BU97941FV_15 Datasheet, PDF (17/27 Pages) Rohm – Multifunction LCD Segment Driver

BU97941FV MAX 104 segments (SEG26×COM4)
●Caution during Power supply ON/OFF
○POR circuit
During power supply rise, because the IC internal circuit and reset pass through an area of unstable low voltage and VDD
starts up, there is a risk that the inside of the IC is not completely reset and wrong operation might occur. In order to
prevent this, P.O.R circuit and Software Reset functions are incorporated. In order to ensure that operation, do as follows
during power supply rise:
1. Set power up conditions to meet the recommended tR, tOFF and Vbot specs below in order to ensure POR operation.
（POR circuit uses VDET type）
(＊The voltage detection of POR differs depending on the used environment etc.
In order to to assure the operation of POR, it is recommended to make Vbot = 0.5V or lower.)
VDD
VDET
tR
tOFF
Vbot
Recommended conditions of tR, tOFF, Vbot
tR
tOFF
Vbot
10ms or lower
1ms or higher
0.5V or lower
VDET
TYP 1.2 V
* VDET is integrated POR detection level
Figure 15. Rise Waveform
2. When the conditions are not met, do the following countermeasures after power supply ON:
(1) Set CSB to ‟H‟.
(2) Turn ON the CSB and execute SWRST command.
In order for the SWRST command to take effect for sure, it is recommended to start up CSB after 1ms after the VDD
level has reached 90%.
※Since the state is irregular until SWRST command input after power supply ON, countermeasure through Software
Reset is not the perfect substitute for P.O.R function so it is important to be careful.
VDD
CSB
Min 1ms
Min 50ns
SWRST command
Figure 16. SWRST command sequence
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