PCF8576D datasheet(8/50 Pages) NXP

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PCF8576D

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Product data sheet

Rev. 10 — 14 February 2011

8 of 50

NXP Semiconductors

PCF8576D

Universal LCD driver for low multiplex rates

• 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 Table 9) 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.

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

()

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

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

on RMS

()

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

LCD

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