Datasheet

10
LM138 , LM338
SNVS771C –MAY 1998–REVISED DECEMBER 2016 www.ti.com
Product Folder Links: LM138 LM338
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7.4 Device Functional Modes
7.4.1 Normal Operation
The device OUTPUT pin sources current necessary to make OUTPUT pin 1.25 V greater than ADJUST terminal
to provide output regulation.
7.4.2 Operation With Low Input Voltage
The device requires up to 3-V headroom (V
I
– V
O
) to operate in regulation. With less headroom, the device may
drop out and OUTPUT voltage is INPUT voltage minus drop out voltage.
7.4.3 Operation at Light Loads
The device passes its bias current to the OUTPUT pin. The load or feedback must consume this minimum
current for regulation or the output may be too high. A 250-Ω feedback resistor between OUTPUT and ADJUST
consumes the worst case minimum load current of 5 mA.
7.4.4 Operation in Self Protection
When an overload occurs, the device shuts down Darlington NPN output stage or reduces the output current to
prevent device damage. The device automatically resets from the overload. The output may be reduced or
alternate between on and off until the overload is removed.