9.2.1.2.4 Design consideration of low-side gate drive (IDRIVE, GLx, SLx)
The VGLS linear regulator of low-side gate driver is biased with respect to AGND. Since the external FET is referenced to bridge ground, any difference between the two grounds may cause the effective gate-source voltage on the low-side MOSFET to increase during high current switching events.
Steps can be taken during the design stage to reduce the severity of this effect
- Avoid excessively fast switching transients in the bridge ( <100ns slew rates on the phase node)
- Ensure low inductance between SLx pin to MOSFET ground
- Ensure low inductance in the path from GLx pin to MOSFET Gate . As a guidance, the below relationships Equation 11 may be used to estimate the highest VGSL expected. The 1V term in the equation is required for additional margin.
Equation 11.
where
- VGSL_SWITCHING is the effective gate-source voltage on the low-side MOSFET
- VGSL is the low-side gate drive voltage with no output load of GLx
- IDRIVEP is the peak source gate current
- Qg is the total gate charge of MOSFET
- Lgate is the parasitic inductance in the path from GLx pin to MOSFET gate