NXP Semiconductors
UM10817
OM13503, PCA8539 demo board
UM10817
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© NXP B.V. 2014. All rights reserved.
User manual
Rev. 1 — 3 September 2014
5 of 13
2.1 Power Supply
Please refer to the schematic diagram of the board, which is given in
1. Via mini-USB connector P1. Now the 5 V come directly from the USB port. This
supply is used for the PCA8539 directly, as well as to supply a 3.3 V regulator. The
output of the regulator is used for the back light and to supply the micro controller.
2. Via an external DC power supply, for which connector P2 has been provided.
Connect a voltage of 5 V (erroneously labeled as 6 V on the PCB) to pin 5. Again,
that voltage is to supply the LCD driver and the 3.3 V regulator which in turn supplies
the microcontroller and the backlight. The voltage connected to pin 1 must not
exceed 16 V (erroneously labeled a 15 V MAX). It is to provide the LCD operating
voltage. Diodes protect against damage in case of wrong polarity.
It is not possible to apply power via the plugged in LPCXpresso board. The USB
connector on the LPCXpresso board is only meant for programming the flash memory.
There are two ways to provide power to the base board:
The PCA8539 includes a temperature compensated internal V
LCD
generator. If the
internal voltage generator for V
LCD
is not used, and one wants to quickly see the optical
result of varying V
LCD
, this can be achieved using the second supply option. Varying the
voltage provided to pin 1 of connector P2 will directly influence the display contrast and
the optimal voltage can be selected. Make sure that the voltage V
LCD
does not exceed
the maximum limit of 16 V of PCA8539. If external V
LCD
is used, jumper JP7 must be
removed and jumper JP8 must be placed. Ensure that the internal voltage generation
(control register settings) is disabled.
Switch SW1 is used to select which of the two power supply options is activated. The 5 V
output of the switch is used to directly supply the PCA8539 LCD driver. Furthermore the
voltage labeled “3V3” is generated with an additional regulator, IC1. This 3.3 V supply is
used to supply the microcontroller board LPCXpresso (via diode D3) and to supply the
back light. At 3.3 V, the backlight draws a current of typically 180 mA, and this is why D3
was included. D3 prevents a current flowing from the LPCXpresso board to the back light
when the USB cable is plugged into the LPCXpresso board, as this current would exceed
the limits of the regulator on the LPCXpresso board.
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.
It is allowed to provide power to the base board while LPCXpresso is connected to a
computer, for example using two USB cables.
2.2 Switches
Three push buttons are present on the board, SW2, SW3 and SW4. They have currently
no function assigned.
