
LCD Controller-Driver
S-4544A
14
Seiko Instruments Inc.
16.2.2 LCD Voltage Command Fine Adjustment Circuit
The contrast can be adjusted by adjusting V5. It is also adjusted through a corresponding command input. V5 is set
by the lower 4 bits of the data bus and can be adjusted to 16 steps. It is effective to adjust V5 together with the LCD
voltage command fine adjustment circuit and the voltage regulator. First, set the fine adjustment data to (0, 1, 1,
1) or (1, 0, 0, 0), and adjust to the optimum contrast using a voltage regulator. The values Ra and Rb are
calculated from the fine adjustment voltage width and minimum voltage of V5 to be set. When the LCD voltage
command fine adjustment circuit is not in use, set the minimum voltage to (0, 0, 0, 0).
16.3
LCD Bias Voltage
A built-in LCD bias resistor creates bias voltage for the LCD drive. The LCD bias can be selected among 1/6.7, 1/5,
and 1/4 with the corresponding command. Since the bias voltage is supplied via the voltage follower to the LCD
driver, current consumption is significantly reduced.
When FNC1 is
“
L
”
and FNC2 is
“
H,
”
it is possible to connect the externally-attached bias resistor directly to pins V1
through V5. A 1/2 or more bias ratio can be freely supplied as an LCD drive voltage. Regardless of the level, the
voltage can be inputted to pins V1 through V4.
When using an externally-attached bias resistor, the S-4544A stops the voltage follower. Select an appropriate
value of resistance of the bias resistor according to the size of the LCD panel and LC capacity.
16.4
Voltage Follower
The voltage follower buffers the LCD bias voltage created by the built-in bias resistor, and supplies it to the LCD
drive circuit. At the same time, the LCD bias voltage is output to pins V1 through V4. Thus, connect a capacitor in
accordance with the size and capacity of the LCD panel to stabilize the LCD bias voltage. It is not possible to output
the LCD bias voltage from pins V1 through V5 or supply the LCD bias voltage to other circuits.
16.5
Reference Voltage Circuit
The reference voltage circuit generates VREF reference voltage of the voltage regulator. There are two values of
VREF depending upon the temperature coefficient. For details, refer to “COMMAND EXPLANATION, 20. Reference
Voltage Temperature Compensation Coefficient Selection.”
D3
0
D2
0
D1
0
D0
0
V5
Minimum Voltage Setting
Default
:
0
1
1
0
1
0
1
0
:
1
1
1
1
Maximum Voltage Setting