PCF8562 查看數據表（PDF） - Philips Electronics

零件编号

产品描述 (功能)

生产厂家

PCF8562

Universal LCD driver for low multiplex rates

Philips Electronics 

Philips Semiconductors

Universal LCD driver

for low multiplex rates

Preliminary specification

PCF8562

6.1 Power-on reset

At power-on the PCF8562 resets to the following starting conditions:

• All backplane outputs are set to VLCD

• All segment outputs are set to VLCD

• Drive mode ‘1 : 4 multiplex with 1⁄3bias’ is selected

• Blinking is switched off

• Input and output bank selectors are reset (as defined in Table 4)

• The I2C-bus interface is initialized

• The data pointer and the subaddress counter are cleared

• Display is disabled.

Data transfers on the I2C-bus should be avoided for 1 ms following power-on to allow completion of the reset action.

6.2 LCD bias generator

Fractional LCD biasing voltages are obtained from an internal voltage divider comprising three resistors connected in

series between VLCD and VSS. The middle resistor can be bypassed to provide a 1⁄2bias voltage level for the 1 : 2

multiplex configuration. The LCD voltage can be temperature compensated externally via the supply to pin VLCD.

6.3 LCD voltage selector

The LCD voltage selector co-ordinates the multiplexing of the LCD in accordance with the selected LCD drive

configuration. The operation of the voltage selector is controlled by MODE SET commands from the command decoder.

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 2.

A practical value for VLCD is determined by equating Voff(rms) with a defined LCD threshold voltage (Vth), typically when

the LCD exhibits approximately 10% contrast. In the static drive mode a suitable choice is VLCD > 3Vth.

Multiplex drive modes of 1 : 3 and 1 : 4 with 1⁄2 bias are possible but the discrimination and hence the contrast ratios are

smaller.

6.3.1 LCD BIAS FORMULAE

Bias is calculated by the formula 1-----+1-----a--

where for 1⁄2 bias, a = 1; for 1⁄3 bias, a = 2.

The

LCD

on

voltage

(Von)

is

calculated

by

the

formula

Vop

N-1-- +

(

N

–

1)

⋅

⎛

⎝

1-----1+-----a--⎠⎞

2

-----------------------------N-------------------------------

The LCD off voltage (Voff) is calculated by the formula Vop a---N-2----–-⋅---(-(-1-2----a+-----+a----)-N-2---)-

where Vop is the resultant voltage at the LCD segment; N is the LCD drive mode: 1 = static, 2 = 1 : 2, 3 = 1 : 3, 4 = 1 : 4.

November 22, 2004

8

Share Link: