INA190: Simulation, hardware & system design tools forum

Hey Saravanan,

This can be a difficult design to accomplish unless you can determine and limit some design considerations.

You should determine how much shunt resistor power dissipation you could allow over whole current range. Also how much error can you allow over whole range as well. This will help you limit amplifiers by their offset and/or gain error.

You most likely will need some relatively large shunt resistor (R1) for measuring uA of current, but R1 probably will not survive Amps of current, so you will have to switch out this resistance from the load.

You most likely will want to have two amplifiers (one for each shunt resistor) because trying to switch the input pins from one shunt to another is not a very practical idea.

It is important to choose a proper amplifier for the low current range. Ideally this amplifier should be high-input impedance (<10nA of input bias current). Some current sense amplifier (CSA) options are INA190, INA2191, INA238, INA228, and INA229. An instrumentation amplifier (such as INA121) is also a possibility depending on what the common-mode voltage is and what supply voltages are available to your design. CSAs are nice when you are measuring current on bus voltages that are much greater than the supply voltage you want to use or when you don't want to spend on precision gain setting resistors.

Other design options are what is your full-scale output range, do you have two ADC inputs or only one, is amplifier driving a SAR ADC with high conversion times (if so, then consider using a buffer op amp to drive the ADC), what is BW of sign you need, etc.

Some high level design options are:

* Use INA2191 (2 channel CSA) with one channel for low current and the other for high current. Additionally you can tie both outputs together and use the ENABLE pin to disable whichever channel is used.

* Use two power monitors (e.g., INA228) and two shunt resistors.

* Use an instrumentation amplifier and use FETs to change the gain setting resistor.

* Use a logarithmic amplifier (LOG114)

* Use a transimpedance amplifier

Here are some links from others trying to accomplish the same thing:

https://e2e.ti.com/support/sensors-group/sensors/f/sensors-forum/1226195/drv425-use-adc-vcm-as-refin-and-inverter-signal-to-increase-dynamic-range?tisearch=e2e-sitesearch&keymatch=large%25252520dynamic%25252520range#

https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/1020081/log114-dynamic-range-and-resolution?tisearch=e2e-sitesearch&keymatch=large%20dynamic%20range#

https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/1040718/instrumentation-amp-for-measuring-current-in-the-1na-to-1ma-range/3851581?tisearch=e2e-sitesearch&keymatch=large%2525252520dynamic%2525252520range#3851581

https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/988330/ina226-wide-current-range-application-with-ua-precision-needs/3651777?tisearch=e2e-sitesearch&keymatch=large%25252525252520dynamic%25252525252520range#3651777

https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/1238015/log114-tina-ti-simulation-error/4681333?tisearch=e2e-sitesearch&keymatch=large%2520dynamic%2520range#4681333

https://www.ti.com/video/6254105503001

If you want some more design specific help, please provide baseline system-level requirements, error, Vcm range, desired/available supply voltages, required signal BW, ADC full-scale range, allowable shunt power dissipation, etc.

Sincerely,

Peter

Hey Priyanka,

We do not have a specific reference design for switching on/off shunt resistors, but it should be a simple circuit using FETs to switch out the high resistance shunt and switch in a short to ground. The low resistance shunt can be kept permanently in series with load because it should not pose any significant loading at low currents.

The logarithmic amplifier LOG114 may be the only thing that can sense such a large dynamic range of current, although it still may be too great. 

Here is the product page for INA2191 which has datasheet on it:

https://www.ti.com/product/INA2191

Sincerely,

Peter