LP1115AQVF datasheet(9/10 Pages) POWER

9 / 10 page

LP1115-01

Dec.-2019

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Page 9 of 10

Preliminary Datasheet

LP1115

Operation Information (Boost Convertor)

The Boost Convertor part of LP1115 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

band gap 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.

The Boost Convertor part of LP1115 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

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.

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