LTC3413 LINER [Linear Technology], LTC3413 Datasheet - Page 8

• Manufacturer Part Number: LTC3413
• Description: 3A, 2MHz Monolithic Synchronous Regulator for DDR/QDR Memory Termination
• Manufacturer: LINER [Linear Technology]

LTC3413
APPLICATIO S I FOR ATIO
Table 1 shows some recommended surface mount
inductors for LTC3413 applications.
Table 1. Recommended Surface Mount Inductors
Manufacturer
Murata
Vishay/Dale
Pulse
Cooper
C
The input capacitance, C
dal wave current at the source of the top MOSFET. To
prevent large voltage transients from occurring, a low ESR
input capacitor sized for the maximum RMS current
should be used. The maximum RMS current is given by:
This formula has a maximum at V
= I
used for design because even significant deviations do not
offer much relief. Note that ripple current ratings from
capacitor manufacturers are often based on only 2000
hours of life which makes it advisable to further derate the
capacitor, or choose a capacitor rated at a higher tempera-
ture than required. Several capacitors may also be paral-
leled to meet size or height requirements in the design.
The selection of C
resistance (ESR) that is required to minimize voltage
ripple and load step transients as well as the amount of
bulk capacitance that is necessary to ensure that the
control loop is stable. Loop stability can be checked by
viewing the load transient response as described in a later
section. The output ripple, V
8
IN
OUT
I
RMS
and C
V
OUT
/2. This simple worst-case condition is commonly
OUT
I
OUT MAX
Selection
I ESR
(
L
Part Number
LQH55DNR47M01
IHLP2525CZPJR47M01
P1166.681T
SD20-R47
OUT
U
)
V
is determined by the effective series
V
OUT
IN
IN
8
U
, is needed to filter the trapezoi-
fC
1
OUT
V
V
OUT
OUT
IN
IN
, is determined by:
W
– 1
= 2V
OUT
Value
( H)
0.47
0.47
0.44
0.47
, where I
U
(m )
DCR
13.0
20.0
4.2
6.0
RMS
The output ripple is highest at maximum input voltage
since I
placed in parallel may be needed to meet the ESR and RMS
current handling requirements. Dry tantalum, special poly-
mer, aluminum electrolytic and ceramic capacitors are all
available in surface mount packages. Special polymer
capacitors offer very low ESR but have lower capacitance
density than other types. Tantalum capacitors have the
highest capacitance density but it is important to only use
types that have been surge tested for use in switching
power supplies.
Aluminum electrolytic capacitors have significantly higher
ESR, but can be used in cost-sensitive applications pro-
vided that consideration is given to ripple current ratings
and long term reliability. Ceramic capacitors have excel-
lent low ESR characteristics but can have a high voltage
coefficient and audible piezoelectric effects. The high Q of
ceramic capacitors with trace inductance can also lead to
significant ringing.
Using Ceramic Input and Output Capacitors
Higher values, lower cost ceramic capacitors are now
becoming available in smaller case sizes. Their high ripple
current, high voltage rating and low ESR make them ideal
for switching regulator applications. However, care must
be taken when these capacitors are used at the input and
output. When a ceramic capacitor is used at the input and
the power is supplied by a wall adapter through long wires,
a load step at the output can induce ringing at the input,
V
mistaken as loop instability. At worst, a sudden inrush of
current through the long wires can potentially cause a
voltage spike at V
When choosing the input and output ceramic capacitors,
choose the X5R or X7R dielectric formulations. These
IN
. At best, this ringing can couple to the output and be
L
increases with input voltage. Multiple capacitors
IN
large enough to damage the part.
sn3413 3413fs