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LTC1530 High Power Synchronous Switching Regulator Controller
FEATURES
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DESCRIPTIO
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High Power Buck Converter from 5V or 3.3V Main Power Adjustable Current Limit in S0-8 with Topside FET RDS(ON) Sensing No External Sense Resistor Required Hiccup Mode Current Limit Protection Adjustable, Fixed 1.9V, 2.5V, 2.8V and 3.3V Output All N-Channel MOSFET Synchronous Driver Excellent Output Regulation: 2% over Line, Load and Temperature Variations High Efficiency: Over 95% Possible Fast Transient Response Fixed 300kHz Frequency Operation Internal Soft-Start Circuit Quiescent Current: 1mA, 45A in Shutdown
The LTC(R)1530 is a high power synchronous switching regulator controller optimized for 5V to 1.3V-3.5V output applications. Its synchronous switching architecture drives two external N-channel MOSFET devices to provide high efficiency. The LTC1530 contains a precision trimmed reference and feedback system that provides worst-case output voltage regulation of 2% over temperature, load current and line voltage shifts. Current limit circuitry senses the output current through the on-resistance of the topside N-channel MOSFET, providing an adjustable current limit without requiring an external low value sense resistor. The LTC1530 includes a fixed frequency PWM oscillator that free runs at 300kHz, providing greater than 90% efficiency in converter designs from 1A to 20A of output current. Shutdown mode drops the LTC1530 supply current to 45A. The LTC1530 is specified for commercial and industrial temperature ranges and is available in the S0-8 package.
, LTC and LT are registered trademarks of Linear Technology Corporation. Pentium is a registered trademark of Intel Corp. AMD-K6 is a registered trademark of Advanced Micro Devices, Inc.
APPLICATIO S
s s
Power Supply for Pentium(R) II, AMD-K6(R)-2, SPARC, ALPHA and PA-RISC Microprocessors High Power 5V to 1.3V-3.5V Regulators
TYPICAL APPLICATIO
+
VIN 5V
100
MBR0530T1 MBR0530T1 0.1F
2.7k
+
10F 0.22F
90
CIN** 1200F x4
EFFICIENCY (%)
80 70 60 50 40 30
1530 F01a
IMAX PVCC C1 150pF CC 0.022F RC 10k
G1 20
Q1*
LO 2H
IFB COMP LTC1530-3.3 G2 GND VOUT
COILTRONICS CTX02-13198
+
Q2*
CO 330F x7
VOUT 3.3V 14A
20 10 TA = 25C 0 0.3 2 8 4 10 6 LOAD CURRENT (A) 12 14
OR PANASONIC ETQP6F2R5HA
AVX TPSE337M006R0100
* SILICONIX SUD50N03-10 ** SANYO 10MV1200GX COILTRONICS (561) 241-7876
Figure 1. Single 5V to 3.3V Supply
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Efficiency vs Load Current
0
1530 F01b
U
U
1
LTC1530
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW PVCC 1 GND 2 *VSENSE / VOUT 3 COMP 4 8 7 6 5 G1 G2 IFB IMAX
Supply Voltage PVCC ........................................................................ 14V Input Voltage IFB (Note 2) ............................................... PVCC + 0.3V IMAX ........................................................ - 0.3V to 14V IFB Input Current (Notes 2,3) ............................ - 100mA Operating Ambient Temperature Range LTC1530C ............................................... 0C to 70C LTC1530I ............................................ - 40C to 85C Maximum Junction Temperature LTC1530C, LTC1530I ...................................... 125C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
ORDER PART NUMBER LTC1530CS8 LTC1530CS8-1.9 LTC1530CS8-2.5 LTC1530CS8-2.8 LTC1530CS8-3.3 LTC1530IS8 LTC1530IS8-1.9 LTC1530IS8-2.5 LTC1530IS8-2.8 LTC1530IS8-3.3
S8 PACKAGE 8-LEAD PLASTIC SO
TJMAX = 125C, JA = 130C/ W *VOUT FOR FIXED VOLTAGE VERSIONS
S8 PART MARKING 1530 153019 153025 153028 153033 1530I 530I19 530I25 530I28 530I33
Consult factory for Military grade parts.
The q denotes specifications that apply over the full operating temperature range, otherwise specifications are at 0C TA 70C. PVCC = 12V unless otherwise noted. (Note 3)
SYMBOL VSENSE VOUT PARAMETER Internal Feedback Voltage Output Voltage CONDITIONS LTC1530CS8 (Note 4)
q
ELECTRICAL CHARACTERISTICS
MIN 1.223 1.216 1.881 1.871 2.475 2.462 2.772 2.758 3.267 3.250 1.6
TYP 1.235 1.235 1.9 1.9 2.5 2.5 2.8 2.8 3.3 3.3 2
MAX 1.247 1.254 1.919 1.929 2.525 2.538 2.828 2.842 3.333 3.350 2.6
UNITS V V V V V V V V V V millimho
LTC1530CS8-1.9 (Note 4)
q
LTC1530CS8-2.5 (Note 4)
q
LTC1530CS8-2.8 (Note 4)
q
LTC1530CS8-3.3 (Note 4)
q
gmERR
Error Amplifier Transconductance
(Note 5)
q
The q denotes specifications that apply over the full operating temperature range, otherwise specifications are at -40C TA 85C. PVCC = 12V unless otherwise noted. (Note 3)
SYMBOL PVCC VUVLO VSENSE PARAMETER Supply Voltage Undervoltage Lockout Voltage Internal Feedback Voltage CONDITIONS (Note 6) (Note 7) LTC1530IS8 (Note 4)
q q
MIN
TYP 3.5
MAX 13.2 3.75 1.247 1.260
UNITS V V V V
1.223 1.210
1.235 1.235
2
U
W
U
U
WW
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LTC1530
The q denotes specifications that apply over the full operating temperature range, otherwise specifications are at -40C TA 85C. PVCC = 12V unless otherwise noted. (Note 3)
SYMBOL VOUT PARAMETER Output Voltage CONDITIONS LTC1530IS8-1.9 (Note 4)
q
ELECTRICAL CHARACTERISTICS
MIN 1.881 1.862 2.475 2.450 2.772 2.744 3.267 3.234
TYP 1.9 1.9 2.5 2.5 2.8 2.8 3.3 3.3 -5 1 15
MAX 1.919 1.938 2.525 2.550 2.828 2.856 3.333 3.366
UNITS V V V V V V V V mV mV mA
LTC1530IS8-2.5 (Note 4)
q
LTC1530IS8-2.8 (Note 4)
q
LTC1530IS8-3.3 (Note 4)
q
VOUT IPVCC
Output Load Regulation Output Line Regulation Operating Supply Current Quiescent Current Shutdown Supply Current
IOUT = 0 to 14A VIN = 4.75V to 5.25V, IOUT = 0 Figure 3, VFB = 0V (Note 8) Figure 3, COMP = 0.5V, VFB = 5V Figure 3, COMP = 0 (Note 9) Figure 4 VCOMP at 0% Duty Cycle VCOMP at Max Duty Cycle (Note 5) (Note 5) VIMAX = 5V VIMAX = 5V VIMAX = 5V Figure 4, Measured at COMP Pin (Note 9) Figure 4, COMP Pulls High, VFB = 0V (Notes 9, 10) Figure 4, COMP Pulls High to G1 (Note 10) Figure 4 Figure 4 Figure 4
q q q q q q q q q q
1.0 45 250 300 2.5 3.5 40 1.6 170 120 100 54 2 200 200 3300 180 0.4 3.5 90 30 81 100 86
1.4 80 350
mA A kHz V V dB
fOSC
Internal Oscillator Frequency Oscillator Valley Voltage Oscillator Peak Voltage
GERR gmERR IMAX
Error Amplifier Open-Loop DC Gain Error Amplifier Transconductance IMAX Sink Current IMAX Sink Current Tempco
2.8 230 300
millimho A A ppm/C mV V/ms ms
VSHDN SRSS t SS t r, t f t NOL DCMAX
Shutdown Threshold Voltage Internal Soft-Start Slew Rate Internal Soft-Start Wake-Up Time Driver Rise and Fall Time Driver Nonoverlap Time Maximum G1 Duty Cycle
140
ns ns %
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: If IFB is taken below GND, it is clamped by an internal diode. This pin handles input currents 100mA below GND without latch-up. In the positive direction, it is not clamped to PVCC. Note 3: All currents into device pins are positive; all currents out of device pins are negative. All voltages are referenced to ground unless otherwise specified. Note 4: The LTC1530 is tested in an op amp feedback loop which regulates VSENSE or VOUT based on VCOMP = 2V for the error amplifier. Note 5: The Open-loop DC gain and transconductance from the VFB pin to the COMP pin are GERR and gmERR respectively. For fixed output voltage versions, the actual open-loop DC gain and transconductance are GERR and gmERR multiplied by the ratio 1.235/VOUT.
Note 6: The total voltage from the PVCC pin to the GND pin must be 8V for the current limit protection circuit to be active. Note 7: G1 and G2 begin to switch once PVCC is the undervoltage lockout threshold voltage. Note 8: Supply current in normal operation is dominated by the current needed to charge and discharge the external FET gates. This current varies with the LTC1530 operating frequency, supply voltage and the external FETs used. Note 9: The LTC1530 enters shutdown if COMP is pulled low. Note 10: Slew rate is measured at the COMP pin on the transition from shutdown to active mode.
3
LTC1530 TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs Load Current
100 90 80
2.510 2.508 2.506 TA = 25C REFER TO FIGURE 2
EFFICIENCY (%)
70 60 50 40 30 20 10 0 0 0.3 2 8 4 10 6 LOAD CURRENT (A) 12 14 TA = 25C REFER TO FIGURE 10
OUTPUT VOLTAGE (V)
2.500 2.498 2.496 2.494 2.492 2.490 0 1 2 3 4 OUTPUT CURRENT (A) 5 6
1530 G02
VSENSE (V)
LTC1530-1.9 VOUT vs Temperature
1.930 1.925 1.920 1.915 1.910
VOUT (V)
VOUT (V)
VOUT (V)
1.905 1.900 1.895 1.890 1.885 1.880 1.875 1.870 -55 -35 -15 5 25 45 65 85 105 125 TEMPERATURE (C)
1530 G04
ERROR AMPLIFIER TRANSCONDUCTANCE (millimho)
LTC1530-3.3 VOUT vs Temperature
3.36 3.35 3.34 3.33 3.32 3.31 3.30 3.29 3.28 3.27 3.26 3.25 3.24 3.23 -55 -35 -15
UNDERVOLTAGE LOCKOUT THRESHOLD (V)
VOUT (V)
5 25 45 65 85 105 125 TEMPERATURE (C)
1530 G06
4
UW
Load Regulation
1.260 1.255 1.250 1.245 1.240 1.235 1.230 1.225 1.220 1.215
LTC1530 VSENSE vs Temperature
2.504 2.502
1.210 -55 -35 -15
5 25 45 65 85 105 125 TEMPERATURE (C)
1530 G03
1530 G01
LTC1530-2.5 VOUT vs Temperature
2.55 2.54 2.53 2.52 2.51 2.50 2.49 2.48 2.47 2.46 2.45 -55 -35 -15 5 25 45 65 85 105 125 TEMPERATURE (C)
1530 G05
LTC1530-2.8 VOUT vs Temperature
2.85 2.84 2.83 2.82 2.81 2.80 2.79 2.78 2.77 2.76 2.75 2.74 -55 -35 -15 5 25 45 65 85 105 125 TEMPERATURE (C)
1530 G06
Undervoltage Lockout Threshold Voltage vs Temperature
4.5 4.3 4.1 3.9 3.7 3.5 3.3 3.1 2.9 2.7 2.5 2.3 -55 -35 -15 5 25 45 65 85 105 125 TEMPERATURE (C)
1530 G08
Error Amplifier Transconductance vs Temperature
2.8 2.6 2.4 2.2 2.0 1.8 1.6 -55 -35 -15
5 25 45 65 85 105 125 TEMPERATURE (C)
1530 G09
LTC1530 TYPICAL PERFOR A CE CHARACTERISTICS
Error Amplifier Open-Loop Gain vs Temperature
ERROR AMPLIFIER OPEN-LOOP DC GAIN (dB)
60
OSCILLATOR FREQUENCY (kHz)
55
330 320 310 300 290 280 270 260
MAXIMUM G1 DUTY CYCLE (%)
50
45
40 -55 -35 -15
5 25 45 65 85 105 125 TEMPERATURE (C)
1530 G10
IMAX Sink Current vs Temperature
300 280
IMAX SINK CURRENT (A)
70
PVCC SHUTDOWN CURRENT (A)
PVCC = 12V G1, G2 ARE NOT SWITCHING
PVCC SUPPLY CURRENT (mA)
260 240 220 200 180 160 140 120 -55 -35 -15 5 25 45 65 85 105 125 TEMPERATURE (C)
1530 G13
Shutdown Threshold Voltage vs Temperature
250 3.0 PVCC = 12V MEASURED AT COMP PIN 2.5
SHUTDOWN THRESHOLD VOLTAGE (mV)
200
OUTPUT VOLTAGE (V)
150
100
50
0 -55 -35 -15
5 25 45 65 85 105 125 TEMPERATURE (C)
1530 G16
UW
Oscillator Frequency vs Temperature
350 340
Maximum G1 Duty Cycle vs Ambient Temperature
92 90 88 86 84 82 7700pF 80 THERMAL SHUTDOWN OCCURS BEYOND THESE POINTS 78 -55 -35 -15 5 25 45 65 85 105 125 AMBIENT TEMPERATURE (C)
1530 G12
PVCC = 12V fOSC = 300kHz G1, G2 CAPACITANCE = 1000pF
2200pF
3300pF 5500pF
250 -55 -35 -15
5 25 45 65 85 105 125 TEMPERATURE (C)
1530 G11
PVCC Supply Current vs Gate Capacitance
PVCC = 12V TA = 25C 60 GATE CAPACITANCE = C = C G1 G2 50 40 30 20 10 0 0
PVCC Shutdown Supply Current vs Temperature
80 75 70 65 60 55 50 45 40 35 PVCC = 12V
1
2
6 GATE CAPACITANCE (nF)
3
4
5
7
8
30 -55 -35 -15
5 25 45 65 85 105 125 TEMPERATURE (C)
1530 G15
1530 G14
Output Overcurrent Protection
Transient Response
2.0 1.5 1.0 0.5 0 0
PVCC = 12V TA = 25C REFER TO FIGURE 2
50mV/DIV
2A/DIV
SHORT-CIRCUIT CURRENT
50s/DIV
1530 G18
1
2
345678 OUTPUT CURRENT (A)
9
10
1530 G17
5
LTC1530
PI FU CTIO S
PVCC (Pin 1): Power Supply for G1, G2 and Logic. PVCC must connect to a potential of at least VIN + VGS(ON)Q1. If VIN = 5V, generate PVCC using a simple charge pump connected to the switching node between Q1 and Q2 (see Figure 1) or connect PVCC to a 12V supply. Bypass PVCC properly or erratic operation will result. A low ESR 10F capacitor or larger bypass capacitor along with a 0.1F surface mount ceramic capacitor in parallel is recommended from PVCC directly to GND to minimize switching ripple. Switching ripple should be 100mV at the PVCC pin. GND (Pin 2): Power and Logic Ground. GND is connected to the internal gate drive circuitry and the feedback circuitry. To obtain good output voltage regulation, use proper ground techniques between the LTC1530 GND and bottom-side FET source and the negative terminal of the output capacitor. See the Applications Information section for more details on PCB layout techniques. VSENSE/VOUT (Pin 3): Feedback Voltage Pin. For the adjustable LTC1530, use an external resistor divider to set the required output voltage. Connect the tap point of the resistor divider network to VSENSE and the top of the divider network to the output voltage. For fixed output voltage versions of the LTC1530, the resistor divider is internal and the top of the resistor divider network is brought out to VOUT. In general, the resistor divider network for each fixed output voltage version sinks approximately 30A. Connect VOUT to the output voltage either at the output capacitors or at the actual point of load. VSENSE/VOUT is sensitive to switching noise injected into the pin. Isolate high current switching traces from this pin and its PCB trace. COMP (Pin 4): External Compensation. The COMP pin is connected to the error amplifier output and the input of the PWM comparator. An RC + C network is typically used at COMP to compensate the feedback loop for optimum transient response. To shut down the LTC1530, pull this pin below 0.1V with an open-collector or open-drain transistor. Supply current is typically reduced to 45A in shutdown. An internal 4A pullup ensures start-up. IMAX (Pin 5): Current Limit Threshold. Current limit is set by the voltage drop across an external resistor connected between the drain of Q1 and IMAX. This voltage is compared with the voltage across the RDS(ON) of the high side MOSFET. The LTC1530 contains a 200A internal pulldown at IMAX to set current limit. This 200A current source has a positive temperature coefficient to provide first order correction for the temperature coefficient of the external N-channel MOSFET's RDS(ON). IFB (Pin 6): Current Limit Sense Pin. Connect IFB to the switching node between Q1's source and Q2's drain. If IFB drops below IMAX with G1 on, the LTC1530 enters current limit. Under this condition, the internal soft-start capacitor is discharged and COMP is pulled low slowly. Duty cycle is reduced and output power is limited. The current limit circuitry is only activated if PVCC 8V. This action eases start-up considerations as PVCC is ramping up because the MOSFET's RDS(ON) can be significantly higher than what is measured under normal operating conditions. The current limit circuit is disabled by floating IMAX and shorting IFB to PVCC. G2 (Pin 7): Gate Drive for the Low Side N-Channel MOSFET, Q2. This output swings from PVCC to GND. It is always low if G1 is high or if the output is disabled. To prevent undershoot during a soft-start cycle, G2 is held low until G1 first transitions high. G1 (Pin 8): Gate Drive for the Topside N-Channel MOSFET, Q1. This output swings from PVCC to GND. It is always low if G2 is high or if the output is disabled.
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LTC1530
BLOCK DIAGRA
ICOMP
COMP 4
ISS MSS FIXED VOUT CSS gm = 2millimho ERR MIN MAX 1.9V 2.5V 2.8V 3.3V R1 23.4k 44.4k 54.9k 68.4k R2 43.2k 43.2k 43.2k 40.8k
MHCL
TEST CIRCUITS
VIN 5V PVCC 12V 10F Q1 LO* Si4410DY 2.4H Q2 Si4410DY
PVCC 12V
750 PVCC
IMAX C1 100pF RC 8.2k CC 0.01F
IFB COMP LTC1530-2.5 G2 GND VOUT *SUMIDA CDRH127-2R4 **AVX TPSE337M006R0100 ***SANYO 10MV1200GX
W
INTERNAL OSCILLATOR LOGIC AND THERMAL SHUTDOWN POWER DOWN 8 G1 DISDR 1 PVCC
-
PWM
+
7 G2
+
-
-
+
-
+
FB 3 R1 3 R2 VOUT VSENSE
VREF
VREF - 3%
VREF + 3% FB 6 IFB
-
CC
+
5 IMAX IMAX
FOR FIXED VOLTAGE VERSIONS
HCL MONO
+
LVC
VREF /2
-
VREF VREF - 3% VREF + 3% VREF /2
VREF
1530 BD
+
+
0.1F G1
CIN*** 1200F x2
+
10F 0.1F PVCC IFB G1 NC NC NC VFB
100
+
CO** 330F x8
VOUT 2.5V 6A
1530 F02
COMP
COMP IMAX LTC1530 G2 VSENSE/VOUT GND
1530 F03
Figure 2
Figure 3
7
LTC1530
TEST CIRCUITS
PVCC 12V
+
0.1F PVCC IFB LTC1530 COMP COMP VOUT G2 GND 3300pF
1530 F04a
tr
10F G1 RISE/FALL
tf 90% 50% 10% tNOL 90% 50% 10% COMP tNOL 50% G1
1530 F04b
G1 3300pF
t SS
G2 RISE/FALL
50%
Figure 4
APPLICATIO S I FOR ATIO
OVERVIEW
The LTC1530 is a voltage feedback, synchronous switching regulator controller (see Block Diagram) designed for use in high power, low voltage step-down (buck) converters. It includes an on-chip soft-start capacitor, a PWM generator, a precision reference trimmed to 1%, two high power MOSFET gate drivers and all the necessary feedback and control circuitry to form a complete switching regulator circuit running at 300kHz. The LTC1530 includes a current limit sensing circuit that uses the topside external N-channel power MOSFET as a current sensing element, eliminating the need for an external sense resistor. If the current comparator, CC, detects an overcurrent condition, the duty cycle is reduced by discharging the internal soft-start capacitor through a voltage-controlled current source. Under severe overloads or output short-circuit conditions, the soft-start capacitor is pulled to ground and a start-up cycle is initiated. If the short circuit or overload persists, the chip repeats soft-start cycles and prevents damage to external components. THEORY OF OPERATION Primary Feedback Loop The LTC1530 compares the output voltage with the internal reference at the error amplifier inputs. The error amplifier outputs an error signal to the PWM comparator. This signal is compared to the fixed frequency oscillator
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sawtooth waveform to generate the PWM signal. The PWM signal drives the external MOSFETs at the G1 and G2 pins. The resulting chopped waveform is filtered by LO and COUT which closes the loop. Loop frequency compensation is typically accomplished with an external RC + C network at the COMP pin, which is the output node of the transconductance error amplifier. MIN, MAX Feedback Loops Two additional comparators in the feedback loop provide high speed fault correction in situations where the error amplifier cannot respond quickly enough. MIN compares the feedback signal to a voltage 3% below the internal reference. If the signal is below the comparator threshold, the MIN comparator overrides the error amplifier and forces the loop to maximum duty cycle, typically 86%. Similarly, the MAX comparator forces the output to 0% duty cycle if the feedback signal is greater than 3% above the internal reference. To prevent these two comparators from triggering due to noise, the MIN and MAX comparators' response times are deliberately delayed by two to three microseconds. These comparators help prevent extreme output perturbations with fast output load current transients, while allowing the main feedback loop to be optimally compensated for stability. Thermal Shutdown The LTC1530 has a thermal protection circuit that disables both internal gate drivers if activated. G1 and G2 are held low and the LTC1530 supply current drops to about 1mA.
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LTC1530
APPLICATIO S I FOR ATIO
Typically, thermal shutdown is activated if the LTC1530's junction temperature exceeds 150C. G1 and G2 resume switching when the junction temperature drops below 100C. Soft-Start and Current Limit Unlike other PWM parts, the LTC1530 includes an on-chip soft-start capacitor that is used during start-up and current limit operation. On power-up, an internal 4A pull-up at COMP brings the LTC1530 out of shutdown mode. An internal current source then charges the internal CSS capacitor. The COMP pin is clamped to one VGS above the voltage on CSS during start-up. This prevents the error amplifier from forcing the loop to maximum duty cycle. The LTC1530 operates at low duty cycle as the COMP pin voltage increases above about 2.4V. The slew rate of the soft-start capacitor is typically 0.4V/ms. As the voltage on CSS continues to increase, MSS eventually turns off and the error amplifier regulates the output. The MIN comparator is disabled if soft-start is active to prevent an override of the soft-start function. The LTC1530 includes another feedback loop to control operation in current limit. Before each falling edge of G1, the current comparator, CC, samples and holds the voltage drop across external MOSFET Q1 with the LTC1530's IFB pin. CC compares the voltage at IFB to the voltage at the IMAX pin. As peak current rises, the voltage across the RDS(ON) of Q1 increases. If the voltage at IFB drops below IMAX, indicating that Q1's drain current has exceeded the maximum desired level, CC pulls current out of CSS. Duty cycle decreases and the output current is controlled. The CC comparator pulls current out of CSS in proportion to the voltage difference between IFB and IMAX. Under minor overload conditions, the voltage at CSS falls gradually, creating a time delay before current limit activates. Very short, mild overloads may not affect the output voltage at all. Significant overload conditions allow the voltage on CSS to reach a steady state and the output remains at a reduced voltage until the overload is removed. Serious overloads generate a large overdrive and allow CC to pull the CSS voltage down quickly, thus preventing damage to the external components.
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By using the RDS(ON) of Q1 to measure output current, the current limit circuit eliminates the sense resistor that would otherwise be required. This minimizes the number of components in the high current power path. The current limit circuitry is not designed to be highly accurate. It is primarily meant to prevent damage to the power supply circuitry during fault conditions. The exact current level where current limiting takes effect will vary from unit to unit as the RDS(ON) of Q1 varies. Figure 5a illustrates the basic connections for the current limit circuitry. For a given current limit level, the external resistor from IMAX to VIN is determined by:
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RIMAX = where,
(ILMAX)RDS(ON)Q1
IIMAX
I ILMAX = ILOAD + RIPPLE 2 ILOAD = Maximum load current IRIPPLE = Inductor ripple current =
fOSC = LTC1530 oscillator frequency = 300kHz LO = Inductor value RDS(ON)Q1 = On-resistance of Q1 at ILMAX IIMAX = 200A sink current
VIN
(VIN - VOUT )(VOUT ) (fOSC)(LO)(VIN)
LTC1530 IMAX
+
RIMAX CIN
+
CC 200A IFB G1 20 Q1 LO VOUT COUT
1530 F05
-
+
G2 Q2
Figure 5a. Current Limit Setting (Use Kelvin-Sense Connections Directly at the Drain and Source of Q1)
9
LTC1530
APPLICATIO S I FOR ATIO
Figure 5b is derived based on the condition that ILMAX = ILOAD + IRIPPLE/2. Therefore, it only provides the minimum RIMAX value. It must be understood that during the initial power-up phase (VOUT = 0V), the initial start-up ILMAX can be much higher than the steady state condition ILMAX. Therefore, RIMAX must be selected with the start-up ILMAX in mind. In general, high output capacitance combined with a low value inductor increases the start-up ILMAX. Figures 6a and 6b plot the start-up ILMAX vs output capacitance and inductance for unloaded and loaded conditions with the current limit circuit disabled. Figures 6a and 6b are provided as examples. Actual ILMAX under start-up conditions must be measured for any application circuit so that RIMAX can be properly chosen. In order for the current limit circuit to operate properly and to obtain a reasonably accurate current limit threshold, the IMAX and IFB pins must be Kelvin sensed at Q1's drain and source pins. A 0.1F decoupling capacitor can also be connected across RIMAX to filter switching noise. In addition, LTC recommends that the voltage drop across the RIMAX resistor be set to 100mV. Otherwise, noise spikes or ringing at Q1's source can cause the actual current limit to be greater than the desired current limit set point. MOSFET Gate Drive The PVCC supply must be greater than the input supply voltage, VIN, by at least one power MOSFET VGS(ON) for efficient operation. This higher voltage can be supplied with a separate supply, or it can be generated using a simple charge pump as shown in Figure 7. The 86% maximum duty cycle ensures sufficient off-time to refresh the charge pump during each cycle. As PVCC is powered up from 0V, the LTC1530 undervoltage lockout circuit prevents G1 and G2 from pulling high until PVCC reaches about 3.5V. To prevent Q1's high RDS(ON) from triggering the current limit comparator while PVCC is slewing, the current limit circuit is disabled until PVCC is 8V. In addition, on start-up or recovery from thermal shutdown, the driver logic is designed to hold G2 low until G1 first goes high.
MINIMUM REQUIRED RIMAX ()
START-UP ILMAX (A)
START-UP ILMAX (A)
10
U
5500 RIMAX 500 ILMAX = ILOAD + IRIPPLE /2 Q1 RDS(ON) = 0.05 0.04 4500 3500 0.03 2500 0.02 1500 0.01 500 0 2 4 6 8 10 12 14 16 18 20 ILMAX (A)
1530 F05b
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Figure 5b. Minimum Required RIMAX vs ILMAX
25 TA = 25C VIN = 5V ILOAD = 0A
20
15 L = 1.2H 10 L = 4.7H 5 L = 2.4H
0 0 2 4 6 8 10 OUTPUT CAPACITANCE (mF) 12
1530 F06a
Figure 6a. Start-Up ILMAX vs Output Capacitance
30 25 20 L = 1.2H 15 10 5 0 L = 4.7H TA = 25C VIN = 5V ILOAD = 10A L = 2.4H
0
2
10 4 6 8 OUTPUT CAPACITANCE (mF)
12
1530 F06b
Figure 6b. Start-Up ILMAX vs Output Capacitance
LTC1530
APPLICATIO S I FOR ATIO
OPTIONAL FOR VIN > 6.5V 13V 1N5243B MBR0530T1 MBR0530T1 VIN
+
10F PVCC G1 Q1 LO G2 Q2 LTC1530 0.22F
Figure 7. Doubling Charge Pump
Power MOSFETs Two N-channel power MOSFETs are required for synchronous LTC1530 circuits. They should be selected based primarily on threshold voltage and on-resistance considerations. Thermal dissipation is often a secondary concern in high efficiency designs. The required MOSFET threshold should be determined based on the available power supply voltages and/or the complexity of the gate drive charge pump scheme. In 5V input designs where a 12V supply is used to power PVCC, standard MOSFETs with RDS(ON) specified at VGS = 5V or 6V can be used with good results. The current drawn from the 12V supply varies with the MOSFETs used and the LTC1530's operating frequency, but is generally less than 50mA. LTC1530 applications that use a 5V VIN voltage and a doubling charge pump to generate PVCC do not provide enough gate drive voltage to fully enhance standard power MOSFETs. Under this condition, the effective MOSFET RDS(ON) may be quite high, raising the dissipation in the FETs and reducing efficiency. In addition, power supply start-up problems can occur with standard power MOSFETs. These start-up problems can occur for two reasons. First, if the MOSFET is not fully enhanced, the higher effective RDS(ON) causes the LTC1530 to activate current limit at a much lower level than the desired trip point. Second, standard MOSFETs have higher GATE threshold voltages than logic level MOSFETs, thereby increasing the PVCC voltage required to turn them on. A
U
+
CIN
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+
VOUT CO
MOSFET whose RDS(ON) is rated at VGS = 4.5V does not necessarily have a logic level MOSFET GATE threshold voltage. Logic level FETs are the recommended choice for 5V-only systems. Logic level FETs can be fully enhanced with a doubler charge pump and will operate at maximum efficiency. Note that doubler charge pump designs running from supplies higher than 6.5V should include a Zener diode clamp at PVCC to prevent transients from exceeding the absolute maximum rating of the pin. After the MOSFET threshold voltage is selected, choose the RDS(ON) based on the input voltage, the output voltage, allowable power dissipation and maximum output current. In a typical LTC1530 buck converter circuit, operating in continuous mode, the average inductor current is equal to the output load current. This current flows through either Q1 or Q2 with the power dissipation split up according to the duty cycle: V DC(Q1) = OUT VIN
1530 F07
VIN - VOUT V DC(Q2) = 1 - OUT = VIN VIN
(
)
The RDS(ON) required for a given conduction loss can now be calculated by rearranging the relation P = I2R.
PMAX(Q1) 2 DC (Q1) IMAX
IN MAX(Q1) 2 MAX
RDS(ON)Q1 =
[] (V )[P = (V )I
OUT
]
RDS(ON)Q2 =
[
PMAX(Q2) 2 DC (Q 2) IMAX
=
(VIN - VOUT )IMAX2
] (V )[P
IN
MAX(Q2)
]
11
LTC1530
APPLICATIO S I FOR ATIO
PMAX should be calculated based primarily on required efficiency or allowable thermal dissipation. A high efficiency buck converter designed for the Pentium II with 5V input and a 2.8V, 11.2A output might allow no more than 4% efficiency loss at full load for each MOSFET. Assuming roughly 90% efficiency at this current level, this gives a PMAX value of: (2.8)(11.2A/0.9)(0.04) = 1.39W per FET and a required RDS(ON) of: RDS(ON)Q1 = 5V 1.39W
2.8V 11.2A2
(
)
= 0.020
RDS(ON)Q2 =
5V 1.39W
(
5V - 2.8V 11.2A2
(
)
)
= 0.025
Note that while the required RDS(ON) values suggest large MOSFETs, the power dissipation numbers are only 1.39W per device or less -- large TO-220 packages and heat sinks are not necessarily required in high efficiency applications. Siliconix Si4410DY or International Rectifier
Table 1. Recommended MOSFETs for LTC1530 Applications
RDS(ON) AT 25C () 0.019 0.020 0.035 0.01 0.0075 0.014 0.028 0.037
MANUFACTURER Siliconix Siliconix ON Semiconductor Fairchild ON Semiconductor IR IR Fuji
PART NO. SUD50N03-10 Si4410DY MTD20N03HDL FDS6680 MTB75N03HDL* IRL3103S IRLZ44 2SK1388
PACKAGE TO-252 SO-8 DPAK SO-8 D2PAK D2PAK TO-220 TO-220
Note: Please refer to the manufacturer's data sheet for testing conditions and detailed information. *Users must consider the power dissipation and thermal effects in the LTC1530 if driving external MOSFETs with high values of input capacitance. Refer to the PVCC Supply Current vs GATE Capacitance in the Typical Performance Characteristics section.
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IRF7413 (both in SO-8) or Siliconix SUD50N03 or Motorola MTD20N03HDL (both in DPAK) are small footprint surface mount devices with RDS(ON) values below 0.03 at 5V of VGS that work well in LTC1530 circuits. With higher output voltages, the RDS(ON) of Q1 may need to be significantly lower than that for Q2. These conditions can often be met by paralleling two MOSFETs for Q1 and using a single device for Q2. Using a higher PMAX value in the RDS(ON) calculations generally decreases the MOSFET cost and the circuit efficiency and increases the MOSFET heat sink requirements. In most LTC1530 applications, RDS(ON) is used as the current sensing element. MOSFET RDS(ON) has a positive temperature coefficient. Therefore, the LTC1530 IMAX sink current is designed with a positive 3300ppm/C temperature coefficient. The positive tempco of IMAX provides first order correction for current limit vs temperature. Therefore, current limit does not have to be set to an increased level at room temperature to guarantee a desired output current at elevated temperatures. Table 1 highlights a variety of power MOSFETs that are suitable for use in LTC1530 applications.
RATED CURRENT (A) 15A at 25C 10A at 100C 10A at 25C 8A at 75C 20A at 25C 16A at 100C 11.5A at 25C 75A at 25C 59A at 100C 56A at 25C 40A at 100C 50A at 25C 36A at 100C 35A at 25C TYPICAL INPUT CAPACITANCE Ciss (pF) 3200 2700 880 2070 4025 1600 3300 1750 JC (C/W) 1.8 -- 1.67 25 1.0 1.8 1.0 2.08 TJMAX (C) 175 150 150 150 150 175 175 150
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LTC1530
APPLICATIO S I FOR ATIO
Inductor Selection
The inductor is often the largest component in an LTC1530 design and must be chosen carefully. Choose the inductor value and type based on output slew rate requirements and expected peak current. The required output slew rate primarily controls the inductor value. The maximum rate of rise of inductor current is set by the inductor's value, the input-to-output voltage differential and the LTC1530's maximum duty cycle. In a typical 5V input, 2.8V output application, the maximum rise time will be:
V - V 1.85 DCMAX IN OUT = L L
A s
where L is the inductor value in H. With proper frequency compensation, the combination of the inductor and output capacitor values determine the transient recovery time. In general, a smaller value inductor improves transient response at the expense of ripple and inductor core saturation rating. A 2H inductor has a 0.9A/s rise time in this application, resulting in a 5.5s delay in responding to a 5A load current step. During this 5.5s, the difference between the inductor current and the output current is made up by the output capacitor. This action causes a temporary voltage droop at the output. To minimize this effect, the inductor value should usually be in the 1H to 5H range for most 5V input LTC1530 circuits. Different combinations of input and output voltages and expected loads may require different values. Once the required inductor value is selected, choose the inductor core type based on peak current and efficiency requirements. Peak current in the inductor is equal to the maximum output load current plus half of the peak-topeak inductor ripple current. Inductor ripple current is set by the inductor's value, the input voltage, the output voltage and the operating frequency. If the efficiency is high, ripple current is approximately equal to: IRIPPLE =
(VIN - VOUT)(VOUT) (fOSC)(LO)(VIN)
where fOSC = LTC1530 oscillator frequency LO = Inductor value
U
Solving this equation for a typical 5V to 2.8V application with a 2H inductor, ripple current is:
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UU
(2.2V)(0.56) = 2AP-P (300kHz)(2H)
Peak inductor current at 11.2A load:
11.2A + 2A = 12.2A 2
The ripple current should generally fall between 10% and 40% of the output current. The inductor must be able to withstand this peak current without saturating, and the copper resistance in the winding should be kept as low as possible to minimize resistive power loss. Note that in circuits not employing the current limit function, the current in the inductor may rise above this maximum under short circuit or fault conditions; the inductor should be sized accordingly to withstand this additional current. Inductors with gradual saturation characteristics (example: powdered iron) are often the best choice. Input and Output Capacitors A typical LTC1530 design places significant demands on both the input and the output capacitors. During normal steady load operation, a buck converter like the LTC1530 draws square waves of current from the input supply at the switching frequency. The peak current value is equal to the output load current plus 1/2 the peak-to-peak ripple current. Most of this current is supplied by the input bypass capacitor. The resulting RMS current flow in the input capacitor heats it and causes premature capacitor failure in extreme cases. Maximum RMS current occurs with 50% PWM duty cycle, giving an RMS current value equal to IOUT/2. A low ESR input capacitor with an adequate ripple current rating must be used to ensure reliable operation. Note that capacitor manufacturers' ripple current ratings are often based on only 2000 hours (3 months) lifetime at rated temperature. Further derating of the input capacitor ripple current beyond the manufacturer's specification is recommended to extend the useful life of the circuit. Lower operating temperature has the largest effect on capacitor longevity.
13
LTC1530
APPLICATIO S I FOR ATIO
The output capacitor in a buck converter under steady state conditions sees much less ripple current than the input capacitor. Peak-to-peak current is equal to inductor ripple current, usually 10% to 40% of the total load current. Output capacitor duty places a premium not on power dissipation but on ESR. During an output load transient, the output capacitor must supply all of the additional load current demanded by the load until the LTC1530 adjusts the inductor current to the new value. ESR in the output capacitor results in a step in the output voltage equal to the ESR value multiplied by the change in load current. An 11A load step with a 0.05 ESR output capacitor results in a 550mV output voltage shift; this is 19.6% of the output voltage for a 2.8V supply! Because of the strong relationship between output capacitor ESR and output load transient response, choose the output capacitor for ESR, not for capacitance value. A capacitor with suitable ESR will usually have a larger capacitance value than is needed to control steady-state output ripple. Electrolytic capacitors rated for use in switching power supplies with specified ripple current ratings and ESR can be used effectively in LTC1530 applications. OS-CON electrolytic capacitors from Sanyo and other manufacturers give excellent performance and have a very high performance/size ratio for electrolytic capacitors. Surface mount applications can use either electrolytic or dry tantalum capacitors. Tantalum capacitors must be surge tested and specified for use in switching power supplies. Low cost, generic tantalums are known to have very short lives followed by explosive deaths in switching power supply applications. AVX TPS series surface mount devices are popular surge tested tantalum capacitors that work well in LTC1530 applications. A common way to lower ESR and raise ripple current capability is to parallel several capacitors. A typical LTC1530 application might exhibit 5A input ripple current. Sanyo OS-CON capacitors, part number 10SA220M (220F/ 10V), feature 2.3A allowable ripple current at 85C; three in parallel at the input (to withstand the input ripple current) meet the above requirements. Similarly, AVX TPSE337M006R0100 (330F/6V) capacitors have a rated maximum ESR of 0.1; seven in parallel lower the net
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output capacitor ESR to 0.014. For low cost applications, the Sanyo MV-GX capacitor series can be used with acceptable performance. Feedback Loop Compensation The LTC1530 voltage feedback loop is compensated at the COMP pin, which is the output node of the gm error amplifier. The feedback loop is generally compensated with an RC + C network from COMP to GND as shown in Figure 8a. Loop stability is affected by the values of the inductor, the output capacitor, the output capacitor ESR, the error amplifier transconductance and the error amplifier compensation network. The inductor and the output capacitor create a double pole at the frequency: fLC = 1 2 LO COUT
W
UU
(
)
The ESR of the output capacitor and the output capacitor value form a zero at the frequency:
fESR =
(2)(ESR)(COUT )
1
The compensation network used with the error amplifier must provide enough phase margin at the 0dB crossover frequency for the overall open-loop transfer function. The zero and pole from the compensation network are:
fZ =
(2)(RC)(CC)
1
and fP =
(2)(RC)(C1)
1
respectively. Figure 8b shows the Bode plot of the overall transfer function. The compensation values used in this design are based on the following criteria, fSW = 12fCO, fZ = fLC, fP = 5fCO. At the closed-loop frequency fCO, the attenuation due to the LC filter and the input resistor divider is compensated by the gain of the PWM modulator and the gain of the error amplifier (gmERR)(RC).
LTC1530
APPLICATIO S I FOR ATIO
Although a mathematical approach to frequency compensation can be used, the added complication of input and/ or output filters, unknown capacitor ESR, and gross operating point changes with input voltage, load current variations and frequency of operation all suggest a more practical empirical method. This can be done by injecting a transient current at the load and using an RC network box to iterate toward the final compensation values or by obtaining the optimum loop response using a network analyzer to find the actual loop poles and zeros. Table 2 shows the suggested compensation components for 5V input applications based on the inductor and output capacitor values. The values were calculated using multiple paralleled 330F AVX TPS series surface mount
VOUT 3 LTC1530 COMP 4 RC CC C1 - ERR + BG
1530 F08a
Figure 8a. Compensation Pin Hook-Up
LOOP GAIN
fSW = LTC1530 SWITCHING FREQUENCY fCO = CLOSED-LOOP CROSSOVER FREQUENCY
fZ
-20dB/DECADE fP fLC fESR fCO FREQUENCY
1530 F08b
Figure 8b. Bode Plot of the LTC1530 Overall Transfer Function
U
tantalum capacitors for the output capacitor. The optimum component values might deviate from the suggested values slightly because of board layout and operating condition differences.
Table 2. Suggested Compensation Network for a 5V Input Application Using Multiple Paralleled 330F AVX TPS Output Capacitors for 2.5V Output
LO (H) 1 1 1 2.7 2.7 2.7 5.6 5.6 5.6 CO (F) 990 1980 4950 990 1980 4950 990 1980 4950 RC (k) 1.3 2.7 6.8 3.6 7.5 18 7.5 15 36 CC (F) 0.022 0.022 0.01 0.022 0.01 0.01 0.01 0.01 0.0047 C1 (pF) 1000 470 220 330 220 68 220 100 47
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An alternate output capacitor is the Sanyo MV-GX series. Using multiple paralleled 1500F Sanyo MV-GX capacitors for the output capacitor, Table 3 shows the suggested compensation components for 5V input applications based on the inductor and output capacitor values.
Table 3. Suggested Compensation Network for a 5V Input Application Using Multiple Paralleled 1500F SANYO MV-GX Output Capacitors for 2.5V Output
LO (H) 1 1 1 2.7 2.7 2.7 5.6 5.6 5.6 CO (F) 4500 6000 9000 4500 6000 9000 4500 6000 9000 RC (k) 3 4 6 8.2 11 16 16 22 33 CC (F) 0.022 0.022 0.022 0.022 0.01 0.01 0.01 0.01 0.01 C1 (pF) 470 330 220 150 100 100 100 68 47
Note: For different values of VOUT, multiply the RC value by VOUT/2.5 and multiply the CC and C1 values by 2.5/VOUT. This maintains the same crossover frequency for the closed-loop transfer function.
15
LTC1530
APPLICATIO S I FOR ATIO
Thermal Considerations
Limit the LTC1530's junction temperature to less than 125C. The LTC1530's SO-8 package is rated at 130C/W and care must be taken to ensure that the worst-case input voltage and gate drive load current requirements do not cause excessive die temperatures. Short-circuit or fault conditions may activate the internal thermal shutdown circuit. LAYOUT CONSIDERATIONS When laying out the printed circuit board (PCB), the following checklist should be used to ensure proper operation of the LTC1530. These items are illustrated graphically in the layout diagram of Figure 9. The thicker lines show the high current power paths. Note that at 10A current levels or above, current density in the PCB itself is a serious concern. Traces carrying high current should be as wide as possible. For example, a PCB fabricated with 2oz copper requires a minimum trace width of 0.15" to carry 10A, and only if trace length is kept short. 1. In general, begin the layout with the location of the power devices. Orient the power circuitry so that a clean power flow path is achieved. Maximize conductor widths but minimize conductor lengths. Keep high current connections on one side of the PCB if possible. If not, minimize the use of vias and keep the current density in the vias to <1A/via, preferably < 0.5A/via. After achieving a satisfactory power path layout, proceed with the control circuitry layout. It is much easier to find routes for the relatively small traces in the control circuits than it is to find circuitous routes for high current paths. 2. Tie the GND pin to the ground plane at a single point, preferably at a fairly quiet point in the circuit, such as the bottom of the output capacitors. However, this is not
16
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always practical due to physical constraints. Connect the low side source to the input capacitor ground. Connect the input and output capacitor to the ground plane. Run a separate trace for the low side FET source to the input capacitors. Do not tie this single point ground in the trace run between the low side FET source and the input capacitor ground. This area of the ground plane is very noisy. 3. Locate the small signal resistor and capacitors used for frequency compensation close to the COMP pin. Use a separate ground trace for these components that ties directly to the GND pin of the LTC1530. Do not connect these components to the ground plane! 4. Place the PVCC decoupling capacitor as close to the LTC1530 as possible. The 10F bypass capacitor shown at PVCC helps provide optimum regulation performance by minimizing ripple at the PVCC pin. 5. Connect the (+) plate of CIN as close as possible to the drain of the upper MOSFET. LTC recommends an additional 1F low ESR ceramic capacitor between VIN and power ground. 6. The VSENSE/VOUT pin is very sensitive to pickup from the switching node. Care must be taken to isolate this pin from capacitive coupling to the high current inductor switching signals. A 0.1F is recommended between the VOUT pin and the GND pin directly at the LTC1530 for fixed voltage versions. For the adjustable voltage version, keep the resistor divider close to the LTC1530. The bottom resistor's ground connection should tie directly to the LTC1530's GND pin. 7. Kelvin sense IMAX and IFB at the drain and source pins of Q1. 8. Minimize the length of the gate lead connections.
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LTC1530
APPLICATIO S I FOR ATIO
PVCC 1 10F 0.1F
+
PVCC LTC1530
2 GND 3 4 VOUT COMP
C1
RC CC
0.1F
Figure 9. LTC1530 Layout Diagram
PVCC 12V 10F
+
0.1F 4 C1 RC CC
PVCC
6 20 COMP IFB LTC1530 7 (SEE TABLE) G2 GND 2 VOUT 3
(SEE TABLE) * SILICONIX SUD50N03-10 ** 3x SANYO 10MV1200GX OR 3x SANYO OS-CON 6SH330K
DEVICE LTC1530-3.3 LTC1530-3.3 LTC1530-2.8 LTC1530-2.8 LTC1530-2.5 LTC1530-2.5 LTC1530-1.9 LTC1530-1.9
OUTPUT CAPACITOR (CO) 7 X330F AVX TPSE337M006R0100 4 X1500F SANYO 6MV1500GX 7 X330F AVX TPSE337M006R0100 4 X1500F SANYO 6MV1500GX 7 X330F AVX TPSE337M006R0100 4 X1500F SANYO 6MV1500GX 7 X330F AVX TPSE337M006R0100 4 X1500F SANYO 6MV1500GX
Figure 10. 5V to 1.9V-3.3V Synchronous Buck Converter PVCC Is Powered from 12V Supply
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BOLD LINES INDICATE HIGH CURRENT PATHS 8 7 6 RIFB Q2 LO VOUT VIN G1 G2 IFB IMAX Q1
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+
CIN
5 RIMAX
+
COUT
1530 F09
2.7k 1 5 IMAX G1 8
VIN 5V
+
CIN** Q1* LO VOUT 1.9V TO 3.3V 14A
1530 F10
+
Q2*
CO (SEE TABLE)
COILTRONICS CTX02-13198 (2H) OR
PANASONIC ETQP6F2R5HA PCC-N6 (2.5H)
RC 10k 15k 8.6k 13k 7.5k 11k 5.6k 8.2k
CC 0.022F 0.022F 0.022F 0.022F 0.022F 0.022F 0.033F 0.022F
C1 150pF 100pF 150pF 100pF 220pF 120pF 220pF 220pF
1530 TA TBL
17
LTC1530
TYPICAL APPLICATIO S
5V to 1.9V-3.3V Synchronous Buck Converter PVCC Is Generated from Charge Pump
VIN 5V MBR0530T1 MBR0530T1 2.7k 1 PVCC
C1
RC CC
(SEE TABLE) * SILICONIX SUD50N03-10 ** 3x SANYO 10MV1200GX OR 3x SANYO OS-CON 6SH330K
DEVICE LTC1530-3.3 LTC1530-3.3 LTC1530-2.8 LTC1530-2.8 LTC1530-2.5 LTC1530-2.5 LTC1530-1.9 LTC1530-1.9
5V to Dual Output (3.3V and 12V) Synchronous Buck Converter
VIN 5V LT1129CS8 OUT ADJ VOUT2 12V C4 0.4A 33F 20V
R1 2.7k 5 4 C1 220pF RC 4.7k CC 0.022F 1 PVCC
IMAX
6 COMP IFB LTC1530-3.3 7 G2 3 GND VOUT 2
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+
0.1F 8 6 20 Q2* 10F 0.22F G1 Q1* LO
+
CIN**
5 4
IMAX
COMP IFB LTC1530 7 (SEE TABLE) G2 3 GND VOUT 2
COILTRONICS CTX02-13198 (2H) OR
+
CO (SEE TABLE)
VOUT 1.9V TO 3.3V 14A
PANASONIC ETQP6F2R5HA PCC-N6 (2.5H)
1530 TA02
OUTPUT CAPACITOR (CO) 7 X330F AVX TPSE337M006R0100 4 X1500F SANYO 6MV1500GX 7 X330F AVX TPSE337M006R0100 4 X1500F SANYO 6MV1500GX 7 X330F AVX TPSE337M006R0100 4 X1500F SANYO 6MV1500GX 7 X330F AVX TPSE337M006R0100 4 X1500F SANYO 6MV1500GX
RC 10k 15k 8.6k 13k 7.5k 11k 5.6k 8.2k
CC 0.022F 0.022F 0.022F 0.022F 0.022F 0.022F 0.033F 0.022F
C1 150pF 100pF 150pF 100pF 220pF 120pF 220pF 220pF
1530 TA TBL
+
D2 D1 MBR0530T1 MBR0530T1
C4 22F 35V
IN
R3 8.25k 1%
+
C2 0.1F 8
+
C3 10F C5 0.22F
+
CIN
R4 3.74k 1%
G1
Q1 R2, 20
L1 Q3
CIN = 3x SANYO 10MV1200GX COUT = 4x SANYO 6MV1500GX L1 = SUMIDA 6383-T018 (PRI = 1H, SEC = 26H) Q1, Q2 = SILICONIX SUD50N03-10 Q3 = SILICONIX Si4450DY
Q2
+
COUT
VOUT1 3.3V 14A
1530 TA09
LTC1530
TYPICAL APPLICATIO S
LTC1530 3.3V to 1.8V, 14A Application
VIN 3.3V
3.3F 10F
D2 MBRS120 D1 MBRS120
2.4k 5 4 C1 100pF RC 13k CC 0.022F
VIN 3.3V
+
47F 2 VIN 30 1 ILIM SW1 LT1107-12 SENSE SW2 4 GND 5 L1** 10H D1 MBR0520
VIN 3.3V
+
3.3F 3 SHDN 1 6 VIN SW VC LT1317 FB 100pF GND 4 5 2.2M 300k
3000pF 33k
U
+ +
1 2 3
VIN GND VOUT
C1 - LTC1517-5 C1+
5 0.22F 4
PVCC
+
0.1F Q1 SUD50N03 20 0.22F L1 2.5H
+
10F 1 IMAX PVCC G1 8 6
CIN 1500F x3
COMP IFB LTC1530-ADJ 7 G2 GND VSENSE 2 3 R2 1.24k 1%
+
Q2 SUD50N03
COUT 1500F x4
VOUT 1.8V 14A
R1 576 1% L1 = PANASONIC ETQP6F2R5HA PCC-N6 CIN = 3x SANYO 6MV1500GX 1530 TA03 COUT = 4x SANYO 6MV1500GX
Other Methods to Generate PVCC Supply from 3.3V Input
L1* 33H D1 MBRS120T3
+
68F 20V
PVCC 12V 1F
3
8
+
10F 20V
PVCC 10V 1F
2
* SUMIDA CD54-330K OR COILCRAFT DT3316-473 ** SUMIDA CD43-100
1530 TA04
19
LTC1530
TYPICAL APPLICATIO S
LTC1530 High Efficiency Boost Converter
R5 0.005 5% C3 1F 16V R2 47k C10 1F 16V C11 470F 6V
VIN 3.3V
D1 FMMD914
+
C8 1F 16V 1
C1 10F 16V
C2 1F 16V C4 100pF C7 0.22F 16V R3 47k Q1 FMMT3904
5 C1- VIN LTC1517-5 4 2 GND C1+ 3 C6 1F 16V VOUT
L1 = COILCRAFT DO3316P-102 L2 = SUMIDA CEE125C-2R1
EFFICIENCY (%)
20
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L2 2.1H C9 0.22F 16V C18 + 330F 10V C17 330F 10V
+ +
C12 470F 6V
L1 1H D3 MBRS140T3 D2 MBR0530T1 Q2 IRF7811 Q3 IRF7811 Q4 IRF7811 C16 330F 10V
R4 360
+ +
C14 330F 10V
+ +
C13 1F 16V C15 330F 10V
VOUT 5V 6A
1 4 C5 0.022F R1 10k COMP
5
6 IFB G2 G1 VSENSE 7 8 3 R6 23.2k 1% R7 71.5k 1%
1530 TA05a
PVCC IMAX LTC1530
GND 2
Efficiency vs Load Current
100 90 80 70 60 50 40 30 20 10 0 0 TA = 25C VIN = 3.3V VOUT = 5V 1 3 4 2 LOAD CURRENT (A) 5 6
1530 TA05b
LTC1530
TYPICAL APPLICATIO S
LTC1530 5V to - 5V Synchronous Inverter
VIN 5V
R1 2.4k
1
5
8 G1 IFB 6 7 3 R2 100
+
C3 10F
C4 0.1F
PVCC IMAX
LTC1530-ADJ G2 4 RC 4.7k CC 0.22F COMP GND 2 VSENSE
D5 MBR0530T1
R11 1k
C5 2.2F 1 87 1/2 2 LTC1693-2
C1 1000pF
C7 1000pF
CIN, COUT = 3x SANYO 10MV1200GX L1 = PANASONIC ETQP6F2R5HA (PCC-N6) Q1,Q2 = SILICONIX SUD50N03-10
R3 1k
D3 1N4148
R5 10k C2 10F
Efficiency vs Load Current
100 90 80 70 TA = 25C
EFFICIENCY (%)
60 50 40 30 20 10 0 0 0.1 1 3 2 LOAD CURRENT (A) 4
1530 TA07b
+
R4 3.09k
5
+
U
+
CIN
R8 560 1/2W
+ C6
R9 680 2.2F
OPTIONAL Z1 12V ZENER 1/2W 3 4
D1 MBR0530T1
6
5
Q1
D2 MBR0530T1 Q3 2N7000 R10 330 D4 1N4148
1/2 LTC1693-2
Q2
VOUT -5V 5A R7 4.7 R6 220 1/6W COUT
+
L1 2.5H
1530 TA07a
21
LTC1530
TYPICAL APPLICATIO S
1,2,3
7,8,9
+
VIN 4V TO 8V
L2 10H C8 4.7F
D1 MBR0520
+
6 3 VIN SHDN LT1317 1 VC GND C6 100pF 4 FB 2 SW 5
R6 2.2M R7 300k RC 4.7k CC 0.22F
C7 3000pF R8 33k
CIN, COUT = 3x SANYO 10MV1200GX CFLY = 2x SANYO 16SA150MK L1 = COILTRONIX CTX02-13198-1 (L1A = 1,2,3 7,8,9; L1B = 10,11,12 4,5,6)
EFFICIENCY (%)
22
U
LTC1530 Synchronous SEPIC Converter
RSENSE 0.02
*
L1A
CFLY
Q2 P-MOSFET 4,5,6 L1B
VOUT
+
CIN Q1 N-MOSFET 10,11,12
R3 3.09k
+
D2 1N4148
VOUT 5V 4A C2 10F
+
COUT
*
R4 1k R2 10k
R9 5.6
R1 2.2k
R5 20
+
C9 4.7F
+
C3 10F
C4 0.1F
1
5
6 8 7 3
+
PVCC IMAX IFB G1 C1 1000pF 4 LTC1530-ADJ G2 COMP GND 2 VSENSE
C5 4.7F 1 4 8 LTC1693-3 7 3
1530 TA08a
L2 = SUMIDA CD43-100 Q1 = SILICONIX N-MOSFET SI4420DY Q2 = SILICONIX P-MOSFET SI4425DY RSENSE = DALE LVR-3 3W
Efficiency vs Load Current
100 90 80 70 60 50 40 30 20 10 0 0 0.5 0.1 1.0 1.5 2.0 2.5 3.0 LOAD CURRENT (A) 3.5 4.0 TA = 25C VIN = 4V VIN = 8V
1530 TA08b
LTC1530
PACKAGE DESCRIPTION U
Dimensions in inches (millimeters) unless otherwise noted.
S8 Package 8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.189 - 0.197* (4.801 - 5.004) 8 7 6 5
0.228 - 0.244 (5.791 - 6.197)
0.150 - 0.157** (3.810 - 3.988)
1 0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254) 0- 8 TYP
2
3
4
0.053 - 0.069 (1.346 - 1.752)
0.004 - 0.010 (0.101 - 0.254)
0.014 - 0.019 (0.355 - 0.483) TYP *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
0.016 - 0.050 (0.406 - 1.270)
0.050 (1.270) BSC
SO8 1298
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.
23
LTC1530
TYPICAL APPLICATION
LTC1530 - 5V to 2.5V, 5A Inverting Polarity Converter
(OPTIONAL) Z1 1N4742A R8 4.7 C5 0.1F MBRS130 GND MBRS130
+
C4 10F
CIN 1500F 6.3V x3
+
1 5 PVCC IMAX 4 COMP
LTC1530-ADJ C1 1000pF RC 5.6k CC 0.1F GND 2 G2 VSENSE 3 7
VIN = -5V CIN, COUT = 3x SANYO 6MV1500GX L1 = PANASONIC ETQP6F2R5HA PCC-N6 Q1,Q2 = SILICONIX SUD50N03-10 RSENSE = DALE LVR-1, 1W
RELATED PARTS
PART NUMBER LTC1266 LTC1430A LTC1553 LTC1628 LTC1629 LTC1702 LTC1709 LTC1735 LTC1753 LTC1772 LTC1873 LTC1929 DESCRIPTION Current Mode Step-Up/Down Switching Regulator Controller High Power Step-Down Switching Regulator Controller 5-Bit Programmable Synchronous Switching Regulator Controller for Pentium II Processor Dual High Efficiency Low Noise Synchronous Step-Down Switching Regulator 20A to 200A PolyPhaseTM Synchronous Controller No RSENSE 2-Phase Dual Synchronous Step-Down Controller 2-Phase Synchronous Controller with 5-Bit VID High Efficiency Synchronous Step-Down Switching Regulator 5-Bit Programmable Synchronous Switching Regulator Controller for Pentium II and Pentium III Processors SOT-23 Step-Down Controller Dual 550kHz 2-Phase Synchronous Controller with 5-Bit VID 2-Phase Synchronous Controller COMMENTS Synchronous N- or P-Channel FETs, Comparator/Low-Battery Detector Synchronous N-Channel FETs, 3.3V to 2.5V Conversion Synchronous N-Channel FETs, Voltage Mode PVCC 20V, 1.8V to 3.5V Output Constant Frequency, Standby 5V and 3.3V LDOs, 3.5V VIN 36V Expandable from 2-Phase to 12-Phase, Uses All Surface Mount Components, No Heat Sink 550kHz, No Sense Resistor Current Mode, VIN to 36V, IOUT Up to 42A, VOUT from 1.3V to 3.5V Drives Synchronous N-Channel FETs, VIN 36V Synchronous N-Channel FETs, Voltage Mode PVCC 14V, 1.3V to 3.5V Output, VRM8.2 to VRM8.4 100% Duty Cycle, Up to 4A, 2.2V to 9.8V VIN Desktop VID Codes, IOUT Up to 25A On Each Channel, 28-Lead SSOP Up to 42A, Uses All Surface Mount Components, No Heat Sink, 3.5V VIN 36V
PolyPhase is a trademark of Linear Technology Corporation.
24
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 q FAX: (408) 434-0507 q www.linear-tech.com
U
RSENSE 0.02
C8 0.22F
R6 2k
R7 22 6 IFB G1
L1 2.5H
+
COUT 1500F 6.3V x3
VOUT* 2.5V 5A
Q2 8 Q1 Z2 BZX55C6V2 1/2W, 6.2V R10 1k R9 10k Q4 2N3904 R1 1.5K Q5 2N3904 GND R12 40k C10 1F R2 1k C9 1F
R11 10k R13 1k
Q3 2N3906
HARD CURRENT LIMIT CIRCUIT (OPTIONAL)
1530 TA06
*FOR HIGHER OUTPUT VOLTAGE (EX 3.3V), INCREASE R8 TO 20 AND INSTALL Z1
1530f LT/TP 0200 4K * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1998

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