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| L1138 Datasheet, PDF (6/8 Pages) Unisonic Technologies – HIGH RIPPLE-REJECTION AND LOW DROPOUT HIGH OUTPUT CURRENT CMOS VOLTAGE REGULATOR | |||
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L1138
Preliminary
CMOS IC
 OPERATION
1. Basic operation
The reference voltage (VREF) and VFB(the output voltage resistance-divided by feedback resistors RS and RF) are
the input for the error amplifier.
VIN
VOUT
Current
Supply
VREF
-
RF
Error
Amplifier
+
Reference
Voltage
VFB
Circuit
RS
VSS
2. Output transistor
A low on-resistance P-channel MOS FET is used as the output transistor. Inverse current flowing from VOUT pin
through a parasitic diode to VIN pin can damage the regulator, so be sure that VOUT does not exceed VIN + 0.3 V.
3. Shutdown pin (ON/OFF pin)
The shutdown pin can start and stop the regulator.The shutdown mode set by this pin can stop the operation of
all internal circuits. The structure of the ON/OFF pin is shown in Fig. 1. When the ON/OFF pin is not used, connect it
to the VSS pin if the logic type is âAâ and to the VIN pin if it is âBâ.
Logic Type
A
A
B
B
ON/OFF Pin
âLâ: Power on
âHâ: Power off
âLâ: Power off
âHâ: Power on
Internal Circuits
Operating
Stopped
Stopped
Operating
VOUT Pin Voltage
Set value
VSS level
VSS level
Set value
Current Consumption
ISS1
ISS2
ISS2
ISS1
UNISONIC TECHNOLOGIES CO., LTD
www.unisonic.com.tw
6 of 8
QW-R502-323.c
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