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TPS53355: High side and Low side FET VDS rating

user4979989
Intellectual 2800 points
Part Number: TPS53355

Hi team,

Could you help to answer below questions about TPS53355 ringing spike?

1. May I know what's the maximum VDS rating of high side FET? I can't find it on the datasheet.

2. In datasheet, we defined the low side FET VDS DC = 25V and AC = 27V.

a. In what's test condition we will use 27V?  

b. What's the rating (25V or 27V) should be used if customer tests steady state ringing spike?

3. Do we have any suggestions about high and low side FET VDS margin? For example we would recommend customer low side FET VDS to be lower than 20V?

Thank you.

Regards,

Allen

  • 0
    TI__Guru**** 191445 points

    Allen,

    1. The absolute maximum rating for the FET VDS is 25 V dc and AC peak 0f 27 V. The peak voltage is to account for the typical overshoot and ringing that may occur when the high side FET is turned on. You should not purposely test in that condition. The maximum recommended input voltage is 15 V, so you should always be operating far from the absolute maximum region. So to answer your direct questions:
    2.  a. Do not test at that 27 V level.
         b. The rating is 15 V DC. Overshoot and ringing should not exceed 22 V.

    3.  Vin  (and VDS) should not be above 15 V DC.  Overshoot and ringing should not exceed 22 V.

  • 0 in reply to JohnTucker
    TI__Intellectual 2800 points
    Hi John,

    To double confirm your reply, could you help to check below?
    Thank you.
    1. H/S VDS (VIN - LL) is 25V DC rating and 27V AC rating?
    2. H/S and L/S overshoot and ringing are both recommended to be lower than 22V?
    3. I'm still confused about the 25V DC and 27V AC spec, I know these are the spec for ringing spike, but in what condition of ringing spike I can use 27V AC?
    During steady state, each switching ringing spike maximum value should be less than 27V AC or 25V DC?

    Regards,
    Allen
  • 0 in reply to user4979989
    TI__Guru**** 191445 points
    Allen,

    There are two sets of ratings Recommended Maximum and Absolute Maximum. The Abs Max ratings are the rating limits where the device may be permanently damaged. The Recommended Maximum limits are the limit where the device functional parameters are guaranteed. Between the Recommended Maximum and the Absolute Maximum, the device will not be damaged, but it is not guaranteed to operate either. The Abs Max ratings align with the break down voltage of the FETs, which is 25 V max DC and 27 V max for transients, The transient condition is not specifically stated. The key point her is that the Recommended Maximum is 15 V for VIN. Both the high side FET and low side FET are connected between VIN and GND, so when the high side is on and the low side is off the high side VDS is approximately VIN. When the high side is off and the low side is on, the low side VDS is also approximately VIN. There may be switching overshoot and ringing on the rising edge of the SW node waveform. So for your use:

    Maximum DC VDS (VIN) should be 15 V DC or less. Maximum peak ringing on the SW node should be less than 22 V. If you exceed those ratings the device may not function properly, but will not be permanently damaged until you exceed the Abs Max ratings. Hope this makes everything clear.