LTC3565_12 Datasheet, PDF (11/22 Pages) Linear Technology – 1.25A, 4MHz, Synchronous Step-Down DC/DC Converter

LTC3565
APPLICATIONS INFORMATION
shows some typical surface mount inductors that work
well in LTC3565 applications.
Table 1. Representative Surface Mount Inductors
MANU-
FACTURER PART NUMBER
MAX DC
VALUE CURRENT DCR HEIGHT
Toko
A914BYW-1R2M=P3: 1.2μH 2.15A 44mΩ 2mm
D52LC
A960AW-1R2M=P3:
D518LC
1.2μH 1.8A 46mΩ 1.8mm
DB3015C-1068AS-1R0N 1.0μH 2.1A 43mΩ 1.5mm
DB3018C-1069AS-1R0N 1.0μH 2.1A 45mΩ 1.8mm
DB3020C-1070AS-1R0N 1.0μH 2.1A 47mΩ 2mm
A914BYW-2R2M-D52LC 2.2μH 2.05A 49mΩ 2mm
A915AY-2ROM-D53LC 2.0μH 3.3A 22mΩ 3mm
Coilcraft LPO1704-122ML
1.2μH 2.1A 80mΩ 1mm
D01608C-222
2.2μH 2.3A 70mΩ 3mm
LP01704-222M
2.2μH 2.4A 120mΩ 1mm
Sumida CR32-1R0
1.0μH 2.1A 72mΩ 3mm
CR5D11-1R0
1.0μH 2.2A 40mΩ 1.2mm
CDRH3D14-1R2
1.2μH 2.2A 36mΩ 1.5mm
CDRH4D18C/LD-1R1 1.1μH 2.1A 24mΩ 2mm
CDRH4D28C/LD-1R0 1.0μH 3.0A 17.5mΩ 3mm
CDRH4D28C-1R1
1.1μH 3.8A 22mΩ 3mm
CDRH4D28-1R2
1.2μH 2.56A 23.6mΩ 3mm
CDRH6D12-1R0
1.0μH 2.80A 37.5mΩ 1.5mm
CDRH4D282R2
2.2μH 2.04A 23mΩ 3mm
CDC5D232R2
2.2μH 2.16A 30mΩ 2.5mm
Taiyo
Yuden
NPO3SB1ROM
N06DB2R2M
1.0μH 2.6A 27mΩ 1.8mm
2.2μH 3.2A 29mΩ 3.2mm
N05DB2R2M
2.2μH 2.9A 32mΩ 2.8mm
Murata LQN6C2R2M04
2.2μH 3.2A 24mΩ 5mm
FDK
MIPW3226DORGM
0.9μH 1.4A 80mΩ 1mm
Catch Diode Selection
Although unnecessary in most applications, a small
improvement in efficiency can be obtained in a few ap-
plications by including the optional diode D1 shown in
Figure 2, which conducts when the synchronous switch
is off. When using Burst Mode operation or pulse skip
mode, the synchronous switch is turned off at a low
current and the remaining current will be carried by the
optional diode. It is important to adequately specify the
diode peak current and average power dissipation so as
not to exceed the diode ratings. The main problem with
Schottky diodes is that their parasitic capacitance reduces
the efficiency, usually negating the possible benefits for
LTC3565 circuits. Another problem that a Schottky diode
can introduce is higher leakage current at high tempera-
tures, which could reduce the low current efficiency.
Remember to keep lead lengths short and observe proper
grounding (see Board Layout Considerations) to avoid ring-
ing and increased dissipation when using a catch diode.
Input Capacitor (C_IN) Selection
In continuous mode, the input current of the converter is a
square wave with a duty cycle of approximately V_OUT/V_IN.
To prevent large voltage transients, a low equivalent series
resistance (ESR) input capacitor sized for the maximum
RMS current must be used. The maximum RMS capacitor
current is given by:
I_RMS ≈ I_MAX
V_OUT(V_IN − V_OUT )
V_IN
where the maximum average output current I_MAX equals
the peak current minus half the peak-to-peak ripple cur-
rent, I_MAX ≅ I_LIM – ΔI_L/2.
This formula has a maximum at V_IN = 2V_OUT, where
I_RMS = I_OUT/2. This simple worst case is commonly used
to design because even significant deviations do not offer
much relief. Note that capacitor manufacturer’s ripple cur-
rent ratings are often based on only 2000 hours lifetime.
This makes it advisable to further derate the capacitor,
or choose a capacitor rated at a higher temperature than
required. Several capacitors may also be paralleled to meet
the size or height requirements of the design. An additional
0.1μF to 1μF ceramic capacitor is also recommended on
V_IN for high frequency decoupling, when not using an all
ceramic capacitor solution.
Output Capacitor (C_OUT) Selection
The selection of C_OUT is driven by the required ESR to
minimize voltage ripple and load step transients. Typically,
once the ESR requirement is satisfied, the capacitance
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