LP6482S datasheet(7/10 Pages) POWER

7 / 10 page

LP6482S-02

May.-2013

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Page 7 of 10

Preliminary Datasheet

LP6482S

Application Information

The LP6482S is current-mode step-down switching

regulator. The device regulates an output voltage as

low as 0.923V. The device can provide continuous

current up to 2.5A to the output with VIN=12V. The

LP6482S uses current-mode architecture to control

the regulator loop. The output voltage is measured at

FB through a resistive voltage divider and amplified

through the internal error amplifier. The output

current of the trans-conductance error amplifier is

presented at COMP pin where a RC network

compensates

the

regulator

loop.

Slope

compensation is added to eliminate sub harmonic

oscillation at high duty cycle. The slope

compensation adds voltage ramp to the inductor

current signal which reduces maximum inductor

peak current at high duty cycles.

The device uses an internal H_side N-channel switch

to step down the input voltage to the regulated output

voltage. Since the H_side n-channel switch requires

gate voltage greater than the input voltage, a boost

BS capacitor is connected between SW and BS to

drive the n-channel gate. The BS capacitor is

internally charged while the switch is off. An internal

6.8Ω switch from SW to GND is added to insure that

SW is pulled to GND when the switch is off to fully

charge the BS capacitor.

Setting the Output Voltage

The output voltage is set through a resistive voltage

divider. The voltage divider divides the output voltage

down by the ratio:

VFB=VOUT×R2/(R1+R2)=0.923V

Thus the output voltage is:

VOUT=0.923V×(1+R1/R2)

Inductor Selection

The inductor is required to supply constant current to

the output load while being driven by the switched

input voltage. A larger value inductor results in less

ripple current and lower output ripple voltage.

However, the larger value inductor has a larger

physical size, higher series resistance, and lower

saturation current. Choose an inductor that does not

saturate under the worst-case load conditions. A

good rule for determining the inductance is to allow

the peak-to-peak ripple current in the inductor to be

approximately 30% of the maximum load current.

The inductance value can be calculated by the

equation:

L=(VOUT)×(VIN-VOUT)/(VIN×f×∆I)

Where VOUT is the output voltage, VIN is the input

voltage, f is the switching frequency, and ΔI is the

peak-to-peak inductor ripple current.

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