RT9080-33
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Low-quiescent 3.3 V supply for running ESP32 and other 3.3 V logic from a single 18650 Li-ion cell. Built around the Richtek RT9080-33 fixed 3.3 V LDO: 600 mA output, ~2 µA quiescent current, ~310 mV dropout at full load, 1.2–5.5 V input. The low quiescent current makes it well suited to deep-sleep IoT nodes.
The cell's 4.2–3.0 V range feeds the regulator through a power switch. Output is regulated 3.3 V down to a cell voltage of about 3.6 V at full load, then tracks the cell minus dropout. A 470 µF reservoir capacitor on the output carries ESP32 Wi-Fi transmit bursts (300–500 mA peaks) without brownout. Output is a 2-pin header: +3V3 and GND.
Use a protected 18650 cell or feed the module from a charger/protection board's OUT+/OUT-. The regulator does not protect the cell from overdischarge.
RT9080-33 Schematic
BT1 (18650 cell) positive to SW1 (SPST power switch). SW1 output is the VIN net. BT1 negative to GND.
U1 RT9080-33GJ5 (TSOT-23-5):
- Pin 1 VIN: VIN net
- Pin 2 GND: GND
- Pin 3 EN: tied to VIN (always enabled; must not float)
- Pin 4 NC: not connected
- Pin 5 VOUT: +3V3 net
C1 1 µF ceramic (X5R/X7R): VIN to GND, input bypass. C2 1 µF ceramic (X5R/X7R, 0603+, ≥10 V): +3V3 to GND, required for LDO stability. C3 10 µF ceramic: +3V3 to GND, transient response. C4 470 µF low-ESR electrolytic or polymer: +3V3 to GND, bulk reservoir for load bursts (observe polarity).
J1 output header: pin 1 +3V3, pin 2 GND.
RT9080-33 Parts List
How to Build the RT9080-33
18650 holder along one edge with SW1 inline on the positive lead. U1 on an SOT-23 adapter or pads in the middle of the board.
C1 directly across U1 pins 1 and 2, and C2 directly across pins 5 and 2, with the shortest possible leads. These two placements matter most for stability.
C3 and C4 between U1 and J1, with C4 next to the output header so the reservoir sits close to the load. J1 at the opposite edge from the cell.
Run a short, wide common ground connecting BT1-, U1 pin 2, all capacitor grounds, and J1 pin 2. Keep the VIN-to-VOUT path short.
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