MP4603 – WHITE LED DRIVER FOR LARGE SIZE TV BACKLIGHTING

MP4603 Rev. 1.0

www.MonolithicPower.com

12

4/27/2012

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© 2012 MPS. All Rights Reserved.MP4603

Selecting the Output Capacitor

The output capacitor normally limits the output

voltage ripple (

the DC value, and ensures a stable feedback

loop. Select an output capacitor value with low

impedance at the switching frequency. Use

ceramic capacitors with X5R or X7R dielectrics

for their low ESR characteristics.

LED

OUT

OUT

sOUT

IN

OUT

IV

C

fV

(V

V

)











Setting the Over Voltage Protection

The output voltages of some converters, such as

buck-boost and boost converters, can rise to very

high levels without a limiting function. Over-

voltage protection (OVP) limits the output voltage

to below the operating rating. Use a voltage

divider to set the OVP point.

OVP

2

R

V1.2V (1

)

R

the

TYPICAL

APPLICATION).

For

most

applications, set the OVP point around 10% to

30% higher than the output voltage. Check that

the set OVP point will not exceed the operation

rating.

FAULT Condition Output

The MP4603 has an open drain output as a

FAULT indicator. Under normal conditions,

FAULT is a high-Z output and can be set to any

desired voltage with external resistors. However,

VSS by 300mV for ~450μs, or OVP triggers at

for this pull down switch is ~100Ω.

PC Board Layout

Place the high-current paths (VSS, VIN and SW)

very close to the device with short, direct, and

wide traces. Place the input capacitor as close as

possible to the VIN and VSS pins. Place the

external feedback resistors next to the FB pin.

Keep the switch node traces short and far away

from the feedback network.

Pay attention to the layout of the high frequency

switching loop, which should be placed as small

as possible.

For buck applications, the high frequency

switching loop is composed of the input capacitor,

the internal switch of IC (VIN pin to SW pin) and

the diode. Place the input capacitor and the

diode close to the IC.

For buck-boost applications, the high frequency

switching loop is composed of the input capacitor,

the internal switch, the diode and the output

capacitor. Place the input and output capacitors

close together, close to the IC, and to the diode.

Top Layer

Bottom Layer

Figure 2: PCB Layout