ZHCSI27C April 2018 – October 2021 LM5036
PRODUCTION DATA
The soft-start functionality limits the inrush current and voltage stress of the power converter. A common requirement for the power converters used in the telecom/datacom applications is to have a monotonic output voltage start-up into pre-biased load conditions where the output capacitor is pre-charged prior to start-up. In a pre-biased load condition, if the synchronous rectifiers are engaged prematurely they will sink current from the pre-charged output capacitors resulting in undesired output voltage dip or even power converter damage. The LM5036 device implements unique circuitry to ensure intelligent turn-on of the synchronous rectifiers such that the output voltage has monotonic start-up.
The start-up process can be divided into two phases:
The pre-biased start-up process is handled automatically by LM5036. The user need only select values for CSS, CSSSR, and the ramp rate of the secondary reference (VREFSec) soft-start Figure 7-8. The circuit of Figure 7-8 uses a comparator to, detect the voltage change of VAUX2 and, release the FET shorting across the secondary soft-start capacitor (CSSSec). This comparator circuit may also be replaced by the transistor based circuit of Figure 8-3.