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Hello,
I need a negative rail to supply some TMUX6221 analog switches. On the input side I have +24V available which then goes through a TPS54202H DC-DC converter to get +5V. To generate the -17V I'm using the +5V input.
Since I'm already using the TPS54202H in the design for the 24V->5V conversion I thought it would be easiest to use this for +5V -> -17V. Can you please review the attached schematic? I'm also using the same 4.7uH, 35mOhm 4.2A inductor as the other design. Probably overkill but makes procurement easier.
Feedback voltage calculations:
Vout = Vref * ((Rtop / Rbot) + 1)
Use 100k for Rtop
Vref = 0.596V
Vout/Vref = (Rtop/Rbot) +1
(Vout/Vref) - 1 = (Rtop/Rbot)
(Rbot)((Vout/Vref) - 1) = Rtop
Rbot = (Rtop) / ((Vout/Vref) - 1)
Rbot = 100k / 29.2
Rbot = 3.42k for 18V
Testing: 18V in = 0.5952Vfb (good)
Or Rbot = 3.633k for 17V
Thanks; I rarely do negative supplies so I probably made some dumb mistake somewhere.
Thanks - this is great. Power Designer shows EN pin connected directly to Vin, but you're right - the datasheet says 7V max on EN. Bug in Webench?
