DRV8847: Datasheet question asking

Jason Ciou

Part Number: DRV8847
Other Parts Discussed in Thread: DRV8833C

Hi team,

My customer has a question about datasheet., please see below question.

1.) Check DRV8847 datasheet MODE pin if Hi-Z is independent bridge interface. The schematic diagram of the independent bridge interface circuit in the datasheet shows that ISEN12 / ISEN34 do not connect Rsense in series but directly connect to GND, Therefore, it is a bit confuse. Is it still necessary to adjust the current in series with Rsense when applied to an independent bridge interface?

over 2 years ago

0 Ryan Kehr over 2 years ago

TI__Guru 54675 points

Jason,

There is no current regulation when in independent mode. That is why no resistor is shown.

Regards,

Ryan

0 Jason Ciou over 2 years ago in reply to Ryan Kehr

TI__Expert 3600 points

Hi Ryne,

So my customer just need to short to GND, am I coorect?

Jason

0 Jason Ciou over 2 years ago in reply to Ryan Kehr

TI__Expert 3600 points

Hi Ryan,

Update my customer question, please see below.

Please continue to ask the following questions. The circuit of our current model DRV8847 is as follows. Some models of Pin#12 have a 0.1uF capacitor to the ground, and some models have no capacitor and are directly floating, (and R1209 is all NC) Does the datasheet work in the independent bridge interface? So in fact, ISense Pin does not need to be connected in series with Rsense; just go directly to the ground?

Jason

0 Ryan Kehr over 2 years ago in reply to Jason Ciou

TI__Guru 54675 points

Jason,

For decoupling of power supply (pin 12), I recommend to ALWAYS have a 0.1uF capacitor to GND. And yes, the ISense pins can be directly shorted to GND in independent made. They must be. Those pins are the GND connection for power FETs.

Regards,

Ryan

0 Jason Ciou over 2 years ago in reply to Ryan Kehr

TI__Expert 3600 points

Hi Ryan,

Thanks, let me update my customer question later.

Jason

0 Jason Ciou over 2 years ago in reply to Ryan Kehr

TI__Expert 3600 points

Hi Ryan,

Excuse me,

update my customer question.

When Pin#14 is connected to 0.1uF, which mode in Table 2 does DRV8847 work in?

Due to the lack of DRV8847 material, it is recommended to use DRV8833C instead. Apart from Pin#14, are there any other differences and peripheral parts that need to be adjusted together

Jason

0 Ryan Kehr over 2 years ago in reply to Jason Ciou

TI__Guru 54675 points

Jason,

With just a cap to GND on mode pin, the input would be HIZ (Z state in table 2). That would select the independent bridge mode which is different logic from the DRV8833C. To have same logic for DRV8833C, the MODE pin on DRV8847 must be tied to GND.

In schematic above, they could simply populate the capacitor for the DRV8833C (VINT) and populate the resistor to GND for DRV8847 (MODE). Then either device could work on their board in the same way.

Nothing else needs to be considered in terms of pinout.

Regards,

Ryan

0 Jason Ciou over 2 years ago in reply to Ryan Kehr

TI__Expert 3600 points

Hi Ryan,

Thanks for your information, I will let my customer know!

Jason

0 Jason Ciou over 2 years ago in reply to Ryan Kehr

TI__Expert 3600 points

Hi Ryan,

Does DRV8833C and DRV8847 have the same driving capability?

Could my customer use DRV8833C to drive the same motor?

it will be used in DLP application.

Jason

0 Ryan Kehr over 2 years ago in reply to Jason Ciou

TI__Guru 54675 points

Jason,

You need to consider Rdson and Iocp (over-current trip level) when comparing drive capability.

DRV8847 - Rdson typical at 25C temp is 1000mohm, Iocp min = 1.6A

DRV8833C - Rdson typical at 25C temp is 1735mohm, Iocp min = 1A

So, DRV8847 is technically stronger, but both can drive 1A. If 1A is the requirement for their motor, both will work fine.

Regards,

Ryan

0 Jason Ciou over 2 years ago in reply to Ryan Kehr

TI__Expert 3600 points

Hi Ryan,

Got it, thanks.

Jason

0 Jason Ciou over 2 years ago in reply to Ryan Kehr

TI__Expert 3600 points

Hi Ryan,

Update my customer question.

Does this description in the DRV8847 spec mean that when working in Independent bridge mode[Mode pin#14 connect a resistor to GND], it is not recommended to use the current regulation function? The reason is?

Jason

0 Ryan Kehr over 2 years ago in reply to Jason Ciou

TI__Guru 54675 points

Jason,

If you think about it, independent mode would be used for 4 separate loads. You only have 2 sense resistors on the device. How would you regulate current with only 2 sense resistors and 4 loads? You would need a separate sense resistor for each load.

Regards,

Ryan

Motor drivers

Motor drivers forum

DRV8847: Datasheet question asking