PCA9620 datasheet(35/71 Pages) NXP

35 / 71 page

PCA9620

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Product data sheet

Rev. 1 — 9 December 2010

35 of 71

NXP Semiconductors

PCA9620

Universal LCD driver for low multiplex rates

In case it is desired to change the charge pump frequency, it is recommended to make a

graph like Figure 26 and understand what the application requirements are. This would

basically imply to find out what would be the maximum VLCD requirements and what would

be the maximum load currents required. Then it can be decided which is the best setting

of bit CPF.

Tuning the charge pump frequency might be a difficult task to do and requires good

knowledge of the application in which the IC is being used; therefore, NXP recommends

to keep the CPF bit set logic 0 to have the maximum charge pump frequency, thus having

the maximum driving strength.

7.4.7 Temperature readout

The PCA9620 has a built-in temperature sensor which provides a 8 bit digital value,

TD[7:0], of the ambient temperature. This value can be read through the I2C interface (see

Figure 49 on page 52). The actual temperature is determined from TD[7:0] using

Equation 11:

(11)

The measurement needs about 5 ms to complete and is repeated periodically as soon as

bit TME is set logic 1 (see Table 9 on page 7). The time between measurements is linked

to the system clock and hence varies with changes in the chosen frame frequency, see

Table 28.

Due to the nature of a temperature sensor, oscillations on the VLCD may occur. To avoid

this, a filter has been implemented in PCA9620. The system is shown in Figure 27.

Like any other filtering, the digital temperature filter (see Figure 27) introduces a certain

delay in the measurement of temperature. This behavior is illustrated in Figure 28.

Table 28.

Temperature measurement update rate

Selected frame frequency

Temperature measurement update rate

60 Hz

3.3 s

200 Hz

1 s

300 Hz

0.67 s

Fig 27. Temperature measurement block with digital temperature filter

T (°C)

0.9375

TD 7:0

[] 40

–

TEMPERATURE

MEASUREMENT

BLOCK

DIGITAL

TEMPERATURE

FILTER

TD[7:0]

unfiltered

TD[7:0]

filtered

enabled or disabled

by bit TFE

To the readout register

via I2C-bus and to

the VLCD compensation

block

013aaa260

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