N Channel High Side Switch and Driver

Discussion in 'The Projects Forum' started by Awstriker, Nov 24, 2009.

  1. Awstriker

    Thread Starter New Member

    Nov 24, 2009
    Hi Guys,

    I have a circuit set up using an N channel Mosfet (VNP10N07) as a high side switch. I'm trying to drive it with an LT1910 protected high side mosfet driver. (Circuit as the LT1910 typical application spec sheet diagram).

    When I directly drive the N channel gate with Vg>Vdd+Vth the intelligent mosfet works correctly. However when I try to use the driver to drive the mosfet, the voltage across the load is Vdd - Vth (I think, it's about 3V lower than Vdd).

    I know the mosfet needs current to drive its internals and it sources this from the gate input. From the data sheet I believe this is typically 0.25 mA and the LT1910 again from the data sheet can provide 40mA on its output gate pin. Measuring in both with the driver and without I get 0.13mA and 0.19mA respectively.

    So to summarise I do get Vds when the mosfet is switched just 3V lower than supply.

    Any Ideas?:confused:
  2. mik3

    Senior Member

    Feb 4, 2008
    The worst case in put current of the MOSFET is 0.5 mA. A gate driver is not supposed to supply a continuous current to the gate but a current pulse as to charge the gate. That is the voltage across the gate drops after the initial charge and the MOSFET turns off (partially).
  3. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    What supply voltage and load current are you working with, and what value are you using for the current sense resistor?