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LMZ34002: Support for -28V

Part Number: LMZ34002
Other Parts Discussed in Thread: LM5168, LM5169


I have an application that needs -28V supply to set the gate bias for a GaN switch.  The application will consume next-to-nothing in current.

Is it possible to extend LMZ34002 to operate as a +12V to -28V converter?  The datasheet front page reports that -17V is the max (or do you call that the min :)) but I do not specifically see anything in the datasheet that would limit this.  Section 12.1 outlines the procedure to set the negative voltage.  It seems like I could increase the Rset resistor to get to a higher negative voltage.  Granted the current capability will drop per figure 33, but I would only need micro-amps.  The absolute max ratings in the datasheet are a little cryptic with regard to Vout and an application with a negative output voltage; however, a total potential of 12 - (-24) = 36V seems to be less than the absolute max of 45V.

If this part is not appropriate, does TI have a different solution that is small and inexpensive?


  • Hello Russell, 

    Since the inductor value inside the module is fixed, the wider output voltage may be an issue for the internal slope compensation. 

    I would recommend using the LM5168 or LM5169 IC in an inverting configuration. Here is an example schematic:

    If you need some help with the component values we can assist you with those.