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DRV8702-Q1: DRV8702-Q1 SHx Impedance in Sleep

Mattia Bianchi
Prodigy 10 points
Part Number: DRV8702-Q1

Hello,

I have a problem with the DRV8702QRHBRQ1 driver.

When the Gate driver is in sleep mode (pin nsleep to GND) the pins SH1 and SH2 are not at High impedance. The voltage on SHx pins drop to 1V compromising the diagnostic I have on the motor terminals.

The diagnostic is on the right side of the schematic and is made with a voltage divider of 3 resistors.

If i disconnect the SHx pins. The voltage is correct.

Could you help us?

What is the minimum pull down resistor values?

Regards

Mattia

  • 0
    TI__Guru 56650 points

    Mattia,

    It is normal for the voltage on SHx pins drop to 1V in sleep mode. In sleep mode, the high side FETs are turned off and the FET's gate are pulled down which generates a leakage path from SHx to ground through the FET's gate to source clamp circuit.

    So, if we want to detect the sleep mode, we need to detect that 1V instead of the half input voltage.

    Regards,

    Wang

  • 0 in reply to Wang5577
    Prodigy 10 points

    Hello,

    So, you are saying that in sleep the GHx is at ground and the gate driver clamp is pulling down the SHx pin with a diode (MOS) and a parallel resistor of 150kOhm, am I right?

    Why in Table 3 is written that SHx are Hi-Z when in sleep?

    On Figure 37 the GH1 cannot go to GND, where I can find this information in the datasheet?

    What would happen if in sleep mode the Motor is shorted to Vbat? The motor will start to move due to the clamp diode and destroy the driver. It seems strange to me.

    Regards

    Mattia

  • 0 in reply to Mattia Bianchi
    TI__Guru 56650 points

    Hello, Mattia,

    In sleep mode, the GHx was pulled down through an internal series resistor which cannot be damaged with a normal output voltage range.

    SHx Hi-Z means the power FETs are off. if SHx is short to the battery or pull-up by the load, a leakage current flows into SHx pin. The leakage current is limited by the internal circuit pull-down resistor, the device won't be damaged. 

    Figure 37? Do you mean the datasheet Figure 37? I cannot find it?

    Regards,

    Wang

  • 0
    Prodigy 10 points

    Hello,

    Sorry but something is not clear to me. Would be possible to have a short phone call?

    About figure 37, I was using an old datasheet. The figure is the 7-9.

    Do you have any suggestion on how to do the diagnostic of a motor (short to Vbatt, short to gnd and open load) with this driver?

    If I understand well. Between SHx and GHx there is a clamp diode and R(OFF) of 150kOhm. GHx in sleep mode is pulled down by a resistor (which value? I cannot find information on the datasheet).

    I now tried to replace R600 (motor terminal pull up used for the diagnostic), see above picture, with a value of 1KOhm (instead of 27kOhm) and I have now 7.5V on SHx pins. It means I have 4.5mA passing through the SHx pin. What is the maximum current?    

  • 0 in reply to Mattia Bianchi
    TI__Guru 56650 points

    Mattia,

    We can have a phone call when I am back office on next Monday. BTW, I am on vacation with limited network access.

    But, if you have two data points: 7.5V@4.5mA and 1V @ ?mA, I think you are able to calculate out the pull-down resister value: Rpull-down = (7.5V-1V)/(4.5mA-?mA).

    In "short to BAT" case, SHx is same as Vbat.

    In "short to ground" case, SHx is below 0.5V.

    Regards,

    Wang

  • 0 in reply to Wang5577
    Prodigy 10 points

    Hello,

    can we have a call today? I am available all day after 9:30 (CEST). 

    My phone number is 0041 91 935 2522. 

    Let me know....

    Regards

  • 0 in reply to Wang5577
    Prodigy 10 points

    Hello,

    can we have a call today? I am available all day after 9:30 (CEST). 

    My phone number is 0041 91 935 2522. 

    Let me know....

    Regards

  • 0 in reply to Mattia Bianchi
    TI__Guru 56650 points

    Mattia,

    Please send me a private message and we can discuss from there or arrange a phone call from there.

    Regards,

    Wang Li