PCA9620 datasheet(36/71 Pages) NXP

36 / 71 page

PCA9620

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Product data sheet

Rev. 1 — 9 December 2010

36 of 71

NXP Semiconductors

PCA9620

Universal LCD driver for low multiplex rates

This delay may cause undesired effects at start-up when the environment temperature

may be different than the reset value of the PCA9620 which is 20 °C. In this case it takes

up to 30 s till the correct measured temperature value will be available. A control bit, TFE,

is implemented to enable or disable the digital temperature filter. This bit is set logic 0 by

default which means that the filter is disabled and the unfiltered environment temperature

value is available to calculate the desired VLCD.

7.4.8 Temperature compensation of VLCD

Due to the temperature dependency of the liquid crystal viscosity the LCD controlling

voltage VLCD might have to be adjusted at different temperatures to maintain optimal

contrast. The temperature behavior of the liquid comes from the LCD manufacturer. The

slope has to be set to compensate for the liquid behavior. Internal temperature

compensation may be enabled via bit TCE.

The ambient temperature range is split up into four equally sized regions and a different

temperature coefficient can be applied to each (see Figure 29). Each coefficient can be

selected from a choice of eight different slopes. Each one of these coefficients (see

Table 29) may be independently selected via the temp-comp-SLA to temp-comp-SLD

commands (see Table 4 on page 5).

(1) Environment temperature, T1 (

°C).

(2) Measured temperature, T2 (

°C).

(3) Temperature deviation,

ΔT=T2 − T1.

Fig 28. Temperature measurement delay

t (s)

160

120

001aal393

(

°C)

(3)

(1)

(2)

ΔT

(

°C)(3)

−4

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