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LM5176-Q1: Please check DRV ON/OFF voltage range. (Vgs range)

Minho Kim
Prodigy 40 points
Part Number: LM5176-Q1
Other Parts Discussed in Thread: LM5176

We are currently using the LM5176-Q1

Regarding the DRV voltage driving the FET connected to the LM5176, the spec doesn't seem to clearly state it, so I'm asking for confirmation.

As shown below, it is explained that the low side is operated with VCC and the high side is operated with the voltage of Cboot. (page.18)

If you look at the VCC voltage as shown below, it is shown that the voltage range operates between [ 6.95, 7.88].

If so, does the gate voltage on the low side and high side turn on the FET with a voltage between [6.95, 7.88]?

In addition, please explain where to check the range of the voltage shown on the gate when the FET is off.

In other words, the voltage range that turns on/off the gate of the FET is not clear, so I ask for confirmation.

 

Best regard

Thank you

  • 0
    TI__Guru 58225 points

    Hello Minho,

    As long as the VCC regulator is in regulation, yes, the FETs are turned on with a voltage of roughly 7.35V.

    The low side gate voltage is with reference to GND, the high-side gate is referenced to the switch node.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Prodigy 40 points

    Hi, Brigitte

    I want to know range when on/off. 

    Because I want to check whether the FET is properly turned on/off in the worst case.

    If you know anything about the voltage range applied to the gate during on/off, please let me know.

    Of course, it may be different depending on the circuit configuration,

    so ideally it would be good if you tell me the range of voltage values that the IC creates to turn the gate on and off.

    Best regard

    Thank you

  • 0 in reply to Minho Kim
    TI__Guru 58225 points

    Hello Minho,

    The voltage on the gate outputs is dependent on the VCC voltage. VCC voltage is in regulation from 6.95V to 7.88V.

    If the voltage on VIN or BIAS is not high enough to reach regulation, it can go down to the VCC UVLO, which is worst case 3.11V.

    In addition, you can find the driver resistance on page 8 of the datasheet. So dependent on the current needed by the FET, the voltage on the driver pin will be reduced due to the transistor resistance.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Prodigy 40 points

    HI, Brigtte

    It can be seen that the high level gate voltage has a minimum value of 6.95.

    If so, what is the max of the low level gate voltage?

    Of course, it is 0V in the low state, but is there no data that specifies how many volts the typcal is max?

    ref) The DRV3220 we used before provided the maximum voltage(0.2V) when the gate-source low state.

  • 0 in reply to Minho Kim
    TI__Guru 58225 points

    Hello Minho,

    In the LM5176 you can find the information of the driver on-resistance. As the voltage drop is dependent on the current needed by the external MOSFET, you can calculate the low level voltage by multiplying the current with the resistance.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Prodigy 40 points

    Hi, Brigtte

    What you are talking about  seems to be the low level of the On state.
    
Assuming that the LM5176 is operating in boost mode, HDRV2 and LDRV2 will be switched on/off.
When HDRV/LDRV is on, it is specified in the spec that the gate voltage of the FET has a range of [6.95, 7.88V].

When HDRV/LDVR is off, I am curious about the range of how much gate voltage is supplied to the FET.

For example, please check if there is a typical range like this [0, 0.2V].
  • +1 in reply to Minho Kim
    TI__Guru 58225 points

    Hello Minho,

    The device is pulling to GND when the switch shall be off. So when there is no current it is 0V. If some  current flows, it can be calculated with the on resistance of the driver FET.

    There is not more specification for this parameter.

    Best regards, 

    Brigitte