14

LTC3832/LTC3832-1

sn3832 3832fs

times that of Q1 in this example. Note also that while the

power dissipation numbers are only 0.83W per device or

less; large TO-220 packages and heat sinks are not neces-

sarily required in high efficiency applications. Siliconix

Si4410DY or International Rectifier IRF7413 (both in

SO-8) or Siliconix SUD50N03-10 (TO-252) or ON Semi-

conductor MTD20N03HDL (DPAK) are small footprint

decreases the MOSFET cost and the circuit efficiency and

increases the MOSFET heat sink requirements.

Table 1 highlights a variety of power MOSFETs for use in

LTC3832 applications.

Inductor Selection

The inductor is often the largest component in an LTC3832

design and must be chosen carefully. Choose the inductor

value and type based on output slew rate requirements. The

maximum rate of rise of inductor current is set by the

inductor’s value, the input-to-output voltage differential and

the LTC3832’s maximum duty cycle. In a typical 3.3V in-

put, 2.5V output application, the maximum rise time will be:

DC

V

V

LL

A

s

MAX

IN

OUT

OO

•(

–

)

.

=

µ

076

quency compensation, the combination of the inductor

and output capacitor values determine the transient recov-

ery time. In general, a smaller value inductor improves

transient response at the expense of ripple and inductor

core saturation rating. A 1

µH inductor has a 0.76A/µs rise

time in this application, resulting in a 6.6

µs delay in

responding to a 5A load current step. During this 6.6

µs,

the difference between the inductor current and the output

current is made up by the output capacitor. This action

causes a temporary voltage droop at the output. To

minimize this effect, the inductor value should usually be

in the 1

µH to 5µH range for most 3.3V input LTC3832

circuits. To optimize performance, different combinations

of input and output voltages and expected loads may

require different inductor values.

Once the required value is known, the inductor core type

can be chosen based on peak current and efficiency

APPLICATIO S I FOR ATIO

Table 1. Recommended MOSFETs for LTC3832 Applications

TYPICAL INPUT

CAPACITANCE

PARTS

AT 25

°C (mΩ)

RATED CURRENT (A)

Siliconix SUD50N03-10

19

15 at 25

°C

3200

1.8

175

TO-252

10 at 100

°C

Siliconix Si4410DY

20

10 at 25

°C

2700

150

SO-8

8 at 70

°C

ON Semiconductor MTD20N03HDL

35

20 at 25

°C

880

1.67

150

DPAK

16 at 100

°C

Fairchild FDS6670A

8

13 at 25

°C

3200

25

150

S0-8

Fairchild FDS6680

10

11.5 at 25

°C

2070

25

150

SO-8

ON Semiconductor MTB75N03HDL

9

75 at 25

°C

4025

1

150

DD PAK

59 at 100

°C

IR IRL3103S

19

64 at 25

°C

1600

1.4

175

DD PAK

45 at 100

°C

IR IRLZ44

28

50 at 25

°C

3300

1

175

TO-220

36 at 100

°C

Fuji 2SK1388

37

35 at 25

°C

1750

2.08

150

TO-220

Note: Please refer to the manufacturer’s data sheet for testing conditions and detailed information.