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DRV8873: Software Device Block Diagram, pins 'DISABLE' & 'nFAULT'

Edan Cass
Prodigy 160 points
Part Number: DRV8873

Hello TI forum, 

I have two questions regard the DRV8873.

1. 'DISABLE' pin

In the data sheet it's written the DRV8873 supports 1.8-V, 3.3-V, 5-V logic inputs.

I want to connect the 'DISABLE' pin to a microcontroller which works with 3.3V power, but I can see internally the 'DISABLE' pin connected to a pull up resistor connected to DVDD.

Regard the DVDD you say this pin is the 5-V internal digital-supply regulator.

How do the two things work together? I mean how can I connect a component that works at 3.3V voltage that you claim the DVR supports, and the internal pin is connected to 5V voltage (DVDD)? If there are collisions it will be problematic. What voltage do I see in the DISABLE pin when it is not connected to anything?

2. 'nFAULT' pin

In the data sheet it's written: 

A VCC supply-voltage pullup is required for the open-drain output nFAULT.

The nFAULT pin has an open-drain output and should be pulled up to a 5-V or 3.3-V supply.

For a 3.3-V pullup the nFAULT pin can be tied to the DVDD pin with a resistor.

I didn't understand how can it be that if I want to use 3.3V pullup for the nFAULT you claim I can tie it to the 'DVDD' if you write about the 'DVDD' that is 5V?

What is correct regard the 'DVDD'; is it only 5V or can be also 3.3V?

Thank you,

Edan

  • 0
    TI__Guru 56650 points

    Edan,

    1. If an input signal can set the DISABLE pin voltage lower than 0.8V, DISABLE pin is logic low.

    If the external pull-up source is 3.3V, it is higher than the input logic-high voltage threshold, it can disable the bridge. Just a 100kOhm is between the internal DVDD and external pull-up source. Since both DVDD and 3.3V are higher than 1.6V, the DISABLE pin is logic-high when the input source is added to DISABLE pin.

    2. You are right. It should be "For a 3.3-V pullup, the nFAULT pin can be tied to an external 3.3V supply with a resistor (see the Application and Implementation section). For a 5-V pullup, the nFAULT pin can be tied to the DVDD pin."

    DVDD should be 5V.