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1997 Apr 04
8
Philips Semiconductors
Product specification
LCD controller/driver
PCF2113x
8
FUNCTIONAL DESCRIPTION
(see Fig.1)
8.1
LCD supply voltage generator
The LCD supply voltage may be generated on-chip.
The voltage generator is controlled by two internal 6-bit
registers, V
A
and V
B
. The nominal LCD operating voltage
at room temperature is given by the relationships:
V
OP(nom)
= [(integer value of register)
×
0.08 + 1.9] V
8.2
Programming ranges (
T
ref
= 27
°
C)
Programmed value range: 1 to 63.
Voltage range: 1.90 to 6.84 V.
Values producing more than 6.5 V at operating
temperature are not allowed.
Operation above this
voltage may damage the device. When programming the
operating voltage the V
LCD
temperature coefficient must
be taken into account.
Values below 2.2 V are below the specified operating
range of the chip and are therefore not allowed.
Value 0 for V
A
and V
B
switches the generator off.
Usually register V
A
is programmed with the voltage for
character mode and register V
B
with the voltage for icon
mode. V
B
must be programmed to FF in character mode
and V
A
must be programmed to 00 in icon mode.
When V
LCD
is generated on-chip the V
LCD
pins should be
decoupled to V
SS
with a suitable capacitor. The generated
V
LCD
is independent of V
DD
and is temperature
compensated. When the generator is switched off an
external voltage may be supplied at connected pins
V
LCD1,2
. V
LCD1,2
may be higher or lower than V
DD
if
external V
LCD
is used.
If internally generated it must not
be lower than V
DD
and
V
DD
.
8.3
LCD bias voltage generator
The intermediate bias voltages for the LCD display are
also generated on-chip. This removes the need for an
external resistive bias chain and significantly reduces the
system current consumption. The optimum value of V
LCD
depends on the multiplex rate, the LCD threshold voltage
(V
th
) and the number of bias levels and is given by the
relationships given in Tables 1 and 2. Using a 5-level bias
scheme for 1 : 18 maximum rate allows V
LCD
< 5 V for
most LCD liquids.
4V
≤
Table 1
Optimum/maximum values for V
OP
(off pixels start darkening; V
off
= V
th
)
Table 2
Minimum values for V
OP
(on pixels clearly visible; V
on
> V
th
)
MUX RATE
NUMBER OF LEVELS
V
on
/V
th
1.272
2.236
V
OP
/V
th
3.7
2.283
V
OP
(typical; for V
th
= 1.4 V)
5.2 V
3.9 V
1 : 18
1 : 2
5
3
MUX RATE
NUMBER OF LEVELS
V
on
/V
th
1.12
1.2
V
OP
/V
th
3.2
1.5
V
OP
(typical; for V
th
= 1.4 V)
4.6 V
2.1 V
1 : 18
1 : 2
5
3
8.4
Oscillator
The on-chip oscillator provides the clock signal for the
display system. No external components are required and
the OSC pin must be connected to V
DD
.
8.5
External clock
If an external clock is to be used this is input at the OSC
pin. The resulting display frame frequency is given by
f
f
frame
3072
=
Only in the power-down state is the clock allowed to be
stopped (OSC connected to V
ss
), otherwise the LCD is
frozen in a DC state.
8.6
Power-on reset
The on-chip power-on reset block initializes the chip after
power-on or power failure. This is a synchronous reset and
requires 3 OSC cycles to be executed.