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TPS63020 over current

K.Hamamoto
Guru 12155 points
Other Parts Discussed in Thread: TPS63020, TPS63020EVM-487

Hi

I have a question about over current limit operation of TPS63020.

I measured current limit operation with TI-EVVM (TPS63020EVM-487). However it was not  such as what I expected.

I have confirmed the datasheet at section 9.3.2(Dynamic Current Limit) and 9.4.1(Softstart and Short Circuit Protection).

That is mentioned that the current limit value is reduced when the output is below 1.2V.

However at the measured data it seem that the current limit is not reduced at below Vo=1.2V.

Why? and How does this device operate at over current?

(Vin=5V)

Please let me know if you have a any question.

Regards,

Koji Hamamoto

  • 0
    TI__Expert 7110 points

    The curve you show reflects the over current behavior at Vout = 3.3V. The device limits the current and therefore Vout drops at higher output currents due to the limit.

    The reduced current for Vout < 1.2V is applicable during start-up.

  • 0 in reply to Florian Feckl
    Guru 12155 points

    Hi Florian-san

    Thank you for quick reply.

    I understand that this current limit operate at high side switch.

    I am considered how this protection works during the output is going to down.

    If this current limit has the following V-I curve, the current increases more than current limit value when the output is low.

    That is very important for the customer application.

    If the current is limited at high side switch of TPS63020,  the current never increase more than current limit value.

    Is that correct?

     

    Regards,

    Koji Hamamoto

  • 0 in reply to K.Hamamoto
    TI__Expert 8420 points
    hi Koji-san,

    When the output goes down (overload or short-circuit), the current can not increase more than the current limit.
    There can be a small fall back or increase like on the V-I curve, but this is valid for a very small range (Isc1 and Isc2 are close). The output will always collapse and stay below the current limit (like in your measurement).

    The current is measured at high side switch to control the average inductor current. It is correct, the average inductor current can never increase more than the current limit value (given for the inductor).

    Regards
    Sabrina
  • 0 in reply to Sabrina
    Guru 12155 points

    Hi Sabrina-san

    Thank you very much for your support.

    I understand. However I have a question.

    As  mentioned on the datasheet, the current limit is decreased at below 1.2V. Is that correct?

    Regards,

    Koji Hamamoto

  • 0 in reply to K.Hamamoto
    TI__Expert 8420 points

    Hi Koji-san,
    When the output voltage is below 1.2V, the current limit is reduced.
    On one hand the protection reduces the current limit and holds back the current from increasing, the main goal is to keep the current below the maximum limit.

    On the other hand the circuit must be able and tries to start again, so there is still current in the device. In this area the device operates with a low duty cycle, so the current measurement is not that accurate. Therefor we do not see a linear decrease of the current on the measurements.


    Regards,

    Sabrina