LP38853_15 Datasheet, PDF (11/30 Pages) Texas Instruments – LP38853 3A Fast-Response High-Accuracy Adjustable LDO Linear Regulator with Enable and Soft-Start

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7 Detailed Description
LP38853
SNVS335E – DECEMBER 2006 – REVISED NOVEMBER 2015
7.1 Overview
The LP38853 is a high-current, low-dropout, fast-response linear regulator capable of sourcing a 3-A load with
only 240-mV dropout. This device operates from two input voltages: V_BIAS provides voltage to internal circuit,
while V_IN is the input voltage supplying power to load. The use of an external bias rail allows the part to operate
from ultra low V_IN voltages. The fast transient response of this device makes it suitable for powering DSP,
microcontroller cores, and post regulators.
7.2 Functional Block Diagram
IN
BIAS
LP38853
Undervoltage
Lockout
Thermal
r_EN
Shutdown
EN
Enable
1.2 V
r_SS
SS
V_REF
OUT
ADJ
I_LIMIT
0.5 V
GND
7.3 Feature Description
7.3.1 Undervoltage Lockout (UVLO)
The bias voltage is monitored by a circuit which prevents the device from functioning when the bias voltage is
below the UVLO threshold of approximately 2.45 V.
As the bias voltage rises above the UVLO threshold the device control circuitry becomes active. There is
approximately 150 mV of hysteresis built into the UVLO threshold to provide noise immunity.
When the bias voltage is between the UVLO threshold and the minimum operating rating value of 3 V the device
is functional, but the operating parameters are not be within the specified limits.
7.3.2 Supply Sequencing
There is no requirement for the order that V_IN or V_BIAS are applied or removed.
One practical limitation is that the soft-start circuit starts charging C_SS when both V_BIAS rises above the UVLO
threshold and the EN pin is above the V_EN(ON) threshold. If the application of V_IN is delayed beyond this point the
benefits of soft start are compromised.
In any case, the output voltage cannot be ensured until both V_IN and V_BIAS are within the range of specified
operating values.
If used in a dual-supply system where the regulator output load is returned to a negative supply, the output pin
must be diode clamped to ground. A Schottky diode is recommended for this diode clamp.
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