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CS8128 Fiches technique(PDF) 5 Page - Cherry Semiconductor Corporation |
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CS8128 Fiches technique(HTML) 5 Page - Cherry Semiconductor Corporation |
5 / 6 page 5 VIN Sense Delay Ref Gnd SHUTDOWN Pwr Gnd VOUT RRST 4.7 kΩ CDelay 0.022µF CO 10µF VOUT (5V) VIN RIN 220Ω CIN 0.022µF TIP42B ROUT 220Ω Gnd CS8128 RESET RBIAS 560Ω RESET Test Circuit Application Information The CS8128 includes an over voltage shutdown circuit which is activated by connecting the SHUTDOWN lead to the input. Shutdown typically occurs at 36V. Grounding the SHUTDOWN lead disables this function. With the overvoltage shutdown disabled, the CS8128 will continue to regulate during an overvoltage condition. The CS8128 includes a thermal shutdown circuit that dis- ables the output when junction temperature exceeds approximately 180˚C. This is a self-protection feature designed to protect the CS8128. The thermal shutdown cir- cuit does not monitor the temperature of the pass transis- tor, which will probably be much hotter. To optimize ther- mal shutdown, board design should minimize the differ- ence in temperature of the CS8128 and the pass device. External Pass Device - Select a pass device that will deliv- er the desired output current, withstand the maximum expected input voltage, and dissipate the resulting power. The CS8128 is compatible with a wide variety of Bipolar and FET pass transistors. Output Capacitor - An output capacitor is required for sta- bility in most applications. Though a 10µF capacitor should be sufficient, regulator stability is dependent on the characteristics of the pass transistor. Capacitor effective series resistance (ESR) also factors in system stability. Some bench work may be required to determine the capacitor characteristics required for use in a particular application. BIAS Resistor - This resistor provides bias current for the CS8128 output stage, and prevents the pass device from “leaking”. It also speeds the turn-off of the pass device during an overvoltage transient. For proper operation over temperature, the recommended value is 560Ω, although it may be increased or decreased for a particular application. ROUT Resistor - This resistor controls the drive current available to the pass transistor. It also determines regula- tor start-up current and short circuit current limit. For bipolar pass transistors, it can be selected by use of the fol- lowing formulae: ROUT = x ßQ1*** ***βQ1 = Pass transistor minimum β @ maximum output current. Typical start-up current and current limit can be calculat- ed as follows: ISTART ≈ + 5mA ILimit ≈ x ßQ1 @ Current Limit For example, if the minimum input voltage is 6V, maxi- mum output current is 1Amp, and minimum transistor β @ 1Amp is 60, then ROUT can be calculated as follows: ROUT ≈ x 60 = 300Ω IStart ≈ + 5mA = 18.3mA With VIN = 14V, and a pass transistor β of 40 @ current limit: ILimit ≈ x 40 = 1.7Amps 14V – 1V 300Ω 4V 300Ω 6V – 1V 1Amp VIN – 1V ROUT 4V ROUT VIN(min) – 1V IOUT(max) External Component Selection Thermal Shutdown Overvoltage Shutdown |
Numéro de pièce similaire - CS8128 |
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Description similaire - CS8128 |
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