LM5015 datasheet(17/28 Pages) TI

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COMP

SOFT-START

CAPACITOR

LM5015

CSS

11 PA

ENABLE

VDD

PWM

CURRENT

LIMIT

1.5V

1.3V

VDD (5V)

1.26V

VOUT

LM5015

VPWR

1.26V

STANDBY

0.45V

SHUTDOWN

OFF

STANDBY

LM5015

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SNVS538C – NOVEMBER 2007 – REVISED APRIL 2013

Figure 19. Remote Standby and Disable Control

SOFT-START

Soft-start is implemented with an external capacitor CSS connected to the SS pin as shown in Figure 20. The SS

discharge MOSFET conducts during Shutdown and Standby modes. When the SS pin is low, the COMP voltage

is held below the PWM offset voltage (1.3V) by the SS buffer amplifier, thus inhibiting PWM pulses. When the EN

pin exceeds the 1.26V standby threshold, the ENABLE signal will turn-off the SS discharge MOSFET and allow

the internal 11 µA current source to charge the SS capacitor. The COMP voltage will follow the SS voltage under

the control of the open-drain SS buffer amplifier. The CSS capacitor will cause the COMP voltage to gradually

increase, until the output voltage achieves regulation, and the error amplifier assumes control of the COMP and

the PWM duty cycle. The CSS capacitor continues charging by the internal 11 µA current source, preventing the

SS voltage from interfering with the normal error amplifier function. During shutdown, the SS discharge MOSFET

conducts to discharge the CSS capacitor.

Figure 20. Soft-Start

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