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CS5231-3GDP5 参数 Datasheet PDF下载

CS5231-3GDP5图片预览
型号: CS5231-3GDP5
PDF下载: 下载PDF文件 查看货源
内容描述: 500毫安, 3.3V线性稳压器,带有辅助控制 [500mA, 3.3V Linear Regulator with Auxiliary Control]
分类和应用: 线性稳压器IC调节器电源电路输出元件
文件页数/大小: 11 页 / 283 K
品牌: CHERRY [ CHERRY SEMICONDUCTOR CORPORATION ]
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Application Circuit  
VOUT  
CS5231-3  
+5V PCI  
VIN  
C1  
33µF  
Gnd  
AuxDrv  
ASIC  
VDD  
M1  
+3.3V VAUX  
C3  
33µF  
C1  
33µF  
*indicates PFET body diode  
Application Information  
external compensation capacitor is required for the linear  
Theory of Operation  
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.  
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 1is 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.  
V
IN  
V
OUT  
V
AUXDRV  
I
= STARTUP 375mA  
OUT  
Figure 1. Initial power-up, VAUX not present ROUT = 8.8.  
The AuxDrv lead is internally connected to a 10kresistor  
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 10kresistor, and the  
PFET will conduct current to the load.  
V
IN  
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 10kpull-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  
V
OUT  
V
AUXDRV  
I
= 375mA V  
= 3.30V  
AUX  
OUT  
Figure 2a. Power-up, VAUX = 3.30V. Note the “oscillatory performance”  
as the linear regulator charges the VOUT node. IOUT × RDS(ON) 130mV  
5