Datasheet

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
the PWM duty cycle. In the event of a fault as determined by V
CC
undervoltage, line undervoltage (UVLO) or
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
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