MPM4730 Over current

DC-DC Power Converters
1

I am using MPM4730 for a new project.
I see ref design using 21.5K resistor to set OC on OC pin.
But I dont see any calculation of resistor value affect on actual over current value set, I dont see this indicated anywhere in the data sheet
Thx
Leor

2

Hello leor.wn,

I’ll check in with our team and follow up with more information.

3

Hi, any update on this?

4

Hello MPS and hello leor.wn,
assuming the OC capacitor is used for current averaging of the 4 switches, and assuming the RC is used to generate a related time constant and assuming the OC threshold is build by a voltage threshold at the OC pin.

  1. Please provide a description to the impact of the resistor / cap value, e.g. to generate a behavior similar to the melting fuse.

  2. Please confirm, in case of, that the I_out_limit is fixed by chip design inline with a user defined current limit setting is not possible.

  3. What is the tolerance of I_out_limit by chip design? I know, that the tolerance of the external components will additionally increase the effective tolerance.

kind regards
Ruediger

5

The R and C calculations can be seen below.

R = 75.24/I_lim(A)

If R is changed, C needs to be changed accordingly to compensate internal CC loop.
C ~= 473/R(kohms)

6

Hi

Thx for this additional info.
Looking at the ref design provided in the datasheet, havibg a R oc of 21.5 this gives Ilim of 3.5A
Although device is generally rated for 1A Iout.
Maybe the switching current limit need to be higher than the designated IOut.
But what should be the relation between them?

Thx

Leor