LTC3526/LTC3526B

0

3526bfd

The LTC3526/LTC3526B will maintain voltage regulation

even when the input voltage is above the desired output

voltage.Notethattheefficiencyismuchlowerinthismode,

and the maximum output current capability will be less.

Refer to the Typical Performance Characteristics.

SHORT-CIRCUIT PROTECTION

The LTC3526/LTC3526B output disconnect feature allows

output short circuit while maintaining a maximum inter-

nally set current limit. To reduce power dissipation under

short-circuit conditions, the peak switch current limit is

reduced to 400mA (typical).

SCHOTTKY DIODE

Although it is not required, adding a Schottky diode from

that this defeats the output disconnect and short-circuit

protection features.

PCB LAYOUT GUIDELINES

The high speed operation of the LTC3526/LTC3526B

demands careful attention to board layout. A careless

layout will result in reduced performance. Figure 2 shows

the recommended component placement. A large ground

pin copper area will help to lower the die temperature. A

multilayer board with a separate ground plane is ideal, but

not absolutely necessary.

COMPONENT SELECTION

Inductor Selection

The LTC3526/LTC3526B can utilize small surface mount

chip inductors due to their fast 1MHz switching frequency.

Inductor values between 3.3µH and 6.8µH are suitable for

most applications. Larger values of inductance will allow

slightly greater output current capability (and lower the

Burst Mode threshold) by reducing the inductor ripple cur-

rent. Increasing the inductance above 10µH will increase

size while providing little improvement in output current

capability.

The minimum inductance value is given by:

L

V

V

V

Ripple V

IN MIN

OUT MAX

IN MIN

OUT

>

(

)

(

)

(

)

(

)

(

•

–

•

M

MAX)

where:

Ripple = Allowable inductor current ripple (amps peak-

peak)

The inductor current ripple is typically set for 20% to

40% of the maximum inductor current. High frequency

ferrite core inductor materials reduce frequency depen-

dent power losses compared to cheaper powdered iron

types, improving efficiency. The inductor should have

low ESR (series resistance of the windings) to reduce the

Figure 2. Recommended Component Placement for Single Layer Board

+

SW

LTC3526

1

GND

MINIMIZE

TRACE ON FB

AND SW

2

MULTIPLE VIAS

TO GROUND PLANE

FB

SHDN

3526 F02

3

6

5

4

applicaTions inFormaTion