Part Number:AM1705
Hello E2E,
I made a custom board for the AM1705 processor and have finished hand-soldering its thermal pad and pins. I am using a TPS650061 to provide power and a reset signal to the processor as per this application note. I verified that the 1.2V, 1.8V, and 3.3V supplies are all working properly when the processor is powered on. I have also populated 64MB of SDRAM and 64MB of NOR Flash (they use a separate 3.3V supply).
However, when I power on the board, there is no activity whatsoever. All I see is some status LEDs turn on elsewhere on my board since their signal lines are internally pulled up by some of the processor's GPIO pins. After some probing, I found that the crystal oscillator is not working and both the input and output are sitting at around 0.7V. I at least expected that the oscillator circuitry would work even if there were problems elsewhere with the processor. I tried removing the crystal and load capacitors and directly injecting a clock signal from a working external 1.2V 24MHz oscillator directly into the processor's OSCIN pin, but that did not do anything to wake up the board. So I don't think it's a problem with my choice of crystal or load capacitors otherwise the external oscillator would have worked.
I have since replaced the processor and crystal oscillator circuitry thinking that I may have damaged the first ones during soldering, but I am getting the exact same symptoms after the replacements. I have looked very carefully for soldering errors but I don't see anything visually or electrically when I probe around. The thermal pad (ground) felt securely fastened to the board after I soldered it (I checked before I soldered any of the pins onto the board).
Does anyone have an idea why the oscillator circuitry is not working and would stay at 0.7V all the time?
Other details:
- TRST pin pulled high (3.3V) so as not to affect the reset sequence
- BOOT pins 7, 3, 2, 1, and 0 are configured to choose UART1 as the boot mode
- No BOOTME signal is received from UART1 on power-up
- UART1 Tx and Rx pins are pulled high for the boot sequence as suggested by the datasheet
- Almost all the processor's supply pins are bypassed with 0.1uF capacitors, and a few have 10uF capacitors
Thanks in advance for your help!