bidirectional current sensing amplifier

Ramakrishna Challa

Prodigy 160 points

Other Parts Discussed in Thread: INA193, INA282, INA285

Dear all,

I have 0.005 Ohm current sense resistor.

What's the best differential amplifier to measure the current (max 500mA).

Specifications 1) High side current measurement

2) The bus voltage is 60V while the Op-amp would be supplied 5V.

3) need to measurement the current in both the directions

I tried INA193 but it measure current in one direction only. Please suggest device that can measure current in both the directions

V=IR Drop across current resistor = 0.005*5m = 25uV, this is very small voltage Any referense schematics would be of great help.

Thanks and Regards

Ramakrishna

over 13 years ago

0 Pete%20Semig over 13 years ago

TI__Mastermind 25805 points

Hello Ramakrishna,

The device with the lowest offset voltage that meets yoru Vcm, directionality, and high-side specifications is the INA282. The issue is that the shunt voltage at minimum current only generates 25uV. The offset voltage of the INA282 is 70uV. Therefore you will need to increse the size of your shunt resistor. I have attached a TINA simulation that may help.

ina282_tina-ti_reference_design.tsc

0 Ramakrishna Challa over 13 years ago in reply to Pete%20Semig

Prodigy 160 points

Hello Pete,

Please Can you provide the PSPICE file (that is usefull in ORCAD simulation) of INA282?

Application:

I have the fuse of 500mA. I need to replace this bi-direction fuse with small sensing circuit.

I have attached the my proposed circuit. Please go through it and provide your comments. I don`t have TINA software for doing simulation.

Can you provide the schematic in pdf or image format that will be usefull for me?

Thanks & Regards

Ramakrishna

6330.fuse.pdf

0 Pete%20Semig over 13 years ago in reply to Ramakrishna Challa

TI__Mastermind 25805 points

Hello Ramakrishna,

I do not have ORCAD, but you can find the PSPICE model for the INA282 in the Product Folder:

http://focus.ti.com/docs/prod/folders/print/ina282.html

An alternate option is to download (free of charge) TI's SPICE simulator (just upgraded to Version 9)...TI-TINA. It is available via the following link:

http://focus.ti.com/docs/toolsw/folders/print/tina-ti.html

As requested, here are screen captures from my simulation:

0 Ramakrishna Challa over 13 years ago in reply to Pete%20Semig

Prodigy 160 points

Dear Pete,

Thanks for your reply. I changed my specification and I need your assistant for choosing the correct high side current sensing amplifier.

Specification:

1) need to sense the current in both the directions ( +20 mA to -20mA)

2) current sensing resistor is as low as possible.

INA282 is one which has 70uV offset voltage. The inbuilt gain is low (50V/V).

I think INA285 is suitable for my application. It has inbuit gain of 1000V/V.

Calculations:
INA285 Specifications
Gain = 1000;
Vsupply = 5V
Vref = Vsupply/2
min current = -20mA
Max current = 20mA
Vsensemax = (Vsupply-0.4-Vref)/Gain
Vsensemax = 2.1mV
Rsensemax = Vsensemax / maxcurrent
Rsensemax = 105mOhm

Is this current sensing amplifier(INA285) is in production?

Is there any amplifier that will provide bi-directional current sensing with high gain then we can use very low current sensing resistor (~10mOhm)?

Please provide your comments on this application.

Thanks

Regards

Ram

0 Pete%20Semig over 13 years ago in reply to Ramakrishna Challa

TI__Mastermind 25805 points

Hello Ram,

It appears as though this post is the same as the following:

http://e2e.ti.com/support/amplifiers/precision_amplifiers/f/14/p/112737/399504.aspx

It contains the answers to your questions.

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bidirectional current sensing amplifier