OTP

NTC

REF

Logic

LM5027A

+

-

5.0V

(20 uA)

OTP HYSTERESIS

1.25V

UVLO

SS

SSSR

OUTA

OUTB

OUTSR

~ 4V

~1V

~2.5V

Expanded view

SR

Soft -Start

UVLO > 2.0V

LM5027A

www.ti.com

SNVS642B – APRIL 2010 – REVISED MARCH 2013

Figure 23. Soft-Start Synchronous Rectifier Timing

External Over-Temperature Protection

An external set-point voltage divider between the REF, OTP, and AGND pins, as shown in Figure 24, is one

method to implement over-temperature protection shutdown. Typically a NTC thermistor is installed as the lower

device of the voltage divider. The divider must be designed such that the voltage at the OTP pin will be greater

than 1.25V when there is not an over-temperature condition, and the OTP pin must drop below 1.25V during an

over-temperature event. OTP hysteresis is accomplished with an internal 20 µA current source that is switched

on or off into the impedance of the external set-point divider. When the OTP pin voltage exceeds 1.25V

threshold, the current source is activated to quickly raise the voltage at the OTP pin. When the OTP pin voltage

falls below the 1.25V threshold, the current source is turned off causing the voltage at the OTP pin to quickly fall.

When OTP falls below 1.25V the LM5027A will go through a soft-stop turn-off sequence.

Figure 24. External OTP Protection

Copyright © 2010–2013, Texas Instruments Incorporated

Submit Documentation Feedback

17

Product Folder Links: LM5027A