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40170 current limit

user4323546
Prodigy 10 points
Other Parts Discussed in Thread: TPS40170, CSD17312Q5

Hello

We are using TPS40170

input 24V output 4V

We have mismatch between calculated over current limit OCP and actual measured one

IOC = 9micro A

RDC 1.2mohm (lower side FET is csd17312Q5)

RLIM = 12KOhm

calculated IOC = 90A

Actual = 10A

can you advise

Regards

Nogi

  • 0
    TI__Mastermind 35185 points

    Hi Nogi,

    Overshoot and ringing at the SW pin or noise at the VIN pin could be causing short circuit protection to trip too soon. Things to try are:

    1. Remove the LDRV go PGND resistor that sets the SCP multiplier to increase the SCP level to 7x OCP. If this allows higher current, it is a very good clue the current limit you are seeing is caused by SCP.
    2. Add resistor in series with BOOT capacitor to slow turn on of the high-side MOSFET. Typical values are 1 to 10 ohms.
    3. Add an RC snubber across the low-side MOSFET.
    4. Change the resistor in series with the VIN pin to 0 ohms.

    If none of these work the next thing to do is look closer at the layout. First an dmost important is the critical switching loop which includes the input capacitor and the two MOSFETs. Secondly the placement of the VIN capacitor is important for SCP since the VIN pin to SW pin voltage is used for sensing the voltage drop across the high-side MOSFET.

    Best Regards,
    Anthony