PCF85134 datasheet(7/40 Pages) NXP

7 / 40 page

PCF85134_1

Product data sheet

Rev. 01 — 17 December 2009

7 of 40

NXP Semiconductors

PCF85134

Universal LCD driver for low multiplex rates

• The I2C-bus interface is initialized

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

• The display is disabled

Remark: Do not transfer data on the I2C-bus for at least 1 ms after a 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 of three

series resistors connected between pins VLCD and VSS. The center resistor is bypassed

by switch if the 1

⁄

2 bias voltage level for the 1:2 multiplex drive mode conﬁguration is

selected.

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 Table 10) 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 Equation 1:

(1)

Table 5.

Biasing characteristics

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

()

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

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

on RMS

()

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

LCD

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