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TPS4811-Q1: Over Current Protection versus Short Circuit Protection

ArTzy
Genius 17385 points
Part Number: TPS4811-Q1

Tool/software:

Hi Experts,

Good day. Seeking your assistance on this query from customer, to enlighten the confusion about the operation of the two-stage current protect "Over Current Protection" and "Short Circuit Protection" for the device TPS48111LQDGSRQ1.

In particular there are numerous references in the datasheet that the Short Circuit Protection uses the C_TMR timer in some way but also has an activation time of 1.2 or 4us. The exact function I want is, the Over Current Protection to use the timer and the Short Circuit protection to be very fast acting. Ideally the over current protection should auto retry, and the short protection should latch off. I don't understand what the purpose of the two protections levels is if they are forced to either both use the timer or both latch off.

Thank you.

Regards,
Archie A.

  • 0
    TI__Expert 8250 points

    Hi Archie, 

    I understand the confusion. Firstly, the 1.2 and 4 us mentioned in section "8.3.4 Short-Circuit Protection" is the Short Circuit Protection propagation delay found in the electrical characteristics table. This is the minimum time required to recognize the FLT given CTMR = 0 F. TPS12111  = 1.2 us.

    The CTMR and latch-off /auto retry functionality may be more easily understood as a general Fault Timer. Both SCP and OC are considered faults and will both utilize the same CTMR configuration. The two faults are considered sperate protection levels since the SCP protection relies on the RISCP value to determine the Isc threshold, and the RIWRN, RIMON, RSNS, and RSET values coordinate to determine the Ioc threshold value. In this way each protection feature is individually configurable for different limits even if the resulting behavior is similar between them. 

    Thank you,

    Sarah

  • 0 in reply to Sarah Raines
    TI__Genius 17385 points

    Hello Sarah,

    Thank you for the guidance. Below is the response shared. Will be continuing by the customer.

    Can't really understand the point of the two triggers if there is no difference in the resulting output.

    The only way can see to make use of this device is to use only the S/C protection and then implement a timed lower-level OC trigger in the controlling MCU using current monitoring. 

    Regards,
    Archie A.

  • 0 in reply to ArTzy
    TI__Expert 8250 points

    Hi Archie, 

    Can your provide the expected load current and type of load? Can you also provide the SCP threshold and slew rate?

    Thanks,

    Sarah

  • 0 in reply to Sarah Raines
    TI__Expert 8250 points

    Hi Archie, 

    The two triggers allow different trigger settings and capture different events. One solution would be to implement an external FET at the ISCP pin and consider controlling that FET with an MCU to allow latch off in certain conditions. 

    Thanks,

    Sarah