Hi,

I'm having some problems with the power supply on my FRDM-KL25Z. When hooked up to the PC via the OPenSDA USB port there seems to be some problem with the onboard voltage regulators / the power supply circuit. I first noticed the issue when trying to use the onboard RGB-led: the red one is quite bright but the blue and green ones are really dim. When powered by the KL25Z-USB port all leds are as bright as expected.

I measured the voltages on the different pins on the connector

powered by the OpenSDA port:

• VIN: 3.6V
• 5V-USB: 4.0V
• 3.3V: 2.3V

powered by the KL25Z port:

• VIN: 4.5V
• 5V-USB: 4.8V
• 3.3V: 2.9V

I'm on a mac mini 2010 model and also tried a powered USB-Hub, the voltages where a little higher, but not as high as you would expect.

Next thing I tried : another USB-cable, results:

more Volts at the pins with both USB connectors and brighter LEDs. AND:

magic smoke from diode D2 :(

Diode D2 is in the power supply circuit right before the 3.3V voltage regulator protecting it from reverse volatge (I guess).

Next thing I tried was powering the board from an external 8V power supply (+8V on VIN and GND to GND, nothing else connected to the board) witch resulted in diode D1 going up in smoke as well :(

Does anybody has an idea whats going wrong on my board?

Cheers

Max

Your first note indicates there was probably a high current consumption on the board (probably at the 3v3 side) since other USB cables and a self-powered USB-hub did not improve the situation and the 3v3 output was too low. That's probably also the reason why D2 broke.
Were there additional loads connected to the Freedom board?
You could also have checked for shorts or heavy loads at the 3v3 side without applying power to the board. Next, you could have measured the current at the 5V side (especially when the self-powered USB-Hub was used).
Another trick you can use if something seems to go wrong (I often use it) : touch the components, starting with the voltage regulators, just to check how hot they get (burnt my fingers on several occasions but it helps to pinpoint the problem).
Your 8V attempt may have killed the board since it seems D2 and the 3v3 regulator got shorted, so the board got powered with 8V, resulting in higher currents and killing D1. If the USB cable was still connected, it's even possible your computer USB port got damaged in the process.


The only way to know if the board is still working :
Disconnect all USB cables from the board.
Without power applied to the board, use a digital multimeter (continuity check) and check if D1, D2 and/or the voltage regulator are shorted. Remove the shorted components. Next, check for shorts on the 3v3 side.

If no shorts are found, carry on with the next step (measure the power supply current with following tests):
Apply 3v3 to the board using a current-limited power supply (limit @50 or 100mA).
Note: OpenSDA is not operational when power is applied to the 3v3 pin.
If you don't have such a power supply, you can also use a power resistor in series with the 3v3 line to limit the max. current, start with a 27ohm resistor. Since the board runs from 1v71 up to 3v6, it should start when the current stays below 55mA (@55mA, the voltage drop over the series resistor will be about 1.5V).
If the current reaches 122mA, the board is probably broken.
It's risky, but you can try lowering the series resistor. Don't go below 12 ohm since the current will rise to 275mA when shorts are present.
The FRDM-KL25Z User's Manual is available at http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=FRDM-KL25Z