Hi, Team
This is a question from a customer about Overcurrent Protection (OCP) of TPS40170.
The customer wants to know the time before OC_FAULT being declared after OCP was detected first.
The mechanism of OCP is explained to a data sheet as follows,
"The OCP level is set by the ILIM pin voltage. A current (IILIM) is sourced into the ILIM pin from which a resistor
RILIM is connected to GND. Resistor RILIM sets the first level of overcurrent limit. The OCP is based on the lowside
FET voltage at the switch-node (SW pin) when the LDRV is ON after a blanking time, which is the product of
inductor current and low-side FET turn-on resistance RDS(on). The voltage is inverted and compared to ILIM pin
voltage. If it is greater than the ILIM pin voltage, then a 3-bit counter inside the device increments the fault-count
by 1 at the start of the next switching cycle. Alternatively, if it is less than the ILIM pin voltage, then the counter
inside the device decrements the fault-count by 1. When the fault-count reaches 7, an overcurrent fault
(OC_FAULT) is declared and both the HDRV and LDRV are turned OFF."
[7.3.4 Overcurrent Protection and Short-Circuit Protection (OCP and SCP) of page 15]
When the time when OCP continues is short, the OC_FAULT is not declared.
The customer wants to know the calculation method of the greatest time when OC is not declared.
Thank you
Toshio Fukumoto
