LP6222SPF datasheet(6/9 Pages) POWER

6 / 9 page

LP6222-01

May.-2018

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Page 6 of 9

Preliminary Datasheet

LP6222

Operation Information

The LP6222 uses a fixed frequency, peak current

mode boost regulator architecture to regulate voltage

at the feedback pin. At the start of each oscillator

cycle the MOSFET is turned on through the control

circuitry. To prevent sub-harmonic oscillations at

duty cycles greater than 50 percent, a stabilizing

ramp is added to the output of the current sense

amplifier and the result is fed into the negative input

of the PWM comparator. When this voltage equals

The output voltage of the error amplifier the power

MOSFET is turned off. The voltage at the output of

the error amplifier is an amplified version of the

difference between the 0.6V bandgap reference

voltage and the feedback voltage. In this way the

peak current level keeps the output in regulation. If

the feedback voltage starts to drop, the output of the

error amplifier increases. These results in more

current to flow through the power MOSFET, thus

increasing the power delivered to the output.

TheLP6222 has internal soft start to limit the amount

of input current at startup and to also limit the amount

of overshoot on the output.

Setting the Output Voltage

Set the output voltage by selecting the resistive

voltage divider ratio. The voltage divider drops the

output voltage to the 0.6V 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

Current Limitation

The internal power-MOS switch current is monitored

cycle-by-cycle and is limited to the value not exceed

4.8A(Typ.). When the switch current reaches the

limited value, the internal power-MOS is turned off

immediately until the next cycle. Keep traces at this

pin as short as possible. Do not put capacitance at

this pin.

Current limit program

A resistor between ISET and GND pin programs

peak switch current. the resistor value be between

10K and 96K .The current limit will be set from 4.8A

to 0.5A .Keep traces at this pin as short as possible.

Do not put capacitance at this pin. To set the over

current trip point according to the following equation:

IOCP=48000 / R3

Diode Selection

To achieve high efficiency, Schottky diode is good

choice for low forward drop voltage and fast

switching time. The output diode rating should be

able to handle the maximum output voltage, average

power dissipation and the pulsating diode peak

current.

Input Capacitor Selection

For better input bypassing, low-ESR ceramic

capacitors are recommended for performance. A

22uF input capacitor is sufficient for most

applications. For a lower output power requirement

application, this value can be decreased.

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