problem with U8A-64-FB96

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ast8346
Active Member
Posts: 39
Joined: Mon Jan 05, 2015 12:58 am

problem with U8A-64-FB96

Post by ast8346 »

Hi
I have a bit of a problem with U8A-64-FB96 chip that I have recently installed on the custom designed board
The problem is that the device appears to be completely invisible for the time composer (windows does not see any device getting connected at all, hence target hardware list is empty) and XTAG-2 (when XTAG is connected, in target hardware it says : XTAG-2 connected to none)
Although it receives power properly, buck converters are working well as well as reset pins
USB PHY receives 24Mhz clock (tested), DP and DN pins are routed correctly, 5v is provided to VSUP directly from USB, 3.3v is provided for VDDIO through a step-down converter, USB VBUS (5v) is connected through a 1k resistor.
AVDD pin is not connected as ADC is not being used.
Please help
Regards,
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lilltroll
XCore Expert
Posts: 956
Joined: Fri Dec 11, 2009 3:53 am
Location: Sweden, Eskilstuna

Post by lilltroll »

First, how did you mount the BGA ?

A test to find out of you have a good connection between pads and BGA balls is to use a multi-meter in diode test mode.

If you connect the positive / red to GND and the negative to your PCB trace (one by one), the voltmeter should show < 0.75 V for ports and < 0.65 V for power pins.
The trick is thus to apply a small negative current to the ports, and check that you get a negative diode voltage. (A large current this way would probably destroy the device).

Check all connected PCB trace this way to ensure that all balls that should be connected is connected.
ast8346
Active Member
Posts: 39
Joined: Mon Jan 05, 2015 12:58 am

Post by ast8346 »

Problem solved. It was a badly connected JTAG header (my bad). A bit strange that PC could not see any device connected to it via USB without it, but it seems to be ok now.
Thanks for the negative current tip, that can be useful.