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INA281: Current sensing amplifier for short circuit current detection in the H-bridge

Vittorio Loggia
Prodigy 50 points
Part Number: INA281
Other Parts Discussed in Thread: INA240

Hi,

I'm redesigning an old project where there is a DC Motor (200W) and H-bridge composed by 4 mosfet IRFS3206 (ID max ~120A / 210A).
On the Vbus (24V-45V) there are 4 big capacitor (10mF).


If I have a short circuit on the motor, I have a very big current on the bridge (>300A).. so my idea is to measure the current flowing in the bridge and if this exceeds 50A open the high-side mosfet so prevent the damage to mosfets.

you have a good portfolio, I did some research, probably INA281 is suitable for this application, .

I'll be using a high-side configuration (I was undecided whether to put it in series with the motor). if I put the limit to 50A or 60A, I think I have enough time to be able to act on the mosfet gates before the short comes.

If I use 2mOhm and gain 20V/V, on the output I have 2.4V (60A) with 2.5V/us I think I'm under the 500us ( or 4V for 100A). 

The trick will not be only opening the high side mosfets, but also keeping the low side mosfet closed in order to avoid currents due to inductive effects.


  • 0
    TI__Mastermind 26465 points

    Vittorio,

    This could work but I would not place in line as the INA281 is a unidirectional device.  If you place anything inline I would suggest the INA240. 

    For the INA281 there are some things that you may look at.  Please look at figure 27, Bandwidth vs Output Voltage.  This will only impact if your output voltage is not higher.  You should be limited by slew rate but I would like you to be aware especially if you lower your Rshunt.

    The other issue is the Overload recovery.  If you have an input voltage (Vsense) lower than 0V or close to VOS of the device, the device could take some time to recover.  This is when either the input or output is saturated and in requires time to get out of this.  If you will not be below this Vsense voltage then it will not be an issue.  If you have this you can add an offset by placing a resistor on IN- to add a little offset to the device.  This will cause an offset and gain error but it will add some offset.  The overload recover is in the datasheet in section 8.2.2.1 Overload Recovery With Negative VSENSE

  • 0 in reply to Javier Contreras4
    Prodigy 50 points

    Thank you very much for your help Javier. 
    Yes, unfortunately I need to use a lower Rshunt because I have high current, and I cannot have a very big power resistor.

    Nominal current is 8/10A, but at the start of the motor (and braking) I have high inrush peak current (40-50A) (fast peak).

    If I put a short circuit on the motor I have very big current, 300A inside the mosfet, beyond absolute maximum ratings.
    So for this reason I'd like to put a circuit to detect the short circuit (70 or 80A) and open high side mosfet (so as to have a margin of intervention).


    RDS of mosfet is about 3mohm (so 6mohm in series of motor resistance).
    I don't have to accurately measure the current, because I need only to check if there is a short circuit or not (lower Rsense = High error).
    Probably for the calculation of the resistance I can take into account 40 / 50A, because 70A is a very short duration peak.
    surely it will be necessary to use to parallel Rshunt or only one with high power.


    Outside the INA I thought of putting a flip flop circuit, consequently to restore the circuit I have to act on it.

    I saw INA240, yes it is bidirectional.
    INA281 is good to measure current on Vbus, I don't need to measure reverse braking current.
    If I put in line I need to use a bidirectional.

    Some application uses desaturation detection, it is good for IGBT but for Mosfet it is not so simple. So I think the only way is current sense.




  • 0 in reply to Vittorio Loggia
    TI__Mastermind 26465 points

    Vittorio,

    Sound good.  Please let me know if you have any specific questions I can help with.

  • 0 in reply to Javier Contreras4
    Prodigy 50 points

    Hi Javier,

    thank you very much for your help. Now I was evaluating different solutions, including that of using a normal High-Side Current Sense Amplifier. 
    if you know applications like mine or similar, where the voltages are not so high (24-50V) and the currents involved are high (40-80A), please let me know. it would be of great help to evaluate different ideas and understand which ones may be useful.