5

LTC3427

3427fa

BLOCK DIAGRA

Σ

+

–

+

IZERO

COMP

1.8V TO 5.25V

GAIN ERROR

AMPLIFIER

CURRENT

SENSE

1.24V

1V

BULK CONTROL

SIGNALS

L1

4.7

µH

OPTIONAL

ANTIRING

SHDN

SHDN

PWM

LOGIC

AND

DRIVERS

START-UP

SOFT-START

SHUTDOWN

AND

THERMAL

SHUTDOWN

SLOPE COMPENSATION

OSCILLATOR

REFERENCE

PWM

COMP

REF

+

+

–

+

1.24V

4

3

SW

1

6

FB

R1

4.7

µF

R2

5

GND

3427 BD

2

EXPOSED PAD

7

2.2

µF

1.8V TO 5V

SW (Pin 1): Switch Pin for the Inductor Connection.

Minimize trace length between SW and the inductor. For

discontinuous inductor current, an internal 200

Ω imped-

frequency ringing, reducing EMI radiation.

GND (Pin 2): Signal and Power Ground. Provide a short,

direct PCB path between GND and the (–) side of the input

and output capacitor(s).

supply and decouple with a 2.2

µF or larger ceramic

SHDN (Pin 4): Shutdown Input. Less than 350mV on

SHDN shuts down the LTC3427. Placing 1V or more on

SHDN enables the LTC3427.

FB (Pin 5): Feedback Input to the Error Amplifier. Connect

resistor divider tap to this pin. Referring to the Block

VV

R

R

⎛

⎝⎜

⎞

⎠⎟

124

1

1

2

.•

Internal Synchronous Rectifier MOSFET. Driver bias is

output filter capacitor(s) should be as short and wide as

possible.

Exposed Pad (Pin 7): Ground for the LTC3427. This pin

must be soldered to the PCB ground plane for electrical

connection and rated thermal performance.

PI FU CTIO S