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전자부품 데이터시트 검색엔진 |
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전자부품 데이터시트 검색엔진 |
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CS5231-3GDPR5 데이터시트(PDF) 5 Page - Cherry Semiconductor Corporation |
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CS5231-3GDPR5 데이터시트(HTML) 5 Page - Cherry Semiconductor Corporation |
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5 / 11 page  Theory of Operation The CS5231-3 is a fixed 3.3V linear regulator that contains an auxiliary drive control feature. When VIN is greater than the typical 4.5V threshold, the IC functions as a linear regu- lator. It provides up to 500mA of current to a load through a composite PNP-NPN pass transistor. An output capacitor greater than 10µF with equivalent series resistance less than 1Ω 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 connect- ed 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 connect- ed 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 auxil- iary supply is turned off. This will result in the linear regu- lator providing current to everything on the auxiliary sup- ply rail. The AuxDrv lead is internally connected to a 10kΩ 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 10kΩ 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 650mV. 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 100mV. The PFET will contin- ues 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 4.5V. During this time, the load continues to be powered by the auxiliary driver. Once the 4.5V VIN threshold is reached, the saturating NPN connected to the AuxDrv lead turns off. The on-chip 10kΩ 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 100mV (typical) after the linear regulator is providing power to the load before the AuxDrv circuitry can be re-enabled. 5 Application Information VIN VOUT VAUXDRV IOUT = STARTUP 375mA Figure 1. Initial power-up, VAUX not present ROUT = 8.8Ω. Application Circuit +5V PCI C1 33µF VIN Gnd VOUT AuxDrv CS5231-3 M1 +3.3V VAUX C1 33µF C3 33µF ASIC VDD *indicates PFET body diode VIN VOUT VAUXDRV IOUT = 375mA VAUX = 3.30V Figure 2a. Power-up, VAUX = 3.30V. Note the “oscillatory performance” as the linear regulator charges the VOUT node. IOUT × RDS(ON) ≈ 130mV |
유사한 부품 번호 - CS5231-3GDPR5 |
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유사한 설명 - CS5231-3GDPR5 |
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