UC2827-1: Push-Pull DRIVE Capability

Vairavan

This is a HUGE MOSFET for a the ±1 A gate drive stage of the UC2827-1. Will it drive it? UC2827-1 UVLO(on) is 9.5V, so let’s say the controller needs 12V to run….12 V is off the chart for the IXFX210N30X3 VGS vs Qg…we are probably talking about 500 nC of gate charge!!!

Q=I x t

tr=tf=Q/I=500nC/1A=500ns

In reality the full 1 A peak is not available (some loss due to delay, inductance, skew, etc) to fully charge/discharge the gate of the MOSFET…I usually use half the peak value for my rise/fall time calculation, which would give:

 tr=tf=Q/I=500nC/0.5A=1µs

safe to say the tr, tf is somewhere between these two values and that’s with 0 Ω in series with the gate.

If a MOSFET with much lower gate charge (higher RDS) can’t be chosen and the UC2827-1 must be used, then I recommend the use of an external gate driver between each PWM output and each low-side MOSFET. This is an easy addition because both MOSFETs in a push-pull are GND referenced, so no level shifting required. TI has a huge portfolio of low-side MOSFET drivers.

Regards,

Steve M