42
8048C–AVR–02/12
ATtiny43U
Battery voltage may start to rise after the boost converter has been stopped but before the
device has been reset, for example if a battery charger is connected. In this case the converter
will start automatically after battery voltage exceeds V
START, clearing the pending request for
reset. Hence, the firmware must be prepared for a situation where stopping the boost converter
does not lead to a device reset. For this purpose, the firmware may choose to monitor the Boost
To stop the boost converter, follow the below procedure:
1.
Write 110x xxxx to the Power Reduction Register, PRR (see
page 34)2.
Within 3 clock cycles of the above, write 10xx xxxx to PRR
3.
Within 4 clock cycles of the first step, write 01xx xxxx to PRR
8.5.2
Switching to Full Duty Cycle Mode of Operation
When duty cycle control is disabled the output voltage of the boost converter will rise as fast as
possible, resulting in a minimum switching time and a maximum idle time for the converter.
To turn on Full Duty Cycle (FDC) mode, follow the below procedure:
1.
Write 110x xxxx to the Power Reduction Register, PRR (see
page 34)2.
Within 3 clock cycles of the above, write 10xx xxxx to PRR
3.
Within 4 clock cycles of the first step, write 111x xxxx to PRR
8.5.3
Switching to Normal (Variable Duty Cycle) Mode of Operation
To return duty cycle control to the boost converter, follow the below procedure:
1.
Write 111x xxxx to the Power Reduction Register, PRR (see
page 34)
8.6
Component Selection
Refer to
Figure 8-8 for component placement and numbering.
Figure 8-8.
Boost Converter Schematic, Including Optional Components.
8.6.1
Inductor
Low inductance increases peak currents of the inductor, creating more interference noise and
lowering the overall efficiency of the converter. Too high inductance values force the converter
into non-stable operation. The boost converter has been optimized for a certain size inductance,
PB0
PB1
PB2
PB3
PB4
PB5
PB6
PB7
VCC
GND
PA7
PA6
PA5
PA4
PA3
PA2
PA1
PA0
VBAT
LSW
C4
C3
C2
C1
R1
L1
D1
VIN
OPTIONAL