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LMZ14202: Enable Input used for Low Voltage output protect

Part Number: LMZ14202

We are performing a Failure Modes and Effects Analysis on a circuit for a device General Electric Transportation sells that performs remote control of locomotives and the device in question is the LMZ14202.  The datasheet covers output overvoltage protection. Okay, good for the failure mode of “output voltage drifts high” we have that failure mode covered.

The other failure mode of concern is “output voltage drifts low”.  Here is the text description text of the under voltage protection in the circuit design.

“EN signal generated from PWR signal or the microcontroller binary output UC_PWR.  Battery is rated for 9V to 12.6V. Assuming the battery is brand new and is 12.6V, the voltage divider will have 2.67V for EN.  This is at powerup time.  This enables U8 to generate 3.3V the microcontroller uses.  Once the microcontroller is powered up, it sends output UC_PWR which is a 3.3V signal.  From here on, U8 is using this signal for under voltage protection.” 


I pasted below some screen captures of parts of the schematic that pertain to this description

This does not quite make sense, because while true if the microcontroller drops UC_PWR, the voltage on EN will drop from 3.3 to 2.67, which does not meet the 1.09 V falling threshold per section in the datasheet.  
So, my question is, will this scheme work for under voltage protect on the VOut from the LMZ14202 device?

Thanks and Best Regards,


Tom Woodbridge

GE Transportation

Digital Solutions – Train Performance

Senior Product System Safety Engineer

T: 321-435-7759



1990 W. NASA Blvd.

Melbourne, FL 32904 USA

General Electric Company