LM74900-Q1: Good way to use the VMON output

Hi Chistophe,

R23 will alter the reading on IMON. RC added has a time constant of around 10ms hence you will see a difference. 

Regards,

Shiven Dhir

So i have to reduce R23 or to remove the RC filter ? 

best regards

I tried both (reduce R23 and remove RC filter). Unfortunately i have very low precision on current measurement. 

This signal is connected on ADC input of MCU and to a OPA to detect very quickly a high current. 

I don't understand what happens. 

I also tried to remove D4

Hi Christophe,

Are you measuring IMON at low current?

IMON reading at low current is expected to be deviated from actual value. At VSNS = 20mV, the accuracy is +- 12.5%

Regards,

Shiven Dhir

Hi Shiven,

Thanks for your feedback. Indeed, i notice very poor precision ot low current. For exemple when the load is drawing 150mA i measure 14mV at VMON ( 30mA after calculation). 

At higher currents the precision is in the range specified ( from 400mA to 3A). 

What can i do to improve my design (by software of hardware) ? What do you mean by "IMON reading at low current is expected to be deviated from actual value" ?

Best regards.

Christophe

What is the minimum Vsense voltage to get an accurate Vmon ? I think i have to use an higher Vsense. My needs is to measure an accurate current from 50mA to 3A

Hi Christophe,

Best achievable is +-12.5% at VSENSE>20mV

Regards,

Shiven Dhir