ML4863

8

Figure 3. 5V, 2A Circuit

Figure 2. 5V, 1A Circuit

47µF

VIN

NDS9955

1µF

Coiltronics

CTX20-4

100m

Ω

VOUT

5V, 1A

ML4863

VIN

SENSE

SHDN

VFB

GND

OUT 2

OUT 1

VCC

400µF

100µF

VIN

NDS9410

NDS9410

1µF

Dale

LPE6562

50m

Ω

VOUT

5V, 2A

ML4863

VIN

SENSE

SHDN

VFB

GND

OUT 2

OUT 1

VCC

800µF

3c.

Specify the inductor’s DC winding resistance:

3d.

Specify the coupled inductor's turn ratio:

Np : Ns = 1:1

4a.

Calculate the minimum output capacitance

required using equation 5.

C

=×

+

050

56

5

25 10

01

6

.

.

.

= 55µF

(5a)

4b.

Establish the maximum ESR for the output

capacitor using equation 6.

R

mV

×

01 012

150

..

= 80m

W

(6a)

Based on these calculations, the design should use two

100µF capacitors, with an ESR of 100m

W each, in parallel

to meet the capacitance and ESR requirements.

5.

As a final design check, evaluate the system

stability using equation 7.

100

6 10

012

5 4

18 10

6

mV

≤×

×

×+

×



!

"

$#

−

()

.(

)

–6

= 360mV (7a)

Since the inequality is met, the circuit should be stable.

Some typical application circuits are shown in Figures 2, 3,

and 4.

LAYOUT

Good PC board layout practices will ensure the proper

operation of the ML4863. Important layout considerations

follow:

• The connection from the current sense resistor to the

SENSE pin of the ML4863 should be made by a

separate trace and connected right at the sense resistor

lead.

the ML4863 for adequate filtering of the IC's internal

bias voltage.

• Trace lengths from the capacitors to the inductor, and

from the inductor to the FET should be as short as

possible to minimize noise and ground bounce.

• Power and ground planes must be large enough to

handle the current the converter has been designed for.

See Figure 5 for a sample PC board layout.