LP6206 datasheet(6/7 Pages) POWER

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Preliminary

Datasheet

LP6206

LP6206 –00 Ver. 1.0 Datasheet

Dec.-2008

- - www.Lowpowersemi.com - -

Page 6 of 7

Operation Information

The LP6206 uses a 500KHz fixed-frequency,

current-mode regulation architecture to regulate the

output voltage. The LP6206 measures the output

voltage through an external resistive voltage divider

and compares that to the internal 1.25V reference to

generate the error voltage to the inductor current to

regulate the output voltage.the use of current-mode

regulation improves transient response and control

loop

sta b ilit y .

When the LP6206 is disable(EN=Low),both power

switches are off. There is no current path from SW

to OUT. There fore, the output voltage discharges to

ground. When the LP6206 is enabled(EN=High),a

limited start-current charges the output voltage

rising to SW, then th part operates in force PWM

mode for regulating the output voltage to the target

value. At the beginning of each cycle, the N-channel

MOSFET switch is turned on, forcing the inductor

current to rise, The current at the source of the

switch is internally measured and converted to a

voltage by the current sense amplifier. That voltage

is compared to the error voltage. When the inductor

current rises sufficiently, the PWM comparator

turns off the switch, forcing the inductor current to

the output capacitor through the internal P-Channel

MOSFET rectifier, which forces the inductor

current to decrease. The peak inductor current is

controlled by the error voltage. Thus the output

voltage controls the inductor current to satisfy the

lode.

Soft-Start

The LP6206 includes a soft-start timer that limits

the voltage at the error amplifier output during

startup to prevent excessive current at the input.This

prevents premature termination of the source

voltage at start-up due to inrush current.This also

Limits thd inductor current at startup,forcing the

input current to rise slowly to the amount required

to regulate the output voltage during soft-start.

Application Information

Component selection

Setting the Output Voltage

Set the output voltage by selecting the resistive

voltage divider ratio. The voltage divider drops the

output voltage to the 1.25V feedback voltage. Use a

100K resistor for R2 of the voltage divider.

Determine the high-side resistor R1 by the equation:

Vout=(R1/R2+1) X VFB

LP6206

OUT

0.22uF

22uF

1.5M

22pF

4.7uH

LP6206

OUT

Vout

5V Typical Application with External Diode(A)

1.5M

Vin

22pF

Cout

22uF

Cout

22uF

500K

22uF

500K

5V Typical Application with External Diode(B)

Vout

PMOS

Vin

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