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CS5233-3GDP5 Datasheet(PDF) 7 Page - ON Semiconductor |
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CS5233-3GDP5 Datasheet(HTML) 7 Page - ON Semiconductor |
7 / 12 page CS5233−3 http://onsemi.com 7 APPLICATIONS INFORMATION INPUT AND OUTPUT VOLTAGE MATRIX Input Outputs VIN VSB 3.3 VAUX AuxDrv/5.0 V Detect VOUT , D2PAK−5 VOUT , SOIC−8 0 V 0 V 0 V On (low) 0 V 0 V 0 V 0 V 3.3 V On (low) 3.3 VAUX 3.3 VAUX 0 V 5.0 V 0 V Off (high) 3.3 VREG @ 500 mA 3.3 VREG @ 500 mA 0 V 5.0 V 3.3 V Off (high) 3.3 VREG @ 500 mA 3.3 VREG @ 500 mA 5.0 V 0 V 0 V Off (high) 3.3 VREG @ 1.5 A 3.3 VREG @ 500 mA 5.0 V 0 V 3.3 V Off (high) 3.3 VREG @ 1.5 A 3.3 VREG @ 500 mA 5.0 V 5.0 V 0 V Off (high) 3.3 VREG @ 1.5 A 3.3 VREG @ 500 mA 5.0 V 5.0 V 3.3 V Off (high) 3.3 VREG @ 1.5 A 3.3 VREG @ 500 mA THEORY OF OPERATION Linear Regulator The CS5233−3 is a dual input fixed 3.3 V linear regulator that contains an auxiliary drive control feature. When VIN alone is present, or VIN and VSB are simultaneously present, the CS5233−3 uses the VIN supply to generate the 3.3 V output at currents of up to 1.5 A. When VSB alone is present, the CS5233−3 uses the VSB supply to generate the 3.3 V output at currents of up to 500 mA. The linear regulator is composed of a composite PNP−NPN pass transistor to provide low−voltage dropout capability. An output capacitor greater than 10 mF with equivalent series resistance (ESR) less than 1.0 W is required for compensation. More information is provided in the Stability Considerations section. Auxiliary Drive Feature The CS5233−3 provides an auxiliary drive feature that allows a load to remain powered even if both supplies to the IC are absent. An external p−channel FET is the only additional component required to implement this function when the auxiliary power supply is available. The PFET gate is connected to the IC’s AuxDrv output, 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 could be forward−biased if the auxiliary supply is not present. This would result in the linear regulator providing current to everything on the auxiliary supply rail. The AuxDrv (5.0 V detect) output is pulled up to the input voltage through an internal resistor when VIN or VSB are available. If VIN and VSB are not available or both drop below 4.4 V, the AuxDrv output goes low, turning on an external PFET that connects the 3.3 V auxiliary supply to the load. The AuxDrv is low only when neither VIN nor VSB are available. There is 100 mV of hysteresis (typical) in the circuitry that determines if VIN or VSB are present. STABILITY CONSIDERATIONS The output capacitor helps determine three main characteristics of a linear regulator: loop stability, load transient response, and start−up delay. The CS5233−3 is designed to be stable with an output capacitor that has a minimum value of 10 mF and an equivalent series resistance less than 1.0 W. To guarantee loop stability, the output capacitor should be located close to the regulator output and ground pins. The load transient response, during the time it takes the regulator to respond, is also determined by the output capacitor. For large changes in load current, the ESR of the output capacitor causes an immediate drop in output voltage given by: DV + DI ESR There is then an additional drop in output voltage given by: DV + DI T C where T is the time for the regulation loop to begin to respond, (typically 4.0 ms for the CS5233−3). If tight output regulation is required with fast changing loads, a capacitor network of tantalum and low ESR ceramic capacitors can be added as close to the load as possible, with enough capacitance and a reduced ESR to minimize the voltage change, as determined by the formulas above. Input Capacitors and the Vin Thresholds A capacitor placed on the VIN pin will help to improve transient response. During a load transient, the input capacitor serves as a charge “reservoir,” providing the needed extra current until the external power supply can |
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