FP6733S9G datasheet(8/11 Pages) FITIPOWER

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FP6733-1.6-JUN-2013

FP6733

fitipower integrated technology lnc.

Application Information

Operation

The FP6733 is designed in a current mode

PFM/PWM scheme which features an automatic

switch PFM/PWM mode to maintain the highest

efficiency and extend battery life.

The quiescent

current is less than 25

μA at no switching status.

The control loop is internally compensated reducing

the amount of external components.

Chip Enable

The FP6733 features a chip enable input pin that

allows on/off control of the regulator.

When

CE=Low, shutdown of the chip occurs and at that

time almost no quiescent current (<1

μA) flows. The

chip

enable

input

TTL/CMOS

compatible.

Connect CE to battery for normal operation.

Current Limit Protection

The FP6733 provides cycle-by-cycle over-current

protection.

Current

limit

accomplished

sensing voltage drop across the drain to source of

power switch.

If the current sense amplifier output

voltage is larger than current-limited threshold level

(Typ. 1.0A), it will immediately turn off power MOS.

Thermal Protection

Thermal protection limits total power dissipation in

the FP6733.

When the junction temperature

exceeds Tj=145

C, the thermal sensor signals the

shutdown logic and turns off most of the internal

circuitry.

The thermal sensor will turn internal

circuitry on again after the IC’s junction temperature

drops 30

C.

Adjustable Output Voltage

The output voltage of FP6733 ranges from 1.25V to

5.0V which is set by the external feedback resistor.

It can be calculated as:

Inductor Selection

A 3.3

μH to 10μH inductor is recommended for

general use.

The value of inductor depends on the

operating frequency.

Higher frequency allows

smaller inductor and capacitor but increasing internal

switching loss.

Two inductor parameters should be

considered, current rating and DCR.

The DCR of

inductor affects the efficiency of the converter.

The

inductor with lowest DCR is chosen for highest

efficiency.

The inductor value can be calculated as:

VI V

IL V

IL: inductor ripple current, usually set 20% x IL,

which defined as:

L f

The inductor should be rated for the maximum

output current (IO(MAX)) plus the inductor ripple

current ( I

L) to avoid saturation.

The maximum

inductor current (IL(MAX)) is given by:

IL MA

I max

Capacitor Selection

The FP6733 is permissible to use ceramic capacitor

for hand held instrument applications.

The value of

capacitor depends on acceptable voltage ripple.

The input capacitor can reduce peak current and

noise at power source.

It should be 10

μF at least

and be increased for better input voltage filtering.

Select the input capacitor to meet the input ripple

current and voltage rating.

When selecting an output capacitor, consider the

output ripple voltage and the ripple current.

The

ESR of capacitor is a major factor to the output

ripple.

For best performance, a low ESR output

capacitor is required.

The ripple voltage is given

by:

IL ESR

f C

The common aluminum-electrolytic capacitors have

high ESR and should be avoided.

Ceramic

capacitors have the lowest ESR in general.

It’s

recommended

use

μF

ceramic

output

capacitors for the FP6733.

Diode Selection

For diode selection, both forward voltage and diode

capacitance need to be considered.

The output

diode should be rated to the output voltage and

peak switch current.

Schottky diodes, with low

forward voltage drop and fast reverse recovery, are

the ideal choices for FP6733 applications.

Make

sure the diode’s peak current rating is at least IPK and

its breakdown voltage excee

ds VOUT.

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