TPS53355: maximum load capacitance

Shifali N 

The simple answer is there is no maximum total output capacitance, but it depends on other factors.

1) If you are not using RCC ripple injection into the feedback and relying on the output voltage ripple to provide the feedback ripple for regulation, as long as you have 15mV of ESR ripple at the feedback voltage after the divider, you can have as much capacitance as you would like.

2) If you are not using RCC ripple injection, but want a little less output voltage ripple, you can add a "feed forward" capacitor across the high-side resistor from VOUT to FB so that you can have 15mV of ripple at Vout coupled directly to FB.  The time-constant of the added capacitor and the VOUT to FB resistor should be as large as, or larger than the ESR x Cout "zero" frequency of the output capacitors.

3) If you are using RCC ripple injection to inject 15mV of ripple into Feedback using an R-C observer across the inductor, the time-constant of the injection R-C (Coupling Capacitor x parallel combination of the feedback divider resistors) should be larger (lower frequency) than the Square-Root (L x C) time-constant of the inductor and output capacitance.

Caution: If there is a long power path between the inductor and the load, a large amount of output capacitance at the load, and the output voltage is sensed at the load, the power path parasitic inductance can introduce an additional double-pole in the power loop which can make the voltage regulation loop unstable.  To counter this, TI recommends making provisions for a series resistor in the remote sense feedback bath, and a capacitor from the local output at the first capacitors after the inductor, this will allow high-frequency regulation to reference the local output voltage without the added delay of the parasitic L-C filter.