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TPS2491 reverse current

litao xia
Prodigy 40 points
Other Parts Discussed in Thread: TPS2491

Hi Ti:

In normal current flows from vcc to sense, then to out of TPS2491, if the voltage of VCC/input drops, current will flow from out to sense, then vcc, Does it damge the TPS2491?  if it is ok, what is the limit voltage? and what is the behavior of TPS2491's Gate in this status?

thanks in advance

Litao

BR///

  • 0
    TI__Mastermind 42795 points
    If the TPS2491 circuit has voltage applied to the output then VCC can be biased ON through the body diode of the FET. In this case, if VCC is above UVLO (~8.7V) and the EN pin is also above 1.35V then GATE will turn on the FET and short out the body diode. If VCC or EN are below UVLO (say only 8.5V on OUT) then GATE will try to turn off the FET and sink current. A case where damage can occur is if the OUT voltage is fairly high and is above the Vgs rating of the FET. If the EN pin was low then GATE would also try to go low and could damage the FET. This in turn might cause follow on damage to TPS2491.
  • 0 in reply to Eric Wright
    Prodigy 40 points
    Hi Eric:
    Thanks your explanation, if the reverse current is large, input B of constant power engine is negative and inverting input of gate control amplifier is also negative, what is their low limit for normal operation? or is all the pins in the absolute maximum ratings range enough?
    Litao
    BR///
  • 0 in reply to litao xia
    TI__Mastermind 42795 points

    Hi Litao,

    Under these conditions, TPS2491 was not designed to protect the up or down stream circuits. TPS2491 will protect when operated within the parameters listed in the recommended operating conditions table. For non-standard or transient operating conditions, a bench test is required with scope probes attached to the nodes of interest. If these nodes can be kept within the ABS MAX ratings of the TPS2491 (and surrounding components such as the MOSFET) then damage should not occur.

    Try to use either the TI EVM or a breadboard for the experiment and then apply the conditions that you are worried about. Observe the waveforms and look for conditions/waves that could damage the TPS2491 and/or other support circuitry.

    Sorry that there is not an easy answer .....

  • 0 in reply to Eric Wright
    Prodigy 40 points

    Hi Eric:

    I will do the test in the real circuitry to see if it is damaged or not, maybe I will put a diode into the circuitry for backup, its anode is from OUT PIN and cathode to VCC PIN, thank you for your warm reply!

    Litao

    BR///

  • 0 in reply to litao xia
    TI__Mastermind 42795 points

    For reverse blocking applications, you can also use back-back MOSFETs as shown in Figure 4 of  http://www.ti.com/lit/an/slua464/slua464.pdf