iMX257 Power Management

[MikeHanssen_ng]

As per the Freescale iMX257 reference PDK design, I am looking at re-using the MC34704A power management chip. However, it appears that it was not really designed for the iMX257, and I am requiring adidtional LDO's externally to compensate for some of the sequencing. Has anyone used this chip successfully on an iMX257, and know of any issues, pitfalls, easier methods of squencing some of the other rails.

I have discovered from Freescale that the NVCC_CRM (3.3V) input actually needs to be sequenced up first before the Core_QVDD (1.45V), so that the NVCC_DRYICE power switch for the RTC does not corrupt the RTC time. (See Errata). The new die V1.2 of the iMX257 fixes part of the problem, but requires this special sequencing. Does anyone else know about this ?

[chengqiang]

hello ,I have seen the  Freescale iMX257 reference PDK design,I find that the GPS model curcuit did not sold the GPS IC,I want to know what kind of IC needs for the drive curcuit.

do you know?

thank you please

[JesseBeeker]

I have looked at the Wolfson in the past and they are as you say good if you need the Codec integration. I am not sure if Dialog has anything in this range but that may be another option. The long life for these consumer parts may be tough to work with. It would be terrible to get a product out and then lose the PMIC down the road in production. I mostly see discrete power supplies for the 25 and 35 devices since there is not an automotive PMIC that matches up. I have a spreadsheet that helps you design, or at least validate power supply selection for i.MX25. Apparently I should redo for this V1.2 device. I will try and do that and post.

[MikeHanssen_ng]

Thanks for the reply. We need the functionality of the internal iMX RTC to remain valid over a power cycle, the RTC is within the DryICE. This is ENGcm11122, which is in the Rev 3 7/2010 errata notes. However, this refers to die version 1.1, and Freescale are releasing die v1.2. This was my question and Answer from Freescale. Q. Can you confirm that this sequencing (CRM, QVDD) is needed on the Version 1.2 die of the iMX257, or is it only needed on the Version 1.1 die of the iMX257 ? A: The new sequence is only for v1.2 and only if you plan on using the power-loss protection feature of DryIce module, otherwise the old recommended sequence is still valid. This still does not answer my question, which I have re-asked Freescale. ** What would you recommend in regards to a well matched power supply / power management chip ? Do you have a reference design ? I looked at Wolfson WM8351/WM8400 and LTC3589. (TI also had the TPS65051) I also have a Codec on board, so absorbing that cost was of interest. Cost is critical, At $3 the MC34704 is not bad, so is a long life, the MC34704 has a 10year gurantee, as does the iMX257.

[JesseBeeker]

I have just caught wind of this. I believe this is mainly if you need the functionality of the DRYICE. Do you have the errata number you are referring to? The posted errata document on the FSL web does not show this. It is Rev3 dated 7/2010. None of the engxxxx showed this. As for the 34704, I know the PDK uses it but I would not recommend it personally as it does have some sequencing mismatch from the i.MX25x datasheet. Clearly the PDK works, but I usually classify those as working design, not reference design.