ltc3527eud-trpbf Linear Technology Corporation, ltc3527eud-trpbf Datasheet - Page 13

• Manufacturer Part Number: ltc3527eud-trpbf
• Description: Dual 800ma/400ma, 1.2mhz/2.2mhz Synchronous Step-up Dc/dc Converters
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
Mode threshold) by reducing the inductor ripple cur-
rent. Increasing the inductance above 10µH will increase
size while providing little improvement in output current
capability.
The minimum inductance value is given by:
Where:
Ripple = Allowable inductor current ripple (amps peak-
to-peak)
V
V
f = Oscillator frequency (MHz)
The inductor current ripple is typically set for 20% to
40% of the maximum inductor current. High frequency
ferrite core inductor materials reduce frequency dependent
power losses compared to cheaper powdered iron types,
improving effi ciency. The inductor should have low ESR
IN(MIN)
OUT(MAX)
L
>
V
IN MIN
= Minimum input voltage
(
= Maximum output voltage
f Ripple V
•
)
• (
V
OUT MAX
•
(
OU
Figure 1. Recommended Component Placement for a Dual-Layer Board
)
T T MAX
–
(
GND
V
V
IN1
IN MIN
MODE SHDN1
)
(
)
)
V
OUT1
V
IN
GND
(series resistance of the windings) to reduce the I
losses, and must be able to support the peak inductor
current without saturating. Molded chokes and some
chip inductors usually do not have enough core area to
support the peak inductor currents of 900mA (500mA)
seen on the LTC3527/LTC3527-1. To minimize radiated
noise, use shielded inductors. See Table 1 for suggested
components and suppliers.
Output and Input Capacitor Selection
Low ESR (equivalent series resistance) capacitors should
be used to minimize output voltage ripple. Multilayer
ceramic capacitors are an excellent choice as they have
extremely low ESR and are available in small footprints.
A 4.7µF to 10µF output capacitor is suffi cient for most
applications. Larger values up to 22µF may be used to
obtain lower output voltage ripple and improve transient
response. X5R and X7R dielectric materials are preferred
for their ability to maintain capacitance over wide voltage
and temperature ranges. Y5V types should not be used.
GND
V
OUT2
SHDN2 FSEL
LTC3527/LTC3527-1
V
GND
IN2
35271 F01
2
R power
13
35271f