BU9728AKV Datasheet, PDF (8/10 Pages) Rohm – LCD driver for segment-type LCDs

Standard ICs
BU9728AKV
The display data input to the command / data register (when C / D is LOW) is written to the DDRAM address and the
address consisting of the specified address + 1, which are indicated by the upper four and lower four bits of the data,
respectively. The four bits of the display data are written sequentially, starting from the MSB, to the MSB of the
DDRAM bits.
MSB
LSB
D7
D6
D5
D4
D3
D2
D1
D0
Specified address
(bit3
bit0) (bit3
Specified address + 1
bit0)
If the Rewrite DDRAM command is input (C / D is HIGH), the four bits of the display data in the Rewrite DDRAM
command are written to the specified DDRAM address.
The four bits of the display data are written sequentially, starting from the MSB, to the MSB of the DDRAM bits.
MSB
LSB
1
0
0
∗
D3
D2
D1
D0
Rewrite DDRAM command
Display data
(4) Timing generator
(bit3
bit0)
Connecting Rf between OSC1 and OSC2 causes the internal oscillator circuit to start oscillating, and generates a dis-
play timing signal. The oscillator can also be started by inputting an external clock.
OSC1
Rf
OSC2
OSC1
OSC2
EXIT CLOCK INPUT
OPEN
Fig. 3 Rf oscillator circuit
(5) LCD drive power supply
Fig. 4 External clock input
The LCD drive power supply is generated by the BU9728AKV. The LCD drive voltage (VLCD) is supplied by VDD - V3,
and the power supply is generated by V1 = 2 • VLCD / 3, V2 = VLCD / 3.
If an external bleeder resistance is used to supply the LCD drive voltage externally, the following relationship must
be observed:
VDD = V1 м V2 м V3 м VSS
VDD
V1
V2
V3
VDD
V1
V2
V3
VSS
VSS
Fig. 5 Example of connection when
using internal power supply
(6) LCD drive circuit
Fig. 6 Example of connection when
using external power supply
The LCD drive circuit is configured of four common drivers and 32 segment drivers. When oscillation begins, select-
ed waveforms are output automatically for valid common outputs by the common counter, and de-selected wave-
forms are output for other outputs.
For segment outputs, drive waveforms are output automatically by the display data and common counter.
The following page shows examples of common / segment output waveforms.
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