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INA200: OVC circuit design

Leonid Gnusin
Prodigy 150 points
Part Number: INA200

Hello,

I faced with problem of the OVC schematic, based on INA200. This is a typical application, based on design in Figure 29 of DS, see attached schematic. The OVC protection is calculated for 334 mA at 24 V. The problem is that there is a current through the BJT transistor connected to C_OUT when circuit receives OVC conditions and it does not disconnect the load, even the current is much larger than the OVC limit.

  • 0
    TI__Genius 14825 points
    Leonid,
    It looks like you have .33A x .33ohms = roughly 110mV, x20 from the gain of the part, then /4 from the divider on the output to cmpin, which sets the limit near .6V, which sounds just about perfect mathwise. Do you see cmpout toggle when not connected to any other part of the circuit and the current threshold exceeded?
  • 0 in reply to Jason Bridgmon
    Prodigy 150 points

    Tnx Jason,
    Yes, I checked that Cmp_out switches when it is opened; Also with BJT it works well. But when I try to connect load throught P-type, it does not switch - Vgs is not small enough to turn it off. I tried different P-types, and it does not work... It looks strange - it's working different in "close" and "open loop" - with and without P-type...

  • 0 in reply to Leonid Gnusin
    TI__Mastermind 27390 points

    Hi Leonid,

    Was a current load used during your tests? It might be part of the problem if this is the case.

    Instead you can use a power resistor, 75ohms and 10W, for example as the load. By adjusting the power supply voltage level, you can achieve different levels of load current, starting with low and ramp up to high enough to trigger the shutdown. Then reamp down, the power should come back up once it is lower than the threshold.

    I did the following calculation, neglecting the small inline resistances. The table shows what voltages to apply and the corresponding currents to expect, as well as the power dissipation of the load resistor. Of course you can use an amp meter to monitor the current load as well.

    Regards,

    Guang-Apps CS Products