10 Layout

10.1 Layout Guidelines

Optimum performance of half-bridge gate drivers cannot be achieved without taking due considerations during

circuit board layout. The following points are emphasized:

1. Low-ESR and low-ESL capacitors must be connected close to the IC between GVDD and GND pins and

between BST and SH pins to support high peak currents being drawn from GVDD and BST during the

turn-on of the external MOSFETs.

2. To prevent large voltage transients at the drain of the top MOSFET, a low-ESR electrolytic capacitor and a

good-quality ceramic capacitor must be connected between the MOSFET drain and ground (GND).

3. To avoid large negative transients on the switch node (SH) pin, the parasitic inductances between the source

of the top MOSFET and the drain of the bottom MOSFET (synchronous rectifier) must be minimized.

4. Grounding considerations:

• The first priority in designing grounding connections is to confine the high peak currents that charge and

discharge the MOSFET gates to a minimal physical area. This will decrease the loop inductance and

minimize noise issues on the gate terminals of the MOSFETs. The gate driver must be placed as close as

possible to the MOSFETs.

• The second consideration is the high current path that includes the bootstrap capacitor, the bootstrap

diode, the local ground referenced bypass capacitor, and the low-side MOSFET body diode. The

bootstrap capacitor is recharged on a cycle-by-cycle basis through the bootstrap diode from the ground

referenced GVDD bypass capacitor. The recharging occurs in a short time interval and involves high

peak current. Minimizing this loop length and area on the circuit board is important to ensure reliable

operation.

10.2 Layout Example

CGVDD for high frequency filtering

CGVDD for IC bias requirements

Input RC filters

CBOOT capacitor

Ground plane

GH gate

resistors and

antiparallel

diode

GL gate

resistors and

antiparallel

diode

LM2105

Figure 10-1. Layout Example

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LM2005

SNVSCB6B – FEBRUARY 2023 – REVISED SEPTEMBER 2023

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