12

KB3511

Kingbor Technology Co.,Ltd

TEL:(86)0755-26508846 FAX:(86)0755-26509052

APPLICATIONS INFORMATION

Figure 3. kB3511 Layout Diagram (See Board Layout Checklist)

RUN2

RUN1

POR

SW2

GND

SW1

MODE/SYNC

KB3511ADJ

C4

C5

L1

L2

R4

R2

R1

R3

BOLD LINES INDICATE HIGH CURRENT PATHS

regulator operating in a 70

°C ambient temperature is

approximately:

which is below the absolute maximum junction tempera-

ture of 125

°C.

Design Example

As a design example, consider using the KB3511 in an

portable application with a Li-Ion battery. The battery

mum of 600mA in active mode and 2mA in standby mode.

needs power in standby, Trickle Mode operation is selected

for good low load efficiency.

First, calculate the inductor value for about 30% ripple

The closest standard value is 10

µF. Since the output

10

µF.

The output voltage can now be programmed by choosing

the values of R1 and R2. To maintain high efficiency, the

current in these resistors should be kept small. Choosing

2

µA with the 0.6V feedback voltage makes R1~300k. A

close standard 1% resistor is 280k, and R2 is then 887k.

The PGOOD pin is a common drain output and requires a

pull-up resistor. A 100k resistor is used for adequate speed.

Figure 1 shows the complete schematic for this design

example.

Board Layout Considerations

When laying out the printed circuit board, the following

checklist should be used to ensure proper operation of the

KB3511. These items are also illustrated graphically in

the layout diagram of Figure 3. Check the following in your

layout:

and GND (exposed pad) as close as possible? This capaci-

tor provides the AC current to the internal power MOSFETs

and their drivers.

3. The resistor divider, R1 and R2, must be connected

terminated near GND (exposed pad). The feedback signals

traces, such as the SW line (Pins 4 and 7), and its trace

should be minimized.

4. Keep sensitive components away from the SW pins. The

routed away from the SW traces and the inductors.

5. A ground plane is preferred, but if not available, keep the

signal and power grounds segregated with small signal

components returning to the GND pin at one point and

6. Flood all unused areas on all layers with copper.

Flooding with copper will reduce the temperature rise of

power components. These copper areas should be con-

L

V

MHz

mA

V

V

H

=

⎝⎜

⎠⎟

=µ

33

2 2

300

1

33

42

107

.

.

.

.

.

Choosing the closest inductor from a vendor of 1.0

µH

inductor, results in a maximum ripple current of:

∆=

µ

−

⎛

⎝⎜

⎞

⎠⎟

=

I

V

MHz

V

V

mA

L

33

22

10

1

33

42

330

.

..

.

.

selection is then based on load step droop instead of ESR

requirements. For a 5% output droop:

C

mA

MHz

V

F

OUT

≈=

µ

3

600

22

5

3 3

49

.( %

.

)

.

−