LT8336 in shutdown mode

Question

We are trying to use the EN input of LT8336 to turn off output voltage, but we still see 12.2V out with 12.6V input voltage and EN/UVLO 0V. Is this expected behavior or is there something wrong with our design/board?

MarkusHP · Accepted Answer

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.)

MarkusHP · Answer

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

MarkusHP · Answer

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

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LT8336 in shutdown mode