AUIRB24427S_15 Datasheet, PDF (16/20 Pages) International Rectifier – Matched propagation delay for both channels

AUIRB24427S
7. Bypass capacitor
The bypass capacitor stores an electrical charge that is released to the power line whenever a transient voltage
spike occurs. It provides a low-impedance supply source and it minimizes the noise generated by the switching
of the outputs.
It is recommended to place the bypass capacitor as close as possible to the gate driver in order to improve its
effectiveness by reducing the effect of parasitic inductance of PCB lines.
The value of bypass capacitor is related to:
a- the current that the gate driver has to provide to the OUTA/B loads during turn-on switching condition;
b- the speed at which the output pin is driven;
c- the maximum allowed drop on power supply pins.
For instance, if it considered that outputs OUTA and OUTB provide 6A source current with 20ns rise time and the
maximum wished drop on VCC pin is 0.1V, then the bypass capacitance can be calculated as:
C  n * I ^T  2 *6A ^20ns  2.4F
(1)
V
0.1V
Where n is the number of outputs that are switching at the same time. In this case it has been considered that OUTA
and OUTB are driven in phase.
Equation 1 does not contain the information about capacitance ESR that introduces a further drop in the power
supply voltage. As a consequence it is recommended to use low ESR capacitances (e.g. X7R dielectric material).
Additional Details
Figure T1: Input/output Timing Diagram
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Sept 29^nd, 2014