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PC8534A-1 Datasheet PDF : 47 Pages
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NXP Semiconductors
PCF8534A
Universal LCD driver for low multiplex rates
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.
Table 5. Discrimination ratios
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------oV--f--f-L-(--RC----MD----S----) V------oV--n---L(--R-C--M-D----S---) D = V-V-----oo--f-n-f--((-R-R---M-M---S-S---)-)
0
1
∞
0.354
0.791
2.236
0.333
0.745
2.236
0.333
0.638
1.915
0.333
0.577
1.732
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 > 3 × Vth.
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-----+1-----a-- , 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:
V on(RMS)
=
V LCD
1-n-
+
(---n----–-n----1----)
×
1-----+1-----a--
2
(1)
where the values for n are
n = 1 for static mode
n = 2 for 1:2 multiplex
n = 3 for 1:3 multiplex
n = 4 for 1:4 multiplex
The RMS off-state voltage (Voff(RMS)) for the LCD is calculated with Equation 2:
V off (RMS) = V LCD n--a---×2----–-(--1-2----a+----+-a----)n--2-
(2)
Discrimination is the ratio of Von(RMS) to Voff(RMS) and is determined from Equation 3:
D = V-V-----oo--f-n-f-(-(-R-R--M-M---S-S--)-) = (-(--aa-----+–-----11---)-)--22----++-----((--nn----–-–----11----))
(3)
PCF8534A_5
Product data sheet
Rev. 05 — 6 August 2009
© NXP B.V. 2009. All rights reserved.
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