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DRV595: Startup voltage in IN+ and IN- pins

Yves Theroux
Prodigy 110 points
Part Number: DRV595

Hi,  (don't know why, put when I enter the part number, AUDIO forum is selected and no possibility to modify it )

we need to generate from 12V a +/-5V @1A output

for we need a small range on the differential input range to perform this

we want to bias IN- to 1.65V  (3.3 / 2)  (resistor network)

and use a 3V3 PWM signal through a RC filter to generate the voltage on IN+

Figure 14 is saying to no use IN+/IN- input until PVCC and AVCC are stable (10ms delay)

Can you be more specific here?  

     1.  provide a NULL differential voltage ?  (what ever is the voltage)

      2. drive both to 0V (to make sure internal LDO is activated)

      3. Let them floating (shall then be NULL diff voltage)

      4. other cases ?

      

in our case, 3V3 will not be present when 12V will appear

so in that case,  IN- and IN+ will be at 0V

If I understand the datasheet, DRV955 will bias these IN pins to 3V0 after power-up

Is there a current limit that could be got from the internal bias circuit ?

Our RC circuit on IN+ will also be biased from the internal bias circuit, again what could be current  level ?

Thanks

  • 0
    TI__Genius 11300 points

    Hi

    thank you for your question.

    let them floating should be ok.

    IN pin will be pulled to 3.0v after power-up.

    The current should be very small and not affect the RC circuit. you can consider it having very high impedance at the input side.

    thanks.

    jess

  • 0 in reply to Jesse Ji
    Prodigy 110 points

    Hi Jesse

    thanks for your feedback

    in our case, it will be difficult to get/make them  (IN pins) floating 

    So is it acceptable to  have both  at 0V at power-up ?

    the way I understand the figure:  Differential signal shall be null at power-up...right ?

    if there is a power glitch, and the differential signal is not null, during this 10ms period 

    what are the potential problems ? (internal circtuit will be back-powered....)

    Can it help if SDZ and HiZ and are driven LOW at power-up?

    Can we get the IC back to normal operation, if the IN signals are both driven to 0V ?

     or

    the AVCC and PVCC supplies shall be turned off and proceed to a nice restart  

    thanks

  • 0 in reply to Yves Theroux
    TI__Genius 11300 points

    Hi Yves

    during power up, IN pins will be biased to 3v. (this is default setting)

    Setting bias as above you request should also be ok.

    about setting IN pins to 0v, if it doesn't affect the bias voltage, it should also be ok. i just worried if setting IN pins 0v, how it can be biased to request voltage.

    i didn't very clear about your setting 0v at power up.

    thanks.

    jesse

  • +1 in reply to Jesse Ji
    Prodigy 110 points

    IN pins are connected to resistor-capacitor network driven by circuit not powered from external DC-DC converter

    (being OFF when the 12V appears). 

    So by default they will be at 0V at power-up.

    so I presume that the internal bias will try to bring them to 3V.

    is it true to say that the important point, is to let these pins being biased by the device?

    shall we have a similar capacitance value on both pins or this is not an issue

    thanks

  • 0 in reply to Yves Theroux
    TI__Genius 11300 points

    Hi Yves

    yes, you are correct. the important point is let these pins can be biased by the device.

    capacitance value on both pins is not a issue.

    thanks.

    jesse