PCA2117DUGSSLASHDA datasheet(45/107 Pages) NXP

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PCA2117

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Product data sheet

Rev. 4 — 8 April 2015

45 of 107

NXP Semiconductors

PCA2117

Automotive LCD driver for character displays

The RMS on-state voltage (Von(RMS)) for the LCD is calculated with Equation 6 and the

RMS off-state voltage (Voff(RMS)) with Equation 7:

(6)

(7)

where the values of a are

a=2 for 1⁄3 bias

a=3 for 1⁄4 bias

and the values for n are

n = 2 for 1:2 multiplex rate

n = 9 for 1:9 multiplex rate

n = 18 for 1:18 multiplex rate.

Discrimination (D) is the ratio of Von(RMS) to Voff(RMS) and is determined from Equation 8.

Discrimination is a term which is defined as the ratio of the on and off RMS voltage across

a segment. It can be thought of as a measurement of contrast.

(8)

Remark:

• Row and column outputs comprise a series resistance RO (see Table 50).

• VLCD is sometimes referred as the LCD operating voltage.

8.4.6.1

Electro-optical performance

Suitable values for Von(RMS) and Voff(RMS) are dependent on the LCD liquid used. The

RMS voltage, at which a pixel is switched on or off, determines the transmissibility of the

pixel.

For any given liquid, there are two threshold values defined. One point is at 10 % relative

transmission (at Vth(off)) and the other at 90 % relative transmission (at Vth(on)), see

Figure 26. For a good contrast performance, the following rules should be followed:

(9)

(10)

Von(RMS) and Voff(RMS) are properties of the display driver and are affected by the selection

of a (see Equation 6), n (see Equation 8), and the VLCD voltage.

Vth(off) and Vth(on) are properties of the LCD liquid and can be provided by the module

manufacturer. Vth(off) is sometimes named Vth. Vth(on) is sometimes named saturation

voltage Vsat.

on RMS





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

LCD

off RMS



–





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

LCD

on RMS



off RMS



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



–



–



–



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

on RMS



th on





off RMS



th off





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