LTC3118_15 Datasheet, PDF (27/38 Pages) Linear Technology – 18V, 2A Buck-Boost DC/DC Converter with Low-Loss Dual Input PowerPath

LTC3118
Applications Information
The traces connecting this capacitor to V_IN1 or V_IN2 and
the ground plane should be made as short as possible.
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 electrolytic
capacitor in parallel with a 1µF ceramic capacitor gener-
ally yields a high performance, low cost solution. In ideal
diode mode, the voltage ripple on each input must be kept
below the V_IN comparator’s 800mV hysteresis to prevent
repetitive switching between V_IN1 and V_IN2 operation when
the input voltages aare similar.
Recommended Input and Output Capacitors
The capacitors used to filter the input and output of the
LTC3118 must have low ESR and must be rated to handle
the large AC currents generated by the switching convert-
ers. 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 these applications
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 some LTC3118 applications. Table 2 provides a partial
listing of appropriate capacitors to use. The choice of
capacitor technology is primarily dictated by a trade-off
between size, leakage current and cost. In backup power
applications, the input or output capacitor might be a super
or ultra capacitor with a capacitance value measuring in
the Farad range. The selection criteria in these applications
are generally similar except that voltage ripple is generally
not a concern. Some capacitors exhibit a high DC leak-
age current which may preclude their consideration for
applications that require a very low quiescent current in
Burst Mode operation.
Table 2. Representative Bypass and Output Capacitors
PART NUMBER
VALUE
(µF)
VOLTAGE
(V)
CAPACITOR TYPE
ESR (mΩ)
12103D226MAT2A
22
25
X5R Ceramic
C2220X226K3RACTU
22
A700D226M016ATE030
22
GRM32ER71E226KE15L
22
25
X7R Ceramic,
16
Aluminum
Polymer 30mΩ
25
X7R Ceramic
PLV1E121MDL1
ECJ-4YB1E226M
82
25
Aluminum
Polymer, 25mΩ
22
25
X5R Ceramic
25TQC22MV
22
16TQC100M
100
25SVPF47M
47
TMK325BJ226MM-T
22
25
POSCAP, 50mΩ
16
POSCAP, 45mΩ
25
OS-CON, 30mΩ
25
X5R Ceramic
CKG57NX5R1E476M
47
25
X5R Ceramic
SIZE
(W × L × H) mm
3.2 × 2.5 × 2.8
5.7 × 5 × 2.4
7.3 × 4.3 × 2.8
3.2 × 2.5 × 2.5
8×8×3
3.2 × 2.5 × 2.5
7.3 × 4.3 × 1.9
7.3 × 4.3 × 3.1
6.6 × 6.6 × 5.9
3.2 × 2.5 × 2.5
6.5 × 5.5 × 5.5
MANUFACTURER
AVX
www. avx.com
Kemet
www.kemet.com
Murata
www.murata.com
Nichicon
www.nichicon.com
Panasonic
www.panasonic.com
Sanyo
www.sanyo.com
Taiyo Yuden
www.t-yuden.com
TDK
www.tdk.com
For more information www.linear.com/LTC3118
3118f
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