LP28300 datasheet(9/10 Pages) POWER

9 / 10 page

Preliminary Datasheet

LP28300

LP28300 – 01 Version

1.1 Datasheet

Sep.-2010

www.lowpowersemi.com

Page 9 of 10

choice is the IHLP-2525AH-01from Vishay Dale.

To calculate the inductor ripple current:

where VBAT is the battery voltage, VIN is the input

voltage, L is the inductance and f is the PWM

oscillator frequency(typically 1.5MHz). Maximum

inductor ripple current occurs at maximum VIN and

VBAT = VIN/2.

Peak inductor current will be:

where IBAT is the maximum battery charging

current.

When sizing the inductor make sure that the peak

current will not exceed the saturation current of the

inductors. Also, ∆IL should never exceed 0.4(IBAT)

as this may interfere with proper operation of the

output short-circuit protection comparator. 1.5µH

provides reasonable inductor ripple current in a

typical application. With 1.5µH and2A charge

current:

and

Layout Considerations

Switch rise and fall times are kept under 5ns for

maximum efficiency. To minimize radiation, the SW

pin and input bypass capacitor leads (between VIN

and PGND) should be kept as short as possible. A

ground plane should be used under the switching

circuitry to prevent inter plane coupling. The

exposed pad must be connected to the ground plane

for proper power dissipation. The other paths

contain only DC and/or 1.5MHz tri-wave ripple

current and are less critical. With the exception of

the input and output filter capacitors(which should

be connected to PGND) all other components that

return to ground should be connected to GND.

LP28300 Datasheet(PDF) 9 Page - Lowpower Semiconductor inc