LTC3530

11

3530fb

The output capacitance is usually many times larger than

the minimum value in order to handle the transient response

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 calculations 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

input to the power stage of the converter, it is recommended

to place at least a 10μF, low ESR ceramic bypass capaci-

minimize any stray resistance from the converter to the

battery or other power source.

Optional Schottky Diodes

Schottky diodes across the synchronous switches B and

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

ing efficiency. Use a surface mount Schottky diode such as

an MBRM120T3 or equivalent. Do not use ordinary rectifier

diodes, since the slow recovery times will compromise

efficiency. For applications with an output voltage above

Output Voltage < 1.8V

The LTC3530 can operate as a buck converter with output

voltages as low as 0.4V. Synchronous switch D is powered

ages, therefore a Schottky diode is required from SW2 to

that Burst Mode operation is inhibited at output voltages

the current limit will be 670mA (typ).

Output Voltage > 4.3V

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

2Ω/1nF series snubber is required between SW1 and

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

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:

Boost:

Table 2. Capacitor Vendor Information

SUPPLIER

PHONE

FAX

WEB SITE

AVX

(803) 448-9411

(803) 448-1943

www.avxcorp.com

Murata

(814) 237-1431, (800) 831-9172

(814) 238-0409

www.murata.com

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

APPLICATIONS INFORMATION