LP6253HSPF datasheet(8/12 Pages) POWER

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LP6253H

Aug.-2017

Email: marketing@lowpowersemi.com

www.lowpowersemi.com

Page 8 of 12

Preliminary Datasheet

LP6253H

Setting the Output Voltage

Set the output voltage by selecting the resistive

voltage divider ratio. The voltage divider drops the

output voltage to the 1.21V feedback voltage. Use a

10K resistor for R2 of the voltage divider. Determine

the high-side resistor R1 by the equation:

VOUT = ( R1 / R2 + 1 ) × VFB

Low-EMI Switch

The device integrates a circuit that removes the

ringing that typically appears on the LX node when

the converter enters discontinuous current mode. In

this case, the current through the inductor ramps to

zero and the rectifying PMOS switch is turned off to

prevent a reverse current flowing from the output

capacitors back to the battery. Due to the remaining

energy that is stored in parasitic components of the

semiconductor and the inductor, a ringing on the LX

pin is induced. The integrated antiringing switch

clamps this voltage to VIN and therefore dampens

ringing.

Pre-Boost Current and Short Circuit Protect

Initially output voltage is lower than battery voltage,

and the LP6253H enters pre-boost phase. During

pre-boost phase, the internal NMOSFET turned

OFF/ON and a constant current is provided from

battery to output until the output voltage close to the

battery voltage. The constant current is limited by

internal controller. If the output short to ground, the

LP6253H also limits the output current to avoid

damage condition.

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 1μH to 4.7μH.

Input Capacitor Selection

For better input bypassing, low-ESR ceramic

capacitors are recommended for performance. A

10μF input capacitor is sufficient for most

applications. A ceramic capacitor or a tantalum

capacitor with a 100nF ceramic capacitor in parallel,

placed close to the IC, is recommended. For a lower

output power requirement application, this value can

be decreased.

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