Tool/software:
Hi Team,
May I know the purpose of adding D8 in the EVM?
It's to clamp the VA during load dump? Although the IC has OVP but maybe we still need to consider the response time(<10us) so we add it just in case.
As for the voltage rating of D8, we should use the voltage rating based on reverse input polarity testing(like -65V during RPP so we choose 75V for D8 in EVM), am I right?
Thank you.
Hi Evan,
LM74930-Q1 can support 200V unsuppressed load transient in common-source topology.
Although the controllers are rated for 70V abs-max but with addition of some supporting components like D1,Rvs,Dz. The controller can be used above its abs-max range.
To minimize the power dissipation across the zener during clamp, a series resistor Rvs is added which limits the current in the path. In any case where charge pump needs to charge, VS requires high current. Startup is a prime example.
As shown in the char graph, when VS is <5V, the Iq is very high, and VS will not get the current it requires due to Rvs. To tackle this, diode is added from VA to VS so that can provide the necessary current.
Diode is active when HGATE is turned-on partially and provides lower impedance path than Rvs and supplies VS.
Diode should be rated higher than Dz.
Regards,
Shiven Dhir
