BU97981KV-E2 Datasheet, PDF (26/50 Pages) Rohm – Multi-function LCD Segment Drivers

BU97981xxx Series MAX 196 segments (SEG49xCOM4)
Datasheet
LED1 Drive-Control (PWM1 “H” width control) Command (PWM1SET)
MSB
LSB
D/C D6 D5 D4 D3 D2 D1 D0 Hex
1^st byte Command
1
0
0
0
1
0
1
0 8Ah
2^nd byte Command
0
0 P11 P10 P9 P8 P7 P6
-
3^rd byte Command
0
0 P5 P4 P3 P2 P1 P0
-
Reset
-
00h
00h
2^nd and 3^rd byte command data are able to set from 00h to 3Fh (described as 8bit binary data).
In case, other value selected, sending command is ignored, and 2^nd and 3^rd byte command data set 3Fh.
In reset state, 2^nd and 3^rd byte command data set 00h.
In case, the command less than 3 byte, sending command are canceled.
According to PWM1SET command, LED1 driving signal is adjustable. PWM “H” width is adjustable by 12bit/8bit
resolution.
Explanation about P11 to P6 data of 2^nd byte command and P5 to P0 data of 3^rd byte command as follows
(The 2^nd byte data are used as upper 6bit, and 3^rd byte data are used as lower 6 bits.)
12bit mode : P11 data is used as MSB of 12 bits, and P0 data is used as LSB.
8bit mode : P11 to P8 are used as invalid bit.
P7 data is used as MSB of 8 bits, and P0 data is used LSB.
LED driving period is decided by the “H” width of PWM signal, generated by PWM generator circuit.
(resolution: 8bit/12bit selectable)
Ex.1
In case of external PWM clock 2MHz, parameter setting value is 2047 (P11 to P0 data: 7FFh)
1bit resolution: 500ns
ALL HI setting: PWM signal frequency about 500Hz, H width about 2.00msec
ALL Low setting: PWM signal frequency about 500Hz, H width 0us (In case of 12bit)
Ex.2
In case of internal PWM clock 40.96KHz(TYP), parameter 127 (P11 to P0 data: 7Fh)
1bit resolution: 24.41us
ALL HI setting: PWM signal frequency about 160Hz, H width about 6.20msec
ALL Low setting: PWM signal frequency about 160Hz, H width 0us (In case of 8bit)
BU97981 series PWM frequency is twice faster than BU9798 series in case of internal OSC clock use.
This command is reflected, synchronizing with a next PWM frame head.
And, LED port output is as follows
INHb=”H” : LED port output LED driving signal.
INHb=”L” : LED port output Hi-Z.
LED port operation does not affect Display ON/OFF state.
PMW(ALL HI）
FFFh(FFh)
(H width : wide _）
Duty shift
PMW(ALL Low）
000h(00h)
(H width : narrrow ）
About the PWM frequency and PWM “H” width calculation
PWM cycle and PWM “H” width, decided by PWM clock cycle is described as follows.
(PWM clock cycle is a minimum unit of PWM “H” width)
PWM frequency = PWM clock cycle × (Number of the steps(12bit = 4096, 8bit =256) – 1)
PWM H width = PWM clock cycle × Parameter set value(12bit: 0 to 4095, 8bit: 0 to 255)
PWM Duty = PWM H width/PWM cycle = Parameter set value / Number of the steps
In case, PWM is generated from internal clock, the PWM cycle varies, according to OSC frequency.
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10.Apr.2015 Rev.006