4 Power Supply and Monitor

Power supply, Power Monitor.

4.1 Power Supply

Important: The Explorer powers the CNANO at 3.3V, and all the pins connected to the CNANO socket are designed for use with 3.3V I/O pins.

The Explorer’s power supply features:

Dedicated 3.3V regulator to power the CNANO and 3.3V peripherals
- The CNANO’s target regulator is disabled while connected to the Explorer
5V peripherals powered directly by USB voltage
A power multiplexer allows power supplied from the on-board USB-C® connector or the CNANO
A current limiting switch with a soft start to protect the board, the current limit set at 2A
On-board power monitoring for voltage and current measurement with four channels

Table 4-1. Power Domain Specifications
Power Domain	Vnom	Vmin - Vmax	Imax
P5V0	5.0V	4.4–5.5V	2.0A
P3V3	3.30V	3.22–3.38V	1.2A
CNANO P3V3	3.30V	3.22–3.38V	1.2A
BRIDGE P3V3	3.30V	3.23–3.37V	150 mA

4.1.1 Power Sources

The two main power sources are:

The USB connector on the CNANO
The USB-C® connector on the Explorer

Current limitations:

The CNANO’s VBUS output has a current limitation of 500 mA
The Explorer’s USB-C® connector can sink different amounts of current based on the USB source (up to 3.0A from a USB-C® source)
Both USB inputs are fed into a power multiplexer, with output current limited to 2.0A

Info: If both USB connectors are powered, the current is sourced through the Explorer's USB-C® connector.

4.1.2 Power Domains


There are four main power domains on the Explorer: P5V0 P3V3 CNANO P3V3 BRIDGE P3V3

CNANO P3V3 is powered by the same regulator as P3V3, separated for dedicated power measurement of the CNANO. It powers the CNANO’s external power input. Refer to CNANO Power Configuration for more information.

Table 4-2. Peripherals Connected to the Different Power Domains
Power Domain	Power Measurement Channel	Peripheral
CNANO P3V3	CH1 (uA), CH4 (mA)	Connected CNANO
P3V3	CH2 (mA)	Touch controller
		I/O expander 2 + button LEDs
		I/O expander 1 + LED row
		I²C EEPROM
		Secure Element
		Proximity and ambient light sensor (digital circuitry)
		Temperature sensor
		OLED display
		SPI EEPROM
		DAC
		Voltage reference
		Microphone circuit
		Speaker circuit
		Potentiometer
		mikroBUS™ socket (3.3V pin)
		MicroSD card socket
		Grove and Qwiic®connector
P5V0	CH3 (mA)	RGB LED
		Digital addressable LEDs
		Servomotor circuit
		Proximity and ambient light sensor (internal LED)
		mikroBUS™ socket (5V pin)
BRIDGE P3V3	-	Power monitor circuit
BRIDGE P3V3	-	USB bridge circuit

4.1.3 Current Limiting Switch

A MIC2008 current limiting switch with an adjustable slew rate is mounted on the board to prevent large inrush currents. The switch has been configured with a current limit of 2.0A by selecting resistor R500 to be 120Ω.

Info: MIC2008 current limit range: 0.2–2.0A. See the MIC2008 data sheet for more information

4.1.4 CNANO Power Configuration

The Explorer supplies the CNANO with a fixed 3.3V. When connected to the Explorer, the on-board regulator of the CNANO is disabled by pulling the VOFF pin low, ensuring no logic level mismatches between the CNANO and the Explorer.

Info: The CNANO's on-board debugger is only powered when the CNANO USB is connected to power.

Important: When connected to the Explorer, the adjustable target voltage feature of the CNANO is disabled.

Figure 4-5. Power Configuration of the Connected CNANO

4.2 Power Monitor

4.2.1 Getting Started with Power Monitor

The on-board PAC1944 quad-channel power monitor circuit allows tracking of the power consumption of peripherals on the Explorer. The measurement data can be accessed through the USB bridge MCP2221A.

To read and visualize power data, download and install the PAC194x/PAC195x Demo Application.

Figure 4-6. PAC194x/PAC195x Demo Application

Open the application and perform the following steps to get started:

Configure the sense resistor value:
1. Channel 1: 51000
2. Channel 2: 75
3. Channel 3: 50
4. Channel 4: 220
Start Acquisition.
Press "Show Plots" to visualize the data.

Important: While using the demo application set the I²C slide switch to the "NC" position, which isolates the PAC1944 and MCP2221A from the rest of the Explorer’s I²C bus.

4.2.2 Power Measurement Channels


The four PAC1944 measurement channels measure three of the four main power domains on the Explorer: P5V0 (CH3) P3V3 (CH2) CNANO P3V3 (CH1 and CH4)

Table 4-3. Measurement Channel Specifications
Default Power Domain	Channel	Current Sense Range	Current Sense Resolution	Sense Resistor
P5V0 (mA)	CH3	≤ 2.00A	30.5 μA	0.050Ω
P3V3 (mA)	CH2	≤ 1.33A	20.3 μA	0.075Ω
CNANO P3V3 (mA)	CH4	≤ 455 mA	6.94 μA	0.220Ω
CNANO P3V3 (μA)	CH1	≤ 1.96 mA	29.9 nA	51.0Ω

Tip: To identify which peripherals are powered by each power domain, see Table 4-2.

Measure CNANO P3V3 Power

CH1 and CH4 measure current to the CNANO P3V3 power domain.

CH1 for µA measurements
CH4 for mA measurements

The user can change which channel is in use by placing or removing the pin jumper on pin header J506.

Important: The sense resistor for CH1 is 51Ω. Currents above 2 mA will cause a significant voltage drop in the voltage supplied to the attached CNANO.


Figure 4-8. Currents Above 2 mA (CH1 bypassed)	Figure 4-9. Currents Below 2 mA (CH1 connected)

Measure External Power

CH1 and CH3 can be disconnected from their default connections to measure current from external sources.

Warning: Remember to connect the GND from the Explorer to the GND of the external source. Do not apply voltages above 9V to the current measurement channels.


Figure 4-10. Connect External Source to CH1 (µA)	Figure 4-11. Connect External Source to CH3 (mA)

4.2.3 Quad Channel Precision Power Monitor


Feature overview: High-side current monitor with four channels 100 mV full-scale range 0-9V full-scale range 16-bit resolution On-chip accumulation of 30-bit power results from energy measurement The PAC1944 may also be accessed by the microcontroller on the CNANO using the I²C bus.

Important: Set the I²C slide switch to the "MCP2221A" position to connect the PAC1944 and MCP2221A to the rest of the I²C bus on the board.