I have an unusual application where the input voltage can vary from 1-12 V DC. This must be converted to 5 V @ ~200-250 mA.
Since there are no available buck-boost converters suitable for this wide input voltage range, I came up with this (simplified) circuit:
The XC61CC5002MR-G is a voltage CMOS supervisory IC which:
- Outputs VCC when VCC > 5 V – this enables the LDO and protects the
boost converter from the higher voltage.
- Outputs 0 V when VCC < 5 V – this disables the LDO and biases the PMOS transistor to allow current to the boost converter.
The boost converter's absolute maximum voltage rating is 6 V, so it needs to be protected at the higher range of input voltage, whilst the LDO is OK up to 13 V.
The circuit worked as intended from 3-12 V, however the PMOS transistor couldn't switch when the input voltage was lower than 3 V, which shouldn't have surprised me since the VGS threshold was about 2 V at 250 mA.
I have also looked at high-side load switches and over-voltage protection ICs, but I cannot find any that will operate over the whole range of the input voltages after browsing for hours on Mouser and DigiKey.
Lastly I have explored using a N-channel MOSFET in the circuit above with an open-drain output variant of the same supervisory IC and a charge pump to bias the NMOS transistor when voltages are low, but to my surprise I couldn't find any charge pumps that work in the 1-5 V range.
I am looking for any suggestions to either make my circuit work with the lower voltages or how else I can achieve this 1-12 V to 5 V conversion without dramatically increasing the PCB footprint or cost. Unfortunately the input voltage cannot be changed, but the power supply can provide more than enough current to run the circuit.