參數(shù)資料
型號(hào)： PCF8820U
廠商： NXP SEMICONDUCTORS
元件分類(lèi)： 顯示驅(qū)動(dòng)器
英文描述： 67 x 101 Grey-scale/ECB colour dot matrix LCD driver
中文描述： LIQUID CRYSTAL DISPLAY DRIVER, UUC235
封裝： BUMP, DIE-235
文件頁(yè)數(shù)： 26/60頁(yè)
文件大小： 316K
代理商： PCF8820U
2000 Dec 07
26
Philips Semiconductors
Product specification
67
×
101 Grey-scale/ECB colour dot matrix
LCD driver
PCF8820
It is not possible to measure temperature in Power-down
mode.
During a temperature measurement, the status register
value remains zero until the measurement has completed
and then the register is updated with the current
temperature value (non-zero value). Because the I
2
C-bus
interface is asynchronous to the temperature
measurement, the value read from the status register
should be validated by reading the status register a few
times.
During a temperature measurement, the temperature
coefficient (TC) has to be selected.
The ideal temperature read-out can be calculated by the
equation:
where T is the on-chip temperature in
°
C and ‘a(chǎn)’ is the
conversion constant (see Chapter 11).
To improve the accuracy of the temperature
measurement, it is recommended that the temperature
read-out is calibrated during the product’s final assembly.
Calibration of the temperature read-out requires a
measurement to be made at a defined ideal temperature.
The offset between the ideal temperature value and the
measured temperature value is calculated by:
TR
offset
= TR
ideal
TR
meas
where TR
meas
is the actual temperature read-out of the
PCF8820.Theoffsetvaluemustbestoredinanon-volatile
register, such as an EEPROM.
A calibrated temperature read-out can be calculated for
each measurement by the equation:
TR
cal
= TR
meas
+ TR
offset
The accuracy after the calibration is
±
10%
±
1 bit of the
difference between the measured temperature and the
calibration temperature. For this reason, it is
recommendedthatacalibrationisperformedatornearthe
most sensitive LCD temperature.
For example: calibration temperature is 25
°
C and the
measured temperature is
20
°
C. The relative error
A =
±
0.10
×
{25
(
20)}
±
1 bit
×
a
A =
±
4.5
±
1.13
A =
±
5.63
°
C.
This calibration accuracy is valid for temperature
measurements made when the supply voltage value is the
same as when it was calibrated.
8.1.7
V
LCD
CONTROL REGISTER
The V
LCDOUT
value can be set by software using the
bits V
OP6
to V
OP0
of the V
LCD
control register.
The programmed value for V
LCD
has to be calculated for a
reference temperature, called the cut-point temperature
T
cp
, using the equation:
V
LCD
(at T
cp
) = a + b
×
V
OP
The values for parameters T
cp
, a and b are given in
Table 7, and their relationship with the V
LCD
control
register values are shown in Fig.20.
The V
LCDOUT
generated is dependent on the operating
temperature T
oper
,theselectedtemperaturecoefficientTC
and the programmed value for V
LCD
at the reference
temperature T
cp
and is calculated by the equation:
V
LCD
(at T
oper
) = V
LCD
(at T
cp
)
×
{1 + TC
×
(T
oper
T
cp
)}
Two overlapping V
LCD
ranges are selectable by bit PRS
(see Table 7 and Fig.20). The maximum voltage that can
be generated depends on the values of V
DD2
and V
DD3
,
and the display load current. At a multiplex rate of 1 : 67,
the optimum operating voltage for the LCD can be
calculated by the equation:
where V
th
is the threshold voltage of the liquid crystal
material used.
The practical value for V
LCD
is determined by equating
V
off(rms)
withthedefinedLCDthresholdvoltage(V
th
),which
is the typically value when the LCD exhibits approximately
10% contrast.
Table 7
Parameter values for programming V
LCD
control
register
TR
ideal
128
T
27
°
C
–
(
)
+
1
a
×
=
SYMBOL
VALUE
UNIT
BIT PRS = 0
BIT PRS = 1
T
cp
a
b
programming
range
23.0
4.500
0.045
23.0
10.215
0.045
°
C
V
V
V
4.5 to 10.215
10.215 to 15.93
V
LCD
67
1
+
+
2
1
67
1
+
-------1
–
×
--------1
V
th
×
6.975
V
th
×
=
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