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 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 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. APPLICATIONS • Microprocessor core supply • Low cost synchronous applications • Voltage Regulator Modules (VRM) 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. ORDERING INFORMATION (1) DEVICE The SC1102 operates at a fixed 200kHz, providing an optimum compromise between efficiency, external component size, and cost. PACKAGE TEMP. RANGE (TJ) SO-14 0 - 125°C 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 R4 10 C1 0.1 U1 SC1102 C2 0.1 1 VCC GND OVP 2 PWRGD 3 OVP 4 5 C7 680/6.3V C8 680/6.3V SS/SHDN 13 VREF 12 OCSET SENSE 11 PHASE BSTH 10 DRVH BSTL PGND DRVL Vin 5V _ 14 PWRGD R3 1k C6 680/6.3V C5 10.0 C3 0.1 SHDN VREF R8 124* R7 127 D1 MBR0520 +12V C4 1.0 6 7 Q1 STP40NE 9 8 R5 3.9 L1 2uH + Q2 STP40NE C9 180/4V R6 2.2 C10 180/4V C11 180/4V C12 180/4V C13 180/4V Vout=2.5V* _ NOTE: *) Vout = 1.265 x (1+R8/R7) Figure 1. 1 © 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 SYNCHRONOUS DC/DC CONTROLLER FOR DISTRIBUTED POWER SUPPLY APPLICATIONS SC1102 September 5, 2000 ABSOLUTE MAXIMUM RATINGS Parameter Symbol Maximum Units VIN -0.3 to 14 V PGND to GND ± 0.5 V PHASE to GND -0.3 to 18 V BSTH to PHASE 14 V VCC, BSTL to GND Thermal Resistance Junction to Case θJC 45 °C/W Thermal Resistance Junction to Ambient θJA 115 °C/W Operating Temperature Range TA 0 to 70 °C Storage Temperature Range TSTG -65 to +150 °C Lead Temperature (Soldering) 10 sec TLEAD 300 °C ESD Rating (Human Body Model) ESD 2 kV ELECTRICAL CHARACTERISTICS o Unless specified: VCC = 4.75V to 12.6V; GND = PGND = 0V; FB = VO; VBSTL = 12V; VBSTH-PHASE = 12V; TJ = 25 C PARAMETER CONDITIONS MIN TYP MAX UNITS Supply Voltage VCC 4.2 Supply Current EN = VCC 6 Line Regulation VO = 2.5V 0.5 % Gain (AOL) 35 dB Input Bias 5 8 µA 220 kHz POWER SUPPLY 12.6 V 10 mA ERROR AMPLIFIER OSCILLATOR Oscillator Frequency 180 200 Oscillator Max Duty Cycle 90 95 % MOSFET DRIVERS DH Source/Sink Current BSTH - DH = 4.5V / DH - PHASE = 2V 1 A DL Source/Sink Current BSTL - DL = 4.5V / DL - PGNDL = 2V 1 A PROTECTION OVP Threshold Voltage OVP Source Current 20 VOVP = 3V % 10 mA Power Good Threshold 88 112 % Dead Time 45 100 ns 220 µA Over Current Set Isource 2.0V ≤ VOCSET ≤ 12V 180 200 NOTE: (1) Specification refers to application circuit (Figure 1). 2 © 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 SYNCHRONOUS DC/DC CONTROLLER FOR DISTRIBUTED POWER SUPPLY APPLICATIONS SC1102 September 5, 2000 ELECTRICAL CHARACTERISTICS (CONT) o Unless specified: VCC = 4.75V to 12.6V; GND = PGND = 0V; FB = VO; VBSTL = 12V; VBSTH-PHASE = 12V; TJ = 25 C PARAMETER CONDITIONS MIN TYP MAX UNITS 1.252 1.265 1.278 V +1 % REFERENCE Reference Voltage Accuracy -1 SOFT START Charge Current VSS = 1.5V 8.0 10 12 µA Discharge Current VSS = 1.5V 1.3 2 2.4 µA PIN CONFIGURATION BLOCK DIAGRAM Top View (14-Pin SOIC) 3 © 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 SYNCHRONOUS DC/DC CONTROLLER FOR DISTRIBUTED POWER SUPPLY APPLICATIONS SC1102 September 5, 2000 PIN DESCRIPTION Pin # Pin Name Pin Function 1 VCC Chip supply voltage 2 PWRGD Logic high indicates correct output voltage 3 OVP Over voltage protection. 4 OCSET Sets the converter overcurrent trip point 5 PHASE Input from the phase node between the MOSFET’S 6 DH High side driver output 7 PGND Power ground 8 DL Low side driver output 9 BSTL Bootstrap, low side driver. 10 BSTH Bootstrap, high side driver. 11 SENSE Voltage sense input 12 VREF Buffered band gap voltage reference. 13 SS/SHDN Soft start. A capacitor to ground sets the slow start time. 14 GND Signal ground NOTE: (1) All logic level inputs and outputs are open collector TTL compatible. CHARACTERISTIC CURVES SC1102 Effiency, Vin=5V SC1102 Voltage Regulation, Vin=5V 100% 2% 90% 1% 3.3V 2.5V 2.0V 1.3V 0% -1% 3.3V 2.5V 2.0V 1.3V 80% 70% 60% -2% 0 0 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12 Current, A Current, A 4 © 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 SYNCHRONOUS DC/DC CONTROLLER FOR DISTRIBUTED POWER SUPPLY APPLICATIONS SC1102 September 5, 2000 Output Ripple Voltage Gate Drive Waveforms 1. VIN = 5V; VO = 3.3V; IOUT = 12A 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 © 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 SYNCHRONOUS DC/DC CONTROLLER FOR DISTRIBUTED POWER SUPPLY APPLICATIONS SC1102 September 5, 2000 Start Up 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 © 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 SYNCHRONOUS DC/DC CONTROLLER FOR DISTRIBUTED POWER SUPPLY APPLICATIONS SC1102 September 5, 2000 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 10µA 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 200µA 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 2µA. When SS/SHDN reaches 0.8V, it then starts to source 10µA 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 10µA 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 © 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 SYNCHRONOUS DC/DC CONTROLLER FOR DISTRIBUTED POWER SUPPLY APPLICATIONS SC1102 September 5, 2000 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 C5 10.0 U1 SC1102 C2 0.1 1 VCC GND 14 PWRGD 2 R3 1k OVP PWRGD SS/SHDN 13 C6 270/16V C7 270/16V C8 270/16V D2 MBRA130 C3 0.1 Vin 12V _ SHDN VREF 3 OVP VREF 12 R9 205* 4 OCSET SENSE 11 R8 127 5 D1 MBR0520 PHASE BSTH DRVH BSTL PGND DRVL 10 Q1 STP40NE C4 6 9 1.0 7 8 R5 3.9 R6 2.2 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 © 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 SYNCHRONOUS DC/DC CONTROLLER FOR DISTRIBUTED POWER SUPPLY APPLICATIONS SC1102 September 5, 2000 Top component side view Top copper view Bottom copper view 9 © 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 SYNCHRONOUS DC/DC CONTROLLER FOR DISTRIBUTED POWER SUPPLY APPLICATIONS SC1102 September 5, 2000 OUTLINE DRAWING SO-14 LAND PATTERN SO-14 ECN00-1311 10 © 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320