INA310A-Q1: Use case of high value of series resistor at input path

DEVENDHIRAN KUMARASAMY

Part Number: INA310A-Q1
Other Parts Discussed in Thread: INA190, INA228, INA238

Tool/software:

We need to monitor the current through a Shunt resistance of 40mOhm.

For the diagnostic purpose, we are planning to keep 1K ohm resistor in series between the IN+ & IN- pins and the shunt resistor.

So now the questions are,

1. Is it allowed to have 1K ohm resistance in front of IN+ & IN- pins of INA310A-Q1 device?

2. What is the functional impact of having high input resistance in front of IN+ & IN- pins of INA310A-Q1 device?

3. Is there any formula or simulation is available to estimate the impact of INA310A-Q1 device due to this configuration?

6 months ago

0 Mallika Senthil 6 months ago

TI__Intellectual 2290 points

Hi Devendhiran,

To address your questions point-by-point:

1. It is not advisable to place a 1k resistor in series with the input pins, a maximum of 10 ohms is allowed.

2. When you place a large input resistance in series with your input pins; (i) there is now a source of additional measurement error (ii) increased loss of accuracy and (iii) mismatch in the voltage drop across resistors.

3. There is a PSPICE model available for simulating the INA310 on the design and development section of this page

https://www.ti.com/product/INA310A-Q1?utm_source=google&utm_medium=cpc&utm_campaign=asc-null-null-GPN_EN-cpc-pf-google-wwe_cons&utm_content=INA310A-Q1&ds_k=INA310A-Q1&DCM=yes&gad_source=1&gclid=EAIaIQobChMIn5zD9uf0hgMVIUl_AB3OzgKcEAAYASAAEgJqBfD_BwE&gclsrc=aw.ds#design-tools-simulation

You can find the input filter design constraints on section 8.1.2 of the following datasheet.
https://www.ti.com/lit/ds/symlink/ina293.pdf?ts=1719253617346&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FINA293

Best,
Mallika Senthil

0 DEVENDHIRAN KUMARASAMY 6 months ago

Prodigy 120 points

Hi Mallika Senthil,

Thanks for your response.

Do we have any differential or Current sense amplifiers available in TI which allowed to use 1K resistor in the input path?

Regards,

Devendhiran K

0 Mallika Senthil 6 months ago in reply to DEVENDHIRAN KUMARASAMY

TI__Intellectual 2290 points

Hi Devendhiran,

Our family of ultra-precise current amplifiers have input bias currents in the nA range, hence can support input filtering with ≤ 1k resistors. However, it's common mode range will not be as wide as the INA310's.
I've attached the INA190 datasheet for your reference.
https://www.ti.com/lit/ds/symlink/ina190.pdf?ts=1719329938135&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FINA190

Best,
Mallika Senthil

0 DEVENDHIRAN KUMARASAMY 6 months ago in reply to Mallika Senthil

Prodigy 120 points

Hi,

Thanks for suggesting the part "INA190" which is good in the bias current perspective but with respect to the allowed minimum negative common mode voltage range at the input pin, it is only -0.2V.

How do we need to protect the input pins during the negative pulse or surge interferences which are very common in the automotive field external interfaces?

In our design either of the INA190 input pin might be directly connected with external connector pin which may expose to the negative pulse or surge conditions.

Do you have any suggested methods to implement this?

Regards,

Devendhiran K

0 DEVENDHIRAN KUMARASAMY 6 months ago in reply to DEVENDHIRAN KUMARASAMY

Prodigy 120 points

Hi,

We are looking for a current sense amplifier or any differential amplifier with the following requirements. They are,

1. Single 5V supply operation
2. 50V/V gain configuration or adjustable
3. Bi-directional current measurement shall be possible. (Unidirectional also would be ok if we get the part in low price)
4. Minimum continuous common mode input voltage need to be ≤ -20V
5. Maximum continuous common mode input voltage need to be ≥ +40V
6. Common mode Input impedance must be ≥100K Ohm
7. Differential mode Input impedance shall be ≥100K Ohm (but it is not mandatory)
8. Input bias current must be in nA range to make use of 1k resistor in the input path

Kindly suggest the any part if the specification matches with the above-mentioned requirements.

Regards,

Devendhiran K

0 Mallika Senthil 6 months ago in reply to DEVENDHIRAN KUMARASAMY

TI__Intellectual 2290 points

Hi Devendhiran,

From the analog side of our current amplifiers, we don't have a device that would satisfy all your requirements, for example the INA241 and INA296 would sustain at a -20V, but wouldn't satisfy your input impedance and input bias requirements. However, our digital current amplifiers can accommodate your requirements, I would suggest the INA238 or INA228, with which you could add an isolation circuit to protect the input pins as shown in the schematic below. I'm attaching a reference design for your reference: https://www.ti.com/tool/TIDA-00313

Best,

Mallika Senthil

Because of the holidays, TI E2E™ design support forum responses will be delayed from Dec. 25 through Jan. 2. Thank you for your patience.

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INA310A-Q1: Use case of high value of series resistor at input path