PCF8533USLASH2DASLASH2 datasheet(5/45 Pages) NXP

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PCF8533_4

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Product data sheet

Rev. 04 — 5 March 2010

5 of 45

NXP Semiconductors

PCF8533

Universal LCD driver for low multiplex rates

6. The I2C-bus interface is initialized.

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

8. 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)

where the values for n are

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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