Adjustable Inverting Buck-Boost (IBB) through current source/sink DAC

[t8y6lp64]

I am trying to design a circuit with an adjustable Inverting Buck-Boost (IBB) using the LM43601. The IBB takes +5 V as input and can produce any voltage in-between -5 V and -24 V. The output voltage should be adjustable through a sink/source current DAC, namely the DS4432. Now the question arises if this is possible, and if so, how should the level shifting look like for the signal between DAC and the FB pin of the IBB?

For reference, I have attached the schematic of the IBB. The FB_NEG label shows where the current shall get injected from the DAC.

[moffy]

I assume that the DAC is on the +5V to 0V side, as well as its control signal, you could use the DAC to drive a PNP current source where the collector of the PNP transistor feeds into the FB_NEG node, you might want a diode in series with it. The more current it feeds in the less the set output voltage, and set up the resistors R11 and R12 for maximum negative output voltage so that when the current source is off you get maximum negative i.e. -24V.

[t8y6lp64]

Thanks for your answer. This is indeed a viable solution, however doing that I would lose half the resolution of the DAC as I would only use it in source mode, right? To actually use the full range, I would require a bidirectional level shifter, or am I making a mistake here?

[mtwieg]

If you need to preserve the bipolar output, I'd recommend referencing the DS4432 to Vout, and translating the logic signals instead. Should be much more straightforward than translating a bidirectional current source.

[moffy]

Thanks for your answer. This is indeed a viable solution, however doing that I would lose half the resolution of the DAC as I would only use it in source mode, right? To actually use the full range, I would require a bidirectional level shifter, or am I making a mistake here?

All you would need is a standard 8 bit DAC and an opamp and transistor, might be worthwhile.