˜

ª

º

ª

º

¬

¼

¬

¼

SS

SS

C

nF

5 t

ms

§

·

˜

¨

¸

©

¹

UV1

IN(off)

UV-FALLING

UV-HYST

UV1

UV2

R

V

V

1

I

R

R

§

·

¨

¸

©

¹

UV1

IN(on)

UV-RISING

UV2

R

V

V

1

R

13

LM5181

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SNVSBM6 – APRIL 2020

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Feature Description (continued)

where

•

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(10)

where

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(11)

voltage drop (approximately 0.6 V at room temperature). If the EN/UVLO voltage is below this hard shutdown

threshold, the internal LDO regulator powers off, and the internal bias-supply rail collapses, shutting down the

bias currents of the LM5181. The LM5181 operates in standby mode when the EN/UVLO voltage is between the

hard shutdown and precision-enable thresholds.

8.3.6 Configurable Soft Start

The LM5181 has a flexible and easy-to-use soft-start control pin, SS/BIAS. The soft-start feature prevents inrush

current impacting the LM5181 and the input supply when power is first applied. This is achieved by controlling

the voltage at the output of the internal error amplifier. Soft start is achieved by slowly ramping up the target

regulation voltage when the device is first enabled or powered up. Selectable and adjustable start-up timing

options include a 6-ms internally-fixed soft start and an externally-programmable soft start.

The simplest way to use the LM5181 is to leave SS/BIAS open. The LM5181 employs an internal soft-start

control ramp and starts up to the regulated output voltage in 6 ms.

start time further reduces the supply current needed to charge the output capacitors while sourcing the required

load current. When the EN/UVLO voltage exceeds the UVLO rising threshold and a delay of 20 µs expires, an

(12)