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SYNCHRONOUS DC/DC CONTROLLER FOR DISTRIBUTED POWER SUPPLY APPLICATIONS
September 5, 2000
SC1102
TEL:805-498-2111 FAX:805-498-3804 WEB:http://www.semtech.com
DESCRIPTION
The SC1102 is a low-cost, full featured, synchronous voltage-mode controller 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 SC1102 is 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, highside drive circuitry, and preset shoot-thru control, allows the use of inexpensive N-channel power switches. SC1102 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 200kHz, providing an optimum compromise between efficiency, external component size, and cost.
FEATURES * 1.265V Reference available * Synchronous operation * Over current fault monitor * On-chip power good and OVP functions * Small size with minimum external components * Soft Start * RDS(ON) Current sensing APPLICATIONS * Microprocessor core supply * Low cost synchronous applications * Voltage Regulator Modules (VRM) ORDERING INFORMATION
DEVICE
(1)
PACKAGE SO-14
TEMP. RANGE (TJ) 0 - 125C
SC1102CSTR SC1102EVB
Evaluation Board
Note: (1) Only available in tape and reel packaging. A reel contains 2500 devices.
APPLICATION CIRCUIT
Typical Distributed Power Supply
+5V
+
R1 1k R2 C1 0.1 R4 10 C2 0.1 1 PWRGD 2 R3 1k OVP PWRGD SS/SHDN 13 VCC U1 SC1102 GND 14 C3 0.1 SHDN C5 10.0 C6 680/6.3V C7 680/6.3V C8 680/6.3V
Vin 5V
_
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 C9 180/4V C10 180/4V C11 180/4V C12 180/4V C13 180/4V L1 2uH
6
DRVH
BSTL
9
+
7
PGND
DRVL
8
Vout=2.5V*
_
NOTE:
*) Vout = 1.265 x (1+R8/R7)
Figure 1.
1 (c) 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
SYNCHRONOUS DC/DC CONTROLLER FOR DISTRIBUTED POWER SUPPLY APPLICATIONS
September 5, 2000
SC1102
ABSOLUTE MAXIMUM RATINGS
Parameter VCC, BSTL to GND PGND to GND PHASE to GND BSTH to PHASE Thermal Resistance Junction to Case Thermal Resistance Junction to Ambient Operating Temperature Range Storage Temperature Range Lead Temperature (Soldering) 10 sec ESD Rating (Human Body Model) JC JA TA TSTG TLEAD ESD Symbol VIN Maximum -0.3 to 14 0.5 -0.3 to 18 14 45 115 0 to 70 -65 to +150 300 2 Units V V V V C/W C/W C C C kV
o
ELECTRICAL CHARACTERISTICS
Unless specified: VCC = 4.75V to 12.6V; GND = PGND = 0V; FB = VO; VBSTL = 12V; VBSTH-PHASE = 12V; TJ = 25 C PARAMETER POWER SUPPLY Supply Voltage Supply Current Line Regulation ERROR AMPLIFIER Gain (AOL) Input Bias OSCILLATOR Oscillator Frequency Oscillator Max Duty Cycle MOSFET DRIVERS DH Source/Sink Current DL Source/Sink Current PROTECTION OVP Threshold Voltage OVP Source Current Power Good Threshold Dead Time Over Current Set Isource NOTE: (1) Specification refers to application circuit (Figure 1). 2 (c) 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 2.0V VOCSET 12V VOVP = 3V 10 88 45 180 200 112 100 220 20 % mA % ns A BSTH - DH = 4.5V / DH - PHASE = 2V BSTL - DL = 4.5V / DL - PGNDL = 2V 1 1 A A 180 90 200 95 220 kHz % 35 5 8 dB A VCC EN = VCC VO = 2.5V 4.2 6 0.5 12.6 10 V mA % CONDITIONS MIN TYP MAX UNITS
SYNCHRONOUS DC/DC CONTROLLER FOR DISTRIBUTED POWER SUPPLY APPLICATIONS
September 5, 2000
SC1102
ELECTRICAL CHARACTERISTICS (CONT)
Unless specified: VCC = 4.75V to 12.6V; GND = PGND = 0V; FB = VO; VBSTL = 12V; VBSTH-PHASE = 12V; TJ = 25 C PARAMETER REFERENCE Reference Voltage Accuracy SOFT START Charge Current Discharge Current VSS = 1.5V VSS = 1.5V 8.0 1.3 10 2 12 2.4 A A 1.252 -1 1.265 1.278 +1 V % CONDITIONS MIN TYP MAX UNITS
o
PIN CONFIGURATION
BLOCK DIAGRAM
Top View
(14-Pin SOIC)
3 (c) 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
SYNCHRONOUS DC/DC CONTROLLER FOR DISTRIBUTED POWER SUPPLY APPLICATIONS
September 5, 2000
SC1102
PIN DESCRIPTION
Pin # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 NOTE: (1) All logic level inputs and outputs are open collector TTL compatible. Pin Name VCC PWRGD OVP OCSET PHASE DH PGND DL BSTL BSTH SENSE VREF SS/SHDN GND Pin Function 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
CHARACTERISTIC CURVES
SC1102 Voltage Regulation, Vin=5V
2% 1% 0% -1% -2% 0 1 2 3 4 5 6 7 8 9 10 11 12 Current, A 100% 90% 3.3V 2.5V 2.0V 1.3V 80% 70% 60% 0 1 2 3 4 5 6 7 8 9 10 11 12 Current, A 3.3V 2.5V 2.0V 1.3V
SC1102 Effiency, Vin=5V
4 (c) 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
SYNCHRONOUS DC/DC CONTROLLER FOR DISTRIBUTED POWER SUPPLY APPLICATIONS
September 5, 2000 Output Ripple Voltage 1. VIN = 5V; VO = 3.3V; IOUT = 12A Gate Drive Waveforms
SC1102
Ch1: Vo_rpl
Ch1: Top FET Ch2: Bottom FET
2. VIN = 5V; VOUT = 1.3V; IOUT = 12A
Ch1: Vo_rpl
Ch1: Top FET Ch2: Bottom FET
5 (c) 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
SYNCHRONOUS DC/DC CONTROLLER FOR DISTRIBUTED POWER SUPPLY APPLICATIONS
September 5, 2000 Start Up
SC1102
Ch1: Vin Ch2: Vss Ch3: Top Gate Ch4: Vout Vin = 5V Vout = 3.3V Iout = 2A Vbst = 12V
Hiccup Mode
Ch1: Vin Ch2: Vss Ch3: Top Gate Ch4: Vout Vin = 5V Vout = 3.3V Vbst = 12V Iout = S.C.
6 (c) 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
SYNCHRONOUS DC/DC CONTROLLER FOR DISTRIBUTED POWER SUPPLY APPLICATIONS
September 5, 2000
SC1102
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. 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 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. 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 highside 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 MOSFET's offvoltage. 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 switcher 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 200 kHz, 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 over-current condition has not occurred the soft-start voltage will continue to rise and level off at about 2.2V.
7 (c) 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
SYNCHRONOUS DC/DC CONTROLLER FOR DISTRIBUTED POWER SUPPLY APPLICATIONS
September 5, 2000
SC1102
THEORY OF OPERATION (CON'T)
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 high-side drive is turned off and the lowside 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 soft-start 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 over-current 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.
APPLICATION CIRCUIT
Typical 12V Application Circuit with Bootstrapped BSTH
+5V
+
R1 1k R2 1.74k C1 0.1 R4 10 C2 0.1 1 PWRGD 2 R3 1k OVP PWRGD SS/SHDN 13 VCC U1 SC1102 GND 14 C3 0.1 SHDN C5 10.0 D2 MBRA130 C6 270/16V C7 270/16V C8 270/16V
Vin 12V
_
VREF 3 OVP VREF 12 R9
205*
4 OCSET SENSE 11 R8 127 5 D1 MBR0520 PHASE BSTH 10 C4 6 DRVH BSTL 9 1.0 7 PGND DRVL 8 R5 3.9 R6 2.2 Q1 STP40NE Q2 STP40NE C9 1.0 L1 4uH
+
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)
8 (c) 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
SYNCHRONOUS DC/DC CONTROLLER FOR DISTRIBUTED POWER SUPPLY APPLICATIONS
September 5, 2000 Top component side view
SC1102
Top copper view
Bottom copper view
9 (c) 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
SYNCHRONOUS DC/DC CONTROLLER FOR DISTRIBUTED POWER SUPPLY APPLICATIONS
September 5, 2000
SC1102
OUTLINE DRAWING SO-14
LAND PATTERN SO-14
ECN00-1311 10 (c) 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

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