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CS5231-3GDPR5 Arkusz danych(PDF) 6 Page - ON Semiconductor |
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CS5231-3GDPR5 Arkusz danych(HTML) 6 Page - ON Semiconductor |
6 / 14 page CS5231−3 http://onsemi.com 6 APPLICATION INFORMATION THEORY OF OPERATION The CS5231−3 is a fixed 3.3 V linear regulator that contains an auxiliary drive control feature. When VIN is greater than the typical 4.5 V threshold, the IC functions as a linear regulator. It provides up to 500 mA of current to a load through a composite PNP−NPN pass transistor. An output capacitor greater than 10 mF with equivalent series resistance less than 1.0 W is required for compensation. More information is provided in the Stability Considerations section. The CS5231−3 provides an auxiliary drive feature that allows a load to remain powered even if the VIN supply for the IC is absent. An external p−channel FET is the only additional component required to implement this function if an auxiliary power supply is available. The PFET gate is connected to the AuxDrv lead. The PFET drain is connected to the auxiliary power supply, and the PFET source is connected to the load. The polarity of this connection is very important, since the PFET body diode will be connected between the load and the auxiliary supply. If the PFET is connected with its drain to the load and its source to the supply, the body diode will be forward−biased if the auxiliary supply is turned off. This will result in the linear regulator providing current to everything on the auxiliary supply rail. The AuxDrv lead is internally connected to a 10 k W resistor and to a saturating NPN transistor that acts as a switch. If the VIN supply is off, the AuxDrv output will connect the PFET gate to ground through the 10 k W resistor, and the PFET will conduct current to the load. As the VIN supply begins to rise, the AuxDrv lead will also rise until it reaches a typical voltage of about 650 mV. The NPN transistor connected to the AuxDrv lead will saturate at this point, and the gate of the PFET will be pulled down to a typical voltage of about 100 mV. The PFET will continue to conduct current to the load. The VIN supply voltage will continue to rise, but the linear regulator output is disabled until VIN reaches a typical threshold of 4.5 V. During this time, the load continues to be powered by the auxiliary driver. Once the 4.5 V VIN threshold is reached, the saturating NPN connected to the AuxDrv lead turns off. The on−chip 10 k W pull−up resistor will pull the PFET gate up to VIN, thus turning the PFET off. The linear regulator turns on at the same time. An external compensation capacitor is required for the linear regulator to be stable, and this capacitance also serves as a charge reservoir to minimize any “glitching” that might result during the supply changeover. Hysteresis is present in the AuxDrv circuitry, requiring VIN to drop by 100 mV (typical) after the linear regulator is providing power to the load before the AuxDrv circuitry can be re−enabled. Figure 13. Initial Power−Up, VAUX Not Present ROUT = 8.8 W IOUT = STARTUP 375 mA VIN VOUT VAUXDRV Figure 14. Power−Up, VAUX = 3.3 V. Note the “Oscillatory Performance” as the Linear Regulator Changes the VOUT Node. IOUT y RDS(ON) 9 130 mV IOUT = 375 mA VAUX = 3.30 V VIN VOUT VAUXDRV Figure 15. Power−Down, VAUX = 3.3 V. Again, Note DV = I RDS(ON) 9 130 mV IOUT = 375 mA VAUX = 3.30 VIN VOUT VAUXDRV |
Podobny numer części - CS5231-3GDPR5 |
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Podobny opis - CS5231-3GDPR5 |
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