LTC3115-1
20
Rev. C
For more information
APPLICATIONS INFORMATION
may be necessary to add an additional small value bypass
capacitor near the V
IN
pin.
When powered through long leads or from a high ESR
power source, a larger value bulk input capacitor may
be required. In such applications, a 47µF to 100µF elec-
trolytic capacitor in parallel with a 1µF ceramic capacitor
generally yields a high performance, low cost solution.
Recommended Input and Output Capacitors
The capacitors used to filter the input and output of the
LTC3115-1 must have low ESR and must be rated to
handle the large AC currents generated by switching con-
verters. This is important to maintain proper functioning
of the IC and to reduce output voltage ripple. There are
many capacitor types that are well suited to such appli-
cations including multilayer ceramic, low ESR tantalum,
OS-CON and POSCAP technologies. In addition, there
are certain types of electrolytic capacitors such as solid
aluminum organic polymer capacitors that are designed
for low ESR and high AC currents and these are also well
suited to LTC3115-1 applications (Table 2). The choice of
capacitor technology is primarily dictated by a trade-off
between cost, size and leakage current. Notice that some
capacitors such as the OS-CON and POSCAP technolo-
gies can exhibit significant DC leakage currents which
may limit their applicability in devices which require low
no-load quiescent current in Burst Mode operation.
Ceramic capacitors are often utilized in switching con-
verter applications due to their small size, low ESR, and
low leakage currents. However, many ceramic capacitors
designed for power applications experience significant
loss in capacitance from their rated value with increased
DC bias voltages. For example, it is not uncommon for
a small surface mount ceramic capacitor to lose more
than 50% of its rated capacitance when operated near
its rated voltage. As a result, it is sometimes necessary
to use a larger value capacitance or a capacitor with a
higher voltage rating than required in order to actually
realize the intended capacitance at the full operating volt-
age. To ensure that the intended capacitance is realized
in the application circuit, be sure to consult the capacitor
vendor’s curve of capacitance versus DC bias voltage.
Table 2. Representative Bypass and Output Capacitors
MANUFACTURER,
PART NUMBER
VALUE
(µF)
VOLTAGE
(V)
SIZE L
×
W
×
H (mm),
TYPE, ESR
AVX
12103D226MAT2A
22
25
3.2
×
2.5
×
2.79
X5R Ceramic
TPME226K050R0075
22
50
7.3
×
4.3
×
4.1
Tantalum, 75mΩ
Kemet
C2220X226K3RACTU
22
25
5.7
×
5.0
×
2.4
X7R Ceramic
A700D226M016ATE030
22
16
7.3
×
4.3
×
2.8
Alum. Polymer, 30mΩ
Murata
GRM32ER71E226KE15L
22
25
3.2
×
2.5
×
2.5
X7R Ceramic
Nichicon
PLV1E121MDL1
82
25
8
×
8
×
12
Alum. Polymer, 25mΩ
Panasonic
ECJ-4YB1E226M
22
25
3.2
×
2.5
×
2.5
X5R Ceramic
Sanyo
25TQC22MV
22
25
7.3
×
4.3
×
3.1
POSCAP, 50mΩ
16TQC100M
100
16
7.3
×
4.3
×
1.9
POSCAP, 45mΩ
25SVPF47M
47
25
6.6
×
6.6
×
5.9
OS-CON, 30mΩ
Taiyo Yuden
UMK325BJ106MM-T
10
50
3.2
×
2.5
×
2.5
X5R Ceramic
TMK325BJ226MM-T
22
25
3.2
×
2.5
×
2.5
X5R Ceramic
TDK
KTJ500B226M55BFT00
22
50
6.0
×
5.3
×
5.5
X7R Ceramic
C5750X7R1H106M
10
50
5.7
×
5.0
×
2.0
X7R Ceramic
CKG57NX5R1E476M
47
25
6.5
×
5.5
×
5.5
X5R Ceramic
Vishay
94SVPD476X0035F12
47
35
10.3
×
10.3
×
12.6
OS-CON, 30mΩ
