LTC3124_15 Datasheet, PDF (16/28 Pages) Linear Technology – 15V, 5A 2-Phase Synchronous Step-Up DC/DC Converter with Output Disconnect

LTC3124
APPLICATIONS INFORMATION
SCHOTTKY DIODE
Although it is not required, adding a Schottky diode from
both SW pins to V_OUT can improve the converter efficiency
by up to 4%. Note that this defeats the output disconnect
and short-circuit protection features of the LTC3124.
COMPONENT SELECTION
windings) to reduce the I²R power losses, and must be
able to support the peak inductor current without saturat-
ing. Molded chokes and most chip inductors usually do
not have enough core area to support the peak inductor
currents of 3A to 4A seen on the LTC3124. To minimize
radiated noise, use a shielded inductor.
See Table 2 for suggested components and suppliers.
Inductor Selection
The LTC3124 can utilize small inductors due to its capa-
bility of setting a fast (up to 3MHz) switching frequency.
Larger values of inductance will allow slightly greater
output current capability by reducing the inductor ripple
current. To design a stable converter the range of induc-
tance values is bounded by the targeted magnitude of the
internal slope compensation and is inversely proportional
to the switching frequency. The Inductor selection for the
LTC3124 has the following bounds:
10
f
µH
>
L
>
3
f
µH
The inductor peak-to-peak ripple current is given by the
following equation:
( ) _Ripple(A)
=
V_IN
• V_OUT – V_IN
f •L • V_OUT
where:
L = Inductor Value in μH
f = Switching Frequency in MHz of One Phase
Table 2. Recommended Inductors
PART NUMBER
VALUE DCR I_SAT
(µH) (mΩ) (A)
SIZE (mm)
W×L×H
Coilcraft XFL4020-102ME
Coilcraft MSS7341T-332NL
Coilcraft XAL5030-332ME
Coilcraft XAL5030-472ME
Coilcraft XAL5050-562ME
Coilcraft XAL6060-223ME
Coilcraft MSS1260T-333ML
1 12 5.4 4.3 × 4.3 × 2.1
3.3 18 3.7 7.3 × 7.3 × 4.1
3.3 23 8.7 5.3 × 5.3 × 3.1
4.7 36 6.7 5.3 × 5.3 × 3.1
5.6 26 6.3 5.3 × 5.3 × 5.1
22 61 5.6 6.3 × 6.3 × 6.1
33 57 4.34 12.3 × 12.3 × 6.2
Coiltronics SD53-1R1-R
Coiltronics DR74-4R7-R
Coiltronics DR125-330-R
Coiltronics DR127-470-R
1.1 20 4.8 5.2 × 5.2 × 3
4.7 25 4.37 7.6 × 7.6 × 4.35
33 51 3.84 12.5 × 12.5 × 6
47 72 5.28 12.5 × 12.5 × 8
Sumida CDR7D28MNNP-1R2NC 1.2 21 5.9 7.6 × 7.6 × 3
Sumida CDMC6D28NP-3R3MC 3.3 31 5 7.25 × 6.7 × 3
Taiyo-Yuden NR5040T3R3N
3.3 35 3.8
5×5×4
TDK LTF5022T-1R2N4R2-LC
TDK SPM6530T-3R3M
TDK VLP8040T-4R7M
1.2 25 4.3 5 × 5.2 × 2.2
3.3 30 6.8 7.1 × 6.5 × 3
4.7 25 4.4 8 × 7.7 × 4
Würth WE-LHMI 74437324010 1 27 9 4.45 × 4.06 × 1.8
Würth WE-PD 7447789002
2.2 20 4.8 7.3 × 7.3 × 3.2
Würth WE-PD 7447779002
2.2 20 6 7.3 × 7.3 × 4.5
Würth WE-PD 7447789003
3.3 30 4.2 7.3 × 7.3 × 3.2
Würth WE-PD 7447789004
4.7 35 3.9 7.3 × 7.3 × 3.2
Würth WE-HCI 7443251000
10 16 8.5 10 × 10 × 5
Würth WE-PD 744770122
22 43 5
12 × 12 × 8
Würth WE-PD 744770133
33 64 3.6 12 × 12 × 8
Würth WE-PD 7447709470
47 60 4.5 12 × 12 × 10
The inductor ripple current is a maximum at the minimum
inductor value. Substituting 3/f for the inductor value in
the above equation yields the following:
( ) _RippleMAX
(A)
=
V_IN
• V_OUT –
3 • V_OUT
V_IN
A reasonable operating range for the inductor ripple cur-
rent is typically 10% 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 efficiency. The
inductor should have low DCR (series resistance of the
Output and Input Capacitor Selection
Low ESR (equivalent series resistance) capacitors should
be used to minimize the output voltage ripple. Multilayer
ceramic capacitors are an excellent choice as they have
extremely low ESR and are available in small footprints.
X5R and X7R dielectric materials are preferred for their
ability to maintain capacitance over wide voltage and tem-
perature ranges. Y5V types should not be used. Although
ceramic capacitors are recommended, low ESR tantalum
capacitors may be used as well.
3124f
16
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