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LT8362: Protect Vin from Reverse Polarity?

Question asked by KIRAMEK on Mar 28, 2018
Latest reply on Apr 2, 2018 by dulcevida

I am designing a SEPIC converter using the LT8362 to output 5V in a 12V automotive application.  The LT8362 was chosen to keep the 5V circuit alive even during cold cranking.  Here is the datasheet:

 

http://cds.linear.com/docs/en/datasheet/8362fa.pdf 

 

Other LT chip datasheets often mention the need for a Schottky diode (or active protection) on Vin to protect against reverse polarity when needed, but the LT8362 datasheet does not specifically mention that at all.  Does that lack of mention in the datasheet mean no reverse polarity protection is needed in LT8362 circuits?  

 

Asking the same question another way, is reverse polarity protection needed for the LT8362 when both Vin & EN/UVLO connect to +12 (car battery) voltage?  (In other words, if GND is accidentally connected to Vin & EN/UVLO, and if +12V is connected accidentally to GND, without any Schottky protection between Vin and Battery Voltage, will reverse polarity fry the LT8362?)

 

The reason I ask is because if no reverse polarity protection is needed, I need not worry about a voltage drop across a Schottky (and I can avoid the expense of an active reverse polarity protection circuit).

 

Last question...

 

The LT8362 datasheet mentions that adding a 100k resistor between the SYNC pin and GND maintains BURST mode operation at light loads but adds SSFM at heavy loads for "reduced EMI."  No caveats are mentioned at all.  Datasheet pages 27 & 28 show 2 circuits that use the 100k resistor, but both are BOOST, not SEPIC circuits.  My question therefore is twofold: (1) What is the disadvantage of using the 100k resistor instead of just tying the SYNC pin to GND? and (2) Will use of the 100k resistor result in any benefits in a SEPIC circuit?

 

Thank you.

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