Datasheet

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Product Note
EA-OEM-011 & EA-OEM-511
The Art of Embedded Systems Development – made Easy™
Note about CLK2_OUT signal
Signal CLK2_OUT (pin CLK2 on the LPC4357) is available at SODIMM pad/pin 115 on the
LPC4357 OEM board. When the external SDRAM (on the LPC4357 OEM board) is used, signal
CLK2_OUT cannot be used for anything. It is an SDRAM clock signal and any distortion on the
signal will affect SDRAM operation.
Signal CLK2_OUT can only be used as a general clock signal if the external SDRAM is not
used/activated. If external SDRAM is not used on the LPC4357 OEM board then there are no
limitations on the core clock frequency of the LPC4357. It can run at up to 204 MHz.
On the OEM base board (on which the LPC4358 OEM board is mounted) SODIMM pad/pin 115
is connected to signal GPIO68_I2S-MCLK, which is routed a long distance over the base board.
This will distort the CLK2_OUT signal seen by the LPC4357 and, as a result, limit the core clock
operating frequency when the external SDRAM is used. The problem limits the frequencies to
96/96MHz (core/emc frequency) and 144/72MHz. By following the solutions outlined below full
operating speed can be achieved, which means 102/102MHz and 204/102MHz operation.
Solution
There are a couple of different hardware solutions depending on how the CLK2_OUT signal is
used.
1. If the LPC4357 OEM board is mounted on a custom designed baseboard and the
CLK2_OUT signal (SODIMM pin 115) is not used and no track is connected to it, then
there nothing has to be done. The SDRAM can run at 102/102MHz and 204/102 MHz.
2. If the LPC4357 OEM board is mounted on a custom designed baseboard and the
CLK2_OUT signal is used then connect a 56 ohm (termination) resistor to ground as close
to SODIMM pin 115 as possible. The signal is available on J4, pin 10 on the OEM base
board. In most cases this solution will work but the margins for 102/102MHz and 204/102
MHz operation is not big. For better margins, see solution 3). Note that this solution will
most likely not work when running the core/emc at lower than full frequency (102/102 or
204/102MHz). It will only work when running at full speed.
For the future, plan to not use the CLK2_OUT signal as an external clock signal. In future
revisions of the LPC4357 OEM board the signal will not be available at pin 115. Note that
the external SDRAM cannot be used anyways if signal CLK2_OUT is used for other
purposes, for example an I2S reference clock.