PCA85176 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2015. All rights reserved.
Product data sheet Rev. 6 — 7 April 2015 21 of 60
NXP Semiconductors
PCA85176
40 x 4 automotive LCD driver for low multiplex rates
7.4 Oscillator
7.4.1 Internal clock
The internal logic of the PCA85176 and its LCD drive signals are timed either by its
internal oscillator or by an external clock. The internal oscillator is enabled by connecting
pin OSC to pin V
SS
. If the internal oscillator is used, the output from pin CLK can be used
as the clock signal for several PCA85176 in the system that are connected in cascade.
7.4.2 External clock
Pin CLK is enabled as an external clock input by connecting pin OSC to V
DD
. The LCD
frame frequency is determined by the clock frequency (f
clk
).
Remark: A clock signal must always be supplied to the device; removing the clock may
freeze the LCD in a DC state, which is not suitable for the liquid crystal.
7.4.3 Timing
The PCA85176 timing controls the internal data flow of the device. This includes the
transfer of display data from the display RAM to the display segment outputs. In cascaded
applications, the correct timing relationship between each PCA85176 in the system is
maintained by the synchronization signal at pin SYNC
. The timing also generates the LCD
frame frequency signal. The frame frequency signal is a fixed division of the clock
frequency from either the internal or an external clock:
7.5 Backplane and segment outputs
7.5.1 Backplane outputs
The LCD drive section includes four backplane outputs BP0 to BP3 which must be
connected directly to the LCD. The backplane output signals are generated in accordance
with the selected LCD drive mode. If less than four backplane outputs are required, the
unused outputs can be left open-circuit.
• In 1:3 multiplex drive mode, BP3 carries the same signal as BP1, therefore these two
adjacent outputs can be tied together to give enhanced drive capabilities
• In 1:2 multiplex drive mode, BP0 and BP2, respectively, BP1 and BP3 all carry the
same signals and may also be paired to increase the drive capabilities
• In static drive mode the same signal is carried by all four backplane outputs and they
can be connected in parallel for very high drive requirements
7.5.2 Segment outputs
The LCD drive section includes 40 segment outputs S0 to S39 which should be
connected directly to the LCD. The segment output signals are generated in accordance
with the multiplexed backplane signals and with data residing in the display register. When
less than 40 segment outputs are required, the unused segment outputs should be left
open-circuit.
