hd66421 Renesas Electronics Corporation., hd66421 Datasheet - Page 33

• Manufacturer Part Number: hd66421
• Description: Ram-provided 160 Channel 4-level Grey Scale Driver For Dot Matrix Graphics Lcd
• Manufacturer: Renesas Electronics Corporation.

Power Supply Circuits
HD66421 has following circuits for power supply
circuit: operational amplifiers, resistive dividers,
bias control circuit and contrast control circuit.
LCD driving voltage, VLCD, must be generated
externally.
LCD Drive Voltage Power Supply Levels: To
drive the LCD, a 6-level power supply are
necessary. These levels are generated internally or
supplied from outside. When an internal voltage
levels generator is chosen, external capacitors are
needed to stabilize these levels. AS the HD66421
incorporates operational amplifiers to these levels,
this circuit gives better quality of display with less
power
programmable.
Bias current of internal operational amplifier is
determined with a resister which is inserted
between IREFM and GND. This resister value is
between 1M
make
operational amplifier. However, too large value
loose operational margin of amplifiers.
Keep following relationship among voltage levels;
Vcc IREFMP > IREFM GND
VLCD > Vcc > GREF GND
VLCD V1O V2O V3O V4O V5O GREF GND
VLCD-Vcc 1.0V
IREFP-IREFM 1.0V
Vcc-GREF 1.0V
Example.1 LCD bias level
12
11
10
9
8
7
6
5
4
3
2
1
0
Preliminary
0
less
consumption.
1/80 duty Display(1/9 bias, VLCD=12V,GND=0V)
power
7
and 5M . Larger resister value
Contrast (R16)
consumption
F
This
divided
17
at
(maximum)
ratio
1F
internal
VLCD
V1O
V2O
V3O
V4O
V5O
is
33
Example 2. LCD bias level
Contrast Control: Internal contrast control
circuit can change the output voltage level of
VLCD by setting data to contrast control register,
R16. VLCD adjustable range are showed below;
• 1/11 bias
•
Partail display function uses 1/4 bias ratio from
VCC to GND. 8 levels of contrast can be selected
with data bit 2 to 0 of R16.
• 1/8 bias
• 1/9 bias
5
4
3
2
1
0
Partial Display
(Example 1.)
0.82 * (Vcc-GND) VCC 0.997 * (VCC-GND)
(Example 2.)
0.73 * (VLCD-GND) VLCD 0.988 * (VLCD-GND)
0.82 * (VLCD-GND) VLCD 0.993 * (VLCD-GND)
0.79 * (VLCD-GND) VLCD 0.992 * (VLCD-GND)
0
Partial Display(1/4 bias,VCC=5V,GND=0V)
Contrast (R16)
4
Rev. 1.1E '99.02.10
(maximum)
HD66421
7
VCC
V1O
V2O
V3O
V4O
V5O