I'm having no luck getting a voltage divider to turn off the TPS54331 when the input voltage drops below a threshold. I've tried using the equations for Ren1 & Ren2 from the datasheet on page 9.
Ren1 = (Vstart - Vstop) / 3uA (Resister between Vin and En pins)
Ren2 = Ven / ((Vstart - Ven)/Ren1 + 1uA) (Resistor between En pin and gnd)
I'm trying to set Vstop (shutdown voltage) to 12.4V. Vout is 5V.
I found that Ren1 could be a 1% 169K and Ren2 17.8K. This divider will draw 30 or 40 uA, but I'd like Vstart to be as close to Vstop as is reasonable. Increasing the resistance increases Vstart.
Anyway, I tested this setup and it never turned off all the way down to 5.something volts where the inductor started making noise. Is there a trick to get the En pin to shut the controller down?
- Brent