LM2830 datasheet(9/33 Pages) TI

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VIN

TON

Inductor

Current

D = TON/TSW

VSW

TOFF

TSW

IPK

Voltage

LM2830

www.ti.com

SNVS454D – AUGUST 2006 – REVISED APRIL 2013

APPLICATIONS INFORMATION

THEORY OF OPERATION

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

a preset switching frequency of 1.6MHz or 3.0MHz. This high frequency allows the LM2830 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 is internally compensated, so it is simple to use and requires few external

components. The LM2830 uses current-mode control to regulate the output voltage. The following operating

description of the LM2830 will refer to the Simplified Block Diagram (Figure 20) and to the waveforms in

Figure 21. The LM2830 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 21. Typical Waveforms

SOFT-START

This function forces VOUT to increase at a controlled rate during start up. During soft-start, the error amplifier’s

reference voltage ramps from 0V to its nominal value of 0.6V in approximately 600 µs. This forces the regulator

output to ramp up in a controlled fashion, which helps reduce inrush current.

OUTPUT OVERVOLTAGE PROTECTION

The over-voltage comparator compares the FB pin voltage to a voltage that is 15% higher than the internal

reference VREF. Once the FB pin voltage goes 15% above the internal reference, the internal PMOS control

switch is turned off, which allows the output voltage to decrease toward regulation.

UNDERVOLTAGE LOCKOUT

Under-voltage lockout (UVLO) prevents the LM2830 from operating until the input voltage exceeds 2.73V (typ).

The UVLO threshold has approximately 430 mV of hysteresis, so the part will operate until VIN drops below 2.3V

(typ). Hysteresis prevents the part from turning off during power up if VIN is non-monotonic.

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