ATtiny43U datasheet(46/182 Pages) ATMEL

46 / 182 page

8048B–AVR–03/09

ATtiny43U

8.7

Typical Applications

A typical use of the boost converter is illustrated in Figure 8-2 on page 37. Components can be

optimized depending on the type of application. Table 8-2, below, presents recommendations for

three different types of applications (cost effective, high output current and long battery life). All

values are guidelines, only.

Notes:

1. Low ESR required.

2. High reverse leakage current, increases current consumption.

3. The diode is the largest individual contributor to battery life. The example diode keeps the

boost converter running and maintains a reasonable efficiency level.

4. Depends on internal resistance of power supply.

5. Depends on load current. May not be sufficient for maximum current rating.

8.8

Characteristics

Electrical characteristics of the boost converter are given in Table 20-7 on page 159. Typical

characteristics can be found under section “Boost Converter” on page 165.

8.9

Potential Limitations

When the device is powered via the boost converter some usage limitiations may apply. For

example, the highest allowed operating frequency of the device depends on supply voltage (see

“Speed Grades” on page 156) and the boost converter output voltage varies within the limits

given in Table 20-7 on page 159. This means that if the design allows the boost converter to go

into Active Low Current Mode the supply voltage will drop periodically, affecting the maximum

allowed operating frequency.

Provided the load current remains sufficiently high the boost converter will never enter Active

Low Current Mode and the supply voltage will remain high enough to run the device at higher

frequencies. The boost converter status bit BS can be used to determine if the boost converter is

in Low Current Mode (see “ADCSRB – ADC Control and Status Register B” on page 47).

Since the entire device is powered from the boost converter output variations will show in all

peripherals. This means that, for example, high levels of I/O pins may vary with supply voltage.

8.10

Bypassing the Boost Converter

It is possible to bypass and disable the boost converter so that the device can be powered

directly from an external supply. To force the boost converter into Stop Mode, connect pin V

BAT

to ground and provide the device with supply directly to the V

CC pin. To permanently disable the

Table 8-2.

Recommended Components and Values for Various Designs

Symbol

Component

Cost Effective

High Current

Battery Life

Unit

Inductor

15 (1)

µH

Schottky diode

10MQ100N

10BQ015 (2)

10BQ040 (3)

Resistor

680

Input Capacitor

1 (4)

4.7

µF

Secondary Input Cap.

100

Output Capacitor

10 (5)

µF

Secondary Output Cap.

–

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