BU21072MUV_16 Datasheet, PDF (21/40 Pages) Rohm – Capacitive Switch Controller ICs

BU21072MUV / BU21078MUV / BU21078FV
Power on sequence
Power supply pin is VDD only. AVDD and DVDD are supplied by each LDO included BU21072/78MUV, so that have no
priority about power on sequence. When VDD reaches to the effective voltage, power-on-reset which initializes the digital
block is released.
Power-On-Reset monitoring VDD, so it should be set to proper value of decoupling capacitor and VDD rise time, so as to
rise to the proper voltage (DVDD→VDD).
Recommended value of external capacitors
VDD
C1 0.1uF VDD decoupling capacitor
C2 1.0uF DVDD decoupling capacitor
C3 2.2uF AVDD decoupling capacitor
VDD
AVDD
DVDD
VDD
C₁
BU21072MUV
C₃
BU21078MUV
BU21078FV
C₂
DVDD
VSS
Over 100usec
GND
AVDD
Figure 14. Arrangement of external decoupling capacitors
3.30V
1.50V
2.73V
Figure 15. Timing chart of power on sequence
When power-on-reset is released, MPU starts initial sequence. Inform by the INT port to the host that the initialization
has been completed. After verify that the initialization has completed, the host will need to resend the command to the IC.
In the case that WDTR is released as well, MPU starts initial sequence. If WDTR has released, all registers have been
initialized. So the host will need to resend the command to the IC.
VDD
Power on Reset
(ActiveLow)
LED0-5
INT
Initialize IC
about 350usec
Hi-Z
about 200usec
Interrupt of Initialization Done
Figure 16. Timing chart of initialization
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14.Jul.2016 Rev.004