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OPA388-Q1: OPA388-Q1 Bi-Directional current sensing for automotive

Shankar Murthy
Prodigy 10 points
Part Number: OPA388-Q1
Other Parts Discussed in Thread: REF5025, OPA388

Tool/software:

Hi we need to sense bi directional current from +/-1200A range. we looked for  OPA388-Q1(In data sheet it has mention +/-1A) , Whether this is suitable for our application(Automotive Battery Disconnect Unit). can any one confirm on this or provide more information on sensing bi-directional current.

Whether we need to use single op-amp for measurement or 2 op-amp with passive circuit(as per datasheet).

  • 0
    Guru 282670 points

    The ±1 A limit is not a property of the device but of the circuit. To adjust the measurement range, adjust RSHUNT and/or VSHUNT.

    U1B is used to buffer the reference voltage. If you already have a low-impedance source for the reference voltage, then you do not need the buffer.

  • 0
    TI__Guru 64110 points

    If you drive the top of the R2 resistor with a reference voltage like REF5025, there is no need for U1B op amp BUT you cannot use R5/R6 resistor divider without the buffer.

    The linear range of the OPA388 output is 150mV from either rail, which means 0.15V < Vout <4.85V on Vs =5V supply (see below).

    Thus, in order to measure +/-1200A current, you must calculate the maximum Vshunt based on the gain you plan to use: Gain = R2/R1 where R1=R3 and R2=R4.

    If you assume Gain =10k/1k = 10 where R1=R3 =1k and R2=R4 =10k, for Vs=5V max Vshunt = (4.85V-2.5V)/Gain = 2.35V/10 = +/-235mV

    Therefore, you would need to use Rshunt = max_Vshunt/max_Iload = 235mV/1200A = ~0.2mohm or less.

    If this is not acceptable due to large power dissipation inside the Rshunt (P = Vshunt*Iload = 0.235*1200A = 282W), you may increase the gain to 1000 (e.g. R1=R3=100ohm and R2=R4=100k), which will allow you to decrease Rshunt down to 2micro-ohm resulting in lowering the maximum power dissipation in Rshunt down to P =   2.35mV*1200A = 2.82W.