SG1577 Dual Synchronous DC/DC Controller Features Description Integrated Two Sets of MOSFET Drivers Wide Range Input Supply Voltage: 8~15V Two Soft-Start / EN Functions The SG1577 is a high-efficiency, voltage-mode, dualchannel, synchronous DC/DC PWM controller for two independent outputs. The two channels are operated out of phase. The internal reference voltage is trimmed to 0.7V±1.5%. It is connected to the error amplifier’s positive terminal for voltage feedback regulation. The soft-start circuit ensures the output voltage can be gradually and smoothly increased from zero to its final regulated value. The soft-start pin can also be used for chip-enable function. When two soft-start pins are grounded, the chip is disabled and the total operation current can be reduced to under 0.55mA. The fixedfrequency is programmable from 60kHz to 320kHz. The Over-Current Protection (OCP) level can be programmed by an external current sense resistor. It has two integrated sets of internal MOSFET drivers. SG1577 is available in 20-pin SOP and DIP packages. Two Independent PWM Controllers Constant Frequency Operation: Free-running Fixed Frequency Oscillator Programmable: 60kHz to 320kHz Programmable Output as Low as 0.7V Internal Error Amplifier Reference Voltage: 0.7V±1.5% Programmable Over-Current Protection (OCP) 30V HIGH Voltage Pin for Bootstrap Voltage Output Over-Voltage Protection (OVP) SOP and DIP 20-pin Applications CPU and GPU Vcore Power Supply Power Supply Requiring Two Independent Outputs Ordering Information Part Number Operating Temperature Range Package Packing Method SG1577SZ -40°C to +85°C 20-pin Small Outline Package (SOP) Tape & Reel SG1577DZ -40°C to +85°C 20-pin Dual In-Line Package (DIP) Tube All packages are lead free per JEDEC: J-STD-020B standard. © 2007 Fairchild Semiconductor Corporation SG1577 • Rev. 1.0.1 www.fairchildsemi.com SG1577 — Dual Synchronous DC/DC Controller April 2008 SG1577 — Dual Synchronous DC/DC Controller Application Diagram Figure 1. Typical Application Internal Block Diagram Figure 2. © 2007 Fairchild Semiconductor Corporation SG1577 • Rev. 1.0.1 Functional Block Diagram www.fairchildsemi.com 2 Figure 3. SOP-20 and DIP-20 Pin Configuration (Top View) Pin Definitions Name Pin # Type Description Switching frequency programming pin. An external resistor connecting from this pin to GND can program the switching frequency. The switching Frequency Select frequency would be 60kHz when RT is open and become 320kHz when a 30kΩ RT resistor is connected. RT 1 IN1 2 Feedback Inverting input of the error amplifier. It is normally connected to the switching power supply output through a resistor divider. COMP1 3 Compensation Output of the error amplifier and input to the PWM comparator. It is used for feedback loop compensation. SS1/ENB 4 Soft Start/Enable A 10µA internal current source charging an external capacitor for soft start. Pull down this pin and pin 17 can disable the chip. CLP1 5 Over Current Protection Over-current protection for high-side MOSFET. Connect a resistor from this pin to the high-side supply voltage to program the OCP level. BST1 6 Boost Supply DH1 7 High-Side Drive CLN1 8 Switch Node DL1 9 Low-Side Drive Low-side MOSFET gate driver pin. PGND 10 Driver Ground Driver circuit GND supply. Connect to low-side MOSFET GND. Supply for high-side driver. Connect to the internal bootstrap circuit. Channel 1, high-side MOSFET gate driver pin. Switch-node connection to inductor. For channel 1 high-side driver’s reference ground. VCC 11 Power Supply DL2 12 Low-Side Drive CLN2 13 Switch Node DH2 14 High-Side Drive BST2 15 Boost Supply Supply for high-side driver. Connect to the internal bootstrap circuit. CLP2 16 Over-Current Protection Over-current protection for the high-side MOSFET. Connect a resistor from this pin to the high-side supply voltage to program the OCP level. SS2/ENB 17 Soft-Start/Enable A 10µA internal current source charging an external capacitor for soft start. Pull down this pin and pin 4 can disable the chip. COMP2 18 Compensation Output of the error amplifier and input to the PWM comparator. It is used for feedback-loop compensation. IN2 19 Feedback Inverting input of the error amplifier. It is normally connected to the switching power supply output through a resistor divider. GND 20 Control Ground © 2007 Fairchild Semiconductor Corporation SG1577 • Rev. 1.0.1 SG1577 — Dual Synchronous DC/DC Controller Pin Configuration Supply voltage input. Low-side MOSFET gate driver pin. Switch-node connection to inductor. For channel 2, high-side driver’s reference ground. Channel 2 high-side MOSFET gate driver pin. Control circuit GND supply. www.fairchildsemi.com 3 Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be operable above the recommended operating conditions and stressing the parts to these levels is not recommended. In addition, extended exposure to stresses above the recommended operating conditions may affect device reliability. The absolute maximum ratings are stress ratings only. All voltage values, except differential voltages, are given with respect to the network ground terminal. Stresses beyond those listed under "absolute maximum ratings" may cause permanent damage to the device. Symbol VCC BST1(or 2) CLN1(or 2) CLN1(or 2) GND Parameter Max. Unit Supply voltage, VCC to GND 16 V BST1(2) to CLN1(2) 16 V 18 V 16 V VCC+0.3 V CLN1(2) to GND for 100ns Transient Min. -4 DH1(or 2) CLN1(or 2) CLN1(or 2), DL1(or 2) PGND -0.3 PGND to GND ±1 V ΘJA Thermal Resistance, Junction-Air 90 °C/W TJ Operating Junction Temperature -40 +125 °C TSTG Storage Temperature Range -65 +150 °C ESD Electrostatic Discharge Protection Level Human Body Model (HBM) 2.5 kV Charged Device Model (CDM) 750 V SG1577 — Dual Synchronous DC/DC Controller Absolute Maximum Ratings Recommended Operating Conditions The Recommended Operating Conditions table defines the conditions for actual device operation. Recommended operating conditions are specified to ensure optimal performance to the datasheet specifications. Fairchild does not recommend exceeding them or designing to absolute maximum ratings. Symbol Parameter Min. Max. Unit VCC Supply voltage +8 +15 V TA Operating Ambient Temperature -40 +85 °C © 2007 Fairchild Semiconductor Corporation SG1577 • Rev. 1.0.1 www.fairchildsemi.com 4 VCC=12V, TA =25°C, unless otherwise noted. Symbol Parameter Conditions Min. Typ. Max. RRT=OPEN 54 60 66 RRT=GND 288 320 352 20kΩ＜RRT -10 Unit Oscillator fosc Oscillator Frequency fosc,rt Total Accuracy DON_MAX Maximum Duty Cycle KHz 10 % 85 90 95 % 0.6895 0.7000 0.7105 V Error Amplifier VREF Internal Reference Voltage VCC=8V,VCC=15V AVOL Open-loop Voltage Gain 77 dB BW Unity Gain Bandwidth 3.5 MHz PSRR Power Supply Rejection Ratio ISOURCE Output Source Current IN1=IN2=0.6V Output Sink Current IN1=IN2=0.8V 500 µA VH COMP Output Voltage IN1=IN2=0.6V 5 V VL COMP Output Voltage IN1=IN2=0.8V 100 mV Soft-start Charge Current VCLP＜VCLN 8 10 12 µA Soft-start Discharge Current VCLP＞VCLN 0.8 1.0 1.2 µA OC Sink Current VCC=12V 90 120 150 µA ISINK 50 60 80 dB 100 µA SG1577 — Dual Synchronous DC/DC Controller Electrical Characteristics Soft Start ISOURCE ISINK Protections IOSCET TOT TOT_HYS VOVP 150 Over-Temperature °C 20 Over-Temperature Hysteresis Over-Voltage Protection of IN VOVP/VIN 112 IDH High-side Current Source VBST - VCLN=12V,VDH - VCLN=6V 1.0 1.7 RDH High-side Sink Resistor VBST - VCLN=12V IDL Low-side Current Source VCC=12V,VDL =6V 1.0 1.7 RDL Low-side Sink Resistor VCC=12V °C 125 % Output TDT Dead Time (1) 3.3 A 4.0 Ω A 3.1 4 Ω VCC=12V, DH & DL=1000pF 10 40 70 ns 3.3 4.3 5.3 mA 0.55 1.00 mA Total Operating Current ICC_OP Operating Supply Current VCC=12V, No load ICC_SBY Standby Current (Disabled) SS1/ENB=SS2/ENB=0V Note: 1. When VDL falls less than 2V relative to VDH rising to 2V. © 2007 Fairchild Semiconductor Corporation SG1577 • Rev. 1.0.1 www.fairchildsemi.com 5 Unless otherwise noted, values are for VCC=12V, TA=+25°C, and according to Figure 1. Figure 4. V5p0 Power On with 1.6A Load Figure 5. V3p3 Power On with 3A Load Figure 6. V5p0 Power On with 15A Load Figure 7. V3p3 Power On with 8A Load Figure 8. V5p0 Power Off with 15A Load Figure 9. V3p3 Power Off with 8A Load © 2007 Fairchild Semiconductor Corporation SG1577 • Rev. 1.0.1 SG1577 — Dual Synchronous DC/DC Controller Typical Performance Characteristics www.fairchildsemi.com 6 Unless otherwise noted, values are for VCC=12V, TA=+25°C, and according to Figure 1. Figure 10. 3p3 & V5p0 Phase Shift with Light Load Figure 11. V3p3 & V5p0 Phase Shift with Heavy Load Figure 12. Dead Time with Light Load (Rise Edge) Figure 13. Dead Time with Light Load (Fall Edge) Figure 14. Dead Time with Heavy Load (Rise Edge) Figure 15. Dead Time with Heavy Load (Fall Edge) © 2007 Fairchild Semiconductor Corporation SG1577 • Rev. 1.0.1 SG1577 — Dual Synchronous DC/DC Controller Typical Performance Characteristics (Continued) www.fairchildsemi.com 7 Unless otherwise noted, values are for VCC=12V, TA=+25°C, and according to Figure 1. Figure 16. Load Transient Response (Step-Up) 20kΩ/22nF in Compensation Loop Figure 17. Load Transient Response (Step-Down) 20kΩ/22nF in Compensation Loop Figure 18. Over-Current Protection (OCP) Figure 19. Over-Current Protection (Hiccup Mode) SG1577 — Dual Synchronous DC/DC Controller Typical Performance Characteristics (Continued) 150 Iocset 1 Iocset 2 140 Iocset (uA) 130 120 110 100 90 -40℃ -25℃ -10℃ 5℃ 20℃ 35℃ 50℃ 65℃ 80℃ 95℃ Temperature (oC) Figure 20. Over-Voltage Protection (OVP) © 2007 Fairchild Semiconductor Corporation SG1577 • Rev. 1.0.1 Figure 21. IOCSET vs. Temperature www.fairchildsemi.com 8 The SG1577 is a dual-channel voltage-mode PWM controller. It has two sets of synchronous MOSFET driving circuits. The two channels are running 180degrees out of phase. The following descriptions highlight the advantages of the SG1577 design. Oscillator Operation The SG1577 has a frequency-programmable oscillator. The oscillator is running at 60kHz when the RT pin is floating. The oscillator frequency can be adjusted from 60kHz up to 320kHz by an external resistor RRT between RT pin and the ground. The oscillator generates a sawtooth wave that has 90% rising duty. Sawtooth wave voltage threshold is from 1.2V to 2.8V. The frequency of oscillator can be programmed by the following equation: Soft Start An internal start-up current (10µA) flows out of SS/EN pin to charge an external capacitor. During the start-up sequence, SG1577 isn’t enabled until the SS/ENB pin is higher than 1.2V. From 1.2V to (1.2 + 1.6 x DON / DON_MAX) V, PWM duty cycle gradually increases following SS/ENB pin voltage to bring output rising. After (1.2 + 1.6 x DON / DON_MAX) V, the soft-start period ends and SS/ENB pin continually goes up to 4.8V. When input power is abnormal, the external capacitor on SS pin is shorted to ground and the chip is disabled. TSOFTSTART = CSS/ENB x 1.6 x DON / DON_MAX / ISOURCE Output Driver The high-side gate drivers need an external bootstrapping circuit to provide the required boost voltage. The highest gate driver’s output (15V is the allowed) on high-side and low-side MOSFETs forces external MOSFETs to have the lowest RDS(ON), which results in higher efficiency. (1) Over-Current Protection (OCP) Over-current protection is implemented by sensing the voltage drop across the drain and the source of external high-side MOSFET. Over-current protection is triggered when the voltage drop on external high-side MOSFET’s RDS(ON) is greater than the programmable current limit voltage threshold. 120µA flowing through an external resistor between input voltage and the CLP pin sets the threshold of current limit voltage. When over-current condition is true, the system is protected against the cycle-by-cycle current limit. A counter counts a series of over-current peak values to eight cycles; the soft-start capacitor is discharged by a 1µA current until the voltage on SS pin reaches 1.2V. During the discharge period, the high-side driver is turned off and the lowside driver is turned on. Once the voltage on SS/ENB pin is under 1.2V, the normal soft-start sequence is initiated and the 10µA current charges the soft-start capacitor again. IL(OCP)= [(RSENSE x IOCSET + VOFFSET) / RDS(ON) (VIN - VOUT) x VOUT / (fOSC x LOUT x VIN x 2) ] (3) fOSC, RT(kHz) = 60kHz + 8522 / RRT(kΩ) Over-Temperature Protection (OTP) SG1577 — Dual Synchronous DC/DC Controller Functional Description The device is over-temperature protected. When chip o temperature is over 150 C, the chip enters tri-state o (high-side driver is turned off). The hysteresis is 20 C. Type II Compensation Design (for Output Capacitors with High ESR) SG1577 is a voltage-mode controller; the control loop is a single voltage feedback path, including an error amplifier and PWM comparator, as shown in Figure 22. To achieve fast transient response and accurate output regulation, an adequate compensator design is necessary. A stable control loop has a 0dB gain crossing with -20dB/decade slope and a phase margin greater than 45°. (2) where, VOFFSET (≒10mV) is the offset voltage contributed by the internal OCP comparator. Error Amplifier The IN1 and IN2 pins are connected to the corresponding internal error amplifier’s inverting input and the outputs of the error amplifiers are connected to the corresponding COMP1 and COMP2 pins. The COMP1 and COMP2 pins are available for control-loop compensation externally. Non-inverting inputs are internally tied to a fixed 0.7V ± 1.5% reference voltage. Figure 22. Closed Loop © 2007 Fairchild Semiconductor Corporation SG1577 • Rev. 1.0.1 www.fairchildsemi.com 9 fP(LC) = 1 fP1 = 0 fZ1 = fP2 High crossover frequency is desirable for fast transient response, but often jeopardizes the system stability. To cancel one of the LC filter poles, place the zero before the LC filter resonant frequency. Place the zero at 75% of the LC filter resonant frequency. Crossover frequency should be higher than the ESR zero, but less than 1/5 of the switching frequency. The second pole should be placed at half the switching frequency. (4) The next step of compensation design is to calculate the ESR zero. The ESR zero is contributed by the ESR associated with the output capacitance. Note that this requires that the output capacitor should have enough ESR to satisfy stability requirements. The ESR zero of the output capacitor is expressed as: 1 2π × CO × ESR (6) 1 = 2π × R 2 × (C1 // C2 ) Figure 24 shows the DC-DC converter gain vs. frequency. The compensation gain uses external impedance networks ZC and Zf to provide a stable, highbandwidth loop. 2π × L O × C O fZ(ESR ) = 1 2π × R 2 × C 2 SG1577 — Dual Synchronous DC/DC Controller 1. Modulator Frequency Equations The modulator transfer function is the small-signal transfer function of VOUT/VE/A. This transfer function is dominated by a DC gain and the output filter (LO and CO) with a double-pole frequency at fLC and a zero at FESR. The DC gain of the modulator is the input voltage (VIN) divided by the peak-to-peak oscillator voltage VRAMP(=1.6V). The first step is to calculate the complex conjugate poles contributed by the LC output filter. The output LC filter introduces a double pole, -40dB / decade gain slope above its corner resonant frequency, and a total phase lag of 180 degrees. The resonant frequency of the LC filter expressed as: (5) 2. Compensation Frequency Equations The compensation network consists of the error amplifier and the impedance networks ZC and Zf, as Figure 23 shows. Figure 24. Bode Plot Figure 23. Compensation Loop © 2007 Fairchild Semiconductor Corporation SG1577 • Rev. 1.0.1 www.fairchildsemi.com 10 (resistor divider), and compensation components (between INx and COMPx pins). Position those components close to their pins with a local, clear GND connection or directly to the ground plane. Layout is important in high-frequency switching converter design. If designed improperly, PCB can radiate excessive noise and contribute to converter instability. Place the PWM power stage components first. Mount all the power components and connections in the top layer with wide copper areas. The MOSFETs of buck, inductor, and output capacitor should be as close to each other as possible to reduce the radiation of EMI due to the high-frequency current loop. If the output capacitors are placed in parallel to reduce the ESR of capacitor, equal sharing ripple current should be considered. Place the input capacitor near the drain of high-side MOSFET. In multi-layer PCB, use one layer as power ground and have a separate control signal ground as the reference for all signals. To avoid the signal ground being affected by noise and have best load regulation, it should be connected to the ground terminal of output. A two-layer printed circuit board is recommended. 2 Use the bottom layer of the PCB as a ground plane and make all critical component ground connections through vias to this layer. Place the bootstrap capacitor near the BSTx and CLNx pins. 8 The resistor on the RT pin should be near this pin and the GND return should be short and kept away from the noisy MOSFET’s GND (which is short together with IC’s PGND pin to GND plane on back side of PCB). 9 Place the compensation components close to the INx and COMPx pins. 10 The feedback resistors for both regulators should be located as close as possible to the relevant INx pin with vias tied straight to the ground plane as required. Follow the below guidelines for best performance: 1 7 11 Minimize the length of the connections between the input capacitors, CIN, and the power switchers (MOSFETs) by placing them nearby. 12 Position both the ceramic and bulk input capacitors as close to the upper MOSFET drain as possible and make the GND returns (from the source of lower MOSFET to VIN capacitor GND) short. 3 Keep the metal running from the CLNx terminal to the output inductor short. 4 Use copper-filled polygons on the top (and bottom, if two-layer PCB) circuit layers for the CLN node. 13 Position the output inductor and output capacitors between the upper MOSFET and lower MOSFET and the load. 5 The small-signal wiring traces from the DLx and DHx pins to the MOSFET gates should be kept short and wide enough to easily handle the several amps of drive current. 14 AGND should be on the clearer plane and kept away from the noisy MOSFET GND. 6 The critical, small-signal components include any bypass capacitors (SMD-type of capacitors applied at VCC and SSx/ENB pins), feedback components © 2007 Fairchild Semiconductor Corporation SG1577 • Rev. 1.0.1 SG1577 — Dual Synchronous DC/DC Controller Layout Considerations 15 PGND should be short, together with MOSFET GND, then through vias to GND plane on the bottom of PCB. www.fairchildsemi.com 11 SG1577 — Dual Synchronous DC/DC Controller Physical Dimensions E H Detail A 1 10 b F c e A D θ L A2 y A1 Detail A Figure 25. 20-Lead Small Outline Package (SOP) Dimensions Millimeter Symbol Min. Typ. Inch Max. Min. A 2.362 2.642 0.093 Typ. 0.104 A1 0.101 0.305 0.004 0.012 A2 2.260 2.337 0.089 0.092 b 0.406 0.016 c 0.203 0.008 D 12.598 E 7.391 e 0.496 7.595 0.291 1.270 H 10.007 L 0.406 F 10.643 0.394 1.270 0.016 © 2007 Fairchild Semiconductor Corporation SG1577 • Rev. 1.0.1 0.299 0.419 0.050 0.020X45° 0.101 0° 0.508 0.050 0.508X45° y θ° 12.903 Max. 8° 0.004 0° 8° www.fairchildsemi.com 12 θ D 11 20 E1 eB E 10 1 A2 L A e b1 A1 b SG1577 — Dual Synchronous DC/DC Controller Physical Dimensions (Continued) Figure 26. 20-Lead Dual In-line Package (DIP) Dimensions Millimeter Symbol Min. Typ. A Inch Max. Min. Typ. 5.334 A1 0.381 A2 3.175 0.210 0.015 3.302 3.429 0.125 0.130 b 1.524 0.060 b1 0.457 0.018 D 24.892 E E1 26.162 26.924 0.980 7.620 6.223 e Max. 6.350 1.030 0.135 1.060 0.300 6.477 0.245 2.540 0.250 0.255 0.100 L 2.921 3.302 3.810 0.115 0.130 0.150 eB 8.509 9.017 9.525 0.335 0.355 0.375 θ° 0° © 2007 Fairchild Semiconductor Corporation SG1577 • Rev. 1.0.1 7° 15° 0° 7° 15° www.fairchildsemi.com 13 SG1577 — Dual Synchronous DC/DC Controller © 2007 Fairchild Semiconductor Corporation SG1577 • Rev. 1.0.1 www.fairchildsemi.com 14