PCA85176(2010) View Datasheet(PDF) - NXP Semiconductors.
Part Name
Description
Manufacturer
PCA85176 Datasheet PDF : 44 Pages
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NXP Semiconductors
PCA85176
Universal LCD driver for low multiplex rates
• Display is disabled
Remark: Do not transfer data on the I2C-bus for at least 1 ms after a power-on to allow
the reset action to complete.
7.2 LCD bias generator
Fractional LCD biasing voltages are obtained from an internal voltage divider of the three
series resistors connected between VLCD and VSS. The center resistor is bypassed by
switch if the 1⁄2 bias voltage level for the 1:2 multiplex configuration is selected.
7.3 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 from the command decoder. 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 5.
Table 5. 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----)
Voff(RMS)
∞
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), typically when the LCD exhibits approximately 10 % contrast. In
the static drive mode a suitable choice is VLCD > 3Vth.
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 1:
PCA85176_1
Product data sheet
Von(RMS)
=
VLCD
--a---2----+-----2---a----+-----n---
n × (1 + a)2
where the values for n are
n = 1 for static drive mode
n = 2 for 1:2 multiplex drive mode
n = 3 for 1:3 multiplex drive mode
n = 4 for 1:4 multiplex drive mode
All information provided in this document is subject to legal disclaimers.
Rev. 01 — 14 April 2010
(1)
© NXP B.V. 2010. All rights reserved.
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