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TPS65321-Q1 Can DC/DC Still Work when LDC Output is Shorted to GND?

KevinZhang123
Expert 5740 points
Other Parts Discussed in Thread: TPS65321-Q1

Hi, Team

An automotive customer GAC plan to use TPS65321-Q1 in their car infotainment system. Both input of DC/DC and LDO are connected to 12V battery, and both output is 5V.

If the output of LDO is shorted to GND, can the DC/DC still work normally?

If the output of DC/DC is shorted to GND, can the LDO still work normally?

Thanks

Kevin

  • 0
    TI__Genius 9645 points

    Hello Kevin,

    I will double-check on bench (I need to get new boards, so stay tuned), but in theory:

    - if the LDO-output is shorted, it limits the current, but still up to 1000mA may flow (or 12V * 1A = 12W). This will quickly heat up the device and trigger the  thermal shut-down, which disables the entire part, i.e. buck and LDO.

    - if the Buck-output is shorted, there is a frequency fold-back that ensures the (repeatedly high inductor-current is given enough time to decay and keep the output voltage low. This requires the switching frequency to be chosen appropriately, please see datasheet sections 7.3.1.12 and 7.3.1.13 for details.

    I get back to you when I validated it on bench.

    Best regards,

    Frank

  • 0 in reply to Frank Dehmelt
    TI__Genius 9645 points

    TPS65321-Q1 Short-Circuit response

    Test-Bench:

    TPS65321-EVM, standard configuration (Vout_Buck=3.3V, Vout_LDO=5V)

    Test conditions:

    Vin_Buck=14V, Vin_LDO=14V, T(A)=25°C

    Setup A: Buck shorted:

    LDO unloaded, Buck-output shorted by applying a load-step between 100mA and 30A at 1A/us.
    The effective current is limited by the short-circuit protection of the IC:

    CH1: Vout_Buck, 500mV/Div
    CH2: Phase-Node, 10V/Div
    CH3: Vout_LDO, 1V/Div
    CH4: Iout_Buck, 1A/Div

    The LDO-output remains stable. The input current (at 14V) was limited to ~300mA.

    Setup B: LDO shorted:

    Buck unloaded, LDO-output shorted by applying a hard short on the output.
    The effective current is limited by the current limit of the IC:

    CH1: Vout_Buck, 500mV/Div
    CH2: Phase-Node, 10V/Div
    CH3: Vout_LDO, 1V/Div
    CH4: Iout_Buck, 1A/Div

    The Buck-output shows a short dip (likely due to the GND-shift), but remains stable.
    The LDO is in hick-up (seen by the output current), limiting the current end re-attempting to drive the output voltage. The input current (at 14V) varied between ~300mA and 500mA. As seen, the buck-output was not compromised during the 45s shown above, however, the case-temperature rose from ~30°C to ~45°C during the test, and if the short is present for a longer time and/or at a higher ambient temperature, the thermal shut-down will kick in and cause the buck-output to be turned off as well.

    Best regards,

    Frank