Specifications
8–16 EPSON
SED1240 Series
Voltage regulating circuit
The boosting voltage generated at V
OUT is output as a
liquid crystal drive voltage of V
5 through the voltage
regulating circuit.
The SED1240 series is provided with a high-precision
constant-voltage source, a 32-step electronic volume
function, and a V
5 voltage regulating resistor. This
permits constructing a high-precision voltage regulating
circuit with a small quantity of parts. The voltage
regulating circuit outputs V
EV and has a temperature
gradient of about –0.04%.
As the V
5 voltage regulating resistor, a built-in resistor or
an external resistor can be selected by command as a
matter of configuration.
[When using an external resistor (No use of V
5 voltage regulating built-in resistor is set by command.)]
The V5 voltage can be obtained from the following expression 1 by adjusting resistors Ra and Rb within the range of
| V
5 | < | VOUT |.
R1 R2 R3
VR
V0
VDD
+
V
5
VEV (constant-voltage source
+ electronic volume)
-
Ra
Rb
V
5
= (1 +
R
b
) • V
EV
..............................
1
R
a
In this case, VEV is determined by the constant-voltage
source in the IC and by setting the electronic volume.
When the electronic volume value is (00000), V
REG
·
=
·
2.0 V, being constant.
For voltage adjustment of V
5 output, connect a variable
resistor among V
R, VDD, and V5. For fine voltage
adjustment of V
5 output, it is recommended to combine
fixed resistors R1 and R3 with variable resistor R2.
[R1, R2 and R3 setup example]
• R1 + R2 + R3 = 1.2 MΩ (Determined by the current
value I
05 flowing between VDD and V5. Supposing I05
≤ 5 µA)
• Minimum voltage of V
5: –6 V (Determined by liquid
crystal characteristic)
• Variable voltage range by R2: –4 to –6 V (Determined
by the liquid crystal characteristic)
• When the electronic volume register is set to (0, 0, 0,
0, 0), V
EV = 2.0 V (TYP). Accordingly, each resistor
value can be calculated by the above conditions and
expression 1 as follows.
R1 = 400 KΩ
R2 = 200 KΩ
R3 = 600 KΩ
Note 1: The input impedance of the V
R pin is high, so
it is necessary to take a proper measure against
noise for short wiring and shielding wiring.