Buck split supply on adp2370

Hi guyz, perhaps it sound kind of silly, but is there any way to generate BOTH negative and positive (+5/-5) volts from a single adp2370? With a boost converter it is quite easy: a couple of extra diodes and capacitors - and voila - a split supply is ready. So can a split power supply be made on a single adp2370?

Thank you, sorry if this question is silly.

  • 0
    •  Super User 
    on Sep 29, 2014 5:28 AM

         Hi Skfir,

         If you only need a few milliamps of current at -5V, you could use a charge-pump arrangement shown below:

    Since the ADP2730's output stage pulls down as well as up, we can model its output as a 600KHz pulse.  With the circuit values shown below, its simulation achieved minus 8 volts with a 2.2 K ohm load. about 4 mA.  You can regulate this down to -5V with a low-power linear regulator, or shunt regulate with a Zener diode.  Diodes D1 and D2 must be Schottkys.

         Another possible method employs a double-winding inductor which acts as a transformer:

         Both of L1's windings enjoy the same magnetic flux, so they see the same AC voltage.  However, the right end of L1's upper winding (the secondary winding) is referenced to ground instead of the positive output.   When the ADP2370's output goes high, L1's secondary goes positive which back-biases D1.   When the ADP2370's SW output goes low, L1 outputs a negative voltage of about the same magnitude to the +5V output voltage.  D1 conducts this to the negative output.  Thus the negative voltage is a diode drop less than the positive output.  The negative output's current comes from the positive output, so more is available here than with the charge-pump method.  I couldn't get this circuit to simulate -- something about a "singular matrix" -- it makes me want to toss my computer out the window like Bob Pease did.

         You'll get better performance with separate, purpose-built plus and minus converters, at the cost of more board space.

         Best regards,