EXTENDING INPUT VOLTAGE RANGE

Figure 4 shows a way to configure the LM2655 so that input

voltages of less than 4V can be converted. This circuit

makes use of the separate analog and power V

the supervisory circuits of the LM2655 are powered through

the AV

is input to the PV

within this range must be applied to AV

be low power because it only needs to supply 5mA. An input

capacitor should be connected across this source, and a

small bypass capacitor should be placed physically close to

the AV

powered by a separate source, the only requirement of the

voltage at PV

desired output voltage. The source connected to PV

also need an input capacitor and bypass capacitor, but the

input capacitor must be selected following the guidelines ex-

plained in the INPUT CAPACITOR section.

OBTAINING OUTPUT VOLTAGES OF LESS THAN 1.25V

Some applications require output voltages less than 1.25V.

The circuit shown in

Figure 5 will allow the LM2655 to do

such a conversion. By referencing the two feedback resis-

tors to V

to V

V

where V

V

adjustable reference following the equation:

V

DS101284-25

FIGURE 3. Programmable output voltage.

DS101284-23

FIGURE 4. Extended input voltage range.

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