Powering addressable LED WS2812 5V when system has only 3.3V
Intro
If you're designing modern battery-powered device most likely you use Li-Ion/LiPo rechargeable battery (typically 3.7V nominal voltage) and 3.3V MCU (ESP32, STM32, EFR32, nRF), so to correctly power up it you can use buck-boost converter, as I described in this article:
Enable Save Mode for your Battery Devices with DC-DC Converters | 🧨 Engineering Schematic Solutions
🔺 Issue Description
If you connect addressable RGB LED WS2812 of similar directly to the 3.3V power rail or battery 3.7V you might get unstable working in edge cases and out of specs.
❔ Causing
And if you use addressable LED for indicating something it need at least 3.5V according to the datasheet, so you can't power in directly using common LiPo/Li-Ion batteries (typical range: 3.0V-4.2V):
| WS2812B-B/W | VDD=3.7V-5.3V |
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🔧 Issue Fix
The most obvious solution is to use another boost or buck-boost converter to power up just RGB LED. The only little detail, is that it should be cheap and small as possible, so I'm showing you one of the good solution for it.
✔ Fixed
Now the simplest powering strategy could be like that:
Estimated Price:
| MPN | Value | Price, 10Q | Price, 500Q |
| XT1861B502MR | Boost 900mV~6.5V SOT-23-3L | $0.0557 | $0.0379 |
| CL10A106KP8NNNC | 10u 10V 0603 | $0.0055 | $0.0042 |
| CL10A226MQ8NRNE | 22u 6.3V 0603 | $0.0075 | $0.0066 |
| FHI2012F-100MT01 | 10uH-±20%-100mA-500mΩ 0805 | $0.0109 | $0.0085 |
| TOTAL PRICE: | $0.0796 | $0.0572 |
Conclusions
- Using normal LED with PWM control not always possible or inconvenient for FW side (but definitely cheaper due to lack of boost 5V and level shifter)
- Cheap and small step-up DC-DC converter can save consistency of your designs and FW code
- Due to limit of output current, if maximum LED current is 12mA, so you can connect up to 100/12=8.33=8 RGB LEDs using proposed schematic parts