LT3663

9

3663fc

For more information For more information www.linear.com/LT3663

applicaTions inForMaTion

Catch Diode

The catch diode conducts current only during switch-off

time. Average forward current in normal operation is

calculated from:

II

VV

V

D AVG

OUT

IN

OUT

IN

()

–

=

to the regulator input voltage. Use a Schottky diode with a

reverse voltage rating greater than the input voltage. The

overvoltage protection feature in the LT3663 keeps the

Input Capacitor

Bypass the input of the LT3663 circuit with a 1µF or higher

value ceramic capacitor of X7R or X5R type. Y5V types

havepoorperformanceovertemperatureandappliedvolt-

age and are not recommended. If the input power source

has high impedance, or there is significant inductance

due to long wires or cables, additional bulk capacitance

may be necessary. This can be provided with a low per-

formance electrolytic capacitor. Step-down regulators

draw current from the input supply in pulses with very

fast rise and fall times. The input capacitor is required

to reduce the resulting voltage ripple at the LT3663 and

to force this very high frequency switching current into

a tight local loop, minimizing EMI. Place the capacitor in

close proximity to the LT3663 and the catch diode; (see

the PCB Layout section).

Output Capacitor

A 10µF or greater ceramic capacitor is recommended to

provide low output ripple and good transient response.

Ceramic capacitors have very low equivalent series re-

sistance (ESR) and provide the best ripple performance.

Use X5R or X7R types and keep in mind that a ceramic

nominal capacitance.

High performance electrolytic capacitors can be used for

the output capacitor. Low ESR is important, so choose

one that is intended for use in switching regulators. Keep

the ESR less than 0.1Ω.

The LT3663 output current limit controls the maximum

current delivered from the LT3663 regulator. This allows

tighter control of the system power dissipation and also

protects the inductor and diode from overheating during

an overload or short circuit condition. A resistor con-

current limits.

OUTPUT CURRENT LIMIT (A)

0.4

140

0.6

75

0.8

48.7

1.0

36.5

1.2

28.7

There may be a reason in some applications to move the

output current limit. The following simple circuit demon-

strates how the output current limit can be adjusted:

Figure 3. Circuit for Multiple Values of Output Current Limit

LT3663

3663 F03

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RB