PC85132/232-1 データシートの表示（PDF） - NXP Semiconductors.
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PC85132/232-1 Datasheet PDF : 65 Pages
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NXP Semiconductors
PCA85132
LCD driver for low multiplex rates
7.3.1 LCD bias generator
Fractional LCD biasing voltages are obtained from an internal voltage divider of three
impedances connected between pins VLCD and VSS. The center impedance is bypassed
by switch if the 1⁄2 bias voltage level for the 1:2 multiplex drive mode configuration is
selected.
7.3.2 Display register
The display register holds the display data while the corresponding multiplex signals are
generated.
7.3.3 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. 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 15.
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.
Table 15. Biasing characteristics
LCD drive
mode
Number of:
LCD bias
Backplanes Levels configuration
static
1
1:2 multiplex 2
1:2 multiplex 2
1:3 multiplex 3
1:4 multiplex 4
2
static
3
1⁄2
4
1⁄3
4
1⁄3
4
1⁄3
V-----o--f--f----R---M-----S---
VLCD
0
0.354
0.333
0.333
0.333
V-----o--n-----R----M----S---
VLCD
1
0.791
0.745
0.638
0.577
D = -V----o---n----R----M----S----
VoffRMS
2.236
2.236
1.915
1.732
A practical value for VLCD is determined by equating Voff(RMS) with a defined LCD
threshold voltage (Vth(off)), typically when the LCD exhibits approximately 10 % contrast. In
the static drive mode, a suitable choice is VLCD > 3Vth(off).
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 -----1------- , where the values for a are
1+a
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 2:
PCA85132
Product data sheet
VonRMS
=
VLCD
--a---2----+-----2---a----+-----n---
n 1 + a2
where the values for n are
n = 1 for static drive mode
n = 2 for 1:2 multiplex drive mode
All information provided in this document is subject to legal disclaimers.
Rev. 4 — 9 April 2015
(2)
© NXP Semiconductors N.V. 2015. All rights reserved.
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