LTC3442 datasheet(14/20 Pages) LINER

14 / 20 page

LTC3442

3442fa

Table 2. Capacitor Vendor Information

SUPPLIER

PHONE

FAX

WEB SITE

AVX

(803) 448-9411

(803) 448-1943

www.avxcorp.com

Murata

(814) 237-1431

(814) 238-0490

www.murata.com

(800) 831-9172

Sanyo

(619) 661-6322

(619) 661-1055

www.sanyovideo.com

Taiyo Yuden

(408) 573-4150

(408) 573-4159

www.t-yuden.com

TDK

(847) 803-6100

(847) 803-6296

www.component.tdk.com

voltages as low as 0.4V. The part is specified at 2.4V

minimum to allow operation without the requirement of a

Schottky diode. Synchronous switch D is powered from

VOUT and the RDS(ON) will increase at low output voltages,

therefore a Schottky diode is required from SW2 to VOUT

to provide the conduction path to the output. Note that

Burst Mode operation is inhibited at output voltages below

1.6V typical.

Output Voltage > 4.3V

A Schottky diode from SW2 to VOUT is required for output

voltages over 4.3V. The diode must be located as close to

the pins as possible in order to reduce the peak voltage on

SW2 due to the parasitic lead and trace inductance.

Input Voltage > 4.5V

For applications with input voltages above 4.5V which

could exhibit an overload or short-circuit condition, a

Ω/1nF series snubber is required between SW1 and

GND. A Schottky diode from SW1 to VIN should also be

added as close to the pins as possible. For the higher input

voltages, VIN bypassing becomes more critical; therefore,

a ceramic bypass capacitor as close to the VIN and SGND

pins as possible is also required.

Operating Frequency Selection

Higher operating frequencies allow the use of a smaller

inductor and smaller input and output filter capacitors,

thus reducing board area and component height. How-

ever, higher operating frequencies also increase the IC’s

total quiescent current due to the gate charge of the four

switches, as given by:

Buck:

Iq = (0.8 • VIN • f) mA

Boost:

Iq = [0.4 • (VIN + VOUT) • f] mA

Buck/Boost: Iq = [f • (1.2 • VIN + 0.4 • VOUT)] mA

The output capacitance is usually many times larger than

the minimum value in order to handle the transient re-

sponse requirements of the converter. For a rule of thumb,

the ratio of the operating frequency to the unity-gain

bandwidth of the converter is the amount the output

capacitance will have to increase from the above calcula-

tions in order to maintain the desired transient response.

The other component of ripple is due to the ESR (equiva-

lent series resistance) of the output capacitor. Low ESR

capacitors should be used to minimize output voltage

ripple. For surface mount applications, Taiyo Yuden or

TDK ceramic capacitors, AVX TPS series tantalum capaci-

tors or Sanyo POSCAP are recommended. See Table 2 for

contact information.

Input Capacitor Selection

Since VIN is the supply voltage for the IC, as well as the

input to the power stage of the converter, it is recom-

mended to place at least a 4.7

µF, low ESR ceramic bypass

capacitor close to the VIN and SGND pins. It is also

important to minimize any stray resistance from the con-

verter to the battery or other power source.

Optional Schottky Diodes

The Schottky diodes across the synchronous switches B

and D are not required (VOUT < 4.3V), but provide a lower

drop during the break-before-make time (typically 15ns)

improving efficiency. Use a surface mount Schottky diode

such as an MBRM120T3 or equivalent. Do not use ordi-

nary rectifier diodes, since the slow recovery times will

compromise efficiency. For applications with an output

voltage above 4.3V, a Schottky diode is required from

SW2 to VOUT.

Output Voltage < 2.4V

The LTC3442 can operate as a buck converter with output

APPLICATIO S I FOR ATIO

LTC3442 Datasheet(PDF) 14 Page - Linear Technology

LTC3442 Datasheet(HTML) 14 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Datasheet Download

Link URL