LTC3124_15 Datasheet, PDF (17/28 Pages) Linear Technology – 15V, 5A 2-Phase Synchronous Step-Up DC/DC Converter with Output Disconnect

LTC3124
APPLICATIONS INFORMATION
When selecting output capacitors, the magnitude of the
peak inductor current, together with the ripple voltage
specification, determine the choice of the capacitor. Both
the ESR (equivalent series resistance) of the capacitor and
the charge stored in the capacitor each cycle contribute
to the output voltage ripple.
The peak-to-peak ripple due to the charge is approximately:
V_{RIPPLE(CHARGE)}(V)
≈
I_P • V_IN
C_OUT • V_OUT
•
f
•2
where:
I_P = Peak inductor current
f = Switching frequency of one phase
The ESR of C_OUT is usually the most dominant factor for
ripple in most power converters. The peak-to-peak ripple
due to the capacitor ESR is:
V_RIPPLE(ESR)(V)
= I_LOAD
•
R_ESR
•
V_OUT
V_IN
where R_ESR = capacitor equivalent series resistance.
The input filter capacitor reduces peak currents drawn
from the input source and reduces input switching noise.
A low ESR bypass capacitor with a minimum value of 10µF
should be located as close to V_IN as possible.
Low ESR and high capacitance are critical to maintain low
output ripple. Capacitors can be used in parallel for even
larger capacitance values and lower effective ESR. Ceramic
capacitors are often utilized in switching converter appli-
cations due to their small size, low ESR and low leakage
currents. However, many ceramic capacitors experience
significant loss in capacitance from their rated value with
increased DC bias voltage. It is not uncommon for a small
surface mount 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 capaci-
tor value or a capacitor with a larger value and case size,
such as 1812 rather than 1206, in order to actually realize
the intended capacitance at the full operating voltage. Be
sure to consult the vendor’s curve of capacitance versus
DC bias voltage. Table 3 shows a sampling of capacitors
suited for the LTC3124 applications.
Table 3: Representative Output Capacitors
Manufacturer,
Part Number
Value
(µF)
Voltage
(V)
AVX,
1206YD226KAT2A
22
16
AVX,
1210YC226KAT2A
22
16
Murata,
22
16
GRM31CR61C226ME15L
Murata,
22
16
GRM32ER71C226KE18K
Murata,
22
16
GRM43ER61C226KE01L
Murata,
47
16
GRM32EB31C476ME15K
Panasonic,
ECJ-4YB1C226M
22
16
Taiyo Yuden,
22
16
EMK316BJ226ML-T
Taiyo Yuden,
22
16
EMK325B7226MM-TR
Taiyo Yuden,
22
16
EMK432BJ226KM-T
TDK,
C5750X7R1C476M
47
16
TDK,
C4532X5R0J107M
100
6.3
Nichicon,
UBC1C101MNS1GS
100
16
Sanyo,
25TQC22MV
22
25
Sanyo,
16TQC47MW
47
16
Sanyo,
16TQC100M
100
16
Sanyo,
25SVPF47M
47
25
AVX, BestCap Series
BZ125A105ZLB
1F
5.5
Cap-XX GS230F
1.2F
4.5
Tecate Powerburst
TPL-100/22X45
100F
2.7
Cooper KR-5R5C155-R 1.5F
5.5
Cooper
HB1860-2R5117-R
Maxwell
BCAP0050-P270
110F
2.5
50F
2.5
SIZE L × W × H (mm)
Type, ESR (mΩ)
3.2 × 1.6 × 1.78,
X5R Ceramic
3.2 × 2.5 × 2.79,
X7R Ceramic
3.2 × 1.6 × 1.8,
X5R Ceramic
3.2 × 2.5 × 2.7,
X7R Ceramic
4.5 × 3.2 × 2.7,
X5R Ceramic
3.2 × 2.5 × 2.5,
X5R Ceramic
3.2 × 2.5 × 2.7,
X5R Ceramic
3.2 × 1.6 × 1.8,
X5R Ceramic
3.2 × 2.5 × 2.7,
X7R Ceramic
4.5 × 3.2 × 2.7,
X5R Ceramic
5.7 × 5 × 2.5,
X7R Ceramic
4.5 × 3.2 × 2.8,
X5R Ceramic
8.3 × 8.3 × 11.5,
Aluminum Polymer
7.3 x 4.3 x 1.9,
POSCAP, 45mΩ
7.3 × 4.3 × 3.1,
POSCAP, 40mΩ
7.3 × 4.3 × 3.1,
POSCAP, 50mΩ
6.6 × 6.6 × 5.9,
OS-CON, 30mΩ
48 × 30 × 6.1,
35mΩ, 4 Lead
39 × 17 × 3.8, 28mΩ
D = 22, H = 45
15mΩ
D = 21.5, H = 7.5
30mΩ
D = 18.5, H = 60
20mΩ
D = 18, H = 40
20 mΩ
For more information www.linear.com/LTC3124
3124f
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