LTC3443 datasheet(12/16 Pages) LINER

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LTC3443

sn3443 3443fs

above calculations in order to maintain the desired tran-

sient 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 ce-

ramic capacitors, AVX TPS series tantalum capacitors or

Sanyo POSCAP are recommended.

Input Capacitor Selection

Since the VIN pin is the supply voltage for the IC it is

recommended to place at least a 4.7µF, low ESR bypass

capacitor.

Table 2. Capacitor Vendor Information

SUPPLIER

PHONE

FAX

WEB SITE

AVX

(803) 448-9411

(803) 448-1943

www.avxcorp.com

Sanyo

(619) 661-6322

(619) 661-1055

www.sanyovideo.com

Taiyo Yuden (408) 573-4150

(408) 573-4159

www.t-yuden.com

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)

of the NMOS to PMOS transition, improving efficiency.

Use a Schottky diode such as a Phillips PMEG2010EA or

equivalent. Do not use ordinary rectifier diodes, since the

slow recovery times will compromise efficiency. For appli-

cations with an output voltage above 4.3V, a Schottky

diode is required from SW2 to VOUT.

Output Voltage < 2.4V

The LTC3443 can operate as a buck converter with output

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.

Output Voltage > 4.3V

A Schottky diode from SW 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

2Ω/1nF series snubber is required between the SW1 pin

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 GND pins as possible is also required.

Operating Frequency Selection

Additional quiescent current due to the output switches

GATE charge is given by:

Buck: 800e–12 • VIN • f

Boost: 400e–12 • (VIN + VOUT) • f

Buck/Boost: f • (1200e–12 • VIN + 400e–12 • VOUT)

where f = switching frequency

Closing the Feedback Loop

The LTC3443 incorporates voltage mode PWM control.

The control to output gain varies with operation region

(Buck, Boost, Buck/Boost), but is usually no greater than

15. The output filter exhibits a double pole response is

given by:

FILTER POLE

OUT

••

•

where COUT is the output filter capacitor.

APPLICATIO S I FOR ATIO

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