LT3493EDCB View Datasheet(PDF) - Linear Technology

Part Name

Description

Manufacturer

LT3493EDCB

1.2A, 750kHz Step-Down Switching Regulator in 2mm × 3mm DFN

Linear Technology 

LT3493

APPLICATIONS INFORMATION

Table 1. Inductor Values

VENDOR

URL

Sumida

www.sumida.com

Toko

www.toko.com

Würth Elektronik www.we-online.com

PART SERIES

CDRH4D28

CDRH5D28

CDRH8D28

A916CY

D585LC

WE-TPC(M)

WE-PD2(M)

WE-PD(S)

INDUCTANCE RANGE (μH) SIZE (MM)

1.2 to 4.7

2.5 to 10

2.5 to 33

4.5 × 4.5

5.5 × 5.5

8.3 × 8.3

2 to 12

1.1 to 39

6.3 × 6.2

8.1 × 8.0

1 to 10

2.2 to 22

1 to 27

4.8 × 4.8

5.2 × 5.8

7.3 × 7.3

Input Capacitor

Bypass the input of the LT3493 circuit with a 1μF or

higher value ceramic capacitor of X7R or X5R type. Y5V

types have poor performance over temperature and ap-

plied voltage and should not be used. A 1μF ceramic is

adequate to bypass the LT3493 and will easily handle the

ripple current. However, 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 performance

electrolytic capacitor.

Step-down regulators draw current from the input sup-

ply in pulses with very fast rise and fall times. The input

capacitor is required to reduce the resulting voltage

ripple at the LT3493 and to force this very high frequency

switching current into a tight local loop, minimizing EMI.

A 1μF capacitor is capable of this task, but only if it is

placed close to the LT3493 and the catch diode; see the

PCB Layout section. A second precaution regarding the

ceramic input capacitor concerns the maximum input

voltage rating of the LT3493. A ceramic input capacitor

combined with trace or cable inductance forms a high

quality (underdamped) tank circuit. If the LT3493 circuit

is plugged into a live supply, the input voltage can ring to

twice its nominal value, possibly exceeding the LT3493’s

voltage rating. This situation is easily avoided; see the Hot

Plugging Safely section.

Output Capacitor

The output capacitor has two essential functions. Along

with the inductor, it filters the square wave generated

by the LT3493 to produce the DC output. In this role it

determines the output ripple so low impedance at the

switching frequency is important. The second function

is to store energy in order to satisfy transient loads and

stabilize the LT3493’s control loop.

Ceramic capacitors have very low equivalent series re-

sistance (ESR) and provide the best ripple performance.

A good value is:

COUT = 65/VOUT

where COUT is in μF. Use X5R or X7R types and keep in

mind that a ceramic capacitor biased with VOUT will have

less than its nominal capacitance. This choice will provide

low output ripple and good transient response. Transient

performance can be improved with a high value capacitor,

but a phase lead capacitor across the feedback resistor

R1 may be required to get the full benefit (see the Com-

pensation section).

For small size, the output capacitor can be chosen ac-

cording to:

COUT = 25/VOUT

where COUT is in μF. However, using an output capacitor

this small results in an increased loop crossover frequency

and increased sensitivity to noise. A 22pF capacitor con-

nected between VOUT and the FB pin is required to filter

noise at the FB pin and ensure stability.

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. The ESR

should be specified by the supplier and should be 0.1Ω

or less. Such a capacitor will be larger than a ceramic

capacitor and will have a larger capacitance, because the

3493fb

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