37
8048C–AVR–02/12
ATtiny43U
8.2.1
Stop Mode
input voltage ,V
natively, the boost converter enters Stop Mode when instructed by firmware to do so.
In this mode of operation the boost converter is not active and current consumption is decreased
to a minimum. This is in order to prevent battery discharge and to avoid battery damage.
The voltage at the converter output, V
CC, has no effect in this mode. The converter monitors the
voltage of the input pin, V
BAT, and waits for it to rise above the start voltage, VSTART (see Table 20-7 on page 162). When there is sufficient voltage at the input the converter exits Stop Mode
and enters Start Mode.
8.2.2
Start Mode
the input voltage, V
Alternatively, the boost converter switches from Active Mode to Start Mode when the output volt-
age drops below V
BOOST.
In this mode of operation the boost converter pumps up the V
CC voltage by switcing at a 50%
duty cycle and high frequency, until it reaches V
BOOST.
All loads should be disconnected during this stage. The boost converter is designed to remain in
Start Mode for a short moment, but it is optimised to bring the microcontroller on line, only. If
there are additional loads connected to the V
CC pin the boost converter may not reach the VCC
voltage required to go into Active Mode.
8.2.3
Active Mode
output voltages are sufficiently high. This means that V
BAT is above VSTART and VCC is above
V
BOOST. If input voltage drops below VSTOP or output voltage drops below VBOOST the converter
will exit Active Mode. Alternatively, firmware can force the boost converter to exit Active Mode
and enter Stop Mode.
In this mode of operation, the boost converter keeps V
page 162 by constantly adjusting the duty cycle between energy charge and discharge phases.
The duty cycle is affected mainly by input voltage, V
BAT, load current, ILOAD, and temperature.
By default, the boost converter operates in Active Regulated Mode but when load current drops
Load Current” . In Active Low Current Mode current consumption is minimised on the expense of
output voltage regulation.
8.2.4
Examples
Figure 8-4 illustrates operating modes and input and output voltages of the boost converter. As
input voltage, V
converter enters Start Mode and output voltage, V
CC, begins to rise. At VBOOST output voltage
the converter exits Start Mode and goes into Active Mode. When output voltage exceeds the
power-on threshold V
troller is released from reset.