SN8F2250B Series
USB 2.0 Full-Speed 8-Bit Micro-Controller
3.4 BROWN OUT RESET
3.4.1 BROWN OUT DESCRIPTION
The brown out reset is a power dropping condition. The power drops from normal voltage to low voltage by external
factors (e.g. EFT interference or external loading changed). The brown out reset would make the system not work well
or executing program error.
VDD
System Work
Well Area
V1
System Work
V2
Error Area
V3
VSS
Brown Out Reset Diagram
The power dropping might through the voltage range that’s the system dead-band. The dead-band means the power
range can’t offer the system minimum operation power requirement. The above diagram is a typical brown out reset
diagram. There is a serious noise under the VDD, and VDD voltage drops very deep. There is a dotted line to separate
the system working area. The above area is the system work well area. The below area is the system work error area
called dead-band. V1 doesn’t touch the below area and not effect the system operation. But the V2 and V3 is under the
below area and may induce the system error occurrence. Let system under dead-band includes some conditions.
DC application:
The power source of DC application is usually using battery. When low battery condition and MCU drive any loading,
the power drops and keeps in dead-band. Under the situation, the power won’t drop deeper and not touch the system
reset voltage. That makes the system under dead-band.
AC application:
In AC power application, the DC power is regulated from AC power source. This kind of power usually couples with AC
noise that makes the DC power dirty. Or the external loading is very heavy, e.g. driving motor. The loading operating
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.
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