LTC3370 datasheet(10/20 Pages) AD

10 / 20 page

LTC3302

Rev. 0

For more information www.analog.com

OPERATION

Voltage Regulation

The LTC3302 is a 5V, 2A monolithic, constant frequency,

peak current mode control, step-down DC/DC converter.

The synchronous buck switching regulators are internally

compensated and require only external feedback resis-

tors to set the output voltage. An internal oscillator, with

the frequency factory programmed or synchronized to an

external clock, turns on the internal top power switch at

the beginning of each clock cycle. Current in the inductor

ramps up until the top switch current comparator trips

and turns off the top power switch. The peak inductor

current at which the top switch turns off is controlled by

an internal VC voltage. The error amplifier regulates VC

by comparing the voltage on the FB node with an internal

500mV reference. An increase in the load current causes

a reduction in the feedback voltage relative to the refer-

ence, causing the error amplifier to raise the VC voltage

until the average inductor current matches the new load

current. When the top power switch turns off, the syn-

chronous power switch turns on and ramps down the

inductor current for the remainder of the clock cycle or,

if in pulse-skipping or Burst Mode operation, until the

inductor current falls to zero. If an overload condition

results in excessive current flowing through the bottom

switch, the next clock cycle is skipped until switch current

returns to a safe level.

The enable pin has a precision 400mV threshold to pro-

vide event-based power-up sequencing by connecting the

EN pin to the output of another buck through a resistor

divider. If the EN pin is low, the device is shut down and

in a low quiescent current state. When the EN pin is above

its threshold, the switching regulator enables.

The LTC3302 has forward and reverse inductor current

limiting, short-circuit protection, output overvoltage pro-

tection, and soft-start to limit inrush current during start-

up or recovery from a short-circuit.

Mode Selection

The LTC3302 operates in three modes set by the MODE/

SYNC pin: pulse-skipping (when the MODE/SYNC pin is

floating), forced continuous (when the MODE/SYNC pin

is set low), and Burst Mode operation (when the MODE/

SYNC pin is set high).

In pulse-skipping mode, the oscillator operates con-

tinuously and positive SW transitions are aligned to the

clock. Negative inductor current is disallowed and, dur-

ing light loads, switch pulses are skipped to regulate the

output voltage.

In forced continuous mode, the oscillator operates contin-

uously. The top switch turns on every cycle and regulation

is maintained by allowing the inductor current to reverse

at light load. This mode allows the buck to run at a fixed

frequency with minimal output ripple. In forced continu-

ous mode, if the inductor current reaches IREVMAX (into

the SW pin), the bottom switch turns off for the remainder

of the cycle to limit the current.

In Burst Mode operation at light loads, the output capaci-

tor is charged to a voltage slightly higher than its regu-

lation point. The regulator then goes into a sleep state,

during which time the output capacitor provides the

load current. In sleep, most of the regulator’s circuitry is

powered down, helping conserve input power. When the

output voltage drops below its programmed value, the

circuitry is powered on and another burst cycle begins.

The sleep time decreases as load current increases. In

Burst Mode operation, the regulator bursts at light loads,

whereas at higher loads it operates in constant frequency

PWM mode.

LTC3370 Datasheet(PDF) 10 Page - Analog Devices

LTC3370 Datasheet(HTML) 10 Page - Analog Devices

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