Rainbow-electronics ATtiny43U Manual de usuario descargar pdf (Pagina 45)

8048B–AVR–03/09

Too high resistor values may lead to Start Mode failures. See “Boost Converter Component Val-

ues” on page 45 for component recommendations and limits.

Capacitor C

should be located close to the device.

8.6.5 Output Capacitors

An output capacitor, C

, is required to keep the output voltage stable at times when energy is

transferred to the inductor. It is recommended to use a capacitor with high capacitance and low

Equivalent Series Resistance, ESR. A large capacitance helps to reduce the voltage ripple at

the output and a low ESR reduces voltage ripple and helps to keep the temperature of the

capacitor within limits.

The recommended capacitance at a given, steady-state load is calculated as follows:

... where T

is the switching frequency of the boost converter, V

is the allowed voltage ripple

and D is the duty cycle, calculated as shown in “Inductor” on page 43.

The recommended ESR is calculated as follows:

A secondary output capacitor, C

, is recommended and should be placed close to the device.

8.6.6 Summary

The table below summarises recommended component values for a typical application.

Note: 1. With these values the LPF provides a 32dB attenuation at the switching frequency of the boost

converter while permitting a supply voltage ripple of about ±200mV

2. Application specific limits may be tighter

OUT

LOAD

D××

--------------------------------------=

ESR

PEAK

---------------

≤

Table 8-1. Boost Converter Component Values

Component Recommended Value Min

(2)

Max

(2)

C = 4.7µF 1µF

C = 100nF

(1)

C = 22µF, ESR < 100mΩ

10µF

C = 100nF 100nF 100nF

= 1µA @ 25°C, V

= 0.5V @ 1A

L = 15µH ±20%, I

MAX

= 700mA, R < 150mΩ

15µH 15µH

R = 680Ω

(1)

1kΩ

1 2 ... 40 41 42 43 44 45 46 47 48 49 50 ... 181 182

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Rainbow-electronics ATtiny43U Manual de usuario Pagina 45

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