Seiko Instruments G1216B1N000-3D0E - Manual (Page 24)

AN.No.G1216B1N000-3D0E
- 21 -
3.5 Contrast Adjustment and Power Supply Example
The LC panel viewing angle and display screen contrast are greatly affected by the ambient
temperature. The recommended LC drive voltage (Vopr) at each temperature is given below. Vopr
is a value at which the best display is visually obtained. This value does not always correspond to the
value at which the best contrast (Cmax.) is obtained. A contrast adjustment circuit example is shown
below:
V
opr
= V
DD
−
V
LC
Temperature ( ° C)
Voltage (V
opr
)
−
20
13.5
0
13.0
25
12.5
50
11.5
70
10.5
V
DD
V
SS
V
LC
G1216
R
A
C1
C2
12 V
R
A
=10 k
Ω
R
B
=1.2 k
Ω
R
V
(variable resistor)
=10 k
Ω
C1, C2=10
µ
F R
V
R
B
5V
3.6 LED Backlight Driver Examples
(1) Example 1
A basic LED backlight driver example is shown in Figure 11.
G1216
R=30
Ω
, (
≥
1/4W)
V
IN
= +5V
LEDA
LEDC
Where resistance “R” is the limit resistance of the LED forward current. The forward current depends
upon the temperature. Especially, it must be decreased at high temperature. For temperature
dependence, refer to forward current reduction characteristics described in 1.8 (1). The operating
temperature for the G1216 ranges from
−
20
°
C to +70
°
C. It is necessary to determine limit resistance
“R” so that the forward current becomes 50 mA or lower at +70
°
C.
Forward voltage VF at each temperature of the LED backlight is shown in Table 3.
Table 3 Forward Voltage At Temperatures
Temperature (Ta) Conditions V
F
min. V
F
typ. V
F
max.
−
20
°
C I
F
=90 mA 3.9 V 4.3 V 4.6 V
+25
°
C I
F
=90 mA 3.8 V 4.1 V 4.4 V
+70
°
C I
F
=50 mA 3.5 V 3.7 V 3.9 V
Figure 10 Contrast Adjustment
Figure 11 LED Backlight Driver Example 1