i.MX7D power down sequencing in different scenarios

[sebastianrespon]

Hello,

i am working on a design using i.MX7D using the PF3000 (without LICELL), and i am trying to figure out how to handle the power-down sequencing. I would appreciate your help regarding the following questions:

1.  What should be done to make shure the reccomended power down sequence of the IMX7D works as described in the datasheet?
2. Do i have to assert a reset on i.MX7D before a Power-Down? What would be the consequences if this is not done?
3. What would be the consequences if the power-down-sequencing is not done as described in the IMX7DCEC datasheet (p.39/40) (i.e. VREF_DRAM is turned off after VDD_SOC, or V_SNVS is turned off before the other voltages)?
4. In Case of a Board-Power-Supply-Faillure the PMIC Input Voltage would be removed. How could damage of the i.MX7D be prevented in such a case?
5. Could the ONOFF-Pin (via INTB from PMIC) be used to turn the i.MX7 off in case of the power supply faillure described above? If not, which pin should be used/ connected to INTB?
   

Thank you very much in advance for your help!

Best regards,

Sebastian

[Yuri]

Hello

  Please look at my comments below.

1.
Please refer to i.MX7 designs :

EVK :

 https://www.nxp.com/webapp/Download?colCode=iMX7D-SABRE-DESIGNFILES&appType=license&Parent_nodeId=14... 

WaRP7 :

Design file for WaRP7 board (Schematics & P... | element14 | Technical Library 

2.
Strictly speaking, no need for reset before power down.

3.

  According to the Datasheet(s) :
“Any deviation from these sequences may result in the following situations:

• Excessive current during power-up phase
• Prevention of the device from booting

• Irreversible damage to the processor (worst-case scenario)”

4.

  Usually capacitors prevent fully unexpected supply voltage removing.

Please refer to Table 7 (Power supply decoupling recommendations)

of the Design Guide.

http://www.nxp.com/assets/documents/data/en/user-guides/IMX7DSHDG.pdf 

5.

  Basically the ONOFF pin may be used to inform PMIC (via PMIC_ON_REQ) to turn

off the i.MX7; but the i.MX7 ONOFF pin in itself does not protect i.MX7 device.

Have a great day,
Yuri

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