTC3546 ABSOLUTE MAXIMUM RATINGS
(Note 1)
VIN1, VIN1D, VIN2, VCCA, VCCD Voltages ......... -0.3V to 6V SYNC/MODE, SW1, SW1D, SW2A, SW2B, RUN1, RUN2, VFB1, VFB2, PHASE, FREQ, ITH1, ITH2, TRACK/SS1, TRACK/SS2, BMC1, BMC2 Voltages ................ -0.3V to (VIN1 or VIN2) + 0.3V
Maximum Difference Between Any of VIN1, VIN1D, VIN2, VCCA, VCCD ..................................0.3V PGOOD1, PGOOD2 Voltage .......................... -0.3V to 6V Operating Junction Temperature Range (Notes 2, 6, 7) ........................................ -40C to 125C Storage Temperature Range................... -65C to 125C
PIN CONFIGURATION
TOP VIEW SYNC/MODE PGOOD2 PGOOD1 VCCA SYNC/MODE PGOOD2 BMC2 22 BMC1 21 TRACK/SS1 20 VFB1 29 19 ITH1 18 PHASE 17 RUN1 16 PGND2 15 PGND1 9 10 11 12 13 14 PGND1D SW1D SW2A SW2B VIN1D SW1 TRACK/SS2 VFB2 ITH2 VCCD RUN2 1 2 3 4 5 6 7 8 9 29 TOP VIEW 28 GNDA 27 FREQ 26 PGOOD1 25 BMC1 24 TRACK/SS1 23 VFB1 22 ITH1 21 PHASE 20 RUN1 19 PGND2 18 PGND1 17 PGND1D 16 SW1 15 SW1D
GNDA
28 27 26 25 24 23 BMC2 1 TRACK/SS2 2 VFB2 3 ITH2 4 VCCD 5 RUN2 6 VIN2 7 VIN1 8
FREQ
VCCA
VIN2 10 VIN1 11 VIN1D 12 SW2A 13 SW2B 14
UFD PACKAGE 28-LEAD (4mm 5mm) PLASTIC QFN
FE PACKAGE 28-LEAD PLASTIC TSSOP
TJMAX = 125C, JA = 34C/W EXPOSED PAD (PIN 29) IS GNDD
TJMAX = 125C, JA = 25C/W EXPOSED PAD (PIN 29) IS GNDD MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH LTC3546EUFD#PBF LTC3546IUFD#PBF LTC3546EFE#PBF LTC3546IFE#PBF LEAD BASED FINISH LTC3546EUFD LTC3546IUFD LTC3546EFE LTC3546IFE TAPE AND REEL LTC3546EUFD#TRPBF LTC3546IUFD#TRPBF LTC3546EFE#TRPBF LTC3546IFE#TRPBF TAPE AND REEL LTC3546EUFD#TR LTC3546IUFD#TR LTC3546EFE#TR LTC3546IFE#TR PART MARKING* 3546 3546 LTC3546FE LTC3546FE PART MARKING* 3546 3546 LTC3546FE LTC3546FE PACKAGE DESCRIPTION 28-Lead (4mm x 5mm) Plastic QFN 28-Lead (4mm x 5mm) Plastic QFN 28-Lead Plastic TSSOP 28-Lead Plastic TSSOP PACKAGE DESCRIPTION 28-Lead (4mm x 5mm) Plastic QFN 28-Lead (4mm x 5mm) Plastic QFN 28-Lead Plastic TSSOP 28-Lead Plastic TSSOP TEMPERATURE RANGE -40C to 85C -40C to 125C -40C to 85C -40C to 125C TEMPERATURE RANGE -40C to 85C -40C to 125C -40C to 85C -40C to 125C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
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LTC3546 ELECTRICAL CHARACTERISTICS
SYMBOL VIN1, VIN1D, VIN2, VCCA, VCCD IFB1, IFB2 VFB1, VFB2 VLINEREG PARAMETER Operating Voltage Range
The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25C. VIN = VCCA = 3.6V, unless otherwise specified. (Note 2)
CONDITIONS VIN1 = VIN1D = VIN2 = VCCA = VCCD MIN 2.25 TYP MAX 5.5 UNITS V
Feedback Pin Input Current Feedback Voltage Reference Voltage Line Regulation %/V is The Percentage Change in VOUT with a Change in VIN Output Voltage Load Regulation Error Amplifier Transconductance Tracking Voltage Offset Tracking Current Source Input DC Supply Current (Note 4) Active Mode Half Active Mode (VRUN1 = VIN, VRUN2 = 0) Half Active Mode (VRUN1 = 0, VRUN2 = VIN) Both Channels in Sleep Mode Shutdown
(Note 3) (Note 3) VIN = 2.25V to 5.5V (Note 3)
l
0.1 0.588 0.6 0.04 0.612 0.2
A V %/V
VLOADREG gm(EA) VTRACK/SS1, VTRACK/SS2 ITRACK/SS1, ITRACK/SS2 IS
ITH1, ITH2 = 0.36V (Note 3) ITH1, ITH2 = 0.84V (Note 3) (Note 3) VTRACK/SS1,2 = 0.3V VTRACK/SS1,2 = 0V
l l
0.02 -0.02 1400
0.2 -0.2 15
% % S mV A
0.8
1.15
1.5
VFB1 = VFB2 = 0.55V, VMODE = VIN, VRUN1 = VRUN2 = VIN VFB1 = 0.55V, VMODE = VIN, VRUN1 = VIN, VRUN2 = 0V VFB2 = 0.55V, VMODE = VIN, VRUN1 = 0V, VRUN2 = VIN VFB1 = VFB2 = 0.75V, VMODE = VIN, VRUN1 = VRUN2 = VIN VRUN1 = VRUN2 = 0V VFREQ: RT = VIN VFREQ: RT = 143k VFREQ: Resistor (Note 5) BMC1 = VIN, VITH1 = 1.4V BMC1 = 0.4V, VITH1 = 0V
l
600 400 400 160 0.2 1.8 1.2 0.75 1.4 2.8 2.25 1.5 1.6 0.45 3.2 0.9 3.2 1.6 4.8 2.4 0.19 0.18 0.19 0.17 0.096 0.085 0.01
990 800 800 300 1 2.9 1.8 4
A A A A A MHz MHz MHz A A A A A A A A
fOSC
Oscillator Frequency
ILIM1 ILIM2 ILIM1+1D
Peak Switch Current Limit on SW1 (1A)
Peak Switch Current Limit on SW2A/B (2A) BMC2 = VIN, VITH1 = 1.4V BMC2 = 0.4V, VITH1 = 0V Peak Switch Current Limit on SW1 + SW1D (2A) Peak Switch Current Limit on SW2A/B + SW1D (3A) SW1 Top Switch On-Resistance (1A) SW1 Bottom Switch On-Resistance SW1D Top Switch On-Resistance (1A) SW1D Bottom Switch On-Resistance SW2A/B Top Switch On-Resistance (2A) SW2A/B Bottom Switch On-Resistance Switch Leakage Current SW1 SW1 Externally Connected to SW1D BMC1 = VIN (Note 8) BMC1 = 0.4V (Note 8) SW2A/B Externally Connected to SW1D BMC2 = VIN (Note 8) BMC2 = 0.4V (Note 8) VIN2 = 3.6V VIN2 = 3.6V VIN2 = 3.6V VIN2 = 3.6V VIN1 = 3.6V VIN1 = 3.6V VIN = 6V VITH1 = 0V VRUN1 = 0V
2.5
ILIM2+1D
3.75
RDS(ON)1 RDS(ON)1D RDS(ON)2 ISW1(LKG)
1
A
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LTC3546 ELECTRICAL CHARACTERISTICS
SYMBOL ISW1D(LKG) PARAMETER Switch Leakage Current SW1D
The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25C. VIN = VCCA = 3.6V, unless otherwise specified. (Note 2)
CONDITIONS VIN = 6V VITH1 = VITH2 = 0V VRUN1 = VRUN2 = 0V VIN = 6V VITH2 = 0V VRUN2 = 0V VIN1, VIN2, VCCA, VCCD Rising VIN1, VIN2, VCCA, VCCD Falling VFB1 Ramping Up, VSYNC/MODE = 0V 2.03 1.86 MIN TYP 0.01 MAX 1 UNITS A
ISW2A/B(LKG)
Switch Leakage Current SW2A/B
0.01
1
A
VUVLO TPGOOD1
Undervoltage Lockout Threshold Threshold for Power Good Percentage Deviation from Regulated VFB1 (Typically 0.6V). Threshold for Power Good Percentage Deviation from Regulated VFB2 (Typically 0.6V). Power Good Pull-Down On-Resistance Power Good Pull-Down On-Resistance Soft-Start Internal Time.
2.14 1.97 -8
2.2 2.03
V V %
TPGOOD2
VFB2 Ramping Up, VSYNC/MODE = 0V
-8
%
RPGOOD1 RPGOOD2 tSS
132 132 VFB from 0% to 95%, VTRACK/SS Is Floating 0.8 0.3 1.2 0.8 0.01
300 300 1.9 1.2 1 0.5
ms V A V V
VRUN1, VRUN2, RUN1, RUN2, and PHASE Threshold VPHASE IRUN1, IRUN2, IPHASE RUN1, RUN2, and PHASE Leakage Current VIN = 6V, VPHASE = 3V, VRUN1 = VRUN2 = 3V
VTLSYNC/MODE SYNC/MODE Threshold Voltage Low to Put the Part into Pulse-Skipping Mode VTHSYNC/MODE SYNC/MODE Threshold Voltage High to Put the Part into Burst Mode Operation VSYNC/MODE ISYNC/MODE VTHFREQ IBMC1, IBMC2 SYNC/MODE Threshold for Clock Synchronization SYNC/MODE Leakage Current FREQ Threshold Voltage High BMC1, BMC2 Leakage Current VIN = 6V, VBMC = 3V VIN = 6V, VSYNC/MODE = 3V VIN - 0.85 VIN - 0.5 0.3 0.8 0.01
1.2 1 0.4
V A V A
Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LTC3546E is guaranteed to meet performance specifications from 0C to 85C. Specifications over the -40C to 125C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The LTC3546I is guaranteed to meet performance specifications over the full -40C to 125C operating junction temperature range Note 3: The LTC3546 is tested in feedback loop which servos VFB1 to the midpoint for the error amplifier (VITH1 = 0.6V) and VFB2 to the midpoint for the error amplifier (VITH2 = 0.6V). Note 4: Total supply current is higher due to the internal gate charge being delivered at the switching frequency.
Note 5: Variable frequency operation with resistor is guaranteed by design and is subject to duty cycle limitations. Note 6: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 125C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature may impair device reliability. Note 7: TJ is calculated from the ambient temperature, TA, and power dissipation, PD, according to the following formula: TJ = TA + (PD * 34C/W) Note 8: Minimum current limit is guaranteed by design and correlation to the RDS(ON)1D, ILIM1 and ILIM2 measurements.
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LTC3546 TYPICAL PERFORMANCE CHARACTERISTICS
OUT1 Burst Mode Operation OUT1 Pulse-Skipping Mode Operation OUT1 Forced Continuous Mode Operation
VOUT 20mV/DIV
VOUT 20mV/DIV
VOUT 20mV/DIV
ILOAD 500mA/DIV
ILOAD 250mA/DIV 2s/DIV SW1D CONNECTED TO SW1 VIN = 3.6V VOUT = 1.8V ILOAD = 300mA
3546 G02
ILOAD 250mA/DIV 1s/DIV SW1D CONNECTED TO SW1 VIN = 3.6V VOUT = 1.2V ILOAD = 100mA
3546 G03
1s/DIV SW1D CONNECTED TO SW1 VIN = 3.6V VOUT = 1.2V ILOAD = 100mA
3546 G04
OUT1 Burst Mode Operation
OUT1 Pulse-Skipping Mode Operation
OUT1 Forced Continuous Mode Operation
VOUT 20mV/DIV
VOUT 20mV/DIV
VOUT 20mV/DIV
ILOAD 200mA/DIV
ILOAD 250mA/DIV 1s/DIV SW1D CONNECTED TO SW2 VIN = 3.6V VOUT = 1.8V ILOAD = 200mA
3546 G05
ILOAD 250mA/DIV 1s/DIV SW1D CONNECTED TO SW2 VIN = 3.6V VOUT = 1.2V ILOAD = 100mA
3546 G06
1s/DIV SW1D CONNECTED TO SW2 VIN = 3.6V VOUT = 1.2V ILOAD = 50mA
3546 G07
OUT2 Burst Mode Operation
OUT2 Pulse-Skipping Mode Operation
OUT2 Forced Continuous Mode Operation
VOUT 20mV/DIV
VOUT 20mV/DIV
VOUT 20mV/DIV
ILOAD 500mA/DIV
ILOAD 500mA/DIV 1s/DIV SW1D CONNECTED TO SW2 VIN = 3.6V VOUT = 2.5V ILOAD = 500mA
3546 G08
ILOAD 500mA/DIV 1s/DIV SW1D CONNECTED TO SW2 VIN = 3.6V VOUT = 1.8V ILOAD = 200mA
3546 G09
1s/DIV SW1D CONNECTED TO SW2 VIN = 3.6V VOUT = 1.8V ILOAD = 100mA
3546 G10
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LTC3546 TYPICAL PERFORMANCE CHARACTERISTICS
OUT2 Burst Mode Operation OUT2 Pulse-Skipping Mode Operation OUT2 Forced Continuous Mode Operation
VOUT 20mV/DIV
VOUT 20mV/DIV
VOUT 20mV/DIV
ILOAD 500mA/DIV
ILOAD 250mA/DIV
ILOAD 250mA/DIV 1s/DIV SW1D CONNECTED TO SW1 VIN = 3.6V VOUT = 1.8V ILOAD = 200mA
3546 G12
1s/DIV SW1D CONNECTED TO SW1 VIN = 3.6V VOUT = 2.5V ILOAD = 300mA
3546 G11
1s/DIV SW1D CONNECTED TO SW1 VIN = 3.6V VOUT = 1.8V ILOAD = 100mA
3546 G13
OUT1 Efficiency vs Load Current
95 SW1D CONNECTED TO SW1 VIN = 3.6V 90 V OUT = 1.8V 85 EFFICIENCY (%) EFFICIENCY (%) 80 75 70 65 60 0.001 Burst Mode OPERATION PULSE SKIP FORCED CONTINUOUS 0.01 0.1 ILOAD (A) 1 10
3546 G14
OUT1 Efficiency vs Load Current
95 SW1D CONNECTED TO SW2 VIN = 3.6V 90 V OUT = 1.8V 85 EFFICIENCY (%) 80 75 70 65 60 0.001 Burst Mode OPERATION PULSE SKIP FORCED CONTINUOUS 0.01 ILOAD (A)
3546 G15
OUT2 Efficiency vs Load Current
100 SW1D CONNECTED TO SW2 95 VIN = 3.6V VOUT = 2.5V 90 85 80 75 70 65 1 60 0.001 0.01 0.1 ILOAD (A) Burst Mode OPERATION PULSE SKIP FORCED CONTINUOUS 1 10
3546 G16
0.1
OUT2 Efficiency vs Load Current
100 SW1D CONNECTED TO SW1 95 VIN = 3.6V VOUT = 2.5V 90 EFFICIENCY (%) EFFICIENCY (%) 85 80 75 70 65 60 0.001 0.01 0.1 ILOAD (A) Burst Mode OPERATION PULSE SKIP FORCED CONTINUOUS 1 10
3546 G17
OUT1 Efficiency vs VIN
100 SW1D CONNECTED TO SW1 98 VOUT = 1.8V 96 EFFICIENCY (%) 94 92 90 88 86 84 82 80 2.25 2.75 3.25 3.75 4.25 VIN (V) 4.75 5.25
3546 G18
OUT1 Efficiency vs VIN
100 SW1D CONNECTED TO SW2 98 VOUT = 1.8V 96 94 92 90 88 86 84 82 80 2.25 2.75 3.25 3.75 4.25 VIN (V) 4.75 5.25
3546 G19
400mA
200mA
2A
1A
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LTC3546 TYPICAL PERFORMANCE CHARACTERISTICS
OUT2 Efficiency vs VIN
100 98 96 EFFICIENCY (%) 600mA EFFICIENCY (%) 94 92 90 88 86 84 82 SW1D CONNECTED TO SW2 VOUT = 2.5V 80 2.25 2.75 3.25 3.75 4.25 VIN (V) 3A 100 98 96 94 92 90 88 86 84 82 SW1D CONNECTED TO SW1 VOUT = 2.5V 80 2.25 2.75 3.25 3.75 4.25 VIN (V) 100s/DIV SW1D CONNECTED TO SW1 VIN = 3.6V VOUT = 1.2V ILOAD = 200mA TO 1.9A 2A
3546 G22
OUT2 Efficiency vs VIN
OUT1 Load Step
VOUT 100mV/DIV 400mA ILOAD 1A/DIV
4.75
5.25
3546 G20
4.75
5.25
3546 G21
OUT1 Load Step
VOUT 100mV/DIV
OUT2 Load Step
OUT2 Load Step
VOUT 100mV/DIV ILOAD 1A/DIV
VOUT 100mV/DIV
ILOAD 250mA/DIV
ILOAD 1A/DIV
100s/DIV SW1D CONNECTED TO SW2 VIN = 3.6V VOUT = 1.2V ILOAD = 100mA TO 0.9A
3546 G23
100s/DIV SW1D CONNECTED TO SW2 VIN = 3.6V VOUT = 1.8V ILOAD = 300mA TO 2.9A
3546 G24
100s/DIV SW1D CONNECTED TO SW1 VIN = 3.6V VOUT = 1.8V ILOAD = 200mA TO 1.9A
3546 G25
OUT1 Efficiency vs Frequency
95 94 93 EFFICIENCY (%) EFFICIENCY (%) 92 91 90 89 88 SW1D CONNECTED TO SW1 87 V = 3.6V IN 86 VOUT = 1.8V ILOAD = 400mA 85 0.5 1.0 1.5 2.0 2.5 3.0 FREQUENCY (MHz) 95 94 93
OUT1 Efficiency vs Frequency
95 94 93 EFFICIENCY (%) 92 91 90 89 88
OUT2 Efficiency vs Frequency
92 91 90 89 88 SW1D CONNECTED TO SW2 87 V = 3.6V IN 86 VOUT = 1.8V ILOAD = 200mA 85 0.5 1.0 1.5 2.0 2.5 3.0 FREQUENCY (MHz)
3.5
4.0
3.5
4.0
SW1D CONNECTED TO SW2 87 V = 3.6V IN 86 VOUT = 2.5V ILOAD = 600mA 85 0.5 1.0 1.5 2.0 2.5 3.0 FREQUENCY (MHz)
3.5
4.0
3546 G26
3546 G27
3546 G28
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LTC3546 TYPICAL PERFORMANCE CHARACTERISTICS
OUT2 Efficiency vs Frequency
95 94 93 EFFICIENCY (%) 92 91 90 89 88 SW1D CONNECTED TO SW1 87 V = 3.6V IN 86 VOUT = 2.5V ILOAD = 400mA 85 0.5 1.0 1.5 2.0 2.5 3.0 FREQUENCY (MHz) RDS(ON) () 0.120 0.115 0.110 0.105 0.100 0.095 0.090 0.085 0.080 0.075 SW1D CONNECTED TO SW1 TA = 27C 0.070 2.0 2.5 3.0 3.5 4.0 VIN (V) N-CHANNEL IMP RDS(ON) () P-CHANNEL IMP
OUT1 RDS(ON) vs VIN
0.24 0.23 0.22 0.21 0.20 0.19 0.18 0.17
OUT1 RDS(ON) vs VIN
P-CHANNEL IMP
N-CHANNEL IMP
3.5
4.0
4.5
5.0
5.5
0.16 SW1D CONNECTED TO SW2 TA = 27C 0.15 2.0 2.5 3.0 3.5 4.0 VIN (V)
4.5
5.0
5.5
3546 G29
3546 G30
3546 G31
OUT2 RDS(ON) vs VIN
0.080 0.075 0.070 RDS(ON) () RDS(ON) () 0.065 P-CHANNEL IMP 0.060 0.055 0.050 2.0 N-CHANNEL IMP SW1D CONNECTED TO SW2 TA = 27C 0.120 0.115
OUT2 RDS(ON) vs VIN
6 4 FREQUENCY VARIATION (%) 2 0 -2 -4 -6 -8 4.5 5.0 5.5
Frequency Variation vs VIN
FREQ 143k TO GND FREQ TO VIN
0.110 0.105 0.100 0.095 0.090 0.085 0.080 0.075 SW1D CONNECTED TO SW1 TA = 27C 0.070 2.0 2.5 3.0 3.5 4.0 VIN (V) N-CHANNEL IMP P-CHANNEL IMP
2.5
3.0
3.5 4.0 VIN (V)
4.5
5.0
5.5
-10 2.0
2.5
3.0
3546 G32
3546 G33
3.5 4.0 VIN (V)
4.5
5.0
5.5
3546 G34
Frequency Variation vs Temperature
2 1 FREQUENCY VARIATION (%) 0 PEAK CURRENT (A) -1 -2 -3 -4 -5 -6 -50 -25 0 55 50 75 TEMPERATURE (C) 100 125 FREQ 143k TO GND FREQ TO VIN 4.0 3.5 3.0
OUT1 Minimum Peak Current vs VBMC1
VIN = 3.6V 6 5
OUT2 Minimum Peak Current vs VBMC2
VIN = 3.6V
SW1D TO SW2 SW1D TO SW1 PEAK CURRENT (A) 4 3 2 1 0 0.25 0.35 0.45 0.55 0.65 0.75 0.85 0.95 VBMC1 (V)
3546 G37
2.5 2.0 1.5 1.0 0.5 0 0.25 0.35 0.45 0.55 0.65 0.75 0.85 0.95 VBMC1 (V)
3546 G36
SW1D TO SW1
SW1D TO SW2
3546 G35
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LTC3546 PIN FUNCTIONS
(UFD/FE)
BMC2 (Pin 1/Pin 4): Burst Mode Clamp for Channel 2. Connect-ing this pin to an external voltage between 0V and 0.6V sets the Burst Mode clamp level. If this pin is pulled to VCCA, an internal Burst Mode clamp level is used. TRACK/SS2 (Pin 2/Pin 5): Tracking input for Channel 2 output or optional external soft-start input. VOUT2 will track an external voltage at this pin. Leaving this pin floating allows VOUT2 to start-up using the internal soft-start. An external soft-start can be programmed by connecting a capacitor between this pin and ground. External soft-start ramp time must be greater than the internal soft-start time of 1.2ms. Refer to the Applications Information section for more details. VFB2 (Pin 3/Pin 6): Feedback voltage from external resistive divider from the Channel 2 regulator output. Nominal voltage for this pin is 0.6V. ITH2 (Pin 4/Pin 7): Error Amplifier Compensation for Channel 2 Regulator. Peak current increases with an increase in the voltage on this pin. Nominal voltage range for this pin is 0V to 1.5V. VCCD (Pin 5/Pin 8): Supply Pin for Internal Digital Circuitry. RUN2 (Pin 6/Pin 9): Low Level Logic Input. Enable for Channel 2. When pulled high, regulator is running. When at 0V, regulator is off. When both RUN1 and RUN2 are at 0V the part is in shutdown. VIN2 (Pin 7/Pin 10): Supply pin for 2A P-channel switch which connects from VIN2 to SW2A/B. VIN1 (Pin 8/Pin 11): Supply pin for 1A P-channel switch which connects from VIN1 to SW1. VIN1D (Pin 9/Pin 12): Supply pin for 1A dependent P-channel switch which connects from VIN1D to SW1D. SW2A (Pin 10/Pin 13): Half of the switch node connection to the inductor for Channel 2. SW2A and SW2B must be externally tied together. This pin swings from VIN2 to PGND2.
SW2B (Pin 11/Pin 14): Half of the switch node connection to the inductor for Channel 2 SW2A and SW2B must be externally tied together. This pin swings from VIN2 to PGND2. SW1D (Pin 12/Pin 15): The Dependent Switch Node Connection. The pin is externally connected to SW1 for a 2A/2A regulator or to SW2A/B for a 3A/1A regulator. Internal circuitry detects which pin SW1D is externally connected to, SW1 or SW2A/B. This pin swings from VIN1D to PGND1D. SW1D switching will be controlled by the output switch to which it is connected, i.e., SW1 or SW2A/SW2B. The dependant 1A power stage can be disabled by floating the SW1D pin. The SW1D pin must never be connected to VIN or GND. When disabled, SW1D is pulled high internally. SW1 (Pin 13/Pin 16): The switch node connection to the Inductor for the Channel 1 regulator. This pin swings from VIN1 to PGND1. PGND1D (Pin 14/Pin 17): Ground for SW1D Switching N-Channel Driver. PGND1 (Pin 15/Pin 18): Ground for SW1 Switching NChannel Driver. PGND2 (Pin 16/Pin 19): Ground for SW2A and SW2B Switching N-Channel Driver. RUN1 (Pin 17/Pin 20): Low Level Logic Input. Enable for Channel 1. When pulled high, regulator is running. When at 0V, regulator is off. When both RUN1 and RUN2 are at 0V the part is in shutdown. PHASE (Pin 18/Pin 21): Low Level Logic Input. Selects Channel 2 regulator switching phase with respect to Channel 1 regulator switching. When pulled high, the SW1 regulator and the SW2A/B regulator are in phase. When PHASE is at 0V the SW1 regulator and the SW2A/B regulator are switching 180 out-of-phase. ITH1 (Pin 19/Pin 22): Error Amplifier Compensation for Channel 1. Peak current increases with an increase in the voltage on this pin. Nominal voltage range for this pin is 0V to 1.5V.
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9
LTC3546 PIN FUNCTIONS
(UFD/FE)
VFB1 (Pin 20/Pin 23): Feedback voltage from external resistive divider from Channel 1 output. Nominal voltage for this pin is 0.6V. TRACK/SS1 (Pin 21/Pin 24): Tracking input for Channel 1 output or optional external soft-start input. VOUT1 will track an external voltage at this pin. Leaving this pin floating allows VOUT1 to start-up using the internal soft-start. An external soft-start can be programmed by connecting a capacitor between this pin and ground. External soft-start ramp time must be greater than the internal soft-start time of 1.2ms. Refer to the Applications Information section for more details. BMC1 (Pin 22/Pin 25): Burst Mode Clamp for Channel 1. Connecting this pin to an external voltage between 0V and 0.6V sets the Burst Mode clamp level. If this pin is pulled to VCCA, an internal Burst Mode clamp level is used. PGOOD1 (Pin 23/Pin 26): Power Good Pin for the 1A Regulator. This common drain logic output is pulled to GND when the output voltage of Channel 1 is below -8% of regulation. FREQ (Pin 24/Pin 27): Frequency Set Pin. When FREQ is at VCCA, the internal oscillator runs at 2.25MHz. When a resistor is connected from this pin to GNDA, the internal oscillator frequency can be varied from 0.75MHz to 4MHz. When using external synchronization this pin compensates
the internal PLL. Typical compensation components are a 200k resistor in series with a 100pF capacitor. GNDA (Pin 25/Pin 28): Ground Pin for Internal Analog Circuitry. VCCA (Pin 26/Pin 1): Supply Pin for Internal Analog Circuitry. SYNC/MODE (Pin 27/Pin 2): Combination Mode Selection and Oscillator Synchronization Pin. This pin controls the operation of the device. When the voltage on the SYNC/MODE pin is > (VIN - 0.5V), Burst Mode operation is selected for both regulators. When the voltage on the SYNC/MODE pin is <0.5V, pulse-skipping mode is selected for both regulators. When the SYNC/MODE pin is held at VIN/2, forced continuous mode is selected for both regulators. The oscillation frequency can be synchronized to an external oscillator applied to this pin. When synchronized to an external clock, pulse-skipping mode is selected. PGOOD2 (Pin 28/Pin 3): Power Good Pin for Channel 2 This common drain logic output is pulled to GND when the output voltage of Channel 2 is below -8% of regulation. Exposed Pad (Pin 29/Pin 29): Digital Ground. Connect to Electrical Ground for substrate and internal digital circuitry. Solder to PCB for rated thermal performance.
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10
LTC3546 FUNCTIONAL DIAGRAM
ITH1 BMC1 ITH LIMIT 1A REGULATOR VIN1
+
VFB1
+ -
SLOPE COMPENSATION ANTI-SHOOT THRU SW1
- -
VB 0.552V
+
+ - +
LOGIC
+ - -
0.63V RUN1 VCCA 1.15A TRACK/SS1
-
INTERNAL SOFT-START MUX
PGND1
+
PGOOD1
VOLTAGE REFERENCE PHASE SYNC/MODE OSCILLATOR FREQ
VCCA
VIN1D 1A DEPENDENT SWITCHES SW1D DEPENDENT SWITCH AUTO DETECT AND CONTROL MUX ANTI-SHOOT THRU PGND1D
GNDA
VCCD
GNDD
PGOOD2
VCCA 1.15A TRACK/SS2 INTERNAL SOFT-START MUX PGND2
+ -
RUN2
0.63V
-
LOGIC
- +
SW2A
+ -
ANTI-SHOOT THRU 0.552V VFB2
SW2B
+
VB
+ -
SLOPE COMPENSATION
- +
ITH LIMIT ITH2 BMC2
- +
2A REGULATOR VIN2
3546 BD
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11
LTC3546 OPERATION
The LTC3546 uses a constant-frequency, current mode architecture. Both channels share the same clock frequency. The PHASE pin sets whether the channels are running in-phase, or 180 out-of-phase. The operating frequency is determined by connecting the FREQ pin to VIN for 2.25MHz operation or by connecting a resistor from FREQ to GNDA for frequencies between 0.75MHz to 4MHz. A 143k resistor to GNDA will set the frequency to 1.5MHz. The part can also be synchronized to an external clock through the SYNC/MODE pin. To suit a variety of applications, the selectable SYNC/MODE pin allows the user to trade-off noise for efficiency. The output voltages are set by external dividers returned to the VFB1 and VFB2 pins. An error amplifier compares the divided output voltage with a reference voltage of 0.6V and adjusts an internal peak inductor current setting accordingly. Peak inductor current during Burst Mode operation can also be set externally through the BMC1 and BMC2 pins. Undervoltage comparators will pull the PGOOD1 or PGOOD2 outputs low when their respective outputs drop below -8% of the set output voltage. The TRACK/SS pins allow for controlled start-up via an externally or internally generated voltage ramp. It can also track an externally applied voltage. A 1A dependent switch, SW1D, can be externally connected to the SW1 output or the SW2A/SW2B output. Internal circuitry auto detects which output SW1D is connected to and controls them accordingly. With this flexibility, the LTC3546 can be configured as either a 2A/2A dual regulator (when SW1D is connected to SW1) or as a 3A/1A dual regulator (when SW1D is connected to SW2A/SW2B). Main Control Loop For each regulator, during normal operation, the P-channel MOSFET power switch is turned on at the beginning of a clock cycle when the VFB voltage is below the 0.6V reference voltage. The current into the inductor and the load increases until the current limit is reached. The switch turns off and energy stored in the inductor flows through the bottom N-channel MOSFET switch into the load until the next clock cycle. The peak inductor current is controlled by the voltage on the ITH pin, which is the output of the 2.5MHz bandwidth error amplifier. The error amplifier compares the VFB pin to the 0.6V reference. When the load current increases, the VFB voltage decreases slightly below the reference. This decrease causes the error amplifier to increase the ITH voltage until the average inductor current matches the new load current. The main control loop is shut down by pulling the RUN pin to ground. When the RUN pin is pulled high, the control loop goes through start-up. Start-up is dependent on the TRACK/SS pin. If TRACK/SS is left floating, an internal soft-start is enabled which will ramp up the output voltage to the desired level in 1.2ms. The output voltage will track the voltage on its associated TRACK/SS pin. If the TRACK/SS pin is connected through a resistor divider from another supply, such as the output voltage from the other LTC3546 regulator, the output voltage will track this supply thus allowing the LTC3546 output voltage to track the other supply start-up. If a capacitor is connected from the TRACK/SS pin to ground, when RUN goes high, an internal 1.15A current source will charge the external capacitor controlling the output voltage start-up. Care must be taken to make sure the external start-up ramp time is greater than the 1.2ms internal start-up time. Low Current Operation Three modes are available to control the operation of the LTC3546 at low currents. All three modes automatically switch from continuous operation to the selected mode when the load current is low. To optimize efficiency, Burst Mode operation can be selected. When the load is relatively light, the LTC3546 automatically switches into Burst Mode operation in which the switches operate intermittently based on load demand. By running cycles periodically, the switching losses which are dominated by the gate charge losses of the power MOSFETs are minimized. The main control loop is interrupted when the output voltage reaches the desired regulated value. A voltage comparator with hysteresis trips when ITH is below 0.24V, shutting off the switches and reducing the power.
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12
LTC3546 OPERATION
The output capacitor and the inductor supply the power to the load until ITH exceeds 0.31V, turning on the switch and the main control loop which starts another cycle. The Burst Mode peak inductor current can be set externally via the BMC pin. When this pin is set somewhere between 0V to 0.6V, the voltage on this pin controls the Burst Mode clamp level. When the BMC pin is pulled to VIN, an internal Burst Mode clamp level is used. For lower output voltage ripple at low currents, pulseskipping mode can be used. In this mode, the LTC3546 continues to switch at constant frequency down to very low currents, where it will eventually begin skipping pulses. Finally, in forced continuous mode, the inductor current is constantly cycled which creates a fixed output voltage ripple at all output current levels. This feature is desirable in telecommunications since the noise is a constant frequency and is thus easy to filter out. Another advantage of this mode is that the regulator is capable of both sourcing current into a load and sinking some current from the output. In forced continuous operation, an overvoltage comparator monitors the VFB pin and decreases the current limit whenever an overvoltage condition is detected (VFB > 0.63V). The SYNC/MODE pin selects what mode the LTC3546 is in. The SYNC/MODE pin sets the mode for both regulators. Dropout Operation When the input supply voltage decreases toward the output voltage, the duty cycle increases to 100% which is the dropout condition. In the dropout condition, the PMOS switch is turned on continuously with the output voltage being equal to the input voltage minus the voltage drops across the internal P-channel MOSFETs and inductors. Low Supply Operation The LTC3546 incorporates an undervoltage lockout circuit which shuts down the part when the input voltage drops below about 2.14V to prevent unstable operation.
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13
LTC3546 APPLICATIONS INFORMATION
A general LTC3546 application circuit is shown in Figure 7. External component selection is driven by the load requirement, and begins with the selection of the inductors L1, and L2. Once L1 and L2 are chosen, CIN, COUT1, and COUT2 can be selected. Operating Frequency Selection of the operating frequency is a trade-off between efficiency and component size. High frequency operation allows the use of smaller inductor and capacitor values. Operation at lower frequencies improves efficiency by reducing internal gate charge losses but requires larger inductance values and/or capacitance to maintain low output ripple voltage. The operating frequency, fO, of the LTC3546 is determined by pulling the FREQ pin to VIN, for 2.25MHz operation, by connecting an external resistor from FREQ to ground, or by driving an external clock signal into SYNC/MODE. When using an external resistor to set the oscillator frequency use the following equation: RT = 2.51*1011 () - 20k fO Assuming a worst-case minimum on-time of 150ns, this can be calculated as: fO(MAX) 6.67 VOUT VIN(MAX)
(MHz )
The minimum frequency is limited by leakage and noise coupling due to the large resistance of RT. Inductor Selection Although the inductor does not influence the operating frequency, the inductor value has a direct effect on ripple current. The inductor ripple current IL decreases with higher inductance and increases with higher VIN or VOUT. IL = V VOUT 1 OUT fO * L VIN
Accepting larger values of IL allows the use of low inductances, but results in higher output voltage ripple, greater core losses, and lower output current capability. A reasonable starting point for setting ripple current is IL = 0.35ILOAD(MAX), where ILOAD(MAX) is the maximum output current. The largest ripple IL occurs at the maximum input voltage. To guarantee that the ripple current stays below a specified maximum, the inductor value should be chosen according to the following equation: L VOUT VOUT 1 fO * IL VIN(MAX)
for 0.75MHz fO 4MHz. Or use Figure 1 to select the value for RT. The maximum operating frequency is also constrained by the minimum on-time (typically 70ns) and duty cycle, especially when forced continuous mode is selected.
500 450 400 350 RT (k) 300 250 200 150 100 50 0 0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 FREQUENCY (MHz) 3546 F01
Figure 1. Frequency vs RT
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14
LTC3546 APPLICATIONS INFORMATION
Burst Mode Operation Considerations There are two factors that determine the load current at which the LTC3546 enters Burst Mode operation: the inductor value and the BMC pin voltage. The transition from low current operation begins when the peak inductor current falls below a level set by the burst clamp. Lower inductor values result in higher ripple current which causes Burst Mode operation to occur at lower load currents. Lower inductor values will also cause a dip in efficiency in the upper range of low current operation. Lower inductor values will also cause the burst frequency to increase in Burst Mode operation. The burst clamp level can be set by the voltage on the BMC pin. If BMC is tied to VIN, an internally set level is used. A BMC pin voltage between 0V and 0.6V will set the burst clamp level (see charts OUT1 Minimum Peak Current vs VBMC1 and OUT2 Minimum Peak Current vs VBMC2 in the Typical Performance Characteristics section). Generally, a higher clamp level results in improved light load efficiency and higher output voltage ripple, while a lower clamp level results in small output voltage ripple at the expense of efficiency. The BMC pin should be connected to ground when Burst Mode operation is not selected.
Table 1.
MANUFACTURER Wurth Elektronik Wurth Elektronik Vishay Vishay Coilcraft Coilcraft Coiltronics Coiltronics Sumida PART NUMBER WE-PD2 MS 7447745012 WE-PD2 MS 74477450056 IHLP-1616AB-11 IHLP-1616AB-11 LPS6225-122 DO1813H-561 SD20-1R2 SD20-R47 CDRH3D23NP-1R5NC VALUE (H) 1.2 0.56 1.2 0.47 1.2 0.56 1.2 0.47 1 MAX DC CURRENT (A) 4.6 6.5 3.75 6 5.4 7.7 2.55 4 2.8 DCR 0.017 0.0078 0.068 0.019 0.04 0.01 0.0275 0.02 0.025 DIMENSIONS L x W x H (mm) 5.2 x 5.8 x 2 5.2 x 5.8 x 2 4.06 x 4.45 x 1.20 4.06 x 4.45 x 1.20 6.2 x 6.2 x 2.5 6.10 x 8.89 x 5.00 5.2 x 5.2 x 2 5.2 x 5.2 x 2 3.8 x 3.8 x 2.3
Inductor Core Selection Different core materials and shapes will change the size/current relationship of an inductor. Toroid or shielded pot cores in ferrite or permalloy materials are small and don't radiate much energy, but generally cost more than powdered iron core inductors with similar electrical characteristics. The choice of which style inductor to use often depends more on the price vs size requirements of any radiated field/EMI requirements than on what the LTC3546 requires to operate. Table 1 shows some typical surface mount inductors that work well in LTC3546 applications. Input Capacitor (CIN) Selection In continuous mode, the input current of the converter can be approximated by the sum of two square waves with duty cycles of approximately VOUT1/VIN and VOUT2/VIN. To prevent large voltage transients, a low equivalent series resistance (ESR) input capacitor sized for the maximum RMS current must be used. Some capacitors have a derating spec for maximum RMS current. If the capacitor being used has this requirement it is necessary to calculate
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15
LTC3546 APPLICATIONS INFORMATION
the maximum RMS current. The RMS current calculation is different if the part is used in-phase or out-of-phase. For in-phase, there are two different equations: VOUT1 > VOUT2: IRMS = 2 * I1* I2 * D2 (1- D1) + I22 D2 - D22 + I12 D1- D12 VOUT2 > VOUT1: IRMS = 2 * I1* I2 * D1(1- D2) + I22 D2 - D22 + I12 D1- D12 Where: D1= VOUT1 V and D2 = OUT2 VIN VIN when VOUT1 - VIN/2 = VOUT2 and when VOUT2 - VIN/2 = VOUT1. As a good rule of thumb, the amount of worst-case ripple is about 75% of the worst-case ripple in the in-phase mode. Note, that when VOUT1 = VOUT2 = VIN/2 and I1 = I2, the ripple is at its minimum. Note that capacitor manufacturer's ripple current ratings are often based on only 2000 hours lifetime. This makes it advisable to further derate the capacitor, or choose a capacitor rated at a higher temperature than required. Several capacitors may also be paralleled to meet the size or height requirements of the design. An additional 0.1F to 1F ceramic capacitor is also recommended on VIN for high frequency decoupling, when not using an all ceramic capacitor solution. Output Capacitor (COUT1 and COUT2) Selection The selection of COUT1 and COUT2 is driven by the required ESR to minimize voltage ripple and load step transients. Typically, once the ESR requirement is satisfied, the capacitance is adequate for filtering. The output ripple (VOUT) is determined by: VOUT IRMS = (I1+ I2) VOUT ( VIN - VOUT ) VIN IL ESR+ 1 8* fO *COUT
( (
)( )(
) )
When D1 = D2, then the equation simplifies to: IRMS = (I1+ I2) D (1- D) or
where the maximum average output currents I1 and I2 equals the peak current minus half the peak-to-peak ripple current: IL1 2 I I2 =ILIM2 - L2 2 I1=ILIM1 - These formula have a maximum at VIN = 2VOUT, where IRMS = (I1 + I2)/2. This simple worst-case is commonly used to determine the worst-case IRMS. For out-of-phase (PHASE pin is at ground), the ripple current can be lower than the in-phase. In the out-of-phase case, the maximum IRMS does not occur when VOUT1 = VOUT2. The maximum typically occurs
where fO = operating frequency, COUT = output capacitance and IL = ripple current in the inductor. The output ripple is highest at maximum input voltage since IL increases with input voltage. Once the ESR requirements for COUT have been met, the RMS current rating generally far exceeds the IRIPPLE(P-P) requirement, except for an all ceramic solution. In surface mount applications, multiple capacitors may have to be paralleled to meet the capacitance, ESR or RMS current handling requirement of the application. Aluminum electrolytic, special polymer, ceramic and dry tantalum capacitors are all available in surface mount packages. The OS-CON semiconductor dielectric capacitor available from Sanyo has the lowest ESR(size) product of any aluminum electrolytic at a somewhat higher price. Special polymer capacitors, such as Sanyo POSCAP offer very , low ESR, but have a lower capacitance density than other types. Tantalum capacitors have the highest capacitance
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16
LTC3546 APPLICATIONS INFORMATION
density, but it has a larger ESR and it is critical that the capacitors are surge tested for use in switching power supplies. An excellent choice is the AVX TPS series of surface tantalums, available in case heights ranging from 2mm to 4mm. Aluminum electrolytic capacitors have a significantly larger ESR, and are often used in extremely cost-sensitive applications provided that consideration is given to ripple current ratings and long term reliability. Ceramic capacitors have the lowest ESR and cost but also have the lowest capacitance density, high voltage and temperature coefficient and exhibit audible piezoelectric effects. In addition, the high Q of ceramic capacitors along with trace inductance can lead to significant ringing. Other capacitor types include the Panasonic specialty polymer (SP) capacitors. Ceramic Input and Output Capacitors Higher value, lower cost ceramic capacitors are now becoming available in smaller case sizes. Because the LTC3546 control loop does not depend on the output capacitor's ESR for stable operation, ceramic capacitors can be used freely to achieve very low output ripple and small circuit size. When choosing the input and output ceramic capacitors, choose the X5R or X7R dielectric formulations. These dielectrics have the best temperature and voltage characteristics of all the ceramics for a given value and size. Great care must be taken when using only ceramic input and output capacitors. When a ceramic capacitor is used at the input and the power is being supplied through long wires, such as from a wall adapter, a load step at the output can induce ringing at the VIN pin. At best, this ringing can couple to the output and be mistaken as loop instability. At worst, the ringing at the input can be large enough to disrupt circuit operation or damage the part. Since the ESR of a ceramic capacitor is so low, the input and output capacitor must instead fulfill a charge storage requirement. During a load step, the output capacitor must instantaneously supply the current to support the load until the feedback loop raises the switch current enough to support the load. The time required for the feedback loop to respond is dependent on the compensation components and the output capacitor size. Typically, 3 to 4 cycles are required to respond to a load step, but only in the first cycle does the output drop linearly. The output droop, VDROOP, is usually about 2 to 3 times the linear droop of the first cycle. Thus, a good place to start is with the output capacitor size of approximately: COUT 2.5 IOUT fOVDROOP
More capacitance may be required depending on the duty cycle and load step requirements. In most applications, the input capacitor is merely required to supply high frequency bypassing, since impedance to the supply is very low. A 10F ceramic capacitor is usually enough for these conditions. Setting the Output Voltage The LTC3546 generates a 0.6V reference voltage between the feedback pin, VFB1 and VFB2, and the signal ground. The output voltage is set by a resistive divider according to the following formula: VOUT1 0.6V 1+ VOUT2 0.6V 1+ R1 R2 R3 R4
Resistor locations are shown in Figure 2.
VOUT1 CFF1 R1 LTC3546 VFB1 R2 VFB2
3546 F02
VOUT2 R3 CFF2
R4
Figure 2. Setting Output Voltages
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17
LTC3546 APPLICATIONS INFORMATION
Keeping the current small (<20A) in these resistors maximizes efficiency, but making the current too small may allow stray capacitance to cause noise problems and reduce the phase margin of the error amp loop. To improve the frequency response, a feedforward capacitor CFF may also be used. Typical values used here are 10pf to 100pf. Great care should be taken to route the VFB node away from noise sources, such as the inductor or an SW line. Shutdown, Soft-Start and Tracking Start-Up The LTC3546 start-up works by comparing two inputs, an internal 1.2ms linear soft-start ramp and the TRACK/SS pin. Whichever input is lower in voltage is the controlling voltage used for start-up. The internal start-up ramps to 0.6V in 1.2ms. If a slower start-up is desired, the TRACK/SS pin has a 1.15A pull up current so a start-up ramp rate can be programmed with an external capacitor, or a voltage divider from another signal can be applied to the TRACK/SS pin. During start-up the controlling voltage must rise above 120mV before the output will start switching. When the RUN pin is low, both the internal 1.2ms soft-start ramp and the TRACK/SS pin are pulled to ground. When the RUN pin is pulled high, both the internal soft-start ramp and the TRACK/SS pin are released. From the time when the RUN pin is asserted until the controlling voltage reaches 0.6V, the regulator is in the start-up state. In this state, the error amplifier will compare the feedback signal at VFB to the controlling voltage (the lower of either the TRACK/SS voltage or the internal ramp voltage) and the regulator will force them to be equal. In this state, the mode of the regulator is forced to pulse skipping. The regulator will continue in this manner until the voltage on the controlling voltage rises above 0.6V. Once the controlling ramp signal is above 0.6V the error amplifier uses the internal 0.6V reference and the operational mode will switch to the mode set by the SYNC/MODE pin. If the TRACK/SS pin is ramped down after start-up, the error amplifier will compare the feedback signal at VFB to the voltage on the TRACK/SS pin once the TRACK/SS voltage drops 6% below the internal reference voltage of 0.6V (0.564V). The regulator will try to force the VFB voltage to equal the TRACK/SS voltage if there is sufficient load current to pull the output low at this rate, otherwise the output will ramp down at the discharge rate of the output capacitor. Once the TRACK/SS voltage drops below about 100mV all switching functions cease and the regulator is forced back into pulse-skipping mode. The operational mode while TRACK/SS is ramping down is set by the MODE/SYNC pin. To use the internal 1.2ms linear soft-start controlling voltage leave the TRACK/SS pin floating. By floating the TRACK/SS pin the internal 1.15A pull up current will pull the TRACK/SS pin up faster than the internal 1.2ms ramp. Care must be taken to insure the TRACK/SS ramp up time (from 0V to 0.6V) is much shorter than the internal 1.2ms ramp time. Parasitic capacitance on this pin should be much smaller than: CPARASITICTRACK / SS < < or CPARASITICTRACK/SS << 2.3nF An externally controlled soft-start ramp is obtained when an external capacitor is connected from the TRACK/SS pin to ground and its ramp rate is slower than the internal soft-start ramp. In this configuration, soft-start times longer than 1.2ms can be achieved. When RUN is pulled high, the internal 1.15A current source charges the external capacitor linearly from 0V. While the TRACK/SS pin is below 0.6V the error amplifier forces the regulator to drive the VFB pin to the voltage on the TRACK/SS pin. Once the VFB pin reaches 0.6V the regulator switches to the internal 0.6V reference. The ramp-up time for the output is calculated as: tRAMP = CTRACK / SS * 0.6 V 1.15A 1.15A * 1.2ms 0.6 V
For this equation to be valid, the ramp time must be greater than 1.2ms thus: CTRACK / SS or CTRACK/SS 2.3nF
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1.15A * 1.2ms 0.6 V
18
LTC3546 APPLICATIONS INFORMATION
The LTC3546 can also track an external voltage during startup by using an external voltage divider to the TRACK/SS pin, and also insuring that the ramp rate on the TRACK/SS pin is slower than the internal 1.2ms ramp rate. As indicated in Figure 3, a resistor divider from an external voltage can be connected to the TRACK/SS pin to allow the start-up of VOUT to ratiometrically track an external voltage VX. For VTRACKSS < 0.6V VOUT = VX * R2X R1+ R2 * R1X + R2X R2
VX R1X LTC3546 VTRACK/SS R2X VFB
3546 F03
VX OUTPUT VOLTAGE
VOUT
TIME
3546 F04
Figure 4. Coincident Tracking
VOUT OUTPUT VOLTAGE R1
VX
VOUT
R2
Figure 3. Tracking External Voltages
Coincident tracking is where VOUT = VX during startup. To implement coincident tracking R1X in Figure 3 is set to the same value as R1 and R2X to the value of R2. Coincident tracking is illustrated in Figure 4. The voltage at TRACK/SS when VX is at its final value should be 0.8V (sufficient margin above the 0.6V reference voltage). Ratiometric tracking is where VOUT VX during startup but rather, it is set to some fractional value of VX. To implement ratiometric tracking (as illustrated in Figure 5), set R1X in Figure 3 to the same value as R1 and R2X to the value of R2 + R. The R added to R2 should be sufficient so that the TRACK/SS voltage is 0.8V when VX is at its final value. The internal 1.15A pull up current on TRACK/SS can cause a tracking error at VOUT when using a resistor divider on TRACK/SS. For example, if a 59k resistor is chosen for R2X, the R2X current will be about 10A (0.6V/59k). In this case, the 1.15A internal current source will cause about 11% (1.15A/10A) tracking error, which is about 66mV referred to VFB. This is acceptable for most applications. If a better tracking accuracy is required, the value of R2X can be reduced or the 1.15A current can be taken into account in the equations.
TIME
3546 F05
Figure 5. Ratiometric Tracking
Table 2 summarizes the different states in which the TRACK/SS can be used.
Table 2. The States of the TRACK/SS Pin
TRACK/SS PIN Capacitor to Ground Floating Resistor Divider RESULT External Soft-Start Internal Soft-Start VOUT Tracking an External Voltage VX
Regardless of the mode implemented, the TRACK/SS pin should never be pulled high externally as this will result in excessive current during shutdown. The LTC3546 can smoothly handle starting up into a prebiased output. The tracking function will pick up from the pre-biased voltage and ramp the output up from there. Mode Selection The SYNC/MODE pin is a multipurpose pin which provides mode selection and frequency synchronization. Connecting this pin to VIN enables Burst Mode operation for both regula3546fb
19
LTC3546 APPLICATIONS INFORMATION
tors. This mode provides the best low current efficiency at the cost of a higher output voltage ripple. When SYNC/MODE is connected to ground, pulse-skipping operation is selected for both regulators. This mode provides a lower output voltage and current ripple at the cost of low current efficiency. Applying VIN/2 results in forced continuous mode for both regulators. This mode creates a fixed output ripple and is capable of sinking some current (about 1/2 * IL). Since the switching noise is constant in this mode, it is also the easiest to filter out. During initial start-up, pulse-skipping mode is forced until the PGOOD pin goes high. The LTC3546 can also be synchronized to an external clock signal by the SYNC/MODE pin. An internal phase locked loop locks to the incoming signal to provide for 180 out-of-phase operation as well as correct slope compensation. With external synchronization the FREQ pin is used for externally compensating the internal phase locked loop. Typical values used for compensation are 200k and 100pf, as shown in Figure 6. During synchronization, the regulator operating mode is forced to pulse skipping. The P-channel switch turn on is synchronized to the rising edge of the external clock. When using an external clock, with the PHASE pin low, the switching of the two channels occur 180 out-of-phase.
LTC3546 FREQ
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estimated using the percentage of overshoot seen at this pin, or by examining the rise time at this pin. The ITH external components shown in the Figure 9 circuit will provide an adequate starting point for most applications. The series R-C filter sets the dominant pole-zero loop compensation. The values can be modified slightly (from 0.5 to 2 times their suggested values) to optimize transient response once the final PC layout is done and the particular output capacitor type and value have been determined. The output capacitors need to be selected because of various types and values determine the loop feedback factor gain and phase. An output current pulse of 20% to 100% of full load current having a rise time of 1s to 10s will produce output voltage and ITH pin waveforms that will give a sense of overall loop stability without breaking the feedback loop. Switching regulators take several cycles to respond to a step in load current. When a load step occurs, VOUT immediately shifts by an amount equal to ILOAD * ESR, where ESR is the effective series resistance of COUT. The ILOAD also begins to charge or discharge COUT generating a feedback error signal used by the regulator to return VOUT to its steady-state value. During this recovery time, VOUT can be monitored for overshoot or ringing that would indicate a stability problem. The initial output voltage step may not be within the bandwidth of the feedback loop, so the standard second order overshoot/DC ratio cannot be used to determine phase margin. The gain of the loop increases with RITH and the bandwidth of the loop increases with decreasing CITH. If RITH is increased by the same factor that CITH is decreased, the zero frequency will be kept the same, thereby keeping the phase the same in the most critical frequency range of the feedback loop. In addition, feedforward capacitors, CFF1 and CFF2, can be added to improve the high frequency response, as shown in Figure 9. Capacitor CFF1 provides phase lead by creating a high frequency zero with R1 which improves the phase margin for the 1A SW1 channel. Capacitor CFF2 provides phase lead by creating a high frequency zero with R3 which improves the phase margin for the 3A SW1D/SW2 channel. The output voltage settling behavior is related to the stability of the closed-loop system and will demonstrate the actual
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200k 100pF
Figure 6. PLL Compensation
Checking Transient Response The ITH pin compensation allows the transient response to be optimized for a wide range of loads and output capacitors. The availability of the ITH pin not only allows optimization of the control loop behavior but also provides a DC-coupled and AC filtered closed loop response test point. The DC step, rise time and settling at this test point truly reflects the closed loop response. Assuming a predominantly second order system, phase margin and/or damping factor can be estimated using the percentage of overshoot seen at this pin. The bandwidth can also be
20
LTC3546 APPLICATIONS INFORMATION
overall supply performance. For a detailed explanation of optimizing the compensation components, including a review of control loop theory, refer to Linear Technology Application Note 76. Although a buck regulator is capable of providing the full output current in dropout, it should be noted that as the input voltage VIN drops toward VOUT, the load step capability does decrease due to the decreasing voltage across the inductor. Applications that require large load step capability near dropout should use a different topology such as SEPIC, Zeta, or single inductor, positive buck boost. In some applications, a more severe transient can be caused by switching in loads with large (>1F) input capacitors. The discharged input capacitors are effectively put in parallel with COUT, causing a rapid drop in VOUT. No regulator can deliver enough current to prevent this problem, if the switch connecting the load has low resistance and is driven quickly. The solution is to limit the turn-on speed of the load switch driver. A hot swap controller is designed specifically for this purpose and usually incorporates current limiting, short-circuit protection, and soft starting. Efficiency Considerations The percent efficiency of a switching regulator is equal to the output power divided by the input power times 100. It is often useful to analyze individual losses to determine what is limiting the efficiency and which change would produce the most improvement. Percent efficiency can be expressed as: %Efficiency = 100% - (P1 + P2 + P3+...) where P1, P2, etc. are the individual losses as a percentage of input power. Although all dissipative elements in the circuit produce losses, four main sources usually account for most of the losses in LTC3546 circuits: 1) LTC3546 VIN current, 2) switching losses, 3) I2R losses, 4) other losses. 1. The VIN current is the DC supply current given in the electrical characteristics which excludes MOSFET driver and control currents. VIN current results in a small (<0.1%) loss that increases with VIN, even at no-load. 2. The switching current is the sum of the MOSFET driver and control currents. The MOSFET driver current results from switching the gate capacitance of the power MOSFETs. Each time a MOSFET gate is switched from low to high to low again, a packet of charge moves from VIN to ground. The resulting charge over the switching period is a current out of VIN that is typically much larger than the DC bias current. The gate charge losses are proportional to VIN and thus their effects will be more pronounced at higher supply voltages. 3. I2R losses are calculated from the DC resistances of the internal switches, RSW, and the external inductor, RL. In continuous mode, the average output current flowing through inductor L is "chopped" between the internal top and bottom switches. Thus, the series resistance looking into the SW pin is a function of both top and bottom MOSFET RDS(ON) and the duty cycle (DC) as follows: RSW = (RDS(ON)TOP)(DC) + (RDS(ON)BOT)(1 - DC) The RDS(ON) for both the top and bottom MOSFETs can be obtained from the Typical Performance Characteristics curves. Thus, to obtain I2R losses: I2R losses = IOUT2(RSW + RL) Where RL is the resistance of the inductor. 4. Other hidden losses such as copper trace and internal battery resistances can account for additional efficiency degradations in portable systems. It is very important to include these "system" level losses in the design of a system. The internal battery and fuse resistance losses can be minimized by making sure that CIN has adequate charge storage and very low ESR at the switching frequency. Other losses including diode conduction losses during dead-time and inductor core losses generally account for less than 2% total additional loss. Thermal Considerations The LTC3546 requires the backplane metal (Pin 29) to be well soldered to the PC board. This gives the UFD package exceptional thermal properties, compared to similar packages of this size, making it difficult in normal opera3546fb
21
LTC3546 APPLICATIONS INFORMATION
tion to exceed the maximum junction temperature of the part. In a majority of applications, the LTC3546 does not dissipate much heat due to its high efficiency. However, in applications where the LTC3546 is running at high ambient temperature with low supply voltage and high duty cycles, such as in dropout, the heat dissipated may exceed the maximum junction temperature of the part. If the junction temperature reaches approximately 150C, both switches in both regulators will be turned off and the SW nodes will become high impedance. To avoid the LTC3546 from exceeding the maximum junction temperature, the user will need to do some thermal analysis. The goal of the thermal analysis is to determine whether the power dissipated exceeds the maximum junction temperature of the part. The temperature rise is given by: TRISE = PD * JA where PD is the power dissipated by the regulator and JA is the thermal resistance from the junction of the die to the ambient temperature. The junction temperature, TJ, is given by: TJ = TRISE + TAMBIENT As an example, consider the case when the LTC3546 is in dropout in both regulators at an input voltage of 3.3V with load currents of 3A (SW1D externally connected to SW2) and 1A. From the Typical Performance Characteristics graph of Switch Resistance, the RDS(ON) resistance of the 3A P-channel switch parallel combination of SW2 and SW1D is 0.06 and the RDS(ON) of the 1A P-channel switch is 0.18. The power dissipated by the part is: PD = I12 RDS(ON)1 + I22 RDS(ON)2 PD = 32 * 0.064 + 12 * 0.19 PD = 0.77W The UFD package junction-to-ambient thermal resistance, JA, is about 34C/W. Therefore, the junction temperature of the regulator operating in a 85C ambient temperature is approximately: TJ = 0.77 * 34 + 85 TJ = 111.2C This junction temperature is obtained from an RDS(ON) at 25C. At 125C the RDS(ON) increases by about 30%. This will put the junction temperature at 122C. If the supply is lower, like 2.25V, the RDS(ON) is higher still. Special care needs to be taken if the part is expected to be operating in dropout so that the maximum junction temperature of 125C is not exceeded. Design Example As a design example, consider using the LTC3546 in a portable application with a Li-Ion battery. The battery provides a VIN = 2.25V to 4.2V. One output requires 1.8V at 2.5A in active mode, and 1mA in standby mode. The other output requires 1.2V at 800mA in active mode, and 500A in stand-by mode. Since both loads still need power in stand-by, Burst Mode operation is selected for good low load efficiency. First, determine what frequency should be used. Higher frequency results in a lower inductor value for a given IL (IL is estimated as 0.35ILOAD(MAX)). Reasonable values for wire wound surface mount inductors are in the 1H and up. Look at the different frequencies with the IL = 0.35ILOAD(MAX).
CONVERTER OUTPUT SW2/SW1D, 1.2V SW1, 1.8V ILOAD(MAX) 2.5A 800mA IL 875mA 280mA
Using the 1.5MHz frequency setting (FREQ = 143k to GNDA) we get the following equations for L1 and L2. L1= L2 = 1.2V 1.2V *1 = 2H 4.2V 1.5MHz * 280mA 1.8V 1.8V *1 = 0.78H 4.2V 1.5MHz * 875mA
Use 1H and 2.2H. COUT selection is typically based on load step rather than the ripple requirements. The minimum required capacitance will increase with a decrease in compensation loop bandwidth and/or increases in maximum load step or output voltage tolerance. A good starting point is about 22F per ampere of output current for a nominal
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22
LTC3546 APPLICATIONS INFORMATION
operating frequency of 1.5MHz and assumes roughly a 300mA/A load step. COUT1 = 22F 280mA * 0.8 A * = 20.5F 300mA A * 0.8 A A 22F 875mA * 2.5A * = 64.2F COUT1 = 300mA A * 2.5A A 2. All, or part, of CIN should connect from Pin 9 to Pin 14 on the same side of the PC board as the chip and as close to the chip as possible, where the SW traces will go directly under the capacitor. CIN provides the AC current to the internal power MOSFETs and their drivers. 3. Are the respective COUT, L closely connected? The (-) plate of COUT1 returns current to PGND1, and the (-) plate of COUT2 returns current to the PGND2. The (-) plate of CIN should also return current to PGND1 and PGND2. 4. The resistor divider, R1 and R2, must be connected between the (+) plate of COUT1 and a ground line terminated near GNDA. The resistor divider R3 and R4, must be connected between the (+) plate of COUT2 and the ground connection terminated to the GNDA pin. The feedback signals VFB1 and VFB2 should be routed away from noise components and traces, such as the SW lines, and its trace should be minimized. 5. When using the RFREQ resistor, the ground connection of the resistor should be terminated to the GNDA pin. When using the internal PLL, the ground connection of the R-C compensation network should be terminated to the GNDA pin. 6. Keep sensitive components away from the SW pins. The input capacitor CIN, the compensation capacitors CFF1, CFF2, CITH1, and CITH2 and all resistors R1, R2, R3, R4, RITH1 and RITH2 should be routed away from the SW traces and the inductors L1 and L2. 7. A ground plane is preferred, but if not available, keep the signal and power grounds segregated with small signal components returning to the SGND pin at one point which is then connected to the PGND1/PGND2/ PGND1D/GNDD pins. 8. Flood all unused areas on all layers with copper. Flooding with copper will reduce the temperature rise of power components. These copper areas should be connected to the Exposed Pad (Pin 29).
The closest values are 22F and 68F . The output voltages can now be programmed by choosing the values of R1, R2, R3, and R4. To maintain high efficiency, the current in these resistors should be kept small. Choosing 2A with the 0.6V feedback voltages makes R2 and R4 equal to 300k. A close standard 1% resistor is 301k. This then makes R1 = 300k. A close standard 1% is 301k. R3 then equals 600k. A close 1% resistor is 604k. The compensation should be optimized for these components by examining the load step response but a good place to start for the LTC3546 is with a 13k and 1000pF filter on both ITH1 and ITH2. The output capacitor may need to be increased depending on the actual transient during a load step. The PGOOD pin is a common drain output and requires a pull-up resistor. A 100k resistor is used for adequate speed. Figure 9 shows a complete schematic for this design. Board Layout Considerations When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the LTC3546. These items are also illustrated graphically in the layout diagram of Figure 7. Check the following in your layout. 1. Make sure SW1, SW2A, SW2B and SW1D are connected on the PC board through a wide piece of copper.
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LTC3546 APPLICATIONS INFORMATION
VIN 2.25V TO 5.5V CIN 22F L2 0.56H CFF2 100pF VIN R3 R4 60.4k 30.1k VIN R5 100k VIN1 VCCA VCCD VIN2 SYNC/MODE PGOOD2 SW2A SW2B RUN2 VFB2 PGOOD1 SW1 SW1D RUN1 VFB1 VIN R1 R2 30.1k 30.1k VIN CFF1 100pF VOUT2 1.8V, 2A L1 0.56H VOUT1 1.2V, 2A R6 100k
COUT2 47F
LTC3546
COUT1 47F
BMC2 TRACK/SS2 PHASE ITH2 PGND2 GNDA
BMC1 TRACK/SS1 FREQ ITH1 PGND1
RITH2 13k CITH2 1000pF
RITH1 13k CITH1 1000pF
RFREQ 143k
EXPOSED PAD
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Figure 7. Typical Schematic for 2A/2A Regulator
5V VIN
C5 22F, X5R R7 100k R8 100k L1 1.0H SW2A R1 316k R3 100k R9 90.9k R6 5.1k C4 470pF C9 0.1F C6 10pF SW2B VFB2 FREQ ITH2 TRACK/SS2 RUN2 PGOOD2
VCC RUN1 PGOOD1
SYNC/MODE LTC3546 SW1 SW1D VFB1 PHASE ITH1 TRACK/SS1 BMC1
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VOUT2 2.5V/2A
L2 1.0H C7 33pF R2 200k R4 100k R5 8.2k C3 330pF
C1 22F, X5R 2
VOUT1 1.8V/2A C2 22F, X5R 2
BMC2 GND
C8 0.1F
fSW = 2.25MHz
Figure 8. A 2.25MHz Fixed Frequency 2A/2A Regulator
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LTC3546 APPLICATIONS INFORMATION
VIN 2.25V TO 5.5V CIN 22F R5 100k L2 0.56H CFF2 100pF VIN R3 R4 95.3k 30.1k VIN VIN1 VCCA VCCD VIN2 SYNC/MODE PGOOD2 SW2A SW2B SW1D RUN2 VFB2 LTC3546 RUN1 VFB1 VIN R1 R2 30.1k 59k VIN PGOOD1 SW1 CFF1 100pF VOUT2 2.5V, 3A L1 1.2H VOUT1 1.8V, 1A R6 100k
COUT2 33F x2
COUT1 22F
BMC2 TRACK/SS2 PHASE ITH2 PGND2 GNDA
BMC1 TRACK/SS1 FREQ ITH1 PGND1
RITH2 13k CITH2 1000pF
RITH1 13k CITH1 1000pF
RFREQ 143k
EXPOSED PAD
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Figure 9. Typical Schematic for 3A/1A Regulator
OUT1 Efficiency (Burst Mode Operation)
100 95 EFFICIENCY (%) 90 85 80 POWER LOSS 75 70 0.001 0.001 0.0001 0.01 0.1 LOAD CURRENT (A) 1
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OUT2 Efficiency (Burst Mode Operation)
100 SW1D CONNECTED TO SW2 VIN = 3.6V 95 VOUT = 2.5V 90 85 80 POWER LOSS 75 70 0.001 0.001 0.0001 EFFICIENCY 100 10 POWER LOSS (W) 1 0.1 0.01
100 10 EFFICIENCY POWER LOSS (W)
0.1 0.01
EFFICIENCY (%)
1
1 0.01 0.1 LOAD CURRENT (A)
10
3546 F09c
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25
LTC3546 PACKAGE DESCRIPTION
UFD Package 28-Lead Plastic QFN (4mm x 5mm)
(Reference LTC DWG # 05-08-1712 Rev B)
0.70 0.05
4.50 0.05 3.10 0.05 2.50 REF 2.65 0.05 3.65 0.05
PACKAGE OUTLINE
0.25 0.05 0.50 BSC 3.50 REF 4.10 0.05 5.50 0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4.00 0.10 (2 SIDES) 0.75 0.05 R = 0.05 TYP PIN 1 NOTCH R = 0.20 OR 0.35 x 45 CHAMFER 27 28 0.40 0.10 1 2
2.50 REF R = 0.115 TYP
PIN 1 TOP MARK (NOTE 6)
5.00 0.10 (2 SIDES)
3.50 REF 3.65 0.10 2.65 0.10
(UFD28) QFN 0506 REV B
0.200 REF 0.00 - 0.05
0.25 0.05 0.50 BSC BOTTOM VIEW--EXPOSED PAD
NOTE: 1. DRAWING PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE MO-220 VARIATION (WXXX-X). 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
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Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
LTC3546 PACKAGE DESCRIPTION
FE Package 28-Lead Plastic TSSOP (4.4mm)
(Reference LTC DWG # 05-08-1663)
Exposed Pad Variation EB
4.75 (.187)
9.60 - 9.80* (.378 - .386) 4.75 (.187) 28 2726 25 24 23 22 21 20 19 18 1716 15
6.60 0.10 4.50 0.10
SEE NOTE 4
2.74 (.108) 0.45 0.05
EXPOSED PAD HEAT SINK ON BOTTOM OF PACKAGE
6.40 2.74 (.252) (.108) BSC
1.05 0.10 0.65 BSC
RECOMMENDED SOLDER PAD LAYOUT
1 2 3 4 5 6 7 8 9 10 11 12 13 14 1.20 (.047) MAX
0 - 8
4.30 - 4.50* (.169 - .177)
0.25 REF
0.09 - 0.20 (.0035 - .0079)
0.50 - 0.75 (.020 - .030)
0.65 (.0256) BSC
0.195 - 0.30 (.0077 - .0118) TYP
0.05 - 0.15 (.002 - .006)
FE28 (EB) TSSOP 0204
NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS 2. DIMENSIONS ARE IN MILLIMETERS (INCHES) 3. DRAWING NOT TO SCALE
4. RECOMMENDED MINIMUM PCB METAL SIZE FOR EXPOSED PAD ATTACHMENT *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.150mm (.006") PER SIDE
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LTC3546 RELATED PARTS
PART NUMBER LTC3406A/ LTC3406B LTC3407A-2 LTC3409 LTC3410/ LTC3410B LTC3411A LTC3412A LTC3417A-2 LTC3419/ LTC3419-1 LTC3542 LTC3544/ LTC3544B LTC3545/ LTC3545-1 LTC3547/ LTC3547B LTC3548/ LTC3548-1/ LTC3548-2 LTC3560 LTC3561 LTC3562 DESCRIPTION 600mA, 1.5MHz, Synchronous Step-Down DC/DC Converters Dual 800mA/800mA 2.25MHz, Synchronous StepDown DC/DC Converter 600mA, 1.7MHz/2.6MHz, Synchronous Step-Down DC/DC Converter 300mA, 2.25MHz, Synchronous Step-Down DC/DC Converters 1.25A, 4MHz, Synchronous Step-Down DC/DC Converter 2.5A, 4MHz, Synchronous Step-Down DC/DC Converter Dual 1.5A/1A, 4MHz, Synchronous Step-Down DC/DC Converter Dual 600mA/600mA 2.25MHz, Synchronous StepDown DC/DC Converters 500mA, 2.25MHz, Synchronous Step-Down DC/DC Converter Quad 100mA/200mA/200mA/300mA, 2.25MHz Synchronous Step-Down DC/DC Converters Triple, 800mA x3, 2.25MHz Synchronous Step-Down DC/DC Converters Dual 300mA, 2.25MHz, Synchronous Step-Down DC/DC Converters Dual 400mA and 800mA IOUT, 2.25MHz, Synchronous Step-Down DC/DC Converters 800mA 2.25MHz, Synchronous Step-Down DC/DC Converter 1.25A, 4MHz, Synchronous Step-Down DC/DC Converter Quad, I2C Interface, 600mA/600mA/400mA/400mA , 2.25MHz Synchronous Step-Down DC/DC Converter COMMENTS 96% Efficiency, VIN(MIN): 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 20A, ISD < 1A, ThinSOTTM Package 95% Efficiency, VIN(MIN): 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40A, ISD < 1A, MS10E, 3mm x 3mm DFN-10 Packages 96% Efficiency, VIN(MIN): 1.6V to 5.5V, VOUT(MIN) = 0.6V, IQ = 65A, ISD < 1A, 3mm x 3mm DFN-8 Package 95% Efficiency, VIN(MIN): 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 26A, ISD < 1A, SC70 Package 95% Efficiency, VIN(MIN): 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 60A, ISD < 1A, MS10, 3mm x 3mm DFN-10 Packages 95% Efficiency, VIN(MIN): 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 60A, ISD < 1A, 4mm x 4mm QFN-16, TSSOP-16E Packages 95% Efficiency, VIN(MIN): 2.3V to 5.5V, VOUT(MIN) = 0.8V, IQ = 125A, ISD < 1A, TSSOP-16E, 3mm x 5mm DFN-16 Packages 95% Efficiency, VIN(MIN): 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 35A, ISD < 1A, MS10, 3mm x 3mm DFN-10 Packages 95% Efficiency, VIN(MIN): 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 26A, ISD < 1A, 2mm x 2mm DFN-6, ThinSOT Packages 95% Efficiency, VIN(MIN): 2.3V to 5.5V, VOUT(MIN) = 0.8V, IQ = 70A, ISD < 1A, 3mm x 3mm QFN-16 Package 95% Efficiency, VIN(MIN): 2.3V to 5.5V, VOUT(MIN) = 0.6V, IQ = 58A, ISD < 1A, 3mm x 3mm QFN-16 Package 95% Efficiency, VIN(MIN): 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40A, ISD < 1A, DFN-8 Package 95% Efficiency, VIN(MIN): 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40A, ISD < 1A, MS10E, 3mm x 3mm DFN-10 Packages 95% Efficiency, VIN(MIN): 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 16A, ISD < 1A, ThinSOT Package 95% Efficiency, VIN(MIN): 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 240A, ISD < 1A, 3mm x 3mm DFN-8 Package 95% Efficiency, VIN(MIN): 2.9V to 5.5V, VOUT(MIN) = 0.425V, IQ = 100A, ISD < 1A, 3mm x 3mm QFN-20 Package
ThinSOT is a trademark of Linear Technology Corporation.
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28 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 1009 REV B * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2009

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