Synchronous Buck Controller

Synchronous Buck Controller for Dynamic Load-Voltage Applications POWER MANAGEMENT Description The SC470 is a single output, constant on-time synchronous-buck, pseudo-fixed frequency, PWM controller intended for use in notebook computers and other battery operated portable devices. Features include high efficiency and fast dynamic response with no minimum on-time. The excellent transient response means that SC470 based solutions will require less output capacitance than competing fixed frequency converters. www.DataSheet4U.com The SC470 is specifically targeted for graphics processor power supplies that require dynamic voltage transition, with a tight 0.85% DC accuracy and a 20% OVP threshold. The frequency is constant until a step-in load or line voltage occurs, at which time the pulse density and frequency will increase or decrease to counter the change in output or input voltage. After the transient event, the controller frequency will return to steady state operation. At light loads, Power-Save Mode enables the SC470 to skip PWM pulses for better efficiency. The output voltage can be adjusted from 0.5V to VCCA. The integrated gate drivers feature adaptive shootthrough protection and soft switching. Additional features include cycle-by-cycle current limit, digital soft-start, overvoltage and under-voltage protection, and a PGD output. SC470 Features Constant on-time for fast dynamic response Programmable VOUT range = 0.5 – VCCA VBAT range = 1.8V – 25V DC current sense using low-side RDS(ON) sensing or RSENSE in source of low-side MOSFET for greater accuracy Resistor programmable on-time Cycle-by-cycle current limit Digital soft-start Combined EN and PSAVE functions Over-voltage/under-voltage fault protection and PGD output 20% OVP threshold for simpler dynamic voltage transition circuitry 5µA typical shutdown current Low quiescent power dissipation 14 lead TSSOP and 16 pin MLPQ (4mm x 4mm) packages Industrial temperature range 0.85% DC accuracy Integrated gate drivers with soft-switching Applications Graphics Cards Embedded Graphics Processors High Performance Processors Typical Application Circuit VBAT 5VSUS 5VSUS VBAT D1 R1 RTON R1 10R U1 EN/PSV TON VOUT R2 VCCA R2 FB PGOOD R4 PGD VSSA VDDP DL C4 C6 1uF PGND 1uF Q2 ILIM + VOUT SC470 BST DH LX R3 C1 0.1uF Q1 C2 10uF L1 VOUT C3 C5 1nF September 27, 2005 1 www.semtech.com SC470 POWER MANAGEMENT Absolute Maximum Ratings(1) 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. Pin Combination TON to VSSA DH, BST to PGND LX to PGND PGND to VSSA www.DataSheet4U.com Symbol Maximum -0.3 to +25.0 -0.3 to +30.0 -2.0 to +25.0 -0.3 to +0.3 -0.3 to +6.0 -0.3 to +6.0 -0.3 to +6.0 -0.3 to +6.0 Units V V V V V V V V °C/W °C/W °C °C °C °C BST to LX DL, ILIM, VDDP to PGND EN/PSV, FB, PGD, VCCA, VOUT to VSSA VCCA to EN/PSV, FB, PGD, VOUT Thermal Resistance, Junction to Ambient - ITSTRT(2) Thermal Resistance, Junction to Ambient - IMLTRT(2) Operating Junction Temperature Range Storage Temperature Range Lead Temperature (Soldering) 10s - Part No. ITSTRT IR Reflow (Soldering) 10s to 30s - Part No. IMLTRT θJA θJA TJ TSTG TLEAD TLEAD 100 31 -40 to +125 -65 to +150 300 260 Notes: 1) This device is ESD sensitive. Use of standard ESD handling precautions is required. 2) Calculated from package in still air, mounted to 3” to 4.5”, 4 layer FR4 PCB with thermal vias under the exposed pad per JESD51 standards. Electrical Characteristics Test Conditions: VBAT = 15V, EN/PSV = 5V, VCCA = VDDP = 5.0V, VOUT = 1.25V, RTON = 1MΩ, 0.1% Resistor Dividers. Parameter Conditions Min 25°C Typ Max -40°C to 125°C Min Max Units Input Supplies VCCA Input Voltage VDDP Input Voltage VIN Input Voltage VDDP Operating Current VCCA Operating Current TON Operating Current Shutdown Current VIN = 1.8V - 25V, Offtime > 800ns FB > regulation point, ILOAD = 0A FB > regulation point, ILOAD = 0A RTON = 1MΩ EN/PSV = 0V VC C A VDDP + VIN  2005 Semtech Corp. 2 5.0 5.0 1.8 70 700 15 -5 5 0 25 4.5 4.5 5.5 5.5 V V V 150 1100 µA µA µA -10 10 1 µA µA µA www.semtech.com SC470 POWER MANAGEMENT Electrical Characteristics (Cont.) Parameter Conditions Min Controller Error Comparator Threshold (FBK Turn-on Threshold (2) www.DataSheet4U.com 25°C Typ Max -40°C to 125°C Min Max Units VCCA = 4.5V to 5.5V, 0°C ≤ TA ≤ 85°C VCCA = 4.5V to 5.5V, -40°C ≤ TA ≤ 85°C Adjust Mode RTON = 1MΩ RTON = 500kΩ 0.500 -0.85% -1% 0.5 +0.85% +1% VC C A 2025 1076 500 V Output Voltage Range On-Time, VBAT = 2.5V V ns ns ns kΩ 1761 936 400 500 1497 796 Minimum Off Time VOUT Input Resistance FB Input Bias Current Over-Current Sensing ILIM Sink Current Current Comparator Offset PSAVE Zero-Crossing Threshold Fault Protection Current Limit (Positive)(3) PGND-LX, RILIM = 5kΩ PGND-LX, RILIM = 10kΩ PGND-LX, RILIM = 20kΩ Current Limit (Negative) Output Under-Voltage Fault Output Over-Voltage Fault Over-Voltage Fault Delay PGD Low Output Voltage PGD Leakage Current PGD UV Threshold PGND-LX With respect to internal reference. With respect to internal reference. FB forced above OV Vth Sink 1mA FB in regulation, PGD = 5V With respect to internal reference. PGND - LX, EN/PSV = 5V DL High PGND - ILIM -1.0 +1.0 µA 10 9.0 -10 11.0 10 µA mV 5 mV 50 100 200 -125 -30 +20 5.0 35 80 170 -160 -40 +16 65 120 230 -90 -25 +24 mV mV mV mV % % µs 0.4 1 -10 -12 -8 V µA %  2005 Semtech Corp. 3 www.semtech.com SC470 POWER MANAGEMENT Electrical Characteristics (Cont.) Parameter Conditions Min Fault Protection (Cont.) PGD Fault Delay VCCA Undervoltage Threshold w w 25°C Typ Max -40°C to 125°C Min Max Units FB forced outside PGD window. Falling (100mV Hysteresis) e 10OC Hyster4 sis U e t 5.0 4.0 1 m 65 3.7 4.3 µs V C Over Temperature Lockoa t u w . D a t Inputs/Outputs Logic Input Low Voltage Logic Input High Voltage Logic Input High Voltage Enable/Power Save Input Resistance Soft Start Soft-Start Ramp Time Under-Voltage Blank Time Gate Drivers Dead Time DL Pull-Down Resistance DL Sink Current DL Pull-Up Resistance DL Source Current DH Pull-Down Resistance DH Pull-Up Resistance DH Sink/Source Current S h e . c o EN/PSV low EN High, PSV low (Pin Floating) EN/PSV high R Pullup to VCCA R Pulldown to VSSA 1.5 1 2.0 3.1 1.2 V V V MΩ MΩ EN/PSV high to PGD high EN/PSV high to UV high 440 440 clks(4) clks(4) DH or DL rising DL low DL = 2.5V DL high DL = 2.5V DH low, BST - LX = 5V DH high, BST - LX = 5V DH = 2.5V 30 0.8 3.1 2 1.3 2 2 1.3 4 4 4 1.6 ns Ω A Ω A Ω Ω A Notes: (1) Calculated from package in still air, mounted to 3” x 4.5”, 4 layer FR4 PCB with thermal vias under the exposed pad per JESD51 standards. (2) When the inductor is in continuous and discontinuous conduction mode, the output voltage will have a DC regulation level higher than the error-comparator threshold by 50% of the ripple voltage. This voltage will vary slightly with load and VBAT. (3) Using a current sense resistor, this measurement relates to PGND minus the voltage of the source on the low-side MOSFET. These values guaranteed by the ILIM Source Current and Current Comparator Offset tests. (4) clks = switching cycles.  2005 Semtech Corp. 4 www.semtech.com SC470 POWER MANAGEMENT Pin Configuration EN/PSV TON BST NC Ordering Information DEVICE(1) SC470IMLTRT(2)(3) SC470ITSTRT(2)(3) PACKAGE MLPQ-16 TSSOP-14 Evaluation Board 16 15 14 13 12 11 10 SC470EVB(4) VOUT VCCA www.DataSheet4U.com 1 2 3 4 5 TOP VIEW DH LX ILIM VDDP Notes: (1) Only available in tape and reel packaging. A reel contains 2500 devices. (2) This product is fully WEEE and RoHS compliant. (3) Lead-free product. This product is J-STD-020B compliant and all homogeneous subcomponents are RoHS compliant. (4) Part-specific evaluation boards - consult factory for availability. FB PGD T 6 7 8 9 VSSA PGND NC MLPQ16: 4X4 BODY TOP VIEW EN/PSV TON VOUT VCCA FB PGD VSSA 1 2 3 4 5 6 7 14 13 12 11 10 9 8 BST DH LX ILIM VDDP DL PGND (14 Pin TSSOP)  2005 Semtech Corp. DL 5 www.semtech.com SC470 POWER MANAGEMENT Pin Descriptions Pin Name VOUT VC C A FB PGD NC VSSA PGND DL VD D P ILIM MLPQ-16# TSSOP-14# 1 2 3 4 5 6 7 8 9 10 3 4 5 6 7 8 9 10 11 Pin Function Output voltage sense input. Connect to VOUT at the load. Supply voltage input for the analog supply. Use a 10Ohm / 1µF RC filter from 5VSUS to VSSA. Feedback input. Connect to a resistor divider from VOUT to VSSA to set the output voltage between 0.5V and VCCA. Power Good open drain NMOS output. Goes high after a fixed clock cycle delay (440 cycles) following power-up. No Connect. Ground reference for analog circuitry. Connect to the bottom of the output capacitor. Power ground. Gate drive output for the low side MOSFET switch. +5V supply voltage input for the gate drivers. Decouple this pin with a 1µF ceramic capacitor to PGND. Current limit input. Connect to drain of low-side MOSFET for RDS(on) sensing, or the source resistor for sensing through a threshold sensing resistor. Phase node (junction of top and bottom MOSFETs and the output inductor) connection. Gate drive output for the high side MOSFET switch. Boost capacitor connection for the high side gate drive. No Connect. Enable/Power Save input . Pull down to VSSA to shut down the IC. Pull-up to enable the IC and activate PSAVE mode. Float to enable the IC and activate continous conduction mode(CCM). If floated, bypass to VSSA with a 10nF ceramic capacitor. This pin is used to sense VBAT through a pullup resistor, RTON, and to set the top MOSFET on-time. Bypass this pin with a 1nF ceramic capacitor to VSSA. Pad for heatsinking purposes. Connect to ground plane using multiple vias. Not connected internally.