The Nordic Thingy:53™ uses the nPM1100 Power Management Integrated Circuit (PMIC) (U3) for power management and battery charging.
The nPM1100 PMIC has two voltage domain outputs:
- Unregulated VSYS output (3.2–4.2 V)
- VOUTB output (3.0 V)
The unregulated VSYS output is used to supply the external 3V3 regulator and the buzzer (BZ1). The 3V3 regulator supplies the RGB LED (LD1) and any external boards connected to the expansion board connector (P1).
The VOUTB domain is configured to 3.0 V and used to supply the nRF5340 System on Chip (SoC), the nRF21540 RF FEM, and all the sensors. The VOUTB output is configured to 3.0 V by connecting VOUTBSET0 and VOUTBSET1 to the DEC pin (A3) (see Output voltage selection (VOUTBSET0, VOUTBSET1) in nPM1100 Product Specification).
The following schematic describes the nPM1100 PMIC.
The current limit of the nPM1100 PMIC's battery charger is set to 400 mA, but the actual charging current depends on the VBUS current limit. The nPM1100 PMIC detects automatically if it is connected to a Standard Downstream Port (SDP), Dedicated Charging Port (DCP), or Charging Downstream Port (CDP) Universal Serial Bus (USB) port and sets the VBUS current limit according to the USB port type.
The following table describes the VBUS current limits for the different USB port types.
| USB port type | VBUS current limit |
|---|---|
| SDP | 100 mA |
| DCP | 500 mA |
| CDP |
The nRF5340 SoC can negotiate a 500 mA limit with the USB host if the USB host supports this. If the 500 mA limit is negotiated, the nRF5340 SoC can set the ISET pin on the nPM1100 PMIC high to set the VBUS current limit to 500 mA.
The nPM1100 PMIC has a charging indication pin CHG and charging error indication pin ERR that signal the charger status to the nRF5340 SoC. The CHG pin is connected to General-Purpose Input/Output (GPIO) P1.00, and the ERR pin is connected to GPIO P1.01. P1.00 and P1.01 have pull-ups enabled. When the nPM1100 PMIC is charging the battery, the CHG pin is pulled low. When a charging error occurs, the ERR pin is pulled low.
The buck regulator on the nPM1100 PMIC can operate in two modes: in hysteretic mode for low load currents and in Pulse Width Modulation (PWM) mode for high load currents. The nPM1100 PMIC switches automatically between the two modes based on the load. For the load threshold values, see nPM1100 Product Specification.
In some cases, such as in high-accuracy ADC measurement, it can be beneficial to force the nPM1100 PMIC to operate in PWM mode. This is done by pulling the MODE pin on the nPM1100 PMIC high by using the TRACEDATA3 (P0.08) pin that is routed to the current measurement and debug interface connector (P9). The nPM1100 PMIC MODE pin is connected to P0.08 and pulled to ground through R7.
The following schematic describes the nPM1100 PMIC status and control.
On Thingy:53 v1.1.0 and higher, the nPM1100 ERR and CHG pins connected to P1.01 and P1.00 are also connected to the P9 connector through the signal switching circuit for nRF7002 EB when inserting the nRF7002 EB to the P9 connector. If the nRF7002 EB is used with the COEX interface while the battery is being charged, it is recommended to cut solder bridges SB10 and SB11.