BU9873 Datasheet, PDF (29/40 Pages) Rohm – I2C BUS Serial Interface RTC with High-precision Oscillation Adjustment

BU9873
Datasheet
13. Notes during Power On
During power on, in IC internal circuit and set, V_DD rises through unstable low voltage area, and IC inside is not
completely reset, and malfunction may occur. To prevent this, functions of POR circuit and LVDD circuit are equipped.
To assure the action, observe the following conditions during power on.
(1) Set SDA = “H” and SCL =“L” or “H”
(2) Start power source so as to satisfy the recommended conditions of t_R, t_OFF, and V_bot for operating POR circuit.
VDD
tR
Recommended conditions of t_R, t_OFF, V_bot
t_R
t_OFF
V_bot
10ms or below 10ms or larger 0.3V or below
tOFF
Vbot
100ms or below 10ms or larger 0.2V or below
0
Figure 33. V_DD rise waveform
(3) Set SDA and SCL so as not to become 'Hi-Z'.
When the above conditions (1) and (2) cannot be observed, take the following countermeasures.
(a) In the case when the above condition (1) cannot be observed. When SDA becomes “L” at power on.
→Control SCL and SDA as shown below, keep SCL=”H” and SDA=”H”.
VDD
SCL
tLOW
SDA
After VDD becomes stable
tHD:DAT tSU:DAT
Figure 34. When SCL="H" and SDA="L"
After VDD becomes stable
tSU:DAT
Figure 35. When SCL="L" and SDA="L"
(b) In the case when the above condition (2) cannot be observed
→After power source becomes stable, execute software reset.
(c) In the case when the above condition (1) and (2) cannot be observed
→Carry out (a), and then carry out (b).
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