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LTC3528

1A, 1MHz Synchronous Step-Up DC/DC Converters in 3mm × 2mm DFN

Linear Technology 

LTC3528/LTC3528B

APPLICATIONS INFORMATION

VIN > VOUT OPERATION

The LTC3528/LTC3528B will maintain voltage regulation

even when the input voltage is above the desired output

voltage. Note that the efficiency is much lower in this

mode, and the maximum output current capability will

be less. Refer to the Typical Performance Characteristics.

SHORT-CIRCUIT PROTECTION

The LTC3528/LTC3528B output disconnect feature allows

an output short circuit while maintaining a maximum

internally set current limit. To reduce power dissipation

under short-circuit conditions, the peak switch current

limit is reduced to 750mA (typical).

SCHOTTKY DIODE

Although not required, adding a Schottky diode from

SW to VOUT will improve efficiency by about 2%. Note

that this defeats the output disconnect and short-circuit

protection features.

PCB LAYOUT GUIDELINES

The high speed operation of the LTC3528/LTC3528B de-

mands careful attention to board layout. A careless layout

will not produce the advertised performance. Figure 2

shows the recommended component placement. A large

ground copper area with the package backside metal pad

properly soldered will help to lower the chip temperature.

A multilayer board with a separate ground plane is ideal,

but not absolutely necessary.

COMPONENT SELECTION

Inductor Selection

The LTC3528/LTC3528B can utilize small surface mount

chip inductors due to their fast 1MHz switching frequency.

Inductor values between 2.2µH and 4.7µH 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

>

VIN(MIN) • VOUT(MAX) – VIN(MIN)

1.2 • Ripple • VOUT(MAX)

µH

where:

Ripple = Allowable inductor current ripple (amps peak-

to-peak)

VIN(MIN) = Minimum input voltage

VOUT(MAX) = Maximum output voltage

+

VIN

CIN

SHDN 1

8 VIN

FB 2

PGOOD 3

LTC3528

7 SGND

6 PGND

VOUT 4

COUT

5 SW

3528 F01

MULTIPLE VIAS

TO GROUND PLANE

Figure 2. Recommended Component Placement for Single Layer Board

3528fd

11

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