FP6770WDG datasheet(6/9 Pages) FITIPOWER

6 / 9 page

FP6770-1.5-OCT-2011

FP6770

85T

fitipower integrated technology lnc.

Application Information

Introduction

The FP6770 is a DC/DC charge pump converter that

produces a regulated 5V output with an input voltage

that range from 2.7V to 5V.

It boosts VIN to get a

regulated output voltage using the charge pump

topology.

Sensing the output voltage through an

internal resistor divider.

When the output voltage is

lower, the internal comparator will increase charge

pump ability, and vice versa. When the charge pump

is enabled, a two-phase non-overlapping clock

activates the charge pump switches.

Efficiency

Let’s take advantage of conversation of charge for

flying capacitor.

Assume that the flying capacitor

has reached its steady state.

AVE

OFF

AVE



(1)

According to the equation (1), the input current is

twice the output current.

OUT

AVE

OFF

AVE

OFF

AVE









The efficiency of charge pump is given below:

OUT











Short Circuit/Thermal Protection

FP6770 have a built-in short circuit current limiting

and an over temperature protection.

During the

short

circuit

condition,

the

output

current

automatically limited at approximately 300mA on

VIN=3V. When the die temperature exceeds 160C,

the thermal protection will shut the charge pump

switching operation down and the die temperature

will reduce afterwards.

When the die temperature

drops below 135

C, the charge pump switching

circuit will restart.

If the fault doesn’t eliminate, the

above protecting operation will repeat again and

again.

It allows FP6770 to continuously work at

short circuit condition without damaging the device.

Shutdown

The output is disconnected from input when SHDN

pin is tied to GND.

In shutdown mode, most circuit

is turned off and the input current gets extremely

low.

Due to high impedance, SHDN pin can’t be

floated.

External Capacitor Selection

Three

external

capacitors

determine

FP6770

performances, in the aspects of output ripple

voltage,

charge

pump

strength

and

transient.

Optimum performance can be obtained by the use of

ceramic capacitors with low ESR.

Because a low ESR ceramic capacitor can reduce

noise and ripple, ceramic capacitor is recommended

for CIN and COUT.

The value of COUT determines the

amount of output ripple voltage.

output

capacitor with larger value results in smaller ripple.

CFLY determine the strength of charge pump. The

larger CFLY means that the larger output current and

larger ripple voltage on VOUT pin.

However, large

CIN and COUT are expected when a large CFLY

applies.

The value of capacitors, which is used

under

operation

condition,

determines

the

performance of a charge pump converter.

And two

factors,

follows,

affect

the

capacitance

capacitor.

There are many kinds of Ceramic capacitors

materials, such as X7R, X5R, Z5U and Y5V.

There

have different ESR, tolerance

in temperature and

differnet cpacitance loss

For example, a X7R or X5R type of capacitor can

retain most of the capacitance at temperature from

-40

C to 85C, but a Z5U or Y5V type will lose most

of the capacitance at that temperature range.

Layout Considerations

Because the high frequency and high transient

current of FP6770, careful consideration of PCB

layout.

Minimize the distance between every

component, CFLY and COUT especially.

It also

minimizes every connection length with a maximum

trace width to achieve the best performance of

FP6770.

Make sure each device connects to

immediate ground plane.

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