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Original question:

INA296A: High side current sensing in the H-bridge and recirculation

INA241A: PWM rejection for 500 KHz PWM frequency?

Benyuan Liu
Prodigy 93 points
Part Number: INA241A
Other Parts Discussed in Thread: DRV8412,

Hi, we are choosing appropriate current sensing scheme for a H-bridge driver (DRV8412/DRV8432). We are planning to operate the H bridge at 500 KHz for a voice coil. Could INA241 be used in-line current sensing? I found that in the datasheet, the maximum PWM frequency of INA241 for PWM rejection is 125 KHz.

  • 0
    Guru 140200 points

    Hi,

    the INA241A has a bandwidth of about 1MHz. See figure 7-9 of datasheet. With a signal frequency of 500kHz you may not have enough gain reserve for a precise measurement. Keep in mind that a 500kHz PWM signal contains lots of far reaching harmonics which heavily exceed the 1MHz bandwidth of INA241A. So, the INA241A may not be fast enough for your application.

    Kai

  • 0 in reply to kai klaas69
    Prodigy 93 points

    So, in order to sense the current of DRV8412 working under PWM=500 KHz, I should use HS sensing with INA296 or LS sensing with a larger bandwidth amplifier? I found the reference design in DRV8412 which is LS sensing,

    Is there any INA or operational amplifiers that could be used in high side current sensing?

  • +1 in reply to Benyuan Liu
    TI__Mastermind 29520 points

    Hello Benyuan,

    The INA241 and the INA296 are our fastest Current Sense Amplifiers (CSAs) we have.  The PWM rejection limitation is for inline sensing as are doing high side sensing then the INA296 will be the one I recommend.    Please be aware the BW of the INA296 is at the gain mentioned so you do not need to divide the bandwidth by the gain used.  Our CSAs have a special input bias that allows for the input voltage to go beyond its supply rails and that is why you may be limited on the high side selection you can use.  

    If this speed is required you may go with a high speed amplifier and use the low side sensing.  

  • 0 in reply to Javier Contreras4
    Prodigy 93 points

    Thank you!

    1, For example INA296A2-Q1: 20 V/V, I could have G=20 in the whole 1.1 MHz (at all gains)? How could I tell whether this bandwidth is enough for HS current sensing when the PWM frequency is set to 500 KHz (VPP=40V, I RMS=6A, R shunt=10mΩ)?

  • 0 in reply to Benyuan Liu
    TI__Mastermind 29520 points

    Hello Benyuan,

    I would simulate the circuit.  Please be aware that the simulation will be representative of the linear operating range of the device. 

  • 0 in reply to Benyuan Liu
    Guru 140200 points

    Hi,

    what harmonics does your PWM signal have?

    Kai

  • 0 in reply to kai klaas69
    Prodigy 93 points

    I could not measure it right now, I left a 0 Ohm inline resistor and INA241 (DNP) for test, I will make one and see the results. Thank you.