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DRV8823 Braking capability and SSTB question

Karim Hafez
Prodigy 50 points
Other Parts Discussed in Thread: DRV8823, DRV8830, DRV8840, CD74HC595, DRV8812, DRV8848, DRV8843, DRV8841

Hello,

I am concidering using the DRV8823 in a product which I am designing to drive 4 DC motors.

It seems that the DRV8823 has everything that we are looking for (12V input, current sense speed control, Full H-bridges, SPI enabled to save pins).

However, the product is required to brake when the motors are not being driven. This of course means shorting the motor pins (both sides GND or both sides VCC).

Q1. Does the DRV8823 do such a thing? or will we require external logic / relays to achieve this?

Another question (actually a confirmation) software related,

I would like to pulse SSTB to latch (like the latch in a shift register) the data as an extra security measure but it looks like pulling it low will disable the outputs (according to the data sheet).

Q2. If I want continouous operation, will I be forced to keep SSTB high and just accept that the first 16 bits will be auto latched?

Thank you in advance.

  • 0
    TI__Mastermind 26065 points
    Hi Karim

    Q1. Yes. DRV8823 does not support a brake control in its own logic. Even the decay bit is set to "0", disable the channel will give coast operation.

    Q2. Yes. In datasheet P10 you can find the statement.

    Best regards,
  • 0 in reply to Wilson Zuo
    Prodigy 50 points
    Thank you for the quick reply Wilson

    Do you have a part from TI that you can suggest to replace the DRV8823 to drive DC Motor(s) either 1 motor, 2 motors, or 4 motors?

    Our requirements are:

    1. Serial interace (I2C or SPI).
    2. Input voltage (8v-12v)
    3. Input current per motor (250mA)
    3. brake and coast enabled.
    3. Variable speed controller
    4. Full H-Bridge (forward and reverse).

    I also checked the DRV8830 which is perfect for us except the output voltage is too low.

    Best regards,

    Karim
  • 0 in reply to Wilson Zuo
    Prodigy 50 points
    Hello Wilson,

    I just read the datasheet of the similar DRV8840 where it states that the DECAY pin will decide brake / coast operation when the ENBL pin is Disabled.

    Are these two not built on similar platforms? Is it not possible that this is also the case for DRV8823 as is for DRV8840?
  • 0 in reply to Karim Hafez
    TI__Mastermind 26065 points

    Hi Karim

    The serial interface just keeps most of our candidates out of the door. Could you consider a serial to parallel interface with a normal motor driver, such as CD74HC595?

    So that you will have 8bits for IO control of the driver.

    In this way, DRV8848, DRV8840 can be used. (Note some of the devices will not brake when disable@decay=slow, such as DRV8823, DRV8812/8813. Some of the devices will do the braking when disable with slow decay setting, such as 8840)

    Best regards,

  • 0 in reply to Wilson Zuo
    Prodigy 50 points

    Hello Wilson,

    Looking at parallel interfaces i came across the DRV8840 which seems to be identical to the DRV8823 (except the fact that the DRV8823 contains four H-Bridges and a serial to parallel logic block).

    The DRV8840 claims that the DECAY pin controls the status of the motor (Brake/Coast) when the ENBL pin is low.

    Is the DRV8823 not build on the same platform as the DRV8840? Will I not be able to brake the motors by setting the xENBL in the DRV8823 to 0 while xDECAY to 1?

    I have considered serial to parallel interface through the use of an I2C enabled I/O expander. However, as you can understand, from a design complexity , troubleshooting, and cost point of view it is better to have everything integrated in one package.

  • 0 in reply to Karim Hafez
    TI__Mastermind 26065 points
    Hi Karim

    I had checked on bench that DRV8823 cann't brake with xENBL -> 0 @decay 0 or 1. DRV8840 is known able to brake the motor with SLOW decay setting.

    It is a pity that right now we don't have a perfect solution to meet all your requirements together.

    Best regards,
  • 0 in reply to Wilson Zuo
    Prodigy 50 points

    Hello Wilson,

    I think that it would be best to drive my application using the DRV8843 from a cost perspective. I actually want the DRV8841 since I have no use for external PWM but it seems that it is not available on Farnell.

    Anyways, is it possible for you to confirm that the DRV8843 can brake the two DC motors just like the DRV8840 can brake a single DC motor? If not then I guess I have no choice but to use DRV8840.

    Thank you!