LP6235 datasheet(4/6 Pages) POWER

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LP6235

Aug.-2017

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Preliminary Datasheet

LP6235

Operation Information

The LP6235 uses a fixend 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.

TheLP6235 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 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

Current Limitation

The internal power-MOS switch current is monitored

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

3A(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.

Inductor Selection

For a better efficiency in high switching frequency

converter, the inductor selection has to use a proper

core material such as ferrite core to reduce the core

loss and choose low ESR wire to reduce copper loss.

The most important point is to prevent the core

saturated when handling the maximum peak current.

Using a shielded inductor can minimize radiated

noise in sensitive applications. The maximum peak

inductor current is the maximum input current plus

the half of inductor ripple current. The calculated

peak current has to be smaller than the current

limitation in the electrical characteristics. A typical

setting of the inductor ripple current is 20% to 40% of

the maximum input current. If the selection is 40%,

the maximum peak inductor current is

The minimum inductance value is derived from the

following equation :

Depending on the application, the recommended

inductor value is between 2.2μH to 10μH.

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