How can we power off the SDRAM on the LPC4357FET256?

[billiespencer]

We are using the Samsung 256 Mb N-die model K4S561632N-LI75 (http://www.samsung.com/global/business/semiconductor/file/2011/product/2010/5/24/425848ds_k4s561632n...) with the CPU --- LPC4357FET256 ARM Cortex-M4/M0|32-bit MCU|NXP.

We have been unsuccessful in putting the SDRAM into a deep sleep mode (turning off).  No mater what we do, the deep sleep current draw stays ~8 mA.  We do not need to preserve the content in the SDRAM.

So, how can we configure the EMC on a Cortex M4 to put the SDRAM in deep sleep (minimal current draw)?

Thanks in advance!

[kerryzhou]

Hi Billie Spencer,

   You can disable the EMC module by set the EMC control register bit0 to 0.

Please try it on your side.

If you still have question, please just let me know!

Have a great day,
Kerry

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[billiespencer]

Dear Kerry,

We your suggestion this morning and did not get the desired results. Let me explain in more detail.

· We are using the LPC4357FET256 ARM Cortex-M4/M0|32-bit MCU|NXP with the SDRAM from Samsung 256 Mb N-die model K4S561632N-LI75

· The baseline case is the board drawing 10.5 mA with the processor in deep power down mode.

· Following your instructions (i.e., setting the EMC control register bit0 to 0), we observed no change in the power draw.

· To understand which component was consuming this power, we physically removed the SDRAM from the board, resulting in the power draw being reduced to 2.5 mA.

· So, we concluded that SDRAM is drawing ~8 mA when the processor is in deep power down mode.

· We scoped the lines going to the SDRAM and confirmed that there is no clock signal going to the SDRAM when the processor is in deep power down mode.

Therefore:

· Our question is how can we reduce the SDRAM power consumption to values consistent with its datasheet specification (see Table 11 on page 8 of http://www.samsung.com/global/business/semiconductor/file/2011/product/2010/5/24/425848ds_k4s561632n....

Thanks in advance for your help!

Bill

[yuriivanov]

You must manually control CKE pin to put SDRAM to power off mode.

[billiespencer]

Thanks, Kerry!

We will try this suggestion in the morning.

Bill