lt3473a Linear Technology Corporation, lt3473a Datasheet - Page 8

• Manufacturer Part Number: lt3473a
• Description: Micropower 1a Boost Converter With Schottky And Output Disconnect
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
LT3473/LT3473A
resulting sum is fed into the positive terminal of the PWM
comparator A2. When this voltage exceeds the level of the
error signal V
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.
8
C
, the SR latch is reset, turning off the power
U
Table 1. Recommended Inductors
PART
DO1605T-682
ME3220-682
MSS6122-682
MSS5131-682
LQH55DN6R8
CDRH5D18-6R2
CDRH4D28-6R8
CDRH5D28-6R2
CRD53-4R7
A918CY-6R2M
(TYPE D62LCB)
A915AY-6R8M
(TYPE D53LC)
U
W
(mΩ)
DCR
200
270
100
60
74
71
81
33
74
62
68
U
RATING (A)
CURRENT
1.45
1.05
1.12
1.68
1.49
1.51
1.1
1.0
2.0
1.4
1.8
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
Taiyo Yuden
AVX
Murata
Kemet
5.4 × 4.2 × 1.8
3.2 × 2.5 × 2.0
6.1 × 6.1 × 2.2
5.1 × 5.1 × 3.1
5.7 × 5.0 × 4.7
5.7 × 5.7 × 2.0
4.7 × 4.7 × 3.0
5.7 × 5.7 × 3.0
6.0 × 5.2 × 3.2
6.0 × 6.0 × 2.0
5.0 × 5.0 × 3.0
DIMENSION
(mm)
Figure 3. Efficiency Comparison of Different Inductors
80
75
65
60
55
70
0
V
V
IN
OUT
MANUFACTURER
Coilcraft
800-322-2645
www.coilcraft.com
Murata
814-237-1431
www.murata.com
Sumida
847-956-0666
www.sumida.com
Toko
408-432-8281
www.tokoam.com
= 3.6V
= 20V
20
LEAD CURRENT l
408-573-4150
843-448-9411
814-237-1431
408-986-0424
TELEPHONE
40
TOKO A915AY-6R8M
SUMIDA CDRH4D28-6R8
SUMIDA CDRH5D18-6R2
COILCRAFT ME3220-682
COILCRAFT MSS5131-682
60
O
(mA)
80
URL
www.t-yuden.com
www.avxcorp.com
www.murata.com
www.kemet.com
3473 F03
100
3473f