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INA240: Application question of INA240

Miles Li1
Intellectual 1640 points
Part Number: INA240

Hi,

Recently, I am very interested in INA240, however, I have some questions that need your help:

1. Compared to general amplifier, what is the difference or adavantage of INAxxx series compared to general amplifier?

2. What is PWM rejection of INA240? How does it function?

Wish to get your reply.

  • 0
    Guru 140200 points

    Hi Miles,

    the INA240 shows an absolutely fantastic common mode mode rejection of 132dB and is particularily suitable for high side applications. A self built differential amplifier with 1% toleranced resistors will provide a common mode rejection of only 40dB, or 60dB with 0.1% toleranced resistors. This is the main advantage.

    Kai

  • 0 in reply to kai klaas69
    TI__Intellectual 1640 points

    Hi Kai,

    Thanks for your reply! As for #2 question, I don't know what PWM rejection is, could you help to explain it?

  • 0 in reply to Miles Li1
    Guru 54087 points

    Hi Miles,

    The point is to measure current by monitoring analog voltage drop across the shunt. Internal circuitry rejects PWM riding on the analog current through a shunt in the state of random fluctuating voltage drops crossing the ±IN pins. Rejection concept often chops/filters the noisy input signal via proprietary switched capacitor bridge not discussed in 240 datasheet.

  • 0 in reply to Miles Li1
    TI__Mastermind 18780 points

    Miles,

    Thanks for using E2E for your question!

    To expound on the information that kai and Gl have already shared, here's a bit more information:

    1. In addition to the information already given by Kai, the other major difference between a conventional amplifier and a current shunt amplifier (CSA) is that a CSA uses an analog front end to power itself off of the inputs when the common mode exceeds the supply of the device. At the trade-off of a small amount of additional bias current, these devices are capable of measuring larger signal voltages (in the INA240's case, this device can measure up to an 80V common mode) than the supply that is being used to power them. With traditional amplifiers, the rail voltage provided must be larger than the common mode being measured. This is valuable, as it often saves additional circuitry such as level shifting from signal to logic in the system. There is a precision labs video that discusses the different types of amplifiers, and they're typical use cases here. 

    2. The PWM rejection block of the INA240 is aimed at applications where there is a pulse width signal travelling across the shunt, such as using the device for in-line motor winding current measurement. The proprietary circuitry Gl mentions helps to chop this unwanted portion of the signal away from the true differential, and allow accurate measurement directly on the line, rather than having to measure multiple signals on the high or low side and estimate current measurements. There is more information here.