NXP Semiconductors
UM10744
OM13500 & OM13500A user manual
UM10744
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© NXP B.V. 2013. All rights reserved.
User manual
Rev. 1 — 23.September 2013
5 of 14
On the board, below the NXP logo, is indicated which version of the board (OM13500
with PCA9620 or OM13500A with PCA8537) it is. The LCD driver positions are located
on the reverse side of the PCB, below the LCD. This location was chosen for layout
reasons, as it results in shorter traces from the driver to the LCD.
2.1 Power Supply
The schematic diagram of the board is shown in
Besides applying power via the plugged in LPCXpresso board, there are three ways to
provide power to the base board:
1. Via mini-USB connector P1. Now the 5V come directly from the USB port.
2. Using two AA batteries. An on-board switching regulator, built around IC4,
generates 5V (5V_Bat). Whenever the batteries are inserted this regulator is
running. The current consumption at no load is very low, in the order of 20 µA.
Nevertheless, it is advisable to remove the jumper labeled “VBAT” when the
board will not be used for a longer time while the batteries are inserted. This will
interrupt the connection between batteries and switching regulator.
3. Via an external AC/DC adapter or DC power supply. The voltage may be in the
range from 7 V to 18 V. For the adapter a plug CON1 has been provided, where
the internal pin is +. It is also possible to connect the voltage to two pins (P3)
using a DC power supply. A diode protects against damage in case of wrong
polarity. Two linear regulators (IC1 and IC2) provide 5V (5V_ext) and the
external V
LCD
voltage VLCD_EXT, in case the internal charge pump is not used.
This external voltage VLCD_EXT can be adjusted using potentiometer POT1.
PCA9620 and PCA8537 include a temperature compensated internal V
LCD
generator.
The third power supply option allows switching quickly between an external supplied or
internal generated V
LCD
. This is useful for evaluating the optical performance as a
function of the voltage V
LCD
, as the external supplied voltage can be varied quickly using
potentiometer POT1. If the external V
LCD
supply option is used also jumper J1 must be
placed. Also the internal charge pump must be disabled.
Switch SW1 is used to select which of the three power supply options is being selected
(5V_BAT, 5V_USB or 5V_EXT). The 5V output of the switch is used to supply the
backlight of the display. Furthermore the voltage labeled “3V3_LPCXPR” is generated
with an additional regulator, IC5. The 3.3V are used to supply the microcontroller board
LPCXpresso, and to supply the logic V
DD
of the LCD driver.
The LPCXpresso board contains a JTAG/SWD debugger called the “LPC-Link” and a
target MCU. LPC-Link is equipped with a 10-pin JTAG header and it seamlessly
connects to the target via USB (the USB interface and other debug features are provided
by NXP’s ARM9 based LPC3154 MCU). When the firmware needs to be updated, the
LPCXpresso board will be connected using the USB to the computer on which the IDE is
installed. In this case, a 3.3V supply is generated on the LPCXpresso board via a linear
regulator which is integrated in the LPC3154. However, this regulator has limited current
delivery capability. If the LPCXpresso board is connected via USB to a computer without
any other supply to the base board, the 3.3V from the LPCXpresso board is used to
supply also the LCD base board. In this case the backlight will have limited intensity, but
enough to see the result of software changes. Supply is via diode D2 and resistor R9.