Hi,
I'm having a problem on an existing design with the compensation feedback loop capacitor of the TPS40077PWPR switcher IC (24V to 3.3V , 2A output).
The compensation loop was calculated with the value of 3.9nF, 6.81K & 220 pF, and has been working fine for about a year (or 500 products).
Now we just catched a batch of board with capacitor of 3.4nF instead of 3.9pF which is causing about 300 mV of ripple noise on the 3.3V output (at 5KHz).
So here are my questions:
1- I am able to fix the ripple by changing the cap with eithier a more accurate 3.9pF cap or with a 4.7nF value. Now How can I be sure that the circuit will be fully stable with a 4.7nF capacitor value ? Is there a high risk to do that change? I wanna use the 4.7nF value to have more headroom for the innaccuracy of the capacitor.
2- I also added the new 4.7nF value and the older 3.9 nF value in the simulator in 2 different simulations, but I just can't see the effect on the output ripple that I observe in my lab with the offset wrong cap. Do you know why I dont see the effect on the output ripple in the simulator?
Thanks
