DRV8842: V_Ref and I_Trip

Fabian Kamm

Part Number: DRV8842

Hello ,

I'm using the DRV8842. In the "Typical Application part given in the datasheet, there is a equation for
calculating I_Trip depending on VREF and R_Sense. Is I_Trip = 1.5A by one directional current or
is the bidirectional current range from -0.75 to +0.75 A.
I want a small R_Sense and the motor maximum current should be +/-1A by 100%.

INA240A2:

Additional i'm also confused by the given equation for calculating R_Sense for the INA240A2.

Im using the differential measurement Figure 8-8. Vs = 5V, and the internal reference for the ADC by the microcontroller is 2.56V.
So i'm also strugggeling what to use as V_Ref... The Internal 2.56, two times 2.56V
cause im measuring birectional or die reference voltage given by the resistor divider?

As the maximum Current i want to use -/+ 1A, so a difference from 2A. What is my I_max... is it 1A or is it 2A?
Could you please help me choosing the right values...

Thank you very much!

F.Kamm

over 3 years ago

0 Pablo Armet over 3 years ago

TI__Mastermind 37683 points

Hi Fabian,

Thanks for posting to the forum.

I will research your questions and provide you with answers by Monday of next week.

0 Pablo Armet over 3 years ago in reply to Pablo Armet

TI__Mastermind 37683 points

Hi Fabian,

If you look at the H-bridge circuit below, current will be regulated only when the current is flowing through the sense resistor but only when the current is flowing from top of resistor to GND. It won't regulate current if the current flows in the opposite direction (fast decay state) or if the current is re circulating (slow decay). So current will be regulated when it is in the driving phase (either forward or reverse).

The sense resistor won't be able to do bidirectional sensing either, so you'll have to add an external bidirectional current sense amplifier.

For the question related to the INA2040A2, I suggest posting the question to the amplifier's E2E forum. I am not familiar with that device.

0 Fabian Kamm over 3 years ago in reply to Pablo Armet

Prodigy 50 points

Hi Pablo,
But if you look on the H-bridge circuit they say current flow "2" reverse/fast decay is flowing through the sense resistor.

+1 Pablo Armet over 3 years ago in reply to Fabian Kamm

TI__Mastermind 37683 points

Fabian,

That's correct but the current is flowing in the opposite direction (from GND to LS-FET source). The VSENSE voltage with respect to GND will be negative. Current regulation will only work when VSENSE is positive with respect to GND. I hope this clears your confusion.

0 Fabian Kamm over 3 years ago in reply to Pablo Armet

Prodigy 50 points

Ah okay. Thank you very much!

Motor drivers

Motor drivers forum

DRV8842: V_Ref and I_Trip