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LT1054: LT1054 giving -4.2 V output

Daniel Morley
Prodigy 150 points
Part Number: LT1054

I am trying to invert a 5 V power supply to a -5 V power supply.   The measured voltage across the -5 V is -4.2 volts not 5V as expected.   

BOM Is

C10 TAP106K016SCS

C13 870055675009

C11 TVA1301-E3

Is there an error in what I am doing?

  • 0
    TI__Guru* 76525 points
    Hi Daniel,

    Thank you for your interests in LT1054. Please note that (copy and paste from the datasheet p. 9): LT1054 is a "negative voltage generator" or negative charge pump" that will output a negative voltage that is proportional to the input voltage (or VCC). With proper supply voltage, VOUT will regulate to an unregulated VOUT that is approximately –VCC (reduced by a small voltage loss). If a lower absolute voltage is desired, VOUT can be
    regulated to that value when proper feedback resistors are applied.

    In your case, the 0.8V seems to be the internal voltage drop or loss in the switches when charging and discharging the switched capacitor. If you want to create -5V solid from +5V source, you may consider two stage: 1st stage in a doubler to generate about +10V from +5V, then use the FB function on the 2nd stage to generate regulated -5V.

    Thanks,
    Youhao Xi, Applications Engineering
  • 0 in reply to Youhao Xi
    Prodigy 150 points
    Thanks Youhao

    I did find the problem for this one after I made the post. It turns out that the voltage on the input was 4.4 V. The PCB i designed was a rush job and I did not add a power plane to board over a foot. So yes the voltage did drop. Thus the part only gave a -4.4 V. We did add a crude power plane to the circuit and the voltage went up to 4.88 and -4.88 respectively. This is not ideal but with in our tolerance. Thanks for your insightful post.

    Regards