PCF8545ATTAY datasheet(21/68 Pages) NXP

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NXP Semiconductors

PCF8545

Universal LCD driver for multiplex rates up to 1:8

HOST

MICRO-

CONTROLLER

2Cb

SDA

SCL

40 to 44 segment

drives

4 to 8 backplanes

LCD PANEL

(up to 320

elements)

PCF8545A

VDD

VSS

aaa-008326

VDD

VLCD

Figure 11. Typical system configuration for the I2C-bus

HOST

MICRO-

CONTROLLER

SDI

SCL

40 to 44 segment

drives

4 to 8 backplanes

LCD PANEL

(up to 320

elements)

PCF8545B

VDD

VSS

aaa-008327

VDD

VLCD

Figure 12. Typical system configuration for the SPI-bus

The host microcontroller maintains the two line I2C-bus or a three line SPI-bus

communication channel with the PCF8545. The appropriate biasing voltages for the

multiplexed LCD waveforms are generated internally. The only other connections

required to complete the system are the power supplies (VDD, VSS, VLCD) and the LCD

panel selected for the application.

The minimum recommended values for external capacitors on VDD and VLCD are 100

nF respectively. Decoupling of VLCD helps to reduce display artifacts. The decoupling

capacitors should be placed close to the IC with short connections to the respective

supply pin and VSS.

7.4 LCD voltage selector

The LCD voltage selector coordinates the multiplexing of the LCD in accordance with

the selected LCD drive configuration. The operation of the voltage selector is controlled

by the set-bias-mode command (see Table 15) and the set-MUX-mode command (see

Table 14).

Fractional LCD biasing voltages are obtained from an internal voltage divider. The

biasing configurations that apply to the preferred modes of operation, together with the

biasing characteristics as functions of VLCD and the resulting discrimination ratios (D), are

given in Table 22.

Discrimination is a term which is defined as the ratio of the on and off RMS voltage

across a segment. It can be thought of as a measurement of contrast.

PCF8545

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

Product data sheet

Rev. 2 — 4 October 2021

21 / 68

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