How much power should our Raspberry Pi CM3 handheld use?

The recommended PSU is 5.1V, 2.5A, but this can be misleading.Are project may need more or less then the recommended PSU. And we may be able to tune performance and prune features to get lower Amperage.

“USB budget”
For USB you should a port can be up to 500mA. With four ports I get approx 240-250mA of them. Plus the drain of the chip it self that handles USB/Ethernet.
So I will say approx 1.2a is allotted to the USB controller.

“CPU Budget”
The Broadcom BCM2837 A53 4 Core w/ VideoCore IV Graphics on a Chip draws the following under load:
Idle: 240mA
1 Core: 400mA
2 Core: 500mA
3 Core: 610mA
4 Core: 720mA

So we should set our headroom to 720mA for the BCM2837. But Note this does not account for configuration adjustments to performance such as forced turbo-mode on CPU that we used for game performance. The total Amp usage, clock rate of CPU, and clock rate of GPU will need to be tuned.

WiFi has a draw between 40-100mA

The LCD panel draws at 430mA at 5V at max back-lighting. This can technically be reduced to lower consumption slightly. At 430mA it is above the 250mA on the USB port which is why the screen does not get driven by the on board USB.

“SD Card Reader”
3.3v at up to 150mA

The Teensy runs various modes. a low Clock 3.3v mode will use less but requires a 3.3v circuit for it.

Typical Current Operating Condition
Teensy Teensy++ Voltage Clock USB Running Idle Sleep
27.3 mA 60.2 mA 5V 16 MHz On 100% 0% 0%
17.9 mA 37.9 mA 5V 8 MHz On 100% 0% 0%
18.9 mA 31.2 mA 5V 16 MHz Off 100% 0% 0%
11.0 mA 17.2 mA 5V 8 MHz Off 100% 0% 0%
6.6 mA 10.7 mA 5V 8 MHz Off 10% 90% 0%
4.5 mA 6.6 mA 5V 2 MHz Off 100% 0% 0%
0.04 mA 0.04 mA 5V Off Off 0% 0% 100%
15.7 mA 31.3 mA 3.3V 16 MHz On 100% 0% 0%
10.6 mA 19.7 mA 3.3V 8 MHz On 100% 0% 0%
6.6 mA 9.3 mA 3.3V 8 MHz Off 100% 0% 0%
4.0 mA 5.6 mA 3.3V 8 MHz Off 10% 90% 0%
2.9 mA 4.0 mA 3.3V 2 MHz Off 100% 0% 0%
0.23 mA 0.23 mA 3.3V Off Off 0% 0% 100%

I will say we need between 4.0mA-32mA

“Final View”
The first thing we can do to save on power is remove the 1200mA’s of the USB host controller. As we are a portable system we will not install a host controller.
Second the WiFi this is 100mA if we can save the headroom for it, including WiFi will allow side loading and multiplayer gaming. Great plus to the system, but ultimately optional.
Third the Teensy for as a game controller, we will set this to as low as possible, this will only handle the buttons and joystick values being sent to the console. We can run in USB off mode, and hopefully 3.3v 8MHz for only 6.6mA-10mA.

The three big draws will be the BCM2837, LCD, and the SD card reader. These are non optional devices.
The BCM2837 we should expect 720mA. (but could be tuned for more or less based on clock rate and core count at expense of performance)
The LCD will 430mA with brightness at max for outdoor usage.
And the SD card reader will draw upto 150mA.