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Synchronous Voltage Mode Controller for Distributed Power Supply Applications
POWER MANAGEMENT Description
The SC1102 and SC1102A are low-cost, full featured, synchronous voltage-mode controllers designed for use in single ended power supply applications where efficiency is of primary concern. Synchronous operation allows for the elimination of heat sinks in many applications. The SC1102s are ideal for implementing DC/DC converters needed to power advanced microprocessors in low cost systems, or in distributed power applications where efficiency is important. Internal level-shift, high-side drive circuitry, and preset shoot-thru control, allows the use of inexpensive N-channel power switches. SC1102s features include temperature compensated voltage reference, triangle wave oscillator and current sense comparator circuitry. Power good signaling, shutdown, and over voltage protection are also provided. The SC1102 operates at a fixed frequency of 200kHz and the SC1102A at 500kHz, providing a choice for optimum compromise between efficiency, external component size, and cost. Two SC1102s can be used together to sequence power up of telecom systems. The power good of the first SC1102 connected to the enable of the second SC1102 makes this possible.
SC1102/SC1102A
Features
1.265V reference available Synchronous operation for high efficiency (95%) RDS(ON) current sensing On-chip power good and OVP functions Small size with minimum external components Soft Start Enable function 14 Pin SOIC lead free package available. Fully WEEE and RoHS compliant
Applications
Microprocessor core supply Low cost synchronous applications Voltage Regulator Modules (VRM) DDR termination supplies Networking power supplies Sequenced power supplies
Typical Application Circuit
Distributed Po Typical Distribut ed P o w er Supply
+5V
+
R1 1k R2 C1 opt. R4 10 C2 0.1 1 U1 SC1102 VCC GND 14 C3 0.1 C5 10.0 C6 680/6.3V C7 680/6.3V C8 680/6.3V
Vin 5V
_
PWRGD 2 0.1 OVP R3 1k PWRGD SS/SHDN 13
SHDN
3
OVP
VREF
12
VREF R8 124*
4
OCSET
SENSE
11 R7 127
5 D1 MBR0520
PHASE
BSTH
10 C4 1.0
+12V Q1 STP40NE R5 3.9 R6 2.2 Q2 STP40NE L1 2uH
6
DRVH
BSTL
9
+
C9 180/4V C10 180/4V C11 180/4V C12 180/4V C13 180/4V
7
PGND
DRVL
8
Vout=2.5V*
_
Figure 1.
NOTE:
*) Vout = 1.265 x (1+R8/R7)
Revision: January 5, 2006
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SC1102/SC1102A
POWER MANAGEMENT Absolute Maximum Ratings
Exceeding the specifications below may result in permanent damage to the device, or device malfunction. Operation outside of the parameters specified in the Electrical Characteristics section is not implied. Exposure to Absolute Maximum rated conditions for extended periods of time may affect device reliability.
Parameter VCC, BSTL to GND PGND to GND PHASE to GND (1) BSTH to PHASE Thermal Resistance Junction to Case Thermal Resistance Junction to Ambient Operating Temperature Range Maximum Junction Temperature Storage Temperature Range Lead Temperature (Soldering) 10 Sec.
Note: (1) -1.5V to 20V for 25ns repetitive every cycle.
Symbol VIN
Maximum -1.0 to 14 0.5 -0.5 to 18 14
Units V V V V C/W C/W C C C C
J C J A TA TJ TSTG TLEAD
45 115 0 to 70 125 -65 to +150 300
Electrical Characteristics
Unless specified: VCC = 4.75V to 12.6V; GND = PGND = 0V; FB = VO; VBSTL = 12V; VBSTH-PHASE = 12V; TJ = 25oC
Parameter Pow er Supply Supply Voltage Supply Current Line Regulation Error Amplifier Gain (AOL) Input Bias Oscillator Oscillator Frequency
Conditions
Min
Typ
Max
Units
VC C EN = VC C VO = 2.5V
4.2 6 0.5
12.6 10
V mA %
35 5 8
dB A
SC1102 SC1102A
170 425 90
200 500 95
230 575
kHz
Oscillator Max Duty Cycle MOSFET Drivers DH Source/Sink DL Source/Sink BSTH - DH = 4.5V, DH- PHASE = 2V BSTL - DL = 4.5V. DL - PGND. = 2V
2
%
1 1
A A
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SC1102/SC1102A
POWER MANAGEMENT Electrical Characteristics (Cont.)
Unless specified: VCC = 4.75V to 12.6V; GND = PGND = 0V; FB = VO; VBSTL = 12V; VBSTH-PHASE = 12V; TJ = 25oC
Parameter PROTECTION OVP Threshold Voltage OVP Source Current Power Good Threshold Dead Time Over current Set Isink Reference Reference Voltage Accuracy Soft Start Charge Current Discharge Current
Conditions
Min
Typ
Max
Units
20 VOVP = 3V 10 88 45 2.0V VOCSET 12V 180 200 112 100 220
% mA % ns A
0C to 70C
1.252 -1
1.265
1.278 +1
V %
VSS = 1.5V VSS = 1.5V
8.0
10 1.5
12
A A
NOTES: (1) Specification refers to application circuit (Figure 1). (2) This device is ESD sensitive. Use of standard ESD handling precautions is required.
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SC1102/SC1102A
POWER MANAGEMENT Pin Configuration
Top View
Ordering Information
Device
(1)
Frequency 200kHz
P ackag e
SC1102CS.TR SC1102CSTRT(2) SC1102ASTR SC1102ASTRT(2) SC1102EVB 500kHz Evaluation Board SO-14
(14-Pin SOIC)
Pin Descriptions
Pin # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Pin Name VC C PWRGD OVP OCSET PHASE DH PGND DL BSTL BSTH SENSE VREF SS/SHDN GND Pin Function
Notes: (1) Only available in tape and reel packaging. A reel contains 2500 devices. (2) Lead free product. This product is fully WEEE and RoHS compliant.
Chip supply voltage Logic high indicates correct output voltage Over voltage protection. Sets the converter overcurrent trip point Input from the phase node between the MOSFET'S High side driver output Power ground Low side driver output Bootstrap, low side driver. Bootstrap, high side driver. Voltage sense input Buffered band gap voltage reference. Soft start. A capacitor to ground sets the slow start time. Signal ground
NOTE: (1) All logic level inputs and outputs are open collector TTL compatible.
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SC1102/SC1102A
POWER MANAGEMENT Block Diagram
Applications Information - Theory of Operation
Synchronous Buck Converter Primary VCORE power is provided by a synchronous, voltage-mode pulse width modulated (PWM) controller. This section has all the features required to build a high efficiency synchronous buck converter, including "Power Good" flag, shut-down, and cycle-by-cycle current limit. The output voltage of the synchronous converter is set and controlled by the output of the error amplifier. The external resistive divider reference voltage is derived from an internal trimmed-bandgap voltage reference (See Fig. 1). The inverting input of the error amplifier receives its voltage from the SENSE pin. The internal oscillator uses an on-chip capacitor and trimmed precision current sources to set the oscillation frequency to 200kHz/500kHz. The triangular output of the oscillator sets the reference voltage at the inverting input of the comparator. The non-inverting input of the comparator receives it's input voltage from the error amplifier. When the oscillator output voltage drops below the error amplifier output voltage, the comparator output goes high. This pulls DL low, turning off the low-side FET, and DH is pulled high, turning on the high-side FET (once the cross-current control allows it). When the oscillator voltage rises back above the error amplifier output voltage, the comparator output goes low. This pulls DH
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low, turning off the high-side FET, and DL is pulled high, turning on the low-side FET (once the cross-current control allows it). As SENSE increases, the output voltage of the error amplifier decreases. This causes a reduction in the ontime of the high-side MOSFET connected to DH, hence lowering the output voltage. Under Voltage Lockout The under voltage lockout circuit of the SC1102 assures that the high-side MOSFET driver outputs remain in the off state whenever the supply voltage drops below set parameters. Lockout occurs if VCC falls below 4.1V. Normal operation resumes once VCC rises above 4.2V. Over-Voltage Protection The over-voltage protection pin (OVP) is high only when the voltage at SENSE is 20% higher than the target value programmed by the external resistor divider. The OVP pin is internally connected to a PNP's collector. Power Good The power good function is to confirm that the regulator outputs are within +/-10% of the programmed level. PWRGD remains high as long as this condition is met. PWRGD is connected to an internal open collector NPN transistor.
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SC1102/SC1102A
POWER MANAGEMENT Applications Information (Cont.)
Soft Start Initially, SS/SHDN sources 10A of current to charge an external capacitor. The outputs of the error amplifiers are clamped to a voltage proportional to the voltage on SS/SHDN. This limits the on-time of the high-side MOSFETs, thus leading to a controlled ramp-up of the output voltages. RDS(ON) Current Limiting The current limit threshold is set by connecting an external resistor from the VCC supply to OCSET. The voltage drop across this resistor is due to the 200A internal sink sets the voltage at the pin. This voltage is compared to the voltage at the PHASE node. This comparison is made only when the high-side drive is high to avoid false current limit triggering due to uncontributing measurements from the MOSFETs off-voltage. When the voltage at PHASE is less than the voltage at OCSET, an overcurrent condition occurs and the soft start cycle is initiated. The synchronous switch turns off and SS/SHDN starts to sink 2A. When SS/SHDN reaches 0.8V, it then starts to source 10A and a new cycle begins. Hiccup Mode During power up, the SS/SHDN pin is internally pulled low until VCC reaches the undervoltage lockout level of 4.2V. Once VCC has reached 4.2V, the SS/SHDN pin is released and begins to source 10A of current to the external soft-start capacitor. As the soft-start voltage rises, the output of the internal error amplifier is clamped to this voltage. When the error signal reaches the level of the internal triangular oscillator, which swings from 1V to 2V at a fixed frequency of 200kHz/500kHz, switching occurs. As the error signal crosses over the oscillator signal, the duty cycle of the PWM signal continues to increase until the output comes into regulation. If an overcurrent condition has not occurred the soft-start voltage will continue to rise and level off at about 2.2V. An over-current condition occurs when the high-side drive is turned on, but the PHASE node does not reach the voltage level set at the OCSET pin. The PHASE node is sampled only once per cycle during the valley of the triangular oscillator. Once an over-current occurs, the highside drive is turned off and the low-side drive turns on and the SS/SHDN pin begins to sink 2uA. The soft-start voltage will begin to decrease as the 2uA of current discharges the external capacitor. When the soft-start voltage reaches 0.8V, the SS/SHDN pin will begin to source 10uA and begin to charge the external capacitor causing the soft-start voltage to rise again. Again, when the softstart voltage reaches the level of the internal oscillator, switching will occur. If the over-current condition is no longer present, normal operation will continue. If the over-current condition is still present, the SS/SHDN pin will again begin to sink 2uA. This cycle will continue indefinitely until the overcurrent condition is removed. In conclusion, below is shown a typical "12V Application Circuit" which has a BSTH voltage derived by bootstrapping input voltage to the PHASE node through diode D1. This circuit is very useful in cases where only input power of 12V is available. In order to prevent substrate glitching, a small-signal diode should be placed in close proximity to the chip with cathode connected to PHASE and anode connected to PGND.
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SC1102/SC1102A
POWER MANAGEMENT Application Circuit
Typical 12V Application Circuit with Bootstrapped BSTH
+5V
+
R1 1k R2 1.74k C1 opt. R4 10 1 PWRGD 2 R3 1k PWRGD SS/SHDN 13 U1 SC1102 VCC GND 14 C3 0.1 SHDN C5 10.0 D2 MBRA130 C6 270/16V C7 270/16V C8 270/16V
Vin 12V
_
C2 0.1
VREF 3 OVP VREF 12 R9 11 R8 127 5 PHASE BSTH 10 C4 1.0 7 PGND DRVL 8 R5 3.9 R6 2.2 Q1 STP40NE Q2 STP40NE C9 1.0 L1 4uH
OVP
4
205*
OCSET
SENSE
D1 MBR0520
6
DRVH
BSTL
9
+
D3 MBRD1035 Optional C10 180/4V C11 180/4V C12 180/4V C13 180/4V C14 180/4V
Vout=3.3V*
_
NOTE:
*) Vout = 1.265 x (1+R9/R8)
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SC1102/SC1102A
POWER MANAGEMENT Typical Characteristics
Output Ripple Voltage Ch1: Vo_rpl 1. VIN = 5V; VO = 3.3V; IOUT = 12A Wave forms are shown for SC1102 and are similiar for SC1102A but at a higher frequency. Gate Drive Waveforms Ch1: Top FET Ch2: Bottom FET
PIN Descriptions
Ch1: Vo_rpl 2. VIN = 5V; VOUT = 1.3V; IOUT = 12A
Ch1: Top FET Ch2: Bottom FET
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SC1102/SC1102A
POWER MANAGEMENT Typical Characteristics (Cont.)
Ch1: Vo_rpl 2. VIN = 5V; VOUT = 1.3V; IOUT = 12A Ch1: Top FET Ch2: Bottom FET
Error Amplifier, Gain and Phase
40 180
PIN Descriptions
35 30 25 Gain (dB) 20 15 Gain 10 5 0 -5 -10 100.0E+0 Phase
135
45
0
1.0E+3
10.0E+3
100.0E+3
1.0E+6
-45 10.0E+6
Frequency (Hz)
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Phase (deg)
90
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SC1102/SC1102A
POWER MANAGEMENT Typical Characteristics (Cont.)
Hiccup Mode
Ch1: Ch2: Ch3: Ch4:
Vin Vss Top Gate Vout
Vin = 5V Vout = 3.3V Vbst = 12V Iout = S.C.
Start Up Mode
Ch1: Vin Ch2: Vss Ch3: Top Gate Ch4: Vout Vin = 5V Vout = 3.3V Iout = 2A Vbst = 12V
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C27 Q4 L1 R8
POWER MANAGEMENT Evaluation Board Schematic
+5V
Vbias
D1
+
D2 U1 C28 GND R5 C4 PWRGD 12 VREF C13 SS/SHDN 13 SHDN R10 C15 14 D5 R7 C5 C6 C7 C8 C9 C10
R1
R2
R4
C2
Vin
_
C3 VCC
1
PWRGD
2
11
OVP 11 10 PHASE 9 R17 R18 C16 R15 C17 Q2 R19 Q3 C19 D4 R16 Q1 BSTH R11 C18 L2 R12 C26 VREF OCSET SENSE DRVH 8 BSTL PGND DRVL
C1
R3
OVP
3
4
R14
5
R13
6
D3
C23 C20 C21 C22
C24 C25
+
7
Vout
_
SC1102/SC1102A
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SC1102/SC1102A
POWER MANAGEMENT Outline Drawing - S0IC - 14
A N
2X
e
D
DIM
A A1 A2 b c D E1 E e h L L1 N 01 aaa bbb ccc
DIMENSIONS INCHES MILLIMETERS MIN NOM MAX MIN NOM MAX
.053 .069 .010 .004 .065 .049 .020 .012 .007 .010 .337 .341 .344 .150 .154 .157 .236 BSC .050 BSC .010 .020 .016 .028 .041 (.041) 14 0 8 .004 .010 .008 1.35 1.75 0.25 0.10 1.65 1.25 0.31 0.51 0.25 0.17 8.55 8.65 8.75 3.80 3.90 4.00 6.00 BSC 1.27 BSC 0.25 0.50 0.40 0.72 1.04 (1.04) 14 0 8 0.10 0.25 0.20
E/2 E1 E
ccc C 1 2X N/2 TIPS
2
3 B
D aaa C A2 A SEATING PLANE C A1 C A-B D
h h
bxN bbb
H GAGE PLANE 0.25
c
SIDE VIEW
NOTES: 1.
SEE DETAIL
A
L (L1) DETAIL
01
A
CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES).
2. DATUMS -A- AND -B- TO BE DETERMINED AT DATUM PLANE -H3. DIMENSIONS "E1" AND "D" DO NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. 4. REFERENCE JEDEC STD MS-012, VARIATION AB.
Land Pattern - SOIC - 14
X
DIM
(C) G Z C G P X Y Z
DIMENSIONS INCHES MILLIMETERS
(.205) .118 .050 .024 .087 .291 (5.20) 3.00 1.27 0.60 2.20 7.40
Y P
NOTES: 1. THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY. CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR COMPANY'S MANUFACTURING GUIDELINES ARE MET. REFERENCE IPC-SM-782A, RLP NO. 302A.
2.
Contact Information
Semtech Corporation Power Management Products Division 200 Flynn Road, Camarillo, CA 93012 Phone: (805)498-2111 FAX (805)498-3804
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