ML4854

PRODUCT SPECIFICATION

REV. 1.0.7 5/6/03

11

components. The PCB layout should be based on some

simple rules to minimize EMI and to ensure good regulation

performances:

1.

Place the IC, inductor, input and output capacitor as

close together as possible.

2.

Keep the output capacitor as close to the ML4854 as

Typically it should be within 0.25 inches or 6 mm.

3.

Keep the traces for the power components wide,

typically > 50 mils or 1.25 mm.

4.

Place the external networks for LBI and FB close to

ML4854, but as far away as possible from the power

components to prevent voltage transient from coupling

into sensitive nodes.

5.

On multilayer boards, use component side copper for

grounding around the IC and connect back to a quiet

ground plane using vias. The ground planes act as

electrostatic shields for some of the RF energy radiated.

6.

The connection of the GND pin of the IC (pin 8) to the

overall grounding system should be directly to the

bottom of the output filter capacitor. A star grounding

system radiating from where the power enters the PCB,

is a recommended practice.

Application Example:

Using ML4854 as a constant current source to drive four LEDs:

The current through the LEDs is maintained constant within a large input voltage range as shown in the diagram below:

L

L = 10

µH

Cin = Cout = 10

µF

R = 62 ohm

D1...D4 = QTLP 600C-EB (blue)

D1

ML4854

1

2

3

4

8

7

6

5

R

D2

Cout

Cin

+

+

+

R

D3

R

D4

R

20

ML4854 feeds LED QTLP 600C-EB

Input Voltage (V)

19.8

19.6

19.4

19.2

19

18.8

18.6

18.4

18.2

18

012

3

4

5