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SS6578 High-Efficiency, Step-Down DC/DC Controller FEATURES 4V to 18V input voltage operation. High-efficiency (up to 95%). Low quiescent current at 90A. Pulse-skipping and pulse-frequency modulation. Inputs-uncommitted current-sense comparator. Duty-cycle adjustable. 90KHz to 280KHz oscillator frequency. Power-saving shutdown mode (8A 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 90A and can be reduced to 8A 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 SS6578CXXX Packing TR: Tape and reel TB: Tubes Packaging S: SO-8 N: PDIP-8 PIN CONFIGURATION SO-8 VIN DUTY SHDN FB TOP VIEW 1 2 3 4 8 CS+ 7 CS6 DRI 5 GND Example: SS6578CSTR a 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 L1 33H + R3 12K R4 3K9 Q1 D1 GS SS32 C4 470F 1 R6 + C1 100F C2 0.1F 1M <15V 2 3 4 VIN DUTY SHDN FB CS+ CSDRI GND 8 7 6 5 R7 ** U1 SS6578 IP = IO,MAX + RS = VO( VIN - VO ) 2VIN x f S x 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=15 VIN15V, R7=0 DC/DC Buck Converter ABSOLUTE MAXIMUM RATINGS VIN Supply Voltage..................................................................................................... 20V DUTY Voltage............................................................................................................ 20V SHDN Voltage............................................................................................................ 15V Operating Temperature Range........................................................................... 0C~70C Storage Temperature Range....................................................................... -65C~ 150C 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=25C, 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 A A V mV V A % 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 35 90 TA = 27C 85 80 Duty Frequency 30 0 25 20 15 10 50 0 20 85 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 20 40 60 80 Fig. 1 VIN ( V) Frequency & Duty Cycle vs. VIN Temperature (C) Fig. 2 Duty Cycle vs.Temperature 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. 1 2 3 4 90 0 10 20 30 40 50 60 70 60 0 Temperature (C) Fig. 3 Frequency vs. Temperature RDUTY (M) Fig. 4 Duty Cycle vs. RDUTY 20 110 Shutdown Current (A) 15 TA=25C TA=0C 10 Quiescent Current (A) 100 TA= 0C 90 TA= 25C 80 T A= 70C 5 TA=70C 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 1M 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. 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 0.1F C2 100F VIN + C1 6.4 ~ 18V 100 VOUT=5V 95 VIN DUTY 5V SHDN FB SS6578 R2 15.4K VIN>15V, R7=15 VIN15V, R7=0 CS+ RS *R7 Q1 33H *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 330F C3 85 VIN=16 V Load Current (mA) Fig. 7 5V Step-Down Converter VIN C1 12 ~ 18V 95 100F 0.1F C2 + Efficiency vs. Load Current VOUT=3.3V VIN DUTY 5V SHDN FB CS+ CSDRI GND SS6578 RS R1** 680 R7 6.8V D2 GS SS32 D1 R1 47K *:Sumida MPP Core Q1 33H *L1 330F C3 + VOUT 90 Efficiency (%) 3.3V/2A 85 R2 27.4K VIN>15V, R7=15 VIN15V, R7=0 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 33H *L1 U1 VIN C3 *RS + C4 10F D2 D3 + 330F 35V SS32 CS+ CSDRI GND C1 100F + C2 0.1F R6 RDUTY DUTY R1 1M FB 1M SHDN R7 ** SS6578 VBATT R3 R2 20/5W LED1 R8 240K + R9 100K C9 4.7F C7 0.1F R10 100K YELLOW 1 PEAK 2 C10 47nF Q3 9014 SW1 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 0.1F 100F R13 470K 0.1F SS6781 Q2 MMBT2222A U3 78L05 + *:Sumida MPP Core VIN C12 1F GND VOUT + C13 10F VIN>15V, R7=15 VIN15V, R7=0 NOTE: RS =0.1, charge current =0.5A 10%, VIN>VBATT +3.5V RS =0.05, charge current =1A10%, VIN>VBATT +4V RS =0.033, 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 +VOUT, 3.3V R1 680 1 2 VIN DUTY SHDN FB CS+ CSDRI GND 8 7 6 5 + C4 330F R2 47K R3 27K + C1 100 C2 0.1F D2 6.8V 3 4 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 Rs R2 100K Q1 SSM4435 D1 SS32 L1 33H C4 470F +VOUT, 3.3V + R3 47K R4 27K + C1 100F 1 VIN D2 LL4148 *** R6 Q2 R1 3K3 1M C2 <15V 0.1uF CS+ 8 CS- 7 DRI GND 6 5 R7 * 2 DUTY 3 SHDN 4 FB C3 1F U1 SS6578 * VIN>15V, R7=15 VIN15V, R7=0* *** R6 can adjust the duty cycle max. It can be 0 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 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 VOUT 3V. (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 VOUT 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 VOUT. Rev.2.02 4/06/2004 www.SiliconStandard.com 9 of 11 SS6578 +VIN 12V Rs 20mR Q2 R6 680 1 VIN CS+ CSDRI GND 8 7 C4 6 1500F/6.3V 5 + L2 D2 SS32 33H FUSE1 +VOUT, 5V/2A Fast 3A + C5 470/16V 2 DUTY C2 0.1F D3 6.8V 3 SHDN R8 12K R9 3K9 4 FB U2 SS6578 Fig 12. Add a Fast Fuse Solution +VIN 12V R1 240K C1 1 Rs R2 10K Q1 PNP mmbt3906 20mR Q2 R6 680 1 VIN 2 DUTY 3 SHDN 4 FB CS+ 8 CS- 7 DRI GND 6 1500F 6.3V 5 R8 12K R9 3K9 L2 33H D2 SS32 +VOUT, 5V/2A + 470F C5 16V C2 0.1F D3 6.8V C4 + 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 A H E MIN 1.35 0.10 0.33 0.19 4.80 3.80 MAX 1.75 0.25 0.51 0.25 5.00 4.00 1.27(TYP) A1 B C D e A C A1 E e H L L 5.80 0.40 6.20 1.27 B 8 LEAD PLASTIC DIP (unit: mm) D SYMBOL A1 E1 MIN 0.381 2.92 0.35 0.20 9.01 7.62 6.09 -- 2.92 MAX -- 4.96 0.56 0.36 10.16 8.26 7.12 10.92 3.81 A2 b E C D A2 A1 L E C eB E1 e eB L 2.54 (TYP) b e 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 |
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