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Low power bidrectional current amplifier; battery-50V to 84V

VT
Genius 3300 points
Other Parts Discussed in Thread: INA210, INA301, INA300

1. I am a application where I need to measure the bidrectional current in a battery powered applicaiton. Source is battery 50V-84V. Shunt is connected on low side.

2. Which amplifier do you suggest, I looked for many thery all specify max 80V CM range or can I use them?

3. Preferable amplifier Vdd=3.3V Low power since it is battery powerd/

  • 0
    TI__Mastermind 22560 points
    Dear Vindhyachal,

    I would not recommend using a part with a specified max at 80 Vcm to attempt to measure voltages higher than that. However, based on your post, it sounds like this is not an issue. If you are measuring on the low side of the load, your Vcm will reside closer to ground than the voltage of the battery, as the load will consume the majority of the line.

    As for a recommendation, there are several followup questions that need to be addressed: what type of output are you desiring? Digital, analog voltage, or analog current? Do you want/need an internal comparator? What level of accuracy are you hoping to measure?

    Let me know what metrics are of concern to the design and I'd be happy to try and point you to some our devices.

    Carolus
  • 0 in reply to Carolus Andrews
    Genius 3300 points

    Attached find the reference board which we will use. It has lots of components/IC also, but removed foe sake of understanding.
    Please note that during operation of battery, Q1 may be off/on, Q2 may be on/off or both Q1/Q2 may be on/off depending upon battery condition.

    To answer your questions:
    1. Analog voltage is required
    2. If comparator output is also there for short circuit, then it would be good.
    3. Accuracy not a issue. We need to shut down Q2 when high current flows through system. That we will do by programming.
    4. Low power is the most important concern, since it is battery powered device.
    5. Should be 3.3V operatable.

    If you can give ur email id, I can share entire schemtic for better understanding.

    My email id: vindhyachal.takniki@gmail.com

    Design1.pdf

  • 0 in reply to VT
    TI__Mastermind 22560 points
    Dear Vindhyachal,

    Based on your concerns, I would recommend looking at the INA210, which is what is mounted in the reference design above. It is 3.3V capable, and is the lowest power device we have that is low side capable. Unfortunately, it does not have a comparator output, but the next device that integrates one on the low side (INA301) consumes considerably more power (up to 700uA at the supply).

    Being mounted as per the reference design, the Vcm of the device will be approximately zero, so even though you are measuring current on a battery of 50-80+V, you will not need to worry about stressing the device.

    Carolus
  • 0 in reply to Carolus Andrews
    Genius 3300 points

    Hi Carolus Andrews,

    One problem I saw is in grounding INA.
    I have attached a updated schematic for your reference. I want to keep the ground as shown. If I keep the ground for INA on right side of sense resistor, then I have to shift LDO/MCU ground also to right side. This will make a continuous current to flows through this sense.
    Since it is battery management system/gauging application, it will add error in capacity gauging.
    For this INA, I only want to measure charging current, as shown in direction indicated.
    Is there any solution possible in this scenario?

    Will send complete schematic by private mesaage to you.

    8802.ckt.pdf

  • 0 in reply to VT
    TI__Mastermind 22560 points

    Dear Vindhyachal,

    Reviewing your schematic, I am a bit confused as to your setup. Will the charger be attached at the load point? Where are you hooking in the charger? As to the ground issue, this is a disadvantage introduced when low side sensing is chosen. You are effectively pedastaling ground up by the shunt resistor, which will introduce a slight error. You will also lose the ability to detect ground faults as a result of low side measurement.

    Carolus

  • 0 in reply to Carolus Andrews
    Genius 3300 points
    Hi Carolus,

    Yes, charger will we connect between BAT20 & Pack- points as in shcematic which I had sent to via message.
    Accuracy is not a concen.
    I have to measure charging current only.
  • 0 in reply to VT
    TI__Prodigy 85 points

    Vindhyachal,

    If you are looking to detect out of range currents to protect the battery and you don't need the actual current reading, the INA300 maybe a good solution to consider as the device has a standby mode which is suitable for battery operated applications.

    Thanks,

    Motaz