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PCF8566T/1,118

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P27P28-P30P31-P33P34-P36P37-P39P40-P42P43-P45P46-P48
PCF8566_7 © NXP B.V. 2009. All rights reserved.
Product data sheet Rev. 07 — 25 February 2009 7 of 48
NXP Semiconductors
PCF8566
Universal LCD driver for low multiplex rates
7.1 Power-on reset
At power-on the PCF8566 resets to the following starting conditions:
• All backplane outputs are set to V
DD
• All segment outputs are set to V
DD
• Drive mode 1:4 multiplex with
1
⁄
3
bias is selected
• Blinking is switched off
• Input and output bank selectors are reset (as defined in Table 8)
• The I
2
C-bus interface is initialized
• The data pointer and the subaddress counter are cleared
Do not transfer data on the I
2
C-bus after a power-on for at least 1 ms to allow the reset
action to complete.
7.2 LCD bias generator
The full-scale LCD voltage (V
oper
) is obtained from V
DD
− V
LCD
. The LCD voltage may be
temperature compensated externally through the V
LCD
supply to pin 12.
Fractional LCD biasing voltages are obtained from an internal voltage divider comprising
three series resistors connected between V
DD
and V
LCD
. The center resistor can be
switched out of the circuit to provide a
1
⁄
2
bias voltage level for the 1:2 multiplex
configuration.
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
mode-set commands from the command decoder. The biasing configurations that apply to
the preferred modes of operation, together with the biasing characteristics as functions of
V
LCD
and the resulting discrimination ratios (D), are given in Table 5.
Fig 4. Typical system configuration
HOST
MICRO-
PROCESSOR/
MICRO-
CONTROLLER
SDA
SCL
OSC
1 17 to 40
13 to 16
2
6
78
512
91011
24 segment drives
4 backplanes
LCD PANEL
(up to 96
elements)
PCF8566
A0 A1 A2 SA0
V
DD
V
DD
V
LCD
V
SS
V
SS
mgg385
R ≤
t
rise
2 C
bus
PCF8566_7 © NXP B.V. 2009. All rights reserved.
Product data sheet Rev. 07 — 25 February 2009 8 of 48
NXP Semiconductors
PCF8566
Universal LCD driver for low multiplex rates
A practical value for V
LCD
is determined by equating V
off(RMS)
with a defined LCD
threshold voltage (V
th
), typically when the LCD exhibits approximately 10 % contrast. In
the static drive mode a suitable choice is V
LCD
>3V
th
.
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 , where the values for a are
a = 1 for
1
⁄
2
bias
a = 2 for
1
⁄
3
bias
The RMS on-state voltage (V
on(RMS)
) for the LCD is calculated with the equation
(1)
where V
LCD
is the resultant voltage at the LCD segment and 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 (V
off(RMS)
) for the LCD is calculated with the equation:
(2)
Discrimination is the ratio of V
on(RMS)
to V
off(RMS)
and is determined from the equation:
(3)
Using Equation 3, the discrimination for an LCD drive mode of
• 1:3 multiplex with
1
⁄
2
bias is
Table 5. Preferred LCD drive modes: summary of characteristics
LCD drive mode Number of: LCD bias
configuration
Backplanes Bias levels
static 1 2 static 0 1 ∞
1:2 multiplex 2 3
1
⁄
2
0.354 0.791 2.236
1:2 multiplex 2 4
1
⁄
3
0.333 0.745 2.236
1:3 multiplex 3 4
1
⁄
3
0.333 0.638 1.915
1:4 multiplex 4 4
1
⁄
3
0.333 0.577 1.732
V
off
RMS
()
V
LCD
--------------------------
V
on
RMS
()
V
LCD
-------------------------
D
V
on
RMS
()
V
off
RMS
()
--------------------------=
1
1a
+
-------------
V
on RMS()
1
n
--- n
1
–()
1
1a
+
-------------


×
2
+
n
------------------------------------------------------------
V
LCD
=
V
off RMS()
a
2
2a
n+()–
n
1a
+()
2
×
---------------------------------
V
LCD
=
V
on RMS()
V
off RMS()
------------------------
a1
+()
2
n
1
–()+
a1
–()
2
n
1
–()+
--------------------------------------------=
3 1.732
=
PCF8566_7 © NXP B.V. 2009. All rights reserved.
Product data sheet Rev. 07 — 25 February 2009 9 of 48
NXP Semiconductors
PCF8566
Universal LCD driver for low multiplex rates
• 1:4 multiplex with
1
⁄
2
bias is
The advantage of these LCD drive modes is a reduction of the LCD full scale voltage V
LCD
as follows:
• 1:3 multiplex (
1
⁄
2
bias):
• 1:4 multiplex (
1
⁄
2
bias):
These compare with when
1
⁄
3
bias is used.
It should be noted that V
LCD
is sometimes referred as the LCD operating voltage.
21
3
----------
1.528
=
V
LCD
6V
off
RMS
()
×
2.449V
off
RMS
()
==
V
LCD
43
×()
3
----------------------
2.309V
off
RMS
()
==
V
LCD
3V
off
RMS
()
=
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PCF8566T/1,118

Mfr. #:
Buy PCF8566T/1,118
Manufacturer:
NXP Semiconductors
Description:
LCD Drivers LCD DVR UNVRSL LOW-MUX
Lifecycle:
New from this manufacturer.
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