L

R

1

R

2

D

1

D2

BOOST

Output

Control

Logic

Current

Limit

Thermal

Shutdown

Under

Voltage

Lockout

Corrective Ramp

Reset

Pulse

PWM

Comparator

Current-Sense Amplifier

+

+

Internal

Regulator

and

Enable

Circuit

Oscillator

Driver

0.3:

Switch

Internal

Compensation

SW

EN

FB

GND

Error Amplifier

-

+

0.8V

ON

OFF

IL

+

-

+

-

+

-

0.88V

-

+

OVP

Comparator

Error

Signal

LM2734Z

SNVS334D – JANUARY 2005 – REVISED JUNE 2008

www.ti.com

BLOCK DIAGRAM

APPLICATION INFORMATION

THEORY OF OPERATION

The LM2734Z is a constant frequency PWM buck regulator IC that delivers a 1A load current. The regulator has

a preset switching frequency of 3MHz. This high frequency allows the LM2734Z to operate with small surface

mount capacitors and inductors, resulting in a DC/DC converter that requires a minimum amount of board space.

The LM2734Z is internally compensated, so it is simple to use, and requires few external components. The

LM2734Z uses current-mode control to regulate the output voltage.

The following operating description of the LM2734Z will refer to the Simplified Block Diagram (BLOCK

DIAGRAM) and to the waveforms in Figure 3. The LM2734Z supplies a regulated output voltage by switching the

internal NMOS control switch at constant frequency and variable duty cycle. A switching cycle begins at the

falling edge of the reset pulse generated by the internal oscillator. When this pulse goes low, the output control

amplifier, which generates an output proportional to the switch current. The sense signal is summed with the

regulator’s corrective ramp and compared to the error amplifier’s output, which is proportional to the difference

off until the next switching cycle begins. During the switch off-time, inductor current discharges through Schottky

regulator loop adjusts the duty cycle (D) to maintain a constant output voltage.

6

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