9. Voltage Regulator
19.1 Features
• Linear Regulation.
• Operating Voltage Range 4.0 - 25V.
• Fixed Output Voltage at 3.3V.
ATmega406 is supplied by the VFET terminal. Operating voltage range atthe VFET terminal is
4.0 - 25V. The Internal Voltage Regulator regulates this voltage down to 3.3V, which is a suitable
supply voltage for the internal logic, I/O lines, and analog circuitry.
An external decoupling capacitor of 1 µF or largeris required for stable operation of the Voltage
Regulator. A larger capacitor will allow larger load currents and increase start-up time.
The block diagram of the Voltage Regulator is shown in Figure 19-1.
Figure 19-1. Voltage Regulator Block Diagram
19.2 Operation
The Regulator will operate in all sleep modes, including Power-off. In this mode the regulator will
automatically reduce the ATmega406's power consumption by turning off supply for all peripheral modules, allowing only the Charger Detect module and the Voltage Regulator itself to
operate.
The Regulator will automatically ensure that it has stable work conditions before allowing itself to
start regulating the VFET terminal. If the voltage at the VFET pin is below the Regulator-on
Threshold voltage, VROT
, the LDO will be switched off.
Powering-up the regulator is either done from the battery side when the smart battery controller
is assembled with the battery pack and there isno charger present, or from the charger side
when a deep discharge has occurred (0V charging).
When powering- up with a charger present, the voltage between the VFET and the PVT pin must
be above a Charge-Threshold voltage, VCH