FC2338 datasheet(8/9 Pages) FS

8 / 9 page

resistor to lower resistor can be set as:

1.65

FBL

FBH

OVP

Where,

RFBL: The lower resistor of the feedback network

RFBH: The upper resistor of the feedback network

VOVP: Output over voltage setting point

If the system have no OVP，this pin will be

connected to GND.

4 Thermal Regulation

The FC2338 integrates thermal regulation function.

When the system is over temperature, the output

current is gradually reduced; the output power and

thermal dissipation are also reduced. The system

temperature is regulated and the system reliability is

improved. The typical thermal regulation temperature

is set to 140℃ internally.

5 Protection Functions

To improve the system reliability, FC2338 offers

protection functions:

When the LED is open circuit, the output voltage will

gradually rise up. The output voltage is sensed by the

FB pin when power MOSFET is turned off. When FB

voltage reaches the OVP threshold, it will trigger fault

logic and the system stops switching.

When the LED is shorted circuit, the switching

frequency will work under 7 kHz. Meanwhile, the

output voltage is low and the VCC pin cannot be

charged up by the output voltage, so the VCC pin

voltage will gradually decrease and finally reaches the

UVLO threshold.

After the system enters into fault condition, the VCC

voltage will decrease until it reaches UVLO threshold.

Then the system will re-start again. If the fault

condition is removed, the system will resume normal

operation.

saturated, the CS peak voltage will be relatively high.

When CS voltage reaches the internal limitation

(1.5V), the power MOSFET will be turned off

instantaneously. This cycle by cycle current limitation

can help protecting the power MOSFET, the inductor

and the output diode.

6 PCB Layouts

The following guidelines should be followed in

FC2338 PCB layout:

Bypass Capacitor

Put the bypass capacitor close to VCC pin, and loop

compensation capacitor to COMP pin.

Ground Path

Keep a short and wide ground path for current sense

resistor. The IC signal ground for COMP and FB

components should be connected to the IC GND.

The Area of Power Loop

The area of main current loop should be as small as

possible to reduce EMI radiation.

FB Pin

Put the divider resistor close to the FB pin as possible,

and keep the trace away to the switching node.

DRAIN Pin

To increase the copper area of DRAIN pin for better

thermal dissipation.

When the output is short circuit or the inductor is

FC2338

2019. 10. 02

8/9

Revision No : 0

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