DRV8303: Shunt Amplifiers

Grady

Part Number: DRV8303
Other Parts Discussed in Thread: DRV8304

Hello All

Currently working on a new design using the DRV8303, but I don't want to use leg shunt resistors. I want to tie all the low side source's of the fets together and have one shunt for all 3 legs.

Now, as the voltage coming off the shunts will be positive and i want as high resolution as possible. Please can you confirm it is ok for me to do the following...

Tie Vref to GND
invert the inputs SN and SP so that SN connects to the GND and SP connects to the low side source's.

So this makes a non-inverting opamp that should give me an output between 0 (GND) and AVDD that is directly proportional to the load through the shunt. The different gains should remain adjustable via the SPI.

Please can you confirm this is all OK before I finish off the schematic?

Thanks

over 7 years ago

0 James Lockridge19 over 7 years ago

TI__Genius 14487 points

Hi Grady,

Our Recommended Operating Conditions table sets the minimum voltage for the VREF pin at 2 V. We only guarantee that the device will operate according to spec within the conditions in that table. Setting VREF to 0 V is not a condition we guarantee.

0 Grady over 7 years ago in reply to James Lockridge19

Prodigy 180 points

Hello James

So I assume from this the OpAmp the DRV8303 uses is not a standard OpAmp used as a differential amplifier? Here is a link to a calculator that can be used www.daycounter.com/.../Op-Amp-Voltage-Calculator.phtml I see no reason why VREF would need to be set at a voltage as all it really does is set the offset to enable negative current measurements. As I only have positive current with a single shunt, it would just be nice to be able to increase the resolution.

Thanks

0 James Lockridge19 over 7 years ago in reply to Grady

TI__Genius 14487 points

Hi Grady,

I understand your reasoning. However, during product definition and design we set the minimum value of VREF to 2 V. Many times specs like this are chosen because of process variations and corner case in the design.

The DRV8304 will allow the VREF pin to go to GND. Would that device work for your application?

0 Grady over 7 years ago in reply to James Lockridge19

Prodigy 180 points

Hello James

Unfortunately not, I need to drive from a 36V lithium battery supply so the IC needs to withstand greater than 42Vdc.

No Matter, if its not recommended I wont risk it. I will stick with VREF at 3.3V.

Thanks

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DRV8303: Shunt Amplifiers