User`s guide

Avoiding Board Bring-Up Problems
i.MX53 System Development User’s Guide, Rev. 1
7-2 Freescale Semiconductor
7.2 Using a Current Monitor to Avoid Power Pitfalls
Excessive current can cause damage to the board. Avoid this problem by using a current-limiting
laboratory supply that has a current read-out to power the main power to the board when bringing up the
board for the first time. This allows the main power to be monitored, which makes it easy to detect any
excessive current.
7.3 Checking for Clock Pitfalls
Problems with the external clocks are another common source of board bring-up issues. Ensure that all of
your clock sources are running as expected.
The EXTAL/XTAL and the ECKIL/CKIL clocks are the main clock sources for 24 MHz and 32 kHz
reference clocks respectively on the i.MX53. Although not required, the use of low jitter external
oscillators to feed CKIH1 or CKIH2 on the i.MX53 can be an advantage if low jitter or special frequency
clock sources are required by modules driven by CKIH1 or CKIH2. See the CCM chapter in the i.MX53
reference manual for details.
When checking crystal frequencies, use an active probe to avoid excessive loading. A parasitic probe
typically inhibits the 32.768 kHz oscillator from starting up. Use the following guidelines:
• CKIL clock should be running at 32.768 kHz (can be generated internally or applied externally)
• EXTAL/EXTAL should be running at 24 MHz (used for the PLL reference)
• CKIH1/CKIH2 can be used as oscillator inputs for low jitter special frequency sources.
• CKIH1 and CKIH2 are optional.
In addition to probing the external input clocks, you can check internal clocks by outputting them at the
debug signals CLKO1 and CLKO2. See the CCM chapter in the i.MX53 reference manual for more details
about which clock sources can be output to those debug signals.
7.4 Avoiding Reset Pitfalls
Follow these guidelines to ensure that you are booting using the correct boot mode.
• During initial power on while asserting the POR_B reset signal, ensure that both your reference
clocks are active before releasing POR_B.
• Follow the recommended power-up sequence specified in the i.MX53 reference manual.
The GPIOs and internal fuses control the i.MX53 boots. For a more detailed description about the different
boot modes, refer to the system boot chapter of the i.MX53 reference manual.