x

x

x

f

1

L

2

!

where

¹

·

©

§

¹

·

©

§

¹

·

©

§

LM8801

SNVS597H – APRIL 2009 – REVISED MAY 2013

www.ti.com

UVLO (UNDER-VOLTAGE LOCK OUT)

The LM8801 has an UVP comparator to turn the power device off in the case the input voltage or battery voltage

is too low. The typical UVP threshold is around 2V with 100 mV hysteresis.

APPLICATION INFORMATION

INDUCTOR SELECTION

There are two main considerations when choosing an inductor; the inductor should not saturate, and the inductor

current ripple is small enough to achieve the desired output voltage ripple. Different manufacturers follow

different saturation current rating specifications, so attention must be given to details. Saturation current ratings

are typically specified at 25°C so ratings at maximum ambient temperature of application should be requested

from manufacturer.

ambient temperature range.

Shielded inductors radiate less noise and should be preferred. There are two methods to choose the inductor

saturation current rating.

Method 1:

The saturation current should be greater than the sum of the maximum load current and the worst case average

to peak inductor current. This can be written as:

(1)

•

•

•

•

L: minimum inductor value including worst case tolerances (30% drop can be considered for method 1)

•

f: minimum switching frequency (5.4 MHz)

•

Method 2:

A more conservative and recommended approach is to choose an inductor that can handle the maximum current

limit of 1300 mA.

The inductor's resistance should be less than around 0.1

Ω for good efficiency. Table 1 lists suggested inductors

and suppliers.

INPUT CAPACITOR SELECTION

A ceramic input capacitor of 2.2 µF, 6.3V is sufficient for most applications. Place the input capacitor as close as

filtering. Use X7R or X5R types; do not use Y5V. DC bias characteristics of ceramic capacitors must be

considered when selecting case sizes like 0402 and 0603.

The input filter capacitor supplies current to the top switch of the LM8801 in the first half of each cycle and

reduces voltage ripple imposed on the input power source. A ceramic capacitor's low ESR provides the best

noise filtering of the input voltage spikes due to this rapidly changing current. Select an input filter capacitor with

sufficient ripple current rating.

The input current ripple can be calculated as:

12

Submit Documentation Feedback

Copyright © 2009–2013, Texas Instruments Incorporated

Product Folder Links: LM8801