SS6578CSTB

SS6578 High-Efficiency, Step-Down DC/DC Controller FEATURES 4V to 18V input voltage operation. High-efficiency (up to 95%). Low quiescent current at 90µA. Pulse-skipping and pulse-frequency modulation. Inputs-uncommitted current-sense comparator. Duty-cycle adjustable. 90KHz to 280KHz oscillator frequency. Power-saving shutdown mode (8µA typical). Push-pull driver output. DESCRIPTION The SS6578 is a high performance step-down DC/DC controller, designed to drive an external P-channel MOSFET to generate programmable output voltages. Two main schemes of Pulse-Skipping and Pulse-Frequency Modulation are employed to maintain low quiescent current and high conversion efficiency under wide ranges of input voltage and loading condition. The SS6578 delivers 10mA to 2A of output current with 87%~93% efficiency at APPLICATIONS • Notebook 5V/3.3V Main Power • Step-Down DC/DC Controller Modules. • Constant-Current Source for Battery Chargers. VIN=9V, VOUT=5V condition. A current-sense comparator with both inverting and non-inverting inputs uncommitted is included to provide the crucial function of either current-limit protection or constant-output current control. When the SS6578 is used in a high-side current-sensing step-down constant-current source, the efficiency is typically greater than 90%. Duty-cycle can be adjusted to greater than 90% by connecting a resistor from DUTY pin to VIN. Quiescent current is about 90µA and can be reduced to 8µA in shutdown mode. The switching frequency range of around 90 kHz to 280 kHz allows small size switching components, which are ideal for battery powered portable equipment. ORDERING INFORMATION S S6578CXXX P acking TR: Tape and reel TB: Tubes P ackaging S: SO-8 N: PDIP-8 PIN CONFIGURATION S O-8 VIN DUTY SHDN FB TOP VIEW 1 2 3 4 8 CS+ 7 CS6 D RI 5 GND E xample: SS6578CSTR à i n SO-8 package, shipped in tape and reel packing (PDIP-8 is only available in tubes) Rev.2.02 4/06/2004 www.SiliconStandard.com 1 of 11 SS6578 TYPICAL APPLICATION CIRCUIT +VIN 6.4~18V +VOUT, 5V * Rs L1 33µH + R3 12K R4 3K9 Q1 D1 GS SS32 C4 470µF 1 R6 + C1 100µF C2 0.1µF 1M 15V, R7=15Ω VIN≤15V, R7=0Ω DC/DC Buck Converter ABSOLUTE MAXIMUM RATINGS VIN Supply Voltage.....…………................................…….............................................. 20V DUTY Voltage.........................................……………...……........................................... 20V SHDN Voltage......................................………….......……............................................. 15V Operating Temperature Range................………….....…….................................... 0°C~70°C Storage Temperature Range......................…………....……........................... -65°C~ 150°C TEST CIRCUIT Refer to TYPICAL APPLICATION CIRCUIT. Rev.2.02 4/06/2004 www.SiliconStandard.com 2 of 11 SS6578 ELECTRICAL CHARACTERISTICS (VIN= 13V, TA=25°C, unless otherwise specified.) PARAMETERS Operation Voltage Quiescent Current Shutdown Mode Current Internal Reference Voltage Driver Sinking "ON Resistance" Driver Sourcing "ON Resistance" Current Limit Sense Threshold Shutdown Threshold VCS+ = 13V 50 0.8 V SHDN < 15V VDUTY = VIN VDUTY = VIN 71 225 VFB = 1.5V V SHDN = 0V 1.16 CONDITIONS MIN. 4 90 8 1.22 16 11 70 1.5 90 2.4 1 TYP. MAX. 20 160 20 1.28 UNIT V µA µA V Ω Ω mV V µA % KHz SHDN Pin Leakage Current Duty Cycle Oscillator Frequency Rev.2.02 4/06/2004 www.SiliconStandard.com 3 of 11 SS6578 TYPICAL PERFORMANCE CHARACTERISTICS 90 TA = 27°C 85 80 35 30 0 90 Duty Frequency 85 25 20 15 10 50 0 20 Frequency (KHz) VIN=5V Duty Cycle (%) 80 Duty (%) 75 70 65 60 55 4 6 8 10 12 14 16 18 75 VIN=13V 70 65 VIN=20V 60 0 Fig. 1 VIN ( V) Frequency & Duty Cycle vs. VIN Temperature (°C) Fig. 2 Duty Cycle vs.Temperature 20 40 60 80 10 290 VIN=5V VIN=20V 90 Frequency (KHz) 240 Duty Cycle (%) 190 VIN=13V 80 VIN=10V VIN=15V 140 VIN=5V 70 VIN=20V RDUTY refer to Typ. App. Circuit. 90 0 10 20 30 40 50 60 70 Temperature (°C) Fig. 3 Frequency vs. Temperature 60 0 RDUTY (MΩ) Fig. 4 Duty Cycle vs. RDUTY 1 2 3 4 20 110 Shutdown Current (µA) 15 TA=25°C TA=0°C Quiescent Current ( µA) 100 TA= 0°C 90 10 TA= 25°C 80 T A= 70°C 5 TA=70°C 70 0 4 6 8 10 12 14 16 18 20 60 4 6 8 10 12 14 16 18 20 VIN (V) Fig. 5 Shutdown Current vs. VIN Fig. 6 VIN (V) Quiescent Current vs. VIN Rev.2.02 4/06/2004 www.SiliconStandard.com 4 of 11 SS6578 BLOCK DIAGRAM Current Limit Comparator VIN 1 + 70mV 8 CS+ DUTY 2 PFM OSC VIN LATCH 7 CS- SHDN 3 + Error Comparator 1.22V Reference Voltage Output Driver 6 DRI FB 4 5 GND PIN DESCRIPTIONS PIN 1: VIN - Input supply voltage - a range of 4V to 18V is recommended. Connecting a resistor R1 to converter output node and a resistor R2 to ground yields the output voltage: VOUT=1.22 x (R1+R2)/ R2 PIN 5: GND - Power ground. PIN 6: DRI - Push-pull driver output to drive an external P-channel MOSFET or PNP transistor. When driving a PNP bipolar transistor, a base resistor and a capacitor to the base of PNP are recommended. - Current-sense comparator inverting input. This pin voltage should go over 2V but should not exceed VIN voltage. PIN 2: DUTY - Duty cycle adjustment pin. To be tied to the VIN pin directly or through a resistor R DUTY to adjust oscillator duty cycle. RDUTY must be over 1MΩ if VIN=20V. See TYPICAL PERFORMANCE CHARACTERISTICS. PIN 3: SHDN- Logical input to shutdown the chip: V SHDN = High for normal operation. V SHDN = Low for shutdown. This pin should not be floating or be forced to over 15V. In shutdown mode DRI pin is held high. PIN 4: FB - Feedback comparator input, to compare the feedback voltage with the internal reference voltage. PIN 7: CS- PIN 8: CS+ - Current sense comparator non-inverting input. This pin voltage should go over 2V but should not exceed VIN voltage. Rev.2.02 4/06/2004 www.SiliconStandard.com 5 of 11 SS6578 APPLICATION EXAMPLES Efficiency vs. Load Current 0.1µF C2 100µF VIN + C1 6.4 ~ 18V 100 VOUT=5V 95 VIN DUTY 5V SHDN FB SS6578 R2 15.4K VIN>15V, R7=15Ω VIN≤15V, R7=0Ω CS+ RS *R7 Q1 33µH *L1 GS SS32 D1 R1 47K *:Sumida MPP Core 80 10 100 1000 DRI GND VOUT 5V/2A + Efficiency (%) CS- 90 VIN=6.4 V VIN=9V 330µF C3 85 VIN=16 V Load Current (mA) Fig. 7 5V Step-Down Converter VIN C1 12 ~ 18V 95 100µF 0.1µF C2 + Efficiency vs. Load Current VOUT=3.3V VIN DUTY 5V SHDN FB CS+ C SDRI GND SS6578 RS R1** 680 R 7 6.8V D2 GS SS32 D1 R1 47K *:Sumida MPP Core Q1 33µH *L1 330µF C3 + VOUT 90 Efficiency (%) 3.3V/2A 85 R2 27.4K VIN>15V, R7=15Ω VIN≤15V, R7=0Ω 80 VIN=16V 75 10 10 1000 **R1 value is based on the current rating of D2 Load Current (mA) Fig. 8 3.3V Step-Down Converter Rev.2.02 4/06/2004 www.SiliconStandard.com 6 of 11 SS6578 APPLICATION EXAMPLES VIN 5~8V R4 1K Q1 D1 SS32 (Continued) 1N4148 33µH *L1 U1 VIN C3 *RS + C4 10µF D2 D3 + 330µF 35V SS32 CS+ CSDRI GND C1 100µF + C2 0.1 µF R6 RDUTY DUTY R1 1M FB 1M SHDN R7 ** SS6578 VBATT R3 R2 20/5W LED1 R8 240K + R9 100K C9 4.7µF C7 0.1µF R10 100K YELLOW 1 PEAK 2 C10 47nF Q3 9014 S W1 LED2 PB SW R12 100K DSW ICON LED2 LED1 GND SEL1 SEL2 MODE 16 15 14 13 12 11 10 9 R16 680 R17 680 GREEN RED LED3 510 U2 R15 680 VBT 3 DIS 4 VTS 5 VCC BAT1 RX BATTERY THERMISTOR 6 R14 + C11 200K C8 7 8 R11 240K ADJ SEL3 TMR 100K RY 100K C6 0.1µF 100µ F R13 470K 0.1µF SS6781 Q2 MMBT2222A U3 78L05 + *:Sumida MPP Core VIN C12 1µ F GND VOUT + C13 10µ F VIN>15V, R7=15Ω VIN≤15V, R7=0Ω NOTE: RS =0.1Ω, charge current =0.5A ±10%, VIN>VBATT +3.5V RS =0.05Ω, charge current =1A±10%, VIN>VBATT +4V RS =0.033Ω , charge current =1.5A ±10%, VIN>VBATT +4.5V Efficiency>90%, measured at CS- node 3~5 NiMH/NiCd Cells Fig. 9 Battery Charger Circuit with High-Side Current-Sensing Constant Current Source Rev.2.02 4/06/2004 www.SiliconStandard.com 7 of 11 SS6578 APPLICATION INFORMATION A. Start Up Design In order to eliminate the over-shoot issue which happens when Vout is under 5V, we offer two solutions for the SS6578 as a buck controller. 1. Buck Converter with 12V