BQ25710EVM-017: Low side gate drivers load

Alex Tikhonov

Part Number: BQ25710EVM-017
Other Parts Discussed in Thread: PMP40441, CSD17551Q3A

Hi. Can you please explain the purpose of additional 150 pF capacitors (C19 and C20) at the gates of low side MOSFETs? I don`t see anything about it in datasheet and related documents.. In another schematic (PMP40441) there are only one additional circuit at the gate of low side buck transistor and rc-snubbers. In first case it seems to slow down turn on/off MOSFETs (total gate charge in spec is 6nC plus additional gs capacitance),in second vice versa(total gate charge in spec is 3.9nC plus additional charge/discharge current pump). Thanks!

over 4 years ago

0 Tiger Zhou over 4 years ago

TI__Mastermind 28275 points

Hi, Alex,

C19 and C20 are sized to increase the effective Cgs in comparison to the Cgd of Q2. This helps prevent the Miller capacitance from driving the MOSFET gate during a high dV/dt event. This is more important when Qgs and Qgd of Q2 are similar in magnitude.

0 Alex Tikhonov over 4 years ago in reply to Tiger Zhou

Prodigy 60 points

Hello Tiger! Many thanks! Can you suggest any related documentation or guide for that issue? As i know Cgs always bigger than Cgd. In related CSD17551Q3A datasheet curve the highest value for Cgd is about 150pF and Ciss is 1 nF at the same time. I tryed to simulate situation with high voltage impulse in spice with IDP090N03L model (Cgs=1.16n, Cgdmax=0.28n) and didnt see any changes with additional capacitor. Maybe i do something wrong with that?

0 Tiger Zhou over 4 years ago in reply to Alex Tikhonov

TI__Mastermind 28275 points

Your approach is very good, systematic. They are optional placeholder capacitors.

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BQ25710EVM-017: Low side gate drivers load