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TPS61178: Load disconnect FET.

Elder Costa
Prodigy 120 points
Part Number: TPS61178

Tool/software:

Parameters of my design: Vin=10-16V, Vout=19V, Iout max =1,6A.

First question: is the TSHORT parameter specified somewhere? It is only mentioned in section 9.2.4.4.3 of the DS and it states it is 30us. Is this value right?

Webench selected Si7135DP which is a beast. The problem is space is limited in my design and its package is relatively large and, if the formula above is right, "it is overkill" is an understatement.

Using my design's parameter makes Qshort = 19 * 20 * 30e-6/2 = 5,7mJ which corresponds to 190W (mean) for 30us.

Looking at the SOA graph for Si7111 (package takes ~1/4th of the area), 20A is between the limits for 1ms and 100us pulses and current for 100us pulse is ~400W @ 20V, it would be more for 30us so this part could be used in my design if my rationale is correct, assuming the 30us (which I guess is typical).

So, my other question are:

2) What are what are the min and max for this TSHORT parameter?

3) Is my rationale above correct? Am I missing something?

4) Could this part be used?

5) If not, any suggestion of a suitable part with small footprint?

Thanks in advance.

  • +1
    TI__Genius 16305 points

    Hi Elder,

    Thank you for reaching out.

    For your questions:

    1. 30us is an estimated value including current rising and shutdown delay.

    Usually, the time will be shorter than 30us.

    2.Tshort is related to the short condition.

    When the device is short with a long wire and the current can rise with a slow slew rate, the time will be longer.

    As is said before, we have a rough test as estimated it to be 30us max.

    3. I think your rationale is right,  Si7135DP is too large for the case, and Si7111 is ok.

    4. The part is acceptable, in our EVM, a 3*3 MOS is used as well.

    5. no other suggestion.

    Best Regards,

    Fergus