Datasheet

LTC3529
8
3529fb
APPLICATIONS INFORMATION
The basic LTC3529 application circuit is shown in the Typi-
cal Application on the front page. The external component
selection is determined by the desired output current and
ripple voltage requirements of each particular application.
However, basic guidelines and considerations for the design
process are provided in this section.
Output Capacitor Selection
A low ESR (equivalent series resistance) output capacitor
should be used at the output of the LTC3529 to minimize
the output voltage ripple. Multilayer ceramic capacitors are
an excellent choice as they have extremely low ESR and
are available in small footprints. X5R and X7R dielectric
materials are strongly recommended over Y5V dielectric
because of their improved voltage and temperature coef-
fi cients. Neglecting the capacitor ESR and ESL (equivalent
series inductance), the peak-to-peak output voltage ripple
can be calculated by the following formula, where f is the
frequency in MHz, C
OUT
is the capacitance in μF, and I
LOAD
is the output current in amps.
ΔV
IVV
CVf
PP
LOAD OUT IN
OUT OUT
−
=
()
–
••
The internal loop compensation of the LTC3529 is designed
to be stable with output capacitor values of 6.5μF or greater.
This complies with USB On-The-Go specifi cations, which
limit the output capacitance to 6.5μF. In general use of the
LTC3529, the output capacitor should be chosen large
enough to reduce the output voltage ripple to acceptable
levels. A 6.8μF to 10μF output capacitor is suffi cient for
most applications. Larger values up to 22μF may be used
to obtain extremely low output voltage ripple and improved
transient response.
Although ceramic capacitors are recommended, low ESR
tantalum capacitors may also be used. A small ceramic
capacitor in parallel with a larger tantalum capacitor is
recommended in demanding applications that have large
load transients.
Input Capacitor Selection
Low ESR input capacitors reduce input switching noise
and reduce the peak current drawn from the battery. It
follows that ceramic capacitors are also a good choice
for input decoupling and should be located as close as
possible to the device. A 3.3μF input capacitor is suffi cient
for most applications. Larger values may be used without
limitation.
Capacitor Vendor Information
Both the input and output capacitors used with the LTC3529
must have low ESR and be designed to handle the large
AC currents generated by switching converters. The ven-
dors in Table 1 provide capacitors that are well suited to
LTC3529 application circuits.
Table 1. Capacitor Vendor Information
MANUFACTURER WEB SITE PHONE FAX
Taiyo Yuden www.t-yuden.com [phone] [phone]
TDK www.component.
tdk.com
[phone] [phone]
Sanyo www.secc.co.jp [phone] [phone]
AVX www.avxcorp.com [phone] [phone]
Murata www.murata.com [phone] [phone]
Sumida www.sales@
us.sumida.com
[phone] [phone]