ST7565S
(B) When an External Resistance is Used (The V5 Voltage Regulator Internal Resistors Are Not Used) (1)
The liquid crystal power supply voltage V5 can also be set
without using the V5 voltage regulator internal resistors (IRS
terminal = “L”) by adding resistors Ra’ and Rb’ between VDD
and VR, and between VR and V5, respectively. When this is
done, the use of the electronic volume function makes it
possible to adjust the brightness of the liquid crystal display
by controlling the liquid crystal power supply voltage V5
through commands.
In the range where | V5 | < | VOUT |, the V5 voltage can be
calculated using equation B-1 based on the external
resistances Ra’ and Rb’.
Rb'
V
5
= 1 +
V
EV
( )
Ra'
Rb'
α
162
= 1 +
1 -
V
REG
( ) ( )
Ra'
α
162
∵ VEV
=
1 -
V
( ) ]
REG
[
V
DD
V
EV(fixed voltage power supply+electronic volume)
External
resistor Ra'
V5
External
resistor Rb'
Figure 11
Consequently, by equations B-2 and B-3,
Setup example: When selecting Ta = 25°C and V5 = –7 V for
ST7565S the temperature gradient = –0.05%/°C.
When the central value of the electron volume register is
(D5, D4, D3, D2, D1, D0) = (1, 0, 0, 0, 0, 0), then α = 31 and
VREG = –2.1V so, according to equation B-1,
Rb'
Ra'
= 3.12
Rb'
Ra'
Rb'
α
162
31
Ra' = 340kΩ
Rb' = 1060kΩ
V
5
= 1 +
1 -
V
REG
( ) ( )
-7V= 1 +
1 -
(-2.1)
( ) ( )
Ra'
162
At this time, the V5 voltage variable range and notch width,
based on the electron volume function, is as given in Table
14.
Moreover, when the value of the current running through
Ra’ and Rb’ is set to 5 uA,
Table 14
V5
Variable Range
Notch width
Min
Typ
Max
Units
V
–8.6
(EV=63)
–7.0
(EV=1,0,0,0,0,0)
–5.3
(EV=0)
52
mV
Ver 0.6c
36/72
2009/09/07
SITRONIX [ SITRONIX TECHNOLOGY CO., LTD. ]
