PCF8545ATT datasheet(24/51 Pages) NXP

24 / 51 page

NXP Semiconductors

PCF8551

Universal 36 × 4 LCD segment driver

8.3.1 Backplane outputs

The LCD drive section includes four backplane outputs COM0 to COM3, which must

be directly connected 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, COM3 carries the same signal as COM1, therefore these

two outputs can be tied together to give enhanced drive capabilities

• In 1:2 multiplex drive mode, COM0 and COM2, respectively, COM1 and COM3 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

8.3.2 Segment outputs

The LCD drive section includes 36 segment outputs SEG0 to SEG35, which must be

directly connected to the LCD. The segment output signals are generated in accordance

with the multiplexed backplane signals and with data residing in the display registers.

When less than 36 segment outputs are required, the unused segment outputs must be

left open-circuit.

9 Power Sequencing

9.1 Power-on

To avoid unwanted artifacts on the display, VLCD must never be asserted before VDD, it is

permitted to assert VDD and VLCD at the same time.

9.2 Power-off

Before turning the power to the device off, the display must be disabled by setting bit DE

to logic 0. To avoid unwanted artifacts on the display, VLCD must never be connected,

while VDD is switched off. It is permitted to switch off VDD and VLCD simultaneously.

9.3 Power sequences

Figure 16 depicts the recommended power-up and power-off sequence.

PCF8551

All information provided in this document is subject to legal disclaimers.

Product data sheet

Rev. 3.1 — 3 May 2021

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