Q: In application, MAX15096 OCP is set to 0.5A (Rcb = 5.49kohm) and Vin is 3.3V. The test result shows the OCP point has >10% tolerance. We don’t specify the tolerance in DS at that low current. Do you have any data to show the tolerance at OCP=0.5A? Thank you.
Ans:
The formula on DS was taken at 12V. But does not change significantly at 3.3V. Probably another 2/3%.
The resistor value used by the customer, I imagine taken from our Datasheet, is definitely wrong at low currents
The approximation of the formula is poor.
The formula that returns the value of the resistor given the Icb threshold must take into account the offset and some non-linearity.
The best approx. is:
R= -122.63 * Icb * Icb + 7382 * Icb + 1322 Ohm
According to this formula the resistor for 0.5A is 4983 Ohm, while the formula in the datasheet 5460 Ohm… the customer resistor…
But again, according to the data I gave you, the precision expected is not great, it is around 30% even when the correct resistor value is used.
If we have customer like this that can buy a significant number of parts, we may think to create a part number with smaller Icb current range.
As an example 2A or 3A that we can easily trim for 1A, 0.5A or whatever is needed with higher precision, within the 10% range.