SS6578 High-Efficiency, Step-Down DC/DC Controller DESCRIPTION FEATURES 4V to 18V input voltage operation. High-efficiency (up to 95%). The SS6578 is a high performance step-down DC/DC controller, designed to drive 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. 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 VIN=9V, VOUT=5V condition. A current-sense • Notebook 5V/3.3V Main Power • Step-Down DC/DC Controller Modules. • Constant-Current Source for Battery Chargers. 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 PIN CONFIGURATION SS6578CXXX Packing TR: Tape and reel TB: Tubes Packaging S: SO-8 N: PDIP-8 SO-8 TOP VIEW VIN 1 8 CS+ DUTY 2 7 CS- SHDN 3 6 DRI FB 4 5 GND 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 1 of 11 SS6578 TYPICAL APPLICATION CIRCUIT +VIN 6.4~18V +VOUT, 5V * Rs Q1 D1 GS SS32 1 + C1 100µF C2 0.1µF R6 2 1M 3 <15V 4 L1 33µH VIN CS+ DUTY CS- SHDN DRI FB GND C4 470µF + R3 12K R4 3K9 8 7 6 R7 5 ** U1 SS6578 IP = IO,MAX + VO( VIN − VO ) 2VIN × f S × L VTH 50mV 0.1VIN fS L = = IP IP 2VIN f S LIO,MAX + VIN VO − VO 2 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 RS = 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 CONDITIONS Operation Voltage MIN. TYP. 4 MAX. UNIT 20 V Quiescent Current VFB = 1.5V 90 160 µA Shutdown Mode Current V SHDN = 0V 8 20 µA 1.22 1.28 V Internal Reference Voltage 1.16 Driver Sinking "ON Resistance" 16 Ω Driver Sourcing "ON Resistance" 11 Ω Current Limit Sense Threshold VCS+ = 13V Shutdown Threshold 50 70 90 mV 0.8 1.5 2.4 V 1 µA SHDN Pin Leakage Current V SHDN < 15V Duty Cycle VDUTY = VIN 71 % Oscillator Frequency VDUTY = VIN 225 KHz Rev.2.02 4/06/2004 www.SiliconStandard.com 3 of 11 SS6578 TYPICAL PERFORMANCE CHARACTERISTICS 90 35 90 30 0 85 Duty 80 Duty (%) Frequency 25 75 20 70 15 65 10 60 50 55 4 6 8 Fig. 1 10 12 14 16 18 VIN=5V Duty Cycle (%) 85 Frequency (KHz) TA = 27°C 80 75 VIN=13V 70 VIN=20V 65 60 0 20 0 VIN ( V) Frequency & Duty Cycle vs. VIN 20 40 60 80 Temperature (°C) Fig. 2 Duty Cycle vs.Temperature 10 VIN=5V 290 90 Duty Cycle (%) Frequency (KHz) VIN=20V 240 VIN=13V 190 140 80 VIN=10V VIN=15V 70 VIN=5V VIN=20V RDUTY refer to Typ. App. 90 0 10 20 30 40 50 60 Circuit. 60 0 70 1 Temperature (°C) Fig. 3 Frequency vs. Temperature 20 3 4 110 Quiescent Current (µA) Shutdown Current (µA) 2 RDUTY (MΩ) Fig. 4 Duty Cycle vs. RDUTY 15 TA=25°C TA=0°C 10 TA=70°C 5 0 4 6 8 10 12 14 16 VIN (V) Fig. 5 Shutdown Current vs. VIN Rev.2.02 4/06/2004 18 20 TA= 0°C 100 90 TA= 25°C 80 T A= 70°C 70 60 4 6 8 Fig. 6 www.SiliconStandard.com 10 12 14 16 18 20 VIN (V) Quiescent Current vs. VIN 4 of 11 SS6578 BLOCK DIAGRAM Current Limit Comparator VIN 1 70mV 8 + CS+ DUTY SHDN 2 3 VIN PFM OSC 6 + FB 7 LATCH CS- DRI Error Comparator 4 1.22V Reference Voltage Output Driver 5 GND PIN DESCRIPTIONS PIN 1: VIN 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 Rev.2.02 4/06/2004 Connecting a resistor R1 to converter output node and a resistor R2 to ground yields the output voltage: - Input supply voltage - a range of 4V to 18V is recommended. - Feedback comparator input, to compare the feedback voltage with the internal reference 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. 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 VIN voltage. www.SiliconStandard.com 5 of 11 SS6578 APPLICATION EXAMPLES VIN CS+ DUTY CS- SHDN DRI C2 100µF 0.1µF Efficiency vs. Load Current VIN + C1 6.4 ~ 18V 100 VOUT=5V RS *L1 GND FB + 330µF C3 GS SS32 D1 SS6578 VOUT 33µH Efficiency (%) *R7 5V/2A 5V 95 Q1 90 VIN=6.4 V 85 R2 R1 15.4K 47K VIN=9V VIN=16 V *:Sumida MPP Core 8010 VIN>15V, R7=15Ω 100 VIN≤15V, R7=0Ω 1000 Load Current (mA) CS- SHDN DRI GND FB VIN C1 12 ~ 18V Efficiency vs. Load Current 95 VOUT=3.3V RS R1** 680 R7 6.8V D2 Q1 *L1 GS SS32 D1 SS6578 R2 R1 27.4K 47K VOUT 33µH 330µF C3 *:Sumida MPP Core + 90 Efficiency (%) CS+ DUTY + 3.3V/2A 5V VIN C2 100µF 0.1µF Fig. 7 5V Step-Down Converter 85 80 VIN=16V VIN>15V, R7=15Ω VIN≤15V, R7=0Ω **R1 value is based on the 75 10 10 1000 Load Current (mA) current rating of D2 Fig. 8 3.3V Step-Down Converter Rev.2.02 4/06/2004 www.SiliconStandard.com 6 of 11 SS6578 APPLICATION EXAMPLES (Continued) VIN 5~8V R4 1N4148 1K 33µH Q1 + *L1 C3 D1 SS32 C2 + 100µF 0.1µF + 330µF 35V SS32 C4 10µF U1 VIN C1 D2 *RS D3 CS+ R6 RDUTY R1 DUTY CS- SHDN DRI 1M 1M FB GND R7 SS6578 ** VBATT R3 R2 SW1 510 LED2 20/5W PB SW LED1 R9 100K 4.7µF 1 DSW PEAK 2 + C9 100K U2 YELLOW R10 100K R8 240K Q3 C10 C7 0.1µF 47nF 9014 ICON VBT R15 3 LED2 DIS 680 4 LED1 VTS 5 GND VCC 6 THERMISTOR BATTERY BAT1 RX R14 7 100K 200K C8 8 RY 100K C6 0.1µF + C11 100µF 0.1µF R11 ADJ SEL1 SEL3 SEL2 TMR MODE LED3 R12 GREEN RED 16 15 R16 R17 680 680 14 13 12 11 10 9 SS6781 240K R13 470K Q2 MMBT2222A U3 78L05 + C12 1µF NOTE: *:Sumida MPP Core VOUT VIN GND + C13 10µF VIN>15V, R7=15Ω VIN≤15V, R7=0Ω 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 the same. happens when Vout is under 5V, we offer two Note: The input voltage rating in this circuit is 12V solutions for the SS6578 as a buck controller. rather than 4V, and the rating can be varied depending on the value of Zener diode D2. 1. Buck Converter with 12V<Vin<18V Please refer to Fig3. 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. The current-sense resistor Rs is used for This solution will limit the temperature rise over-current protection. Due to concerns about of MOSFET Q1. The smaller the resistor value, the power loss, cost, and size, many users do not the lower temperature rise. The resistor value is use Rs in their buck converter application. determined by the reverse current rating of the Damage caused by unexpected current (over Zener diode. Refer to its databook for the reverse current rating. Note that the current is rating current) could be done to Q1, U1 and the strictly limited by the spec. circuits attached to VOUT when Rs is not used. A temperature rise of 1°C for Q1 results from the For the calculation of Rs, please refer to the addition of R1=680ohm, D2=6.8V to the original formula of Rs in “Typical Application” above. condition (Vin=12V, Vout=3.3V and IOUT=1.5A). Yet, the efficiency of the system remains nearly +VOUT, 3.3V 12V< +V IN <15V L1 33µH Rs Q1 SSM4435 D1 SS32 R1 680 1 2 + C1 100µ C2 0.1µF 3 4 D2 6.8V VIN CS+ DUTY CS- SHDN DRI FB GND 8 7 + C4 330µF 6 5 R2 47K R3 27K U1 SS6578 Fig. 10 DC/DC Buck Converter VOUT=3.3V Rev.2.02 4/06/2004 www.SiliconStandard.com 8 of 11 SS6578 +VIN = 5~18V +VOUT, 3.3V Rs C1 100µF *** R6 D2 LL4148 1M Q2 C3 1µF * Q1 SSM4435 R2 100K + C2 <15V 0.1uF R1 3K3 L1 33µH D1 SS32 C4 470µF 1 VIN CS+ 8 2 DUTY CS- 7 3 SHDN DRI 4 FB GND + R3 47K R4 27K R7 6 * 5 U1 SS6578 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 A fuse can be selected to pass (abbreviated as SCP) does not always exist in the start up current, but open quickly the DC-DC converter circuit. The fact is usually with a large unexpected current. Of the DC-DC converter provides the circuits course, attached to VOUT with low power or low is needed after short circuit. 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 3. of the fuse Design 2: shown as Fig. 13. Method: Add a SCP circuit Note: 1. The time constant, which is 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. replacement Design1: shown as Fig. 12. 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. Method: Add a fast fuse to VOUT. 3. The condition for applying this design is VOUT ≥3V. Rev.2.02 4/06/2004 www.SiliconStandard.com 9 of 11 SS6578 +VIN 12V FUSE1 +VOUT, 5V/2A Rs L2 20mR 33µH Fast 3A D2 SS32 Q2 R6 680 + C5 470µ/16V C2 0.1µF D3 6.8V 1 VIN CS+ 2 DUTY CS- 3 SHDN 4 FB 8 7 C4 6 1500µF/6.3V DRI + R9 3K9 5 GND R8 12K U2 SS6578 Fig 12. Add a Fast Fuse Solution +VIN 12V R1 240K C1 1µ +VOUT, 5V/2A Rs R2 10K Q1 PNP mmbt3906 L2 33µH 20mR Q2 D2 SS32 R6 680 D3 6.8V + 470µF C5 16V C2 0.1µF 1 VIN 2 DUTY 3 SHDN 4 FB CS+ 8 CS- 7 DRI GND 6 1500µF 6.3V 5 C4 + R8 12K R9 3K9 U2 SS6578 LL4148 D1 Short Circuit Protection Fig 13. Add A Short Circuit Protection Circuit Solution Rev.2.02 4/06/2004 www.SiliconStandard.com 10 of 11 SS6578 PHYSICAL DIMENSIONS 8 LEAD PLASTIC SO (unit: mm) D SYMBOL MIN MAX A 1.35 1.75 A1 0.10 0.25 H E e B 0.33 0.51 C 0.19 0.25 D 4.80 5.00 E 3.80 4.00 e A A1 C B 1.27(TYP) H 5.80 6.20 L 0.40 1.27 L 8 LEAD PLASTIC DIP (unit: mm) D E1 E A2 A1 C L SYMBOL MIN MAX 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 eB b e 2.54 (TYP) eB — 10.92 L 2.92 3.81 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 infringement 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. Rev.2.02 4/06/2004 www.SiliconStandard.com 11 of 11