I'm trying to set the 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 6V. Vout is 5V. ( Ro1= 10k , Ro2 = 1.87k )
I set Ren1 1% 333K and Ren2 68K. ( and a couple of other combos )
Anyway, I tested this setup and it does not turn completely off ( no switching) until VIN level is down to 3.1 V. This is true of both rising Vin and falling Vin. I slowly turn up an external power supply to vin , and there starts some slight switching at 3.1V . As I increase Vin to 3.8V these is continuous switching, although Vout is spikey and less than the 5V set point. Finally , when Vin is raised to 5.3V, then the output is steady 5V as expected and this continoues good VOut of 5V as raise Vin up to 12V input that will normally be used.. However as I lower Vin the output contiunes to behave as described above ( in the Vin rising case). There appears to be no UVLO where the switching should turn off completely if Vin falls below a certain threshold.
Can you get the switching to completely stop at a controlled Vin level ?
Todd
Values used ( designators based on the DS) : Ren1 =333k , Ren2= 68k , Css=10nF,
c1comp=1nF, c2comp=27pF, R3comp=32k ,
C1vin=10uF+10nF, cboot=100nF , Ro1=10k, Ro2=1.87k, Lo=12uH , Cout=47uf+10uF+100nF