PCF8562TTSLASH2 datasheet(6/36 Pages) NXP

6 / 36 page

PCF8562_3

Product data sheet

Rev. 3 — 2 December 2008

6 of 36

NXP Semiconductors

PCF8562

Universal LCD driver for low multiplex rates

• All backplane outputs are set to VLCD

• All segment outputs are set to VLCD

• The selected drive mode is: 1:4 multiplex with 1

⁄

3 bias

• Blinking is switched off

• Input and output bank selectors are reset

• The I2C-bus interface is initialized

• The data pointer and the subaddress counter are cleared (set to logic 0)

• Display is disabled

Data transfers on the I2C-bus must be avoided for 1 ms following power-on to allow the

reset action to complete.

7.2 LCD bias generator

Fractional LCD biasing voltages are obtained from an internal voltage divider consisting of

three impedances connected in series between VLCD and VSS. The middle resistor can be

bypassed to provide a 1

⁄

2 bias voltage level for the 1:2 multiplex conﬁguration. The LCD

voltage can be temperature compensated externally using the supply to pin VLCD.

7.3 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

mode-set command (see Section 7.17) 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 5.

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.

Bias is calculated by

, where the values for a are

a = 1 for 1

⁄

2 bias

a = 2 for 1

⁄

3 bias

The RMS on-state voltage (Von(RMS)) for the LCD is calculated with the equation

Table 5.

Discrimination ratios

LCD drive

mode

Number of:

LCD bias

conﬁguration

Backplanes

Levels

static

∞

1:2 multiplex

⁄

0.354

0.791

2.236

1:2 multiplex

⁄

0.333

0.745

2.236

1:3 multiplex

⁄

0.333

0.638

1.915

1:4 multiplex

⁄

0.333

0.577

1.732

off RMS

()

LCD

--------------------------

on RMS

()

LCD

-------------------------

on RMS

()

off RMS

()

--------------------------

-------------

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