Nominal Animal
Well-known member
I'm in the process of designing a carrier board for using a Teensy LC/3.1/3.2 to interface to an Odroid HC1 single-board computer. The power source for both is a regulated +5VDC 6A supply, but I want some headroom, so assume it's 8A. They share the ground.
The Teensy is connected to the Odroid HC1 via level shifter to an UART (1.8V Rx/Tx only, no hw handshaking; using Teensy pins 0 and 1 for this).
Teensy is powered from either the +5VDC, or USB if connected to another computer (although normally this should only occur when there is no +5VDC supply).
To also power some OLED displays and such, I'm using a separate 3.3V voltage regulator for the Teensy and its peripherals. I expect the total 3.3V load to be under 500mA.
Thing is, I also want the Teensy to be able to power off the Odroid HC1 (after issuing a software shutdown; it cannot disconnect itself from the power supply, so I want Teensy to do this).
To this end, I've designed the small circuit below. If someone more experienced could sanity-check it, I'd be very grateful.
The +5VDC 8A input is at the top. The controlled +5VDC supply to the Odroid HC1 is on the right.
The pins used on the Teensy are on the left: 3.3V for supplying the regulated power to Teensy, VUSB for obtaining the USB bus voltage if connected to another computer, and pin 2 for controlling the power to the Odroid HC1 (high disables, defaults to enabled).
Any suggestions for the 10µF filter cap? Should I add more filtering?
Should I add a pull-down resistor for pin 2, to ensure it is low at bootup? (I do want the +5VDC to Odroid HC1 to default to enabled.)
The power control block is a P-channel MOSFET (NDP6020P), driven using an NPN transistor (2N3904).
The two 4.7k resistors are just a guess, to limit the current to about 1 mA. Recommendations?
The 1N4001 diode is just for safety, in case of a slightly inductive load.
Two Schottky diodes are used to select between the two input sources (regulated +5VDC in, or VUSB).
I included a 500mA PTC for overcurrent protection. Should I also add a ferrite?
What kind of smoothing capacitor would be best on the 3.3V regulator output? Is additional filtering recommended/needed?
If I get this thing working, the schematics will be in Public Domain at EasyEda.
The Teensy is connected to the Odroid HC1 via level shifter to an UART (1.8V Rx/Tx only, no hw handshaking; using Teensy pins 0 and 1 for this).
Teensy is powered from either the +5VDC, or USB if connected to another computer (although normally this should only occur when there is no +5VDC supply).
To also power some OLED displays and such, I'm using a separate 3.3V voltage regulator for the Teensy and its peripherals. I expect the total 3.3V load to be under 500mA.
Thing is, I also want the Teensy to be able to power off the Odroid HC1 (after issuing a software shutdown; it cannot disconnect itself from the power supply, so I want Teensy to do this).
To this end, I've designed the small circuit below. If someone more experienced could sanity-check it, I'd be very grateful.
The +5VDC 8A input is at the top. The controlled +5VDC supply to the Odroid HC1 is on the right.
The pins used on the Teensy are on the left: 3.3V for supplying the regulated power to Teensy, VUSB for obtaining the USB bus voltage if connected to another computer, and pin 2 for controlling the power to the Odroid HC1 (high disables, defaults to enabled).
Any suggestions for the 10µF filter cap? Should I add more filtering?
Should I add a pull-down resistor for pin 2, to ensure it is low at bootup? (I do want the +5VDC to Odroid HC1 to default to enabled.)
The power control block is a P-channel MOSFET (NDP6020P), driven using an NPN transistor (2N3904).
The two 4.7k resistors are just a guess, to limit the current to about 1 mA. Recommendations?
The 1N4001 diode is just for safety, in case of a slightly inductive load.
Two Schottky diodes are used to select between the two input sources (regulated +5VDC in, or VUSB).
I included a 500mA PTC for overcurrent protection. Should I also add a ferrite?
What kind of smoothing capacitor would be best on the 3.3V regulator output? Is additional filtering recommended/needed?
If I get this thing working, the schematics will be in Public Domain at EasyEda.