We are troubleshooting our custom board using the i.MX280 with a 5V only power supply. Our board fails during Power_Prep stage. We've ensured that Power_Prep.c has 5V only mode defined and battery mode commented out. We have no problems booting with the i.MX28 EVK, only our board fails.
External power supply for VDD5V
Debug UART used sb_loader.exe
Tried fully assembled board and one with only required components placed... both fail the same way.
Our hardware is set up for VDD5V only as outlined in AN4199
Our boot resistors are set to boot from SD card. With no SD card installed, on power up we get 0x8020a014 as expected and the processor presumably enters USB recovery mode. At this point the voltages are as follows:
VDD5V = 5.09
VDD4P2 = 0.868
VDDIO = 3.20
VDDA = 1.87
VDDD = 1.20
Now we use sb_loader.exe to send the boot file imx28_ivt_uboot.sb (bootlet version 1.1.0) and receive the following output:
PowerPrep start initialize power...
Configured for 5v only power source. Battery powered operation disabled.
After this no more messages from the DUART and the voltages are:
VDD5V = 5.04
VDD4P2 = 4.54
VDDIO = 1
VDDA = 0.2
VDDD = 0
After placing printf() statements in Power_Prep.c in and out of each function, we see that the last function called is PowerPrep_InitDcdc4p2Source();.
See attached scope image of VDD4P2 rail:
1. Any ideas for failure cause?
2. Prior to running imx28_ivt_uboot.sb, what should the power rail voltages be when processor simply has VDD5V applied (no bootlet yet)?
3. Where in this power process is the 100mA current limitation (page 4, section 3.2 AN4199 (http://cache.freescale.com/files/32bit/doc/app_note/AN4199.pdf?fasp=1&WT_TYPE=Application%20Notes&WT_VENDOR=FREESCALE&WT…)? We see just over 100mA on our board and i.MX28 EVK when only the processor is powered.
Thanks in advance!