0

0

VIN

VD

TON

t

t

Inductor

Current

D = TON/TSW

VSW

TOFF

TSW

IL

IPK

SW

Voltage

LM2830, LM2830-Q1

www.ti.com

SNVS454E – AUGUST 2006 – REVISED DECEMBER 2014

7 Detailed Description

7.1 Overview

The LM2830 device is a constant frequency PWM buck regulator IC that delivers a 1.0-A load current. The

regulator has a preset switching frequency of 1.6 MHz or 3.0 MHz. This high frequency allows the LM2830

device to operate with small surface-mount capacitors and inductors, resulting in a DC-DC converter that

requires a minimum amount of board space. The LM2830 device is internally compensated, so it is simple to use

and requires few external components. The LM2830 device uses current-mode control to regulate the output

voltage.

The following operating description of the LM2830 device will refer to the Simplified Block Diagram (Functional

Block Diagram) and to the waveforms in Figure 18. The LM2830 device supplies a regulated output voltage by

switching the internal PMOS 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 internal PMOS control switch. During this on-time, the SW pin voltage (VSW)

swings up to approximately VIN, and the inductor current (IL) increases with a linear slope. IL is measured by the

current sense 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 between the feedback voltage and VREF. When the PWM comparator output goes high, the

output switch turns off until the next switching cycle begins. During the switch off-time, inductor current

discharges through the Schottky catch diode, which forces the SW pin to swing below ground by the forward

voltage (VD) of the Schottky catch diode. The regulator loop adjusts the duty cycle (D) to maintain a constant

output voltage.

Figure 18. Typical Waveforms

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Product Folder Links: LM2830 LM2830-Q1