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SI-8033S Datasheet(PDF) 6 Page - Sanken electric |
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SI-8033S Datasheet(HTML) 6 Page - Sanken electric |
6 / 6 page 85 1. Soft Start Connecting a capacitor to terminal no. 5 permits a soft start at power- on. Delay time Td and rise time Ts can roughly be calculated as shown below. (However, the values may slightly vary in an actual application.) If the capacitance of C3 is increased, it takes longer to discharge C3 after VIN is turned off. Therefore, it is recommended to set the value within 10 µF. When not using the soft start function, keep terminal no. 5 open. Td= 0.7 ×C3 (sec) 20 ×10–6 Ts= 4.845 ×C3 (sec) VIN ×20×10–6 SI-8000S S.S. C3 VIN VO Td TS 5 2. Output ON/OFF control Output can be turned on and off by using the soft start terminals. Set the soft start terminal voltage to VSSL (0.2V typ.) or less to stop output. To switch the potential at the soft start terminals, drive the open collector of the transistor. Since the discharge current from C3 flows to the ON/OFF control transistor, limit the current for protec- tion. The SS terminal is pulled up to the power supply in the IC and no external voltage can be applied. SI-8000S S.S + ON/OFF S.S. 5 C3 SI-8000S S.S. 5 ON/OFF Applications qSI-8000S Series (3) Sensing terminal Output voltage sensing terminal VOS should be connected as close to output capacitor C2 as possible. If the terminal is far from the capacitor, the decreasing regulation and increasing switching ripple may result in abnormal oscillation. + L1 5 VOUT VIN GND C1 C2 D1 SI-8000S Example of basic pattern Top view (with part names) 3. Variable Output Voltage The output voltage can be increased by connecting a resistor to VOS terminal No. 4. (There is no way of decreasing the voltage) (1) Variable output voltage with single external resistor SI-8000S 2 4 VO' GND C2 REX VS IVS L 3 The output voltage adjustment resistance REX is calculated as follows: REX= VO'–VS IVS VS : Set output voltage of product VO' : Adjusted output voltage IVS : Inflow current to Vs terminal * The temperature characteristics of output voltage worsen because the value REX is not compensated for temperature. The Vs value fluctuates by up to ±20% depending on the IC product. Since the output voltage fluctuates more, a semi-fixed resistor is necessary for accurate output voltage adjustment. If Vs and REX are constant, the range of output voltage fluctuation can be expressed as follows: ∆VO'(%)=±20• VO'–VS VO' ∆VO':Adjusted output voltage (2) Variable output voltage with two external resistors SI-8000S 2 4 VO GND C2 REX1 REX2 IREX1 IVS VS L 3 The output voltage adjustment resistances REX1 and REX2 are calculated as follows: REX1= VO'–VS S•IVS REX2= VS (S-1)•IVS S:Stability factor Bypassing the current to REX2 improves the temperature charac- teristics and voltage fluctuation ranges more than the method of (1). Stability factor S indicates the ratio of REX1 to Vs terminal inflow current. Increasing the S value improves the fluctuations of the temperature characteristics and output voltage. (Usually 5 to 10) If the Vs and REX values are constant, the output voltage fluctua- tion range can be calculated as follows: ∆VO'(%)= ±20 • VO'–VS S VO' |
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