LTM4612

Hi wataru, 

If your VD cap is shorted then the input supply should be shorted. This isn't expected to cause damage to the LTM4612 if there is a reasonable current limit on the LTM4612 input supply, otherwise if very heavy load is allowed through this short path this may cause damage to the input filter components and module substrate. To consider this failure case it may be a good idea to set a reasonably low input current limit on the LTM4612 input supply (or add a fuse or hotswap on the input path if necessary). 

Thanks. 

Thank you for your reply.

When short-circuited due to failure of the capacitor connected to Vd pin, or when near short-circuited state,
how much current flows to the input?
I am applying a current limit of 5 A to the input part, but will the device be destroyed before reaching this limit value?
Vd pin is behind the input filter circuit, so I think that it will have some impedance even if shorting Vd pin itself.
The current value at that time ,How much is the normal current value?

Hi wataru, 

The current depends on the impedance from GND to Vd to Vin, note the input filter DCR is ~ 10mOhm. 5A should be fine and not destructive to the module but likely you can lower the current limit closer based on your operating conditions. You can estimate normal steady state max input current based on the efficiency curve for the operating conditions where max. input current would be (Vout x Max load current) / ( Vin x Efficiency ) which would likely be lower than 5A. During start-up into a load the inrush current could momentarily be higher, but this peak inrush current can be controlled by the value of a soft-start cap placed at the Track/SS pin. 

Thanks. 

Thank you for your response.

Hi wataru, 

Yes, if VD cap short is of concern it would be recommended that an input current limit appropriate for your full load operating conditions and considering start-up inrush current for your design would help to resolve the concern (ie protect the module from damage due to a VD short to GND). 

Thanks.