USBpwrME

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Test jig working
KS-Elektronikdesign • 04/16/2026 at 11:39 • 0 comments

Since i'll be manufacturing a bigger batch of the USBpwrME all units needs to be tested before sent out to customers. Of course I built a test jig that tests all functions with as little interactions as possible. Making a test jig is actually more complicated than one might first imagine. Connecting the DUT with banana connectors to input power and then connecting the USB connectors for readout and manipulation of the DUT gives some challenges both with creating a hardware that work in parallel with the DUT but also writing firmware to cover all test scenarios.

Thera are 2 "major" mistakes i did when designing the test jig. The first one and was easy to fix. I use three relays for switching things on the USB connectors. But when implementing the firmware i could not get the relays to switch. Looking at the schematic i noticed in the symbol that the coil is actually polarized for this specific relay. Doublechecked the datasheet and yes, i needed to modify the board and swap +-. Easy fix that could have been avoided.

The second issue is hard to predict and cannot be fixed in good way more than with the implemented test sequences.

On the USBpwrME there is a wrong polarity input protection that i test by inverting the input power thru a relay and check that it shuts of. What i did not predict that the GND of the DUT is connected to the GND of the test jig not only by the input to the DUT but also by the GND shield och the USB connectors. So when i invert the input power to the DUT i actually short-circuit the power of the test jig du to the USB connection. This can be solved in hardware but i added a step in the test sequence to not connect the USB cables until this test is performed. It adds some testing time but it works!
Following test sequence is implemented in Firmware. The green boxes are automated test steps while the purple boxes are action required by tester. After a failed test each ADC value presented on the display and the E..x error code to make it easier to trouble shoot.
Test jig designed.
KS-Elektronikdesign • 03/20/2026 at 15:44 • 0 comments

Since i'm planning to build a bigger batch of USBpwrMe i actually need to test each unit in a fast and repeatable way. Therefore i have designed a test jigg that will measure all functions.

Following steps will be performed

1 It will measure the current consumption of the board to see if there is excessive power consumption

2 It will change polarity on the DUT and measure if there is any voltage on the output.

3 It will will apply resistors on the D+ and D- lines och the USB-A connector and measure so that expected voltage appears.

4 It will apply resistors on the CC1 and CC2 line for the USB-C connector. Vbus1, Vbus2, CC1 and CC2 are measured. If negotiation is correct it will enable Vbus.

5 It will change input voltage from 5V to 6V and test so that the OVP protection works.

6 Finally it will test the OVP mode switch by telling user to turn of OVP. And measures that Vbus goes on.

The test will hopefuuly test a unit under 5s. It will have a PIC MCU and display for clear testinstruction and results

The Gerber files are already sent to manufacturer and ar in production. Now you might wonder why a choose a to small borad that won't fit the display. Well at first i did. And when i uploaded the gerbers files it was aorund 40Usd to get it manufactured and shipped. By reducing the height of the board with 3cm the cost was 12Usd. Since it's only a testjigg and will be built into a casing i rather save some money

The PCB has 4 layer stackup. Not reallt needed but it's much easier to route the signals and takes less time. The schematic and routing tok around 5hours.

Below you can se the different layers.

TOP Layer

INNER 1 Layer

INNER 2 Layer

BOTTOM
TUSB319Q1 negotiation chip
KS-Elektronikdesign • 03/17/2026 at 17:39 • 0 comments

The TUSB319 chip handles the USB-C negotiation and it works fine. I verified all functions and voltages on pins with a attached and detached device. All pins work as they should but there is a pin that named DIR and is pulled up to 5V. As far as i understand it's a pin that shows the orientation of the inserted usb connector. It should change when inserting the connector. But for me it's always 5V. I have so far not figured out why. I'm not sure either what this pin is actually for more than as to be monitored by a external MCU or something.

I found a block diagram on TI homepage which i used for comparison.

Need to look more into it.
Bad soldering
KS-Elektronikdesign • 03/17/2026 at 14:03 • 0 comments
Manufacturing test batch
KS-Elektronikdesign • 03/17/2026 at 14:02 • 0 comments

So i decided to try to manufacture a test batch of 10pcs at a factory to see if there are any issues with the layout. I expected some issues with soldering of the small chip U2. And yes there were some boards where this component is not correctly soldered.
What really surprised me was that 2 boards came with destroyed components and pcb, really disappointed and i'm in contact with the factory to get an answer on what happened. Not really hoping to much.
I'm planing to do some crowdfunding on this project and and the campaign is in pre launch stage so i guess there is time to improve production!
Heat tests
KS-Elektronikdesign • 03/17/2026 at 13:55 • 0 comments

It was really hard to load the board in good way to be able to draw 6A. Connection gets easy warm and contact resistance makes a big impact on measurements.
Well anyway i did many tests to make sure that the board and components are within specification regarding max temperature. All in all there are god margins.
layout
KS-Elektronikdesign • 03/17/2026 at 13:49 • 0 comments

I have done a lot tests en verified the functions. most of the design work as intended. I also designed the layout to decrease the current path resistance as much as possible and managed to make a 2 layer board and it worked perfect. Then i decided that the orange OVP warning LED is really handy so i was forced to go up to 4 layer board to make that work :)
The schematic and some details.
KS-Elektronikdesign • 03/17/2026 at 13:44 • 0 comments

The schematic is fairly simple and i really wanted to avoid to use a MCU to make it easy if i decided to make some kind of product of it.
Ill try to go thru the block of the schematic and try to explain on how it works.. in i higher level.
"Input block"
The input block is really simple and is basically made up by Q1 which is used for reverse polarity protection and a LDO with 5V output to power the internal circuits on the boards.
"OVP block"
A simple low cost OP connected as comparator that enables the load switch Q8 to supply the USB-A and USB-C Vbus. This is if the input voltage is below 5.6-5.7V. When above there will be no output voltage to protect the DUT.
The switch S1 will ground the input of the comparator and forcing the output to enable the load switch. This disables the OVP and pass thru voltage.
Vbus for USB-C is not on by default and is controlled by U2. Therefore to also force Vbus high the switch also controls Q2 regardless what is negotiated on Vbus C.
When OVP is disabled the orange LED D8 is turned ON to notify user that OVP is not active!
"USB-A negotiation"
Vbus for USB-A is always enabled according to the standard and the U4 IC basically tells the DUT that the maximum allowed charging current is 2A (10W)
"USB-C negotiation"
By default the Vbus for USB-C is disabled and is only enabled when a successful negotiation is performed with the DUT. This is entirely handled by U2 which also can allow up to 3A charging current (15W).
A real attempt
KS-Elektronikdesign • 03/17/2026 at 13:18 • 0 comments

So going forward i decided to think thru what i want to achieve and how to do.

I decided on following requirements.

-Input voltage 3-20V

-Current capability 6A total

-OVP, over voltage protection

-Wrong polarity protection

-Charging negotiation at 5V

-OVP protection manually controlled if needed.

-Fit most power supplies in terms of binding post distance.