Calculate Current from Battery

Thread Starter

sekhar916

Joined Jan 5, 2017
12
Hi Guys,
I have a project where I have to calculate current consuming by the Board.
We are using MAX4372F High-Side Current-Sense Amplifier with Voltage Output. The Voltage output is connected to ADC of the Micro-controller.
From the BAT_CURNT_SNS will be the ADC value. How to calculate Current in milliAmps.
The Sense resistor is 0.01Ohm and Gain is 50
Attached is the circuit diagram. Capture1.PNG
 

ebeowulf17

Joined Aug 12, 2014
3,307
Also, the schematic shows 10% tolerance resistors. I have to assume you want better than 10% accuracy in your measurements, and it doesn't cost too much to get much better specs.
 

Thread Starter

sekhar916

Joined Jan 5, 2017
12
hi 916,
This clip from the d/s shows the scaling, why have you chosen a 0.01R Sense resistor for milliamp application.?
E
Because out maximum Iload is 10A. SO according to the d/s for 10A load the sense resistor should be 10mOhm. SO i am using 0.01Ohm sense resistor
 

ericgibbs

Joined Jan 29, 2010
18,766
hi 916,
The reason for my query is that you want to calculate the actual current in milli-amps, yet you have set the Rsense for 10Amps.
ie: 10,000mA
Resolving to +/- 1 mAmp
Full Scale Accuracy of the MAX4372 is only 0.18% .
E
 
Last edited:

Thread Starter

sekhar916

Joined Jan 5, 2017
12
hi 916,
The reason for my query is that you want to calculate the actual current in milli-amps, yet you have set the Rsense for 10Amps.
ie: 10,000mA
Resolving to +/- 1 mAmp
Full Scale Accuracy of the MAX4372 is only 0.18% .
E
If we go with the datasheet for Iload of 10A the sense resistor should be 10mOhms.Milliamps is just a notation for me. If the output is in Amperes I will just multiply with 1000. I dont want to have decimal values, Thats why i have mentioned it as milliAmps.
 

ericgibbs

Joined Jan 29, 2010
18,766
OK, thanks for the explanation.
Looking at post #2 image, for a Gain of 50, with a 10mOhm resistor the Vout for 10A will be 5V.

Vout=1V is == 2Amps
Vout-0.1V is == 0.2A
Is this what you are asking.?
E
 

Thread Starter

sekhar916

Joined Jan 5, 2017
12
OK, thanks for the explanation.
Looking at post #2 image, for a Gain of 50, with a 10mOhm resistor the Vout for 10A will be 5V.

Vout=1V is == 2Amps
Vout-0.1V is == 0.2A
Is this what you are asking.?
E
Yes
But the Vout is connected to ADC of the Microcontroller. So from the ADC how to calculate Vout ? From that Vout calculate Current.
 

ericgibbs

Joined Jan 29, 2010
18,766
hi,
If the MCU Vref for its ADC is set for 5V and assuming its a 12Bit ADC, 5V input to the ADC would give a ADC count of 1023,

Is that what you mean.?

Is this a Homework assignment.?
E
 

Thread Starter

sekhar916

Joined Jan 5, 2017
12
hi,
If the MCU Vref for its ADC is set for 5V and assuming its a 12Bit ADC, 5V input to the ADC would give a ADC count of 1023,

Is that what you mean.?

Is this a Homework assignment.?
E
No this is not my homework project. I am into firmware development and for the first time I am using Current sense amplifier
Yes the Vref is 3.3 here. 8 bit ADC and input voltage is 16.8V, the ADC count 254
 

ericgibbs

Joined Jan 29, 2010
18,766
OK,
With a 3.3V ADC Vref you will have to ensure that Vout from the MAX4372 does not exceed 3.3V, you could use a resistive potential divider to set a MAX4372 of 5Vout to 3.3V max
So for an ADC input of 3.3V from a divider would give 255 counts for a 10Amp current thru the 10mOhm Shunt.
 
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