LT8336 in shutdown mode

Hello,

the LT8336 ia synchronous Boost regulator, hence it 'features' a DC path from input to output, even when part is in shutdown and even when the catch diode is replaced by a FET. Reason is the parasitic body diode of the synchronous FET.

If this behaviour is undesired you would need a Boost with explicit 'output disconnect' feature (LTC3121, but different VIn, IOUT performance).

2nd option would be the SEPIC topology, which offers a coupling cap and has therefore no DC path from input to output.

Hi Markus,

Shutting down the controller while still under Vin=12V and DC loaded (Iout = 0.5A for example) would damage the controller?

Thanks,

Nir

Hello,

as the body diode of the top-FET would 'see' this 0.5A load current with a certain drop (much higher than normal diodes) power loss in the LT8336 might get large with possible bad consequences for the LT8336. I would not allow this scenario to the application or at least limit the load current during shutdown to smaller (and tested) values.

kind regards

Markus

Hello,

as the body diode of the top-FET would 'see' this 0.5A load current with a certain drop (much higher than normal diodes) power loss in the LT8336 might get large with possible bad consequences for the LT8336. I would not allow this scenario to the application or at least limit the load current during shutdown to smaller (and tested) values.

kind regards

Markus

Hi,

So I guess there is no option but to use a load switch at VIN or VOUT in order to achieve a full shutdown...

Thanks for your reply.

Nir 

Hello Nir,

to avoid this additional work I would recommend to use a DC/DC regulator in a SEPIC topology, this requires a 2nd (or coupled inductor), but features a 'no DC path' between input and output. Hence you have a full shutdown without any additional load switch.

LT8330, LT8362 or LT8365 feature your voltage and current range, low IQ and AEC-Q100 qual.

kind regards

Markus