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:

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

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 currents 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: The current is drawn from the Explorer’s USB-C input when both USB connectors are powered.

4.1.2 Power Domains

There are four main power domains on the Explorer.

P5V0


This power domain powers the following: RGB LED Digital Addressable LEDs circuit (default power option) Servomotor circuit (default power option) Internal LED on the Proximity and Ambient Light Sensor +5V pin of the mikroBUS™ Socket

The P5V0 power domain is available on the unmounted 1x2 pin header J508.

BRIDGE P3V3

This power domain is independent of the three other domains and powers:

USB Bridge circuit
Power Monitor circuit

P3V3

This power domain powers almost all of the peripherals on the Explorer except the ones listed above. The P3V3 power domain is available from the unmounted 1x2 pin header J512.

CNANO P3V3

Powered by the same regulator as P3V3, separated for dedicated power measurement of the CNANO. It powers the CNANO’s external power input. See 4.1.4 CNANO Power Configuration for more details.

4.1.3 Current Limiting Switch

A MIC2008 current limiting switch with an adjustable slew rate is mounted on the board to ensure a steady slew rate and prevent large inrush currents. The switch has been configured with the following limits using external components on the board:

Slew rate: 2 V/ms
Current limit: 2.0A

Info: MIC2008 current limit range: 0.2–2.0A.

Resistor R500 sets the current limit and capacitor C503 the slew rate. The user may alter the current limit and/or slew rate by changing the mounted resistor/capacitor. See the MIC2008 data sheet for more information on calculating the current limit and slew rate.

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 sense resistor values.
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: Set the I²C slide switch to the "NC" position while using the demo application to isolate the PAC1944 and MCP2221A from the rest of the I²C bus on the board.

4.2.2 Power Measurement Channels


The four PAC1944 measurement channels are set up to measure three main power domains on the Explorer - P5V0 (CH3), P3V3 (CH2), and CNANO P3V3 (CH1 and CH4).

Table 4-2. 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: An overview of which peripherals are connected to which power domain is available in the section 4.1.2 Power Domains.

Measure CNANO P3V3 Power

CH1 and CH4 measure current to the CNANO P3V3 power domain. CH1 is intended for µA measurements, and 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


The PAC1944 may also be accessed by the microcontroller on the CNANO using the I²C bus. 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

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.