FR9765 datasheet(10/11 Pages) FITIPOWER

10 / 11 page

FR9765-1.0-MAR-2012

FR9765

85T

fitipower integrated technology lnc.

Application Information (Continued)

I=0.3 IO T(MA

VIN VO T

VO T

FOSC I VIN

Where VIN is the maximum input voltage.

Compensation Components Selection

FR9765

COMP

Select the appropriate compensation value by

following procedure:

1. Calculate the R4 value with the following equation:

CO T 0.1 FOSC VO T

G A GCS VR F

where GEA is the error amplifier voltage gain, and

GCS is the current sense gain.

2. Calculate the C5 value with the following equation:

R4 0.1 FOSC

External Boost Diode Selection

For 5V input or 5V output applications, it is

recommended to add an external boost diode.

This

helps improving efficiency.

The boost diode can be

a low cost one, such as 1N4148.

FR9765

VIN

1N4148

This diode is also recommended for high duty cycle

operation (when duty cycle > 65%) and high output

voltage (VOUT > 12V) applications.

PCB Layout Recommendation

The

device’s

performance

and

stability

are

dramatically

affected

PCB

layout.

recommended to follow these general guidelines

shown as below:

1. Place the input capacitors and output capacitors

as close to the device as possible.

The traces

which connect to these capacitors should be as

short and wide as possible to minimize parasitic

inductance and resistance.

2. Place VIN bypass capacitors close to the VIN pin.

3. Place feedback resistors close to the FB pin.

4. Place compensation components close to the

COMP pin.

5. Keep the sensitive signal (FB, COMP) away from

the switching signal (SW).

6. The exposed pad of the package should be

soldered to an equivalent area of metal on the

PCB.

This area should connect to the GND

plane and have multiple via connections to the

back of the PCB as well as connections to

intermediate PCB layers.

The GND plane area

which connects to the exposed pad should be

maximized to improve thermal performance.

7. Multi-layer PCB design is recommended.

VIN

VOUT

GND

Exposed

Pad

Figure 15. Block Diagram of FR9765

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