Dears
1. Could you explain below parameter: VTRIP,VocL,Iocp ; and what's the difference between I ocp and I limit and max output current ?
2.In page 16,Equation 3, Rds(on)'s value is ?
3.In Typical Application, what's the meaning of I over :11A ? and what's the relationship with I ocp in Euation 18 ?
4.In Figure 34 Typical Application Circuit,its R trip =120K, is it calculated through Equation 18 ?and Icop value is ?
Fandy,
I no longer directly support TPS53318, but let me try to answer your questions during the transition time.
1. The current limit is valley detect current limit. I recently wrote a blog that explains the general operating principle here:
The current limit i set with the Rtrip resistor from the TRIP pin to GND. Itrip is a current source inside the IC that sets the Vtrip voltage. Vtrip = Rtrip x I trip. Valid Vtrip internal voltage for the TPS53318 is 0.4 V to 1.2 V which corresponds to a Rtrip range from 40 k to 120 k ohm. Vocl is just the internal threshold. It is teh Vtrip value divided b32 (the 32 in the denominator of eq 3). You don't need to be concerned with this. Iocp is the valley current limit threshold. It is
Iocp = (66.5 / 12.3) - (ILp-p / 2). For whatever reason ILp-p (the peak to peak inductor ripple current) is not specified as a condition.
ILp-p / 2 = (1 / 2 x L x fsw) x ((Vin - Vout) x (Vout / Vin)
Max output current is your maximum load current and is Iocp + ( ILp-p / 2 )
2. You don't need to know the RDSon value. Just use Rtrip / 12.3 instead of Vtrip / (32 x RDSon) in the equation 3. Make sure to use 12.3 not 12.3 x 10^3 if your Rtrip value is in kohm (datasheet mistake!).
3. 11 is the OCP value of the dc load current when the valley current protection is reached. Eq 18 is just Eq 3 rearranged to solve for Rtrip.
4. Might be another error there. I calculate Rtrip = 109 k not 120 k.
