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CS8121YTVA5 Datasheet(PDF) 5 Page - ON Semiconductor |
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CS8121YTVA5 Datasheet(HTML) 5 Page - ON Semiconductor |
5 / 8 page If the input voltage rises above 30V (e.g. load dump), the output shuts down. This response protects the internal cir- cuitry and enables the IC to survive unexpected voltage transients. Using an emitter sense scheme, the amount of current through the NPN pass transistor is monitored. Feedback circuitry insures that the output current never exceeds a preset limit. Should the junction temperature of the power device exceed 180°C (typ) the power transistor is turned off. Thermal shutdown is an effective means to prevent die overheating since the power transistor is the principle heat source in the IC. The CS8121 contains two microprocessor compatible con- trol functions: and (Figure 3). Function The function switches the output transistor. When the voltage on the lead exceeds 2.9V typ, the output pass transistor turns off, leaving a high impedance facing the load. The IC will remain in Sleep mode, drawing only 250µA, until the voltage on the lead drops below 2.1V typ. Hysteresis (800mV) is built into the function to provide good noise immunity. Function A signal (low voltage) is generated as the IC pow- ers up (VOUT > VOUT - 100mV) or when VOUT drops out of regulation (VOUT < VOUT - 140mV, typ). 40mV of hysteresis is included in the function to minimize oscillations. The output is an open collector NPN transistor, controlled by a low voltage detection circuit. The circuit is functionally independent of the rest of the IC, thereby guaranteeing that the RESET signal is valid for VOUT as low as 1V. An external RC network on the lead (Figure 4) pro- vides a sufficiently long delay for most microprocessor based applications. RC values can be chosen using the following formula: RTOT × CRST where: RTOT = RRST in parallel with RIN, RIN = µP port impedance, CRST = delay capacitor, tDelay = desired delay time, VRST = VSAT of lead (0.7V @ turn - on), and VT = µP logic threshold voltage. RESET RESET ] [ RESET RESET RESET RESET ENABLE ENABLE ENABLE ENABLE RESET ENABLE 5 Regulator Control Functions Figure 4. RC Network for Delay RESET Circuit Description: continued –tDelay ln ) VT – VOUT VRST – VOUT ( RESET CS8121 VOUT CRST RRST 10 µF tantalum 5V to µP and System Power to µP RESET Port (1) = NO RESET DELAY CAPACITOR (2) = WITH RESET DELAY CAPACITOR FOR 7V < VIN < 26V VOUT VRT(ON) ENABLE VRT(OFF) (1) (2) VIN VIN(HI) HI LO VR PEAK VR SAT VR PEAK RESET Figure 3. Circuit Waveforms for the CS8121 |
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