SS6578CNTB

SS6578 SSC | Alldatasheet

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Technical content

www.SiliconStandard.com 1 of 11 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.

APPLICATIONS

• Notebook 5V/3.3V Main Power
• Step-Down DC/DC Controller Modules.
• Constant-Current Source for Battery Chargers.

DESCRIPTION

The SS6578 is a high performance step-down DC/DC controller, designed to drive an external P-channel MOSFET to generate programmable out put 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 voltag e and loading condition. The SS6578 delivers 10mA to 2A of out put current with 87% ~93% efficiency at V IN=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 co nnecting a resistor from DUTY pin to V IN. Quiescent current is about 90 µA 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 PIN CONFIGURATION SO-8 TOP VIEW DRI CS+ DUTY FB CS- GND VIN SHDN SS6578CXXX Packing TR: Tape and reel TB: Tubes Packaging S: SO-8 N: PDIP-8 Example: SS6578CSTR à in 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 2 of 11 SS6578 TYPICAL APPLICATION CIRCUIT VIN 1 DUTY 2 SHDN 3 FB 4 GND 5 DRI 6 CS- 7 CS+ 8 U1 SS6578 12K 3K9 0.1µF +VIN 6.4~18V +VOUT, 5V Rs * + C4 470µF GS SS32 100µF <15V 33µH LfV2 )V V(VI I SIN OINO MAX,OP × × −+ = 2OOINMAX,OSIN SIN P P TH S V V VLIfV2 LfV1.0 I mV50 I VR − + = = = VIN: Input voltage VOUT: Output voltage fS: Working frequency L= Inductor value IO,MAX: Maximum Output current VTH: Current Limit Sense Threshold **VIN>15V, R7=15Ω VIN≤ 15V, R7=0Ω DC/DC Buck Converter ABSOLUTE MAXIMUM RATINGS TEST CIRCUIT Refer to TYPICAL APPLICATION CIRCUIT. Rev.2.02 4/06/2004

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ELECTRICAL CHARACTERISTICS

(VIN= 13V, TA=25°C, unless otherwise specified.) PARAMETERS CONDITIONS MIN. TYP. MAX. UNIT Operation Voltage 4 20 V Quiescent Current VFB = 1.5V 90 160 µA Shutdown Mode Current VSHDN = 0V 8 20 µA Internal Reference Voltage 1.16 1.22 1.28 V Driver Sinking "ON Resistance" 16 Ω Driver Sourcing "ON Resistance" 11 Ω Current Limit Sense Threshold VCS+ = 13V 50 70 90 mV Shutdown Threshold 0.8 1.5 2.4 V SHDN Pin Leakage Current VSHDN < 15V 1 µA Duty Cycle VDUTY = VIN 71 % Oscillator Frequency VDUTY = VIN 225 KHz SS6578 Rev.2.02 4 /06/2004

www.SiliconStandard.com 4 of 11 SS6578 TYPICAL PERFORMANCE CHARACTERISTICS Fig. 1 Frequency & Duty Cycle vs. VIN VIN ( V) Duty (%) Duty 4 6 8 10 12 14 16 18 20 TA = 27°C Frequency Frequency (KHz) Temperature (°C) Fig. 2 Duty Cycle vs.Temperature Duty Cycle (%) VIN=5V 0 20 40 60 80 VIN=20V VIN=13V Temperature (°C) Fig. 3 Frequency vs. Temperature Frequency (KHz) 0 10 20 30 40 50 60 7090 140 190 240 290 VIN=5V VIN=13V VIN=20V RDUTY (MΩ ) Fig. 4 Duty Cycle vs. RDUTY Duty Cycle (%) 0 1 2 3 4 VIN=20V VIN=10V VIN=15V VIN=5V RDUTY refer to Typ. App. Circuit. VIN (V) Fig. 5 Shutdown Current vs. VIN Shutdown Current (µA) 20 4 6 8 10 12 14 16 18 TA=0°C TA=25°C TA=70°C VIN (V) Fig. 6 Quiescent Current vs. VIN Quiescent Current (µA) 4 6 8 10 12 14 16 18 2060 100 110 TA= 25°C TA= 70°C TA= 0°C Rev.2.02 4/06/2004

www.SiliconStandard.com 5 of 11 SS6578 BLOCK DIAGRAM 70mV 8 5 4 Current Limit Comparator Output Driver GND DRI CS+ CS- VIN PFM OSC 1.22V Reference Voltage Error Comparator DUTY FB SHDN VIN LATCH PIN DESCRIPTIONS PIN 1: VIN - Input supply voltage - a range of 4V to 18V is recommended. PIN 2: DUTY - Duty cycle adjustment pin. To be tied to the VIN pin directly or through a resistor RDUTY to adjust oscillator duty cycle. R DUTY must be over 1MΩ if VIN=20V. See TYPICAL PERFORMANCE CHARACTERISTICS. PIN 3: SHDN- Logical input to shutdown the chip: VSHDN = High for normal operation. VSHDN = 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. Connecting a resistor R1 to converter outp ut node and a resistor R2 to ground yields the output voltage: V OUT=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 bas e resistor and a capacitor to the base of PNP are recommended. PIN 7: CS- - Current-sense comparator inverting input . This pin voltage should go over 2V but should not exceed VIN voltage. PIN 8: CS+ - Current sense comparator non-inverting input . This pin voltage should go over 2V but should not exceed V IN voltage. Rev.2.02 4/06/2004

www.SiliconStandard.com 6 of 11 SS6578 APPLICATION EXAMPLES SS6578 CS+ CS- DRI DUTY FB GND SHDN VIN *:Sumida MPP Core VOUT VIN 6.4 ~ 18V 33µH 5V/2A 100µF + 15.4K 47K 0.1µF 330µF C3 GS SS32 + *L1 C1 C2 RS *R7 VIN>15V, R7=15Ω VIN≤ 15V, R7=0Ω Load Current (mA) Efficiency vs. Load Current Efficiency (%) 100 10 100 100080 VIN=6.4 V VIN=9V VIN=16 V VOUT=5V Fig. 7 5V Step-Down Converter SS6578 CS+ CS- DRI DUTY FB GND SHDN VIN *:Sumida MPP Core VOUT VIN 12 ~ 18V 33µH 3.3V/2A 100µF + 27.4K 47K 0.1µF 330µF C3 GS SS32 + *L1 C1 C2 RS R1 680 6.8V VIN>15V, R7=15Ω VIN≤ 15V, R7=0Ω R1 value is based on the current rating of D2 Load Current (mA) Efficiency vs. Load Current 10 10 1000 VOUT=3.3V Efficiency (%) VIN=16V Fig. 8 3.3V Step-Down Converter Rev.2.02 4/06/2004

www.SiliconStandard.com 7 of 11 SS6578 APPLICATION EXAMPLES (Continued) 1N4148 SS32 SS32 *L1 33µH *RS 100µF *:Sumida MPP Core VBATT 10µF 330µF 35V BATTERY + + CS+ CS- DRI DUTY FB GND VIN VIN 5~8V RDUTY SS6578 PEAK VBT DIS VTS VCC ADJ 6 SEL3 7 TMR 8 MODE 9 SEL2 10 SEL1 11 GND 12 LED1 13 LED2 14 ICON 15 DSW 16 SS6781 240K 100K BAT1 R10 100K 4.7µF 0.1µF C10 47nF R15 680 510 R2 20/5W SW1 PB SW R12 100K R16 680 R17 680 R14 200K 0.1µF C11 100µF RX 100K R11 240K RY 100K C6 0.1µF R13 470K MMBT2222A LED2 GREEN LED3 RED LED1 YELLOW 9014 THERMISTOR + + 78L05 U3 VIN VOUT GND C12 1µF C13 10µF SHDN VIN>15V, R7=15Ω VIN≤ 15V, R7=0Ω 0.1µF 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

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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<Vin<18V When the SS6578 is used in a Buck Circuit with VOUT<5V, add a resistor R1 of 680 ohm and a Zener diode D2 of 6.8V. This solution will limit the temperature rise of MOSFET Q1. The smaller the resistor value, the lower temperature rise. The resistor value is determined by the reverse current rating of the Zener diode. Refer to its databook for the reverse current rating. Note that the current is strictly limited by the spec. A temperature rise of 1°C for Q1 results from the addition of R1=680ohm, D2=6.8V to the original condition (Vin=12V, Vout=3.3V and I OUT=1.5A). Yet, the efficiency of the system remains nearly the same. Note: The input voltage rating in this circuit is 12V rather than 4V, and the rating can be varied depending on the value of Zener diode D2. Please refer to Fig3. The current-sense resistor Rs is used for over-current protection. Due to concerns about the power loss, cost, and size, many users do not use Rs in their buck converter application. Damage caused by unexpected current (over rating current) could be done to Q1, U1 and the circuits attached to VOUT when Rs is not used. For the calculation of Rs, please refer to the formula of Rs in “Typical Application” above. VIN 1 DUTY 2 SHDN 3 FB 4 GND 5 DRI 6 CS- 7 CS+ 8 U1 SS6578 47K 27K 0.1µF 12V< +VIN <15V +VOUT, 3.3V 330µF SS32 100µ 6.8V 680 Rs SSM4435 L1 33µH Fig. 10 DC/DC Buck Converter VOUT=3.3V Rev.2.02 4/06/2004

www.SiliconStandard.com 9 of 11 SS6578 VIN 1 DUTY 2 SHDN 3 FB 4 GND 5 DRI 6 CS- 7 CS+ 8 U1 SS6578 47K 27K 0.1uF +VIN = 5~18V +VOUT, 3.3V Rs 470µF SS32 + 100µF L1 33µH SSM4435 3K3 1µF LL4148 100K <15V *** * VIN>15V, R7=15Ω VIN≤ 15V, R7=0Ω * *** R6 can adjust the duty cycle max. It can be 0Ω Fig 11. DC/DC Buck Converter VOUT=3.3V B. Short Circuit Protection Design 1. As we know, Short Circuit Protection (abbreviated as SCP) does not always exist in the DC-DC converter circuit. The fact is usually the DC -DC converter provides the circuits attached to VO UT with low power or low voltage. Sometimes there is less concern about safety, as the probability of short-circuit is quite low. That gives users reasons to ignore the use of an SCP circuit. However, we would still like to point out the importance of the protection. With SCP, the system will be well protected in any situation. Two SCP circuits are introduced as follows for your reference. 2. Design1: shown as Fig. 12. Method: Add a fast fuse to V OUT. A fuse can be selected to pass the start up current, but open quickly with a large unexpected current. Of course, replacement of the fuse is needed after short circuit. 3. Design 2: shown as Fig. 13. Method: Add a SCP circuit Note: 1. The time constant, which is directly related to R1 and C1, has a serious effect on the circuit. 2. Circuit can be recovered by removing the short circuit event from the system. 3. The condition for applying this design is V OUT ≥ 3V. Rev.2.02 4 /06/2004

www.SiliconStandard.com 10 of 11 SS6578 VIN 1 DUTY 2 SHDN 3 FB 4 GND 5 DRI 6 CS- 7 CS+ 8 U2 SS6578 12K 3K9 C2 0.1µF +VOUT, 5V/2A Rs 20mR + C4 1500µF/6.3V SS32 470µ/16V +VIN 12V L2 33µH 6.8V 680 FUSE1 Fast 3A Fig 12. Add a Fast Fuse Solution VIN 1 DUTY 2 SHDN 3 FB 4 GND 5 DRI 6 CS- 7 CS+ 8 U2 SS6578 12K 3K9 C2 0.1µF +VOUT, 5V/2A Rs 20mR + C4 1500µF 6.3V SS32 470µF +VIN 12V L2 33µH 6.8V 680 240K PNP 10K D1 LL4148 Short Circuit Protection mmbt3906 16V Fig 13. Add A Short Circuit Protection Circuit Solution Rev.2.02 4/06/2004

Information furnished by Silicon Standard Corporation is believed to be accurate and reliable. However, Silicon Standard Corporation makes no guarantee or warranty, express or implied, as to the reliability, accuracy, timeliness or completeness of such information and assumes no responsibility for its use, or for infri ngement of any patent or other intellectual property rights of third parties that may result from its use. Silicon Standard reserves the right to make changes as it deems necessary to any products described herein for any reason, including without limitation enhancement in reliability, functionality or design. No license is granted, whether expressly or by implication, in relation to the use of any products described herein or to the use of any information provided herein, under any patent or other intellectual property rights of Silicon Standard Corporation or any third parties. www.SiliconStandard.com 11 of 11 SS6578 PHYSICAL DIMENSIONS

8 LEAD PLASTIC SO (unit: mm)

A 1.35 1.75 A1 0.10 0.25 B 0.33 0.51 C 0.19 0.25 D 4.80 5.00 E 3.80 4.00 e 1.27(TYP) H 5.80 6.20 L 0.40 1.27 D H e A B C E L

8 LEAD PLASTIC DIP (unit: mm)

A1 0.381 — A2 2.92 4.96 b 0.35 0.56 C 0.20 0.36 D 9.01 10.16 E 7.62 8.26 E1 6.09 7.12 e 2.54 (TYP) eB — 10.92 b e L eB E C D L 2.92 3.81 Rev.2.02 4/06/2004