The optional external gate driver resistors, RGSRC and RGSNK, along with the diode are used to:
- Limit ringing caused by parasitic inductances and capacitances
- Limit ringing caused by high voltage switching dv/dt, high current switching di/dt, and body-diode reverse recovery
- Fine-tune gate drive strength for sourcing and sinking
- Reduce electromagnetic interference (EMI)
The TPSI3052-Q1
has a pullup structure with a P-channel MOSFET with a peak source current of 1.5A.
Therefore, the peak source current can be predicted with:
Equation 7.
where
- RGSRC: external turn-on resistance.
- RDSON_VDRV: TPSI3052-Q1 driver on resistance in high state. See Electrical Characteristics.
- VVDDH: VDDH voltage. Assumed 15.1V in this
example.
- RGFET_INT: external power transistor
internal gate resistance, found in the power transistor data sheet. Assume 0Ω
for this example.
- IO+: peak source current. The minimum
value between 1.5A, the gate driver peak source current, and the calculated
value based on the gate drive loop resistance.
For this example, RDSON_VDRV = 2.5Ω,
RGSRC = 10Ω,
and RGFET_INT = 0Ω results in:
Equation 8.
Similarly, the TPSI3052-Q1 has a pulldown structure with an N-channel MOSFET with a peak
sink current of 3.0A. Therefore, assuming RGFET_INT = 0Ω, the peak sink
current can be predicted with:
Equation 9.
where
- RGSRC: external turn-on resistance.
- RGSNK: external turn-off resistance.
- RDSON_VDRV: TPSI3052-Q1 driver on resistance in low state. See Section 5.9.
- VVDDH: VDDH voltage. Assumed 15.1V in this
example.
- VF: diode forward voltage drop.
Assumed 0.7V in this example.
- IO-: peak sink current. The minimum
value between 3.0A, the gate driver peak sink current, and the calculated value
based on the gate drive loop resistance.
For this example, assuming RDSON_VDRV = 1.7Ω, RGSRC = 10Ω, RGSNK =
5.0Ω, and RGFET_INT = 0Ω, results in:
Equation 10.
Importantly, the estimated peak current is also influenced by PCB layout and load capacitance. Parasitic inductance in the gate driver loop can slow down the peak gate drive current and introduce overshoot and undershoot. Therefore, TI strongly recommends to minimize the gate driver loop.