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DRV8353R: Query on RT/SD pin biasing

Ishan Panchal
Intellectual 640 points
Part Number: DRV8353R
Other Parts Discussed in Thread: DRV8353, LM5008

Hi,

As per absolute maximum ratings in datasheet of DRV8353 the max voltage on RT/SD pin should not be more than 7VDC.

I am planning to use single supply so VM and VDRAIN supply will be same that is from a battery rated 60VDC.

In the EVM schematic RT/SD pin is connected to VM via a 274K resistor. In this case voltage on this pin will be more than 7VDC.

Please explain this connection so that I can move further with the design.

  • 0
    TI__Guru 73235 points

    Hello

    Both the LM5008 and the DRV8353 indicate that the Abs max for that pin is 7V.

    In the case of the LM5008 data sheet it refers to "all other inputs to ground".

    The device uses the current into the RT/SD input to set Ton.  This current is 

    set by the resistor between RT/SD and VIN.

    Since a current is flowing, the voltage on the RT/SD input will be lower than

    VIN.  According to the LM5008 data sheet, this voltage will be between 1.5V and 3V; so it is safe.

    There is a Zener diode on the RT/SD input for protection.  This Zener will breakdown somewhere

    above about 7V and is used for ESD protection.  If the voltage on this pin were to be forced above

    7V, without the required series resistance, then this input could be damaged.

    However, since the series resistance is required for correct operation, there is no danger of damage 

    in a properly designed application.  The series resistance will also limit the current to the Zener during any

    unforeseen catastrophic failure modes.

    Thanks

  • 0 in reply to Frank De Stasi
    Intellectual 640 points

    Hi Frank,

    Thanks for the detailed explanation..!!!

    I understood, now I can move further with the design.

    Thanks,
    IP