LM5025A

SNVS293E – DECEMBER 2004 – REVISED MARCH 2013

www.ti.com

Soft-Start

The softstart feature allows the power converter to gradually reach the initial steady state operating point, thus

reducing start-up stresses and surges. At power on, a 20µA current is sourced out of the softstart pin (SS) into

an external capacitor. The capacitor voltage will ramp up slowly and will limit the COMP pin voltage and therefore

second level current limit, the output gate drivers are disabled and the softstart capacitor is fully discharged.

When the fault condition is no longer present a softstart sequence will be initiated. Following a second level

current limit detection (CS2), the softstart current source is reduced to 1µA until the first output pulse is

generated by the PWM comparator. The current source returns to the nominal 20µA level after the first output

pulse (~1V at the SS pin).

Thermal Protection

Internal Thermal Shutdown circuitry is provided to protect the integrated circuit in the event the maximum junction

temperature is exceeded. When activated, typically at 165°C, the controller is forced into a low power standby

state with the output drivers and the bias regulator disabled. The device will restart after the thermal hysteresis

(typically 25°C). During a restart after thermal shutdown, the softstart capacitor will be fully discharged and then

charged in the low current mode (1µA) similar to a second level current limit event. The thermal protection

feature is provided to prevent catastrophic failures from accidental device overheating.

Application Circuit: Input 36-78V, Output 3.3V, 30A

Figure 16. Application Circuit

14

Submit Documentation Feedback

Copyright © 2004–2013, Texas Instruments Incorporated

Product Folder Links: LM5025A