SN8P2977
8-Bit Micro-Controller with Regulator, PGIA, 24-bit ADC
SONiX TECHNOLOGY CO., LTD
Page 45
Version 1.7
induces noise and overlaps with the DC power. VDD drops by the noise, and the system works under unstable power
situation.
The power on duration and power down duration are longer in AC application. The system power on sequence protects
the power on successful, but the power down situation is like DC low battery condition. When turn off the AC power,
the VDD drops slowly and through the dead-band for a while.
3.4.2
THE SYSTEM OPERATING VOLTAGE DECSRIPTION
To improve the brown out reset needs to know the system minimum operating voltage which is depend on the system
executing rate and power level. Different system executing rates have different system minimum operating voltage.
The electrical characteristic section shows the system voltage to executing rate relationship.
Vdd (V)
System Rate (Fcpu)
System Mini.
Operating Voltage.
System Reset
Voltage.
Dead-Band Area
Normal Operating
Area
Reset Area
Normally the system operation voltage area is higher than the system reset voltage to VDD, and the reset voltage is
decided by LVD detect level. The system minimum operating voltage rises when the system executing rate upper even
higher than system reset voltage. The dead-band definition is the system minimum operating voltage above the system
reset voltage.
3.4.3
BROWN OUT RESET IMPROVEMENT
How to improve the brown reset condition?
There are some methods to improve brown out reset as following.
LVD reset
Watchdog reset
Reduce the system executing rate
LVD reset:
VDD
VSS
System Normal Run
System Stop
LVD Detect Voltage
Power On
Delay Time
Power
System Status
Power is below LVD Detect
Voltage and System Reset.
The LVD (low voltage detector) is built-in Sonix 8-bit MCU to be brown out reset protection. When the VDD drops and
is below LVD detect voltage, the LVD would be triggered, and the system is reset. The LVD detect level is different by
each MCU. The LVD voltage level is a point of voltage and not easy to cover all dead-band range. Using LVD to
improve brown out reset is depend on application requirement and environment. If the power variation is very deep,
violent and trigger the LVD, the LVD can be the protection. If the power variation can touch the LVD detect level and
make system work error, the LVD can’t be the protection and need to other reset methods. More detail LVD information
is in the electrical characteristic section.