BU97931FV Datasheet, PDF (15/32 Pages) Rohm – Multifunction LCD Segment Driver

BU97931FV MAX 112 segments (SEG28×COM4)
○LED drive-control (PWM “H” width control) command (PWMSET)
MSB
D/C D6 D5 D4 D3 D2
1st byte Command
1
0
0
0
1
0
2nd byte Command
0
0
0
0
0
0
3rd byte Command
0
0 P5 P4 P3 P2
LSB
D1 D0 Hex
1
0 8Ah
P7 P6
-
P1 P0
-
Reset
-
00h
00h
2nd and 3rd byte command data can be set from 00h to 3Fh (described as 8-bit binary data).
In case other value is selected, sending command is ignored and 2nd and 3rd byte command data are set to 3Fh.
In reset state, 2nd and 3rd byte command data are set to 00h.
In case the command is less than 3 byte, sending command is cancelled.
According to PWMSET command, LED driving signal is adjustable. PWM “H” width is adjustable by 8-bit resolution.
Explanation about P7 to P6 data of 2nd byte command and P5 to P0 data of 3rd byte command are as follows:
(The 2nd byte data are used as upper 2bit, and 3rd byte data are used as lower 6 bits.)
8bit mode : P7 data is used as MSB of 8 bits, and P0 data is used LSB.
LED driving period is determined by the “H” width of PWM signal, generated by PWM generator circuit (resolution : 8bit).
Ex)
In case external PWM clock is 125KHz, parameter setting value is 127 ( 7Fh )
1-bit resolution : 8us
ALL HI set : PWM signal frequency about 500Hz, H width about 2.00msec
ALL LOW set : PWM signal frequency about 500Hz, H width 0usec (in case 8bit resolution)
This command is reflected, synchronizing with a next PWM frame head.
And, LED port output is as follows. LED port operation does not affect Display ON/OFF state.
PWM (ALL HI）
FFh
(H width: wide)
PWM (ALL Low）
Duty shift
00h
(H width: narrow）
(*)PWM frequency and PWM “H” width calculation.
PWM cycle and PWM “H” width, decided by PWM clock cycle are described as follows.
(PWM clock cycle is a minimum unit of PWM “H” width)
PWM frequency = PWM clock cycle × (Number of the steps (8bit =256) - 1 )
PWM H width = PWM clock cycle × Parameter set value (8bit: 0 to 255)
PWM Duty = PWM H width/PWM cycle = Parameter set value / Number of the steps
In case PWM is generated from the internal clock, the PWM cycle varies depending on the OSC frequency.
In case LED is used as back light of LCD panel and PWM is generated from internal clock,
there is a possibility that the display will flicker. For such cases, please use under the PWM width ALL “L”
or ALL “H” setting only.
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10.Apr.2015 Rev.004