LPC3131/41 Developer’s Kit - User’s Guide
Page 9
Copyright 2012 © Embedded Artists AB
3
LPC3131/41 OEM Board Design
This chapter contains detailed information about the electrical and mechanical design of the
LPC3131/41 OEM Board
. Note that it is version 1.2 of the board that is presented. Differences from
version 1.1 and 1.0 are small and can be seen in the schematic (first page). The schematic can be
downloaded in pdf format from the support page, and is recommended to have printed out while
reading this chapter.
The following subsections describe in more detail each part of the design.
3.1.1
Page 2: Powering
Page 2 of the schematic contains the power supplies of the
LPC3131/41 OEM Board
.
3.1.1.1
1.8V and 3.3V Voltages
The LPC3131/41 requires three voltages; 1.2V for the core, 1.8V for the memory interface and 3.3V for
the rest of the i/o interfaces. The 1.8V and 3.3V voltages are fixed and 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 LPC3131/41 and other components
on the
LPC3131/41 OEM Board
.
3.1.1.2
1.2V Adjustable Core 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 LPC3131/41. The adjustment is done via an I2C channel, I2C1 in the
LPC3131/41 case. The core voltage can be adjusted as a power save feature. By lowering the voltage,
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 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 LPC3131/41. To
minimize the risk of accidentally setting the voltage the I2C channel is disconnected via R56/R57
(which are 0 ohm resistors/jumpers that are not mounted). R56/R57 is the only thing that differs
between v1.0 and v1.1 of the board. On v1.0, the I2C1 of the LPC3131/41 is always connected to the
LTC3447.
See the LPC3131/41 datasheet for exact details about ranges, but it is in the region of 1.1-1.3V. 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.
3.1.1.3
Input Voltage
The input voltage to the
LPC3131/41 OEM Board
is given by the requirements of the LM3671 and
LTC3447. A recommended input voltage range is 3.4 – 5.5V. 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 step down switching regulators on the
LPC3131/41 OEM
Board
.
3.1.1.4
OTP VPP Voltage
The VPP power to the LPC3131 is fixed to 1.2V. The LPC3141 has on-chip OTP (One-Time
Programmable) fuses that can be programmed. 3.3V must be applied to VPP during programming.
The OTP voltage switch (U4) is mounted on
LPC3141 OEM Boards
, but not on
LPC3131 OEM
Boards
.
