Why VDDHIGH_IN power up before VDDARM and VDDSOC for i.MX6QuadPlus compare to i.MX6Quad SABRE AI?

[m_c]

In the i.MX6Quad SABRE AI, VDDHIGH_IN power up after VDDARM and VDDSOC.

In the i.MX6QuadPlus SABRE AI, VDDHIGH_IN power before VDDARM and VDDSOC.

Why?

[art]

Since the VDD_HIGH_IN power rail supplies the on-chip LDO_1P1 voltage regulator that, in turns, supplies the 24MHz oscillator circuit, better is to apply VDD_HIGH_IN first (after or together with VDD_SNVS_IN) during the power-up sequence to provide enough time for the 24MHz oscillator for getting up and running stable before POR_B is released.

Have a great day,
Artur

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[igorpadykov · Accepted solution]

Hi m.c.

VDDHIGH_IN powers regulators as shown on Figure 50-1. Power system overview

i.MX6DQ Reference Manual, powering it first provides more smooth power-up sequence.

So later i.MX6QuadPlus design use this option. Datasheet describes power-up sequence as follows:

"Power-Up Sequence - For power-up sequence, the restrictions are as follows:
• VDD_SNVS_IN supply must be turned ON before any other power supply. It may be connected
(shorted) with VDD_HIGH_IN supply."

Best regards
igor
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