L

R1

R2

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

-

+

1.25V

ON

OFF

+

-

+

-

+

-

1.375V

OVP

Comparator

Error

Signal

-

+

LMR12007

www.ti.com

SNVS982 – SEPTEMBER 2013

Block Diagram

Figure 19.

APPLICATION INFORMATION

THEORY OF OPERATION

The LMR12007 is a constant frequency PWM buck regulator IC that delivers a 750mA load current. The

regulator has a preset switching frequency of either 550kHz (LMR12007Y) or 1.6MHz (LMR12007X). These high

frequencies allow the LMR12007 to operate with small surface mount capacitors and inductors, resulting in

DC/DC converters that require a minimum amount of board space. The LMR12007 is internally compensated, so

it is simple to use, and requires few external components. The LMR12007 uses current-mode control to regulate

the output voltage.

The following operating description of the LMR12007 will refer to the Simplified Block Diagram (Figure 19) and to

the waveforms in Figure 20. The LMR12007 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 logic turns on the

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 between the

next switching cycle begins. During the switch off-time, inductor current discharges through Schottky diode D1,

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

Copyright © 2013, Texas Instruments Incorporated

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