TS-7970 Errata

From embeddedTS Manuals
Issue Status Description
RS232 prevents booting on REV A Workarounds available, fixed in REV B

Early TS-7970 REV A boards may fail to boot if RS232 is connected before the board is powered. A small amount of RS232 idle negative voltage leaks from the transceiver to the FET controlling the switched 5V. The FET will not toggle while the output has a negative voltage, so the 5V rail never comes up. If this is a concern or if the issue is seen, we can rework the board to have a 2.5ohm resistor from SW_5V to 5V_A on U47 pins 4 and 5. REV A boards shipped after 01/13/2016 include this fix.

Boot is prevented if the USB Device port (not host) is plugged in without the console enable jumper. Fixed in REV C

If the console jumper is not installed the silabs has USB VBUS, but no data signals. This puts the USB device into a locked up state while it waits to communicate on this bus. Due to this lockup it is unable to monitor voltages and turn on the SW_5V to the reset of the board. The fix is to disconnect VBUS from the silabs which is done on the REV C PCB. A cable without VCC can be made to work around the issue, or submit an RMA.