lpcware

LPC1857 not booting and getting very hot

Discussion created by lpcware Employee on Jun 15, 2016
Latest reply on Aug 15, 2017 by Carlos_Mendoza
Content originally posted in LPCWare by paul.nichols@grabba.com on Sun Feb 21 19:25:33 MST 2016
Hi,

I am having issues with some of our custom PCB based on LPC1857. On power connection to the CPU and peripherals the processor will not boot and gets very hot. The processor pulls ~750mA at 1.1V (the 750mA draw is enough to hold our 3.3V switchmode down to 1.1V)

A quick removal of power followed by re-connecting power results in a successful boot each time. This error condition is not observed on all boards (approximately 50% of 20 board prototype run)

Notable Items:
[list]
  [*] If we have a Red Probe+ attached(through JTAG) when the battery is plugged the board boots everytime (the error condition is never observed)
  [*] With no power connected and the Red Probe+ JTAG interface connected the 3.3V rail pre-charges to ~1V,TDO & TDI are at ~1.5V and TCK has 50kHz non-continuous clock signal
  [*] If we have a LPC-Link2 attached (through JTAG) the problem condition is observed
  [*] Holding reset low during battery insertion/pwoer connection) has seemingly no effect on if the problem state is entered or not
  [*] The 3.3V rail has ~100uF of bulk capacitance on the output of the switch mode (3.3V)
  [*] The battery net has ~50uF of bulk capacitance at the input of the switch mode (3.3V)
  [*] There is no VBUS present at the time of test. The VBUS pin is 0V
  [*] DBGEN and TRST are tied to 3.3V through 10k pull-ups
  [*] TDO, TDI, TMS are tied to 3.3V through 10k pull-ups
  [*] TCK is tied to ground through a 10k pull-down
  [*] P2_7 (boot source) is tied to 3.3V through a 10k pull-up
[/list]

The problem seems to happen prior to the CPU booting (as holding reset has no effect on whether the problem condition is observed or not)

I have attached schematics of our power and JTAG connection

Any advice would be greatly appreciated.

Thanks
Paul

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