Hi,
As far as I understand the LM51561H has 2 enable levels at the UVLO/EN:
- @0.5V Vcc is regulated to min(Vin,7V). The controller starts drawing current
- @1.5V the controller starts pumping PWM and the converter starts working well.
My issue is that I have a startup circuit that charges a cap on the BIAS pin. Once UVLO passes 0.5V and the controller starts drawing current the cap on the bias pin discharges and I never pass the 1.5V level UVLO and I never start pumping PWM. I'm stuck on the 0.5V level. Is there a way to disable the 0.5V enable level? to regulate Vcc and start pumping PWM at the same time once I pass 1.5V?
Currently, I've solved the issue by using an external comparator connected to the UVLO such that when I exceed my desired voltage on the bias pin I set UVLO pin HIGH and immediately pass both UVLO thresholds and however this is not an ideal solution.
Also, the DS doesn't state the current drawn by the controller when UVLO pin is between 0.5V and 1.5V.