Chapter 5
Avoiding board bring-up problems
5.1 Introduction
This chapter provides recommendations for avoiding typical mistakes when bringing up a board for the first time. These
recommendations consist of basic techniques that have proven useful in the past for detecting board issues and preventing/
locating the three most typical issues encountered: power, clocks, and reset.
5.2 Avoiding power pitfalls - current
Excessive current can cause damage to the board. Avoid this problem by using a current-limiting laboratory supply set to the
expected typical main current draw (at most). Monitor the main supply current with an ammeter when powering up the board for
the first time. You can use the supply's internal ammeter (if it has one). By monitoring the main supply current and controlling the
current limit, any excessive current can usually be detected before permanent damage occurs.
In lieu of this approach, you can simply ohm out all the board power rails to ground before the board testing and verify that there
are no short circuits. If there are none, you should be able to apply power to the board with a high degree of confidence that there
are no shorts that would cause excessive current leading to board and/or component damage.
5.3 Avoiding power pitfalls - voltage
Incorrect voltage rails are a common power pitfall. To avoid this mistake, create a basic table called a voltage report before board
bring-up/testing. This table helps to validate that all the supplies are reaching the expected levels.
To create a voltage report, list the following:
• Board voltage sources
• Default power-up values for the board voltage sources
• Best location on the board to measure the voltage level of each supply
Carefully determine the best measurement location for each power supply to avoid a large voltage drop (IR drop) on the board,
which causes inaccurate voltage values to be measured. The following guidelines produce the best voltage measurements:
• Measure closest to the load (in this case the i.MX8 processor).
• Make two measurements: the first after the initial board power-up and the second while running a heavy use-case that
stresses the i.MX8 processor.
Ensure that the supplies that power the i.MX8 meet the DC electrical specifications, as listed in the chip-specific data sheet.
See Table 40 for a sample voltage report.
NOTE: This report table is for the i.MX8 QM Development Platform. Sample voltage reports for customer PCBs will be different
from this, depending on the processor and Power Management IC (PMIC) used and the assignment of the PMIC power resources.
Table 40. Sample voltage report
Source Net Name
Expected
(V)
Measured
(V)
Measure
point
Comment
Ext 5V SMPS VCC_EXT_5V0 5.0 V TP27
Main 5 V supply for
the board
Table continues on the next page...
NXP Semiconductors
i.MX8 QM / i.MX8 QXP Hardware Developer’s Guide, Rev. 2.4p, 06/2021
User's Guide 81 / 89
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