APPLICATION

INFORMATION

DESIGN PROCEDURE

The

dc-dc converter is intended for systems powered by a single-cell, up to triple-cell alkaline,

NiCd, NiMH battery with a typical terminal voltage between 0.9V and 4.5V. It can also be used in

systems powered by one-cell Li-ion or Li-polymer with a typical voltage between 2.7V and 4.2V.

Additionally, any other voltage source with a typical output voltage between 0.9 V and 4.5 V can power

systems where the

is used. Due to the nature of boost converters, the output voltage

regulation is only maintained when the input voltage applied is lower than the programmed output

voltage.

Setting The Output Voltage

For the

adjustable output version, the internal 1.23V reference voltage is compared to the

voltage at the FB pin to generate an error signal at the output of the error amplifier. A voltage divider from

The use of 1% accuracy metal film resistor is recommended for the better output voltage accuracy. To

minimize the power consumption under light loads, it is desirable to choose large resistance values for

both R1 and R2.

Table1 lists the recommended values for particular output voltage settings.

R2( )

R1( )

3.3V

1.02M

604K

5.0V

1.02M

332K

Fixed Output Voltage

The

has two fixed output voltage options: 3.3V and 5V. An internal resistor divider is connected to

the FB pin internally, which eliminates the need for external feedback resistors. When designing with

the fixed output voltage option, remember to leave the FB pin open; otherwise the output voltage

will be affected. However, a feed-forward capacitor can still be added between the FB pin and

Inductor Selection

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