User manual

LPC3250 Developer’s Kit v2 - User’s Guide

Page 12

There are 2.2 kohm pull-up resistors (pull-ups are always needed on I2C busses) on the board on both

I2C channels.

3.1.6 Schematic Page 3: 1.2V and 1.8V Fixed Voltages

The LPC3250 requires three fixed voltages; 1.2V for the core, 1.8V for the memory interface and 3.15-

3.3V for the rest of the i/o interfaces. The 1.2V and 1.8V voltages are generated by two LM3671MF

step-down switching regulators from National Semiconductor. These regulators are capable of

generating 600mA, which by far exceed the needed current by the LPC3250 and other components on

the LPC3250 OEM Board. The 3.15-3.3V voltage is the input voltage to the LPC3250 OEM Board, see

below.

The Real-time clock also needs a 1.2V power, which is generated by a LDO (MIC5232).

3.1.7 Schematic Page 3: 1.2V Adjustable Voltage

The core 1.2V voltage is adjustable and is generated by the step down switching regulator LTC3447

from Linear Technologies. This regulator is capable of generating 600mA, which also by far exceed the

needed current by the LPC3250. The adjustment is done via an I2C channel, I2C1 in the LPC3250

case. The core voltage can be adjusted as a power save feature. By lowering the voltage (down to

0.9V), the total power consumption can be lowered but the clock frequency of the core must then also

be lowered. This is a trade-off that is important for hand held/portable equipment. Note that it is the

user’s responsibility not to program the LTC3447 to generate too high core voltage, which is

possible. The LTC3447 can generate voltages up to 2V, which by far exceed the limits for the

LPC3250.

See the LPC3250 datasheet for exact details about voltage ranges, but it is in the region of 1.1-1.39V.

Also see the LTC3447 datasheet for details about how to adjust the voltage (it is a write-only register).

The I2C address for the LTC3447 is indicated in the schematic.

Note that a core voltage of 1.35V should be programmed when working with the external DDR

SDRAM.

3.1.8 Schematic Page 3: Input Voltage

The input voltage to the LPC3250 OEM Board is given by the requirements of the LPC3250. The

recommended input voltage range is 3.15V to 3.3V. The input supply must be stable but there are no

special needs for bulk capacitors close to the power pins on the expansion connectors. The needed

capacitors are placed close to the switched step down switching regulators on the LPC3250 OEM

Board.

Note that the LPC3250 OEM Board is sensitive to input noise on the input voltage. The peak-to-peak

noise should be below 10mV. A linear regulator to feed the input voltage is strongly recommended.

3.1.9 Schematic Page 4: External Memories

Page 4 of the schematic contains the external memory interface and the external memories. The

memory interface uses a 16-bit databus and operates at 1.8V level, which minimizes power

consumption.

3.1.10 Schematic Page 4: DDR SDRAM

A 512 MBit (64 MByte) Mobile DDR SDRAM is used (MT46H32M16LF from Micron). The chip is

connected to EMC_DYCS0_N (memory bank #0 for dynamic RAM) at address range 0x8000 0000 –

0x9FFF FFFF.

Note that memory bank #1 for dynamic RAM is not available (i.e., signal EMC_DYCS1_N is not used).