LT3473A Ver la hoja de datos (PDF) - Linear Technology
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LT3473A Datasheet PDF : 12 Pages
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LT3473/LT3473A
APPLICATIO S I FOR ATIO
resulting sum is fed into the positive terminal of the PWM
comparator A2. When this voltage exceeds the level of the
error signal VC, the SR latch is reset, turning off the power
switch Q1. The error amplifier sets the peak current level
to keep the output in regulation. If the error amplifier’s
output increases, more current is delivered to the output;
if it decreases, less current is delivered.
The LT3473 includes an internal power Schottky diode and
a PNP transistor, Q2, for output disconnect. Q2 discon-
nects the load from the input during shutdown. The part
also has a power good indication pin, PGOOD. When the
FB voltage reaches within 100mV of the reference voltage,
the comparator A4 turns on Q5, sinking current from
PGOOD pin.
The LT3473 has thermal shutdown feature with threshold
at about 145°C.
Inductor Selection
A 6.8µH inductor is recommended for the LT3473. The
minimum inductor size that may be used in a given appli-
cation depends on required efficiency and output current.
Inductors with low core losses and small DCR (copper
wire resistance) at 1.2MHz are good choices for LT3473
applications. Some inductors in this category with small
size are listed in Table 1. The efficiency comparison of
different inductors is shown in Figure 3.
80
VIN = 3.6V
VOUT = 20V
75
70
65
TOKO A915AY-6R8M
60
SUMIDA CDRH4D28-6R8
SUMIDA CDRH5D18-6R2
COILCRAFT ME3220-682
COILCRAFT MSS5131-682
55
0
20
40
60
80 100
LEAD CURRENT lO (mA)
3473 F03
Figure 3. Efficiency Comparison of Different Inductors
Capacitor Selection
The small package of ceramic capacitors makes them
suitable for LT3473 applications. X5R and X7R types of
ceramic capacitors are recommended because they retain
their capacitance over wider voltage and temperature
ranges than other types such as Y5V or Z5U. A 4.7µF input
capacitor, a 0.47µF output capacitor and a 2.2µF capacitor
bypassing output disconnect PNP are sufficient for most
LT3473 applications.
Table 2. Recommended Ceramic Capacitor Manufacturers
MANUFACTURER
TELEPHONE
URL
Taiyo Yuden
408-573-4150
www.t-yuden.com
AVX
843-448-9411
www.avxcorp.com
Murata
814-237-1431
www.murata.com
Kemet
408-986-0424
www.kemet.com
Table 1. Recommended Inductors
PART
DCR
(mΩ)
CURRENT
RATING (A)
DIMENSION
(mm)
MANUFACTURER
DO1605T-682 200
1.1
ME3220-682
270
1.0
MSS6122-682 100
1.45
MSS5131-682
60
1.05
5.4 × 4.2 × 1.8
3.2 × 2.5 × 2.0
6.1 × 6.1 × 2.2
5.1 × 5.1 × 3.1
Coilcraft
800-322-2645
www.coilcraft.com
LQH55DN6R8
74
2.0
5.7 × 5.0 × 4.7
Murata
814-237-1431
www.murata.com
CDRH5D18-6R2 71
1.4
CDRH4D28-6R8 81
1.12
CDRH5D28-6R2 33
1.8
CRD53-4R7
74
1.68
5.7 × 5.7 × 2.0
4.7 × 4.7 × 3.0
5.7 × 5.7 × 3.0
6.0 × 5.2 × 3.2
Sumida
847-956-0666
www.sumida.com
A918CY-6R2M 62
1.49
(TYPE D62LCB)
A915AY-6R8M 68
1.51
(TYPE D53LC)
6.0 × 6.0 × 2.0
5.0 × 5.0 × 3.0
Toko
408-432-8281
www.tokoam.com
3473f
8
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