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| 型号： | LT3474IFE-1#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 11/20页 |
| 文件大小： | 0K |
| 描述： | IC LED DRVR HP CONS CURR 16TSSOP |
| 标准包装： | 2,500 |
| 恒定电流： | 是 |
| 拓扑： | PWM，降压（降压） |
| 输出数： | 1 |
| 内部驱动器： | 是 |
| 类型 - 主要： | 车载，背光 |
| 类型 - 次要： | 颜色，白色 LED |
| 频率： | 200kHz ~ 2MHz |
| 电源电压： | 3.5 V ~ 36 V |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 16-TSSOP（0.173"，4.40mm）裸露焊盘 |
| 供应商设备封装： | 16-TSSOP-EP |
| 包装： | 带卷 (TR) |
| 工作温度： | -40°C ~ 125°C |
LT3474/LT3474-1
APPLICATIONS INFORMATION
Inductor Selection and Maximum Output Current
A good first choice for the inductor value is
900kHz
L = ( V OUT + V F ) ?
f
where V F is the voltage drop of the catch diode (~0.4V), f
is the switching frequency and L is in μH. With this value
the maximum load current will be 1.1A, independent of
input voltage. The inductor’s RMS current rating must be
greater than the maximum load current and its saturation
current should be at least 30% higher. For highest ef?ciency,
the series resistance (DCR) should be less than 0.2Ω.
Table 2 lists several vendors and types that are suitable.
For robust operation at full load and high input voltages
(V IN > 30V), use an inductor with a saturation current
higher than 2.5A.
Table 2. Inductors
The optimum inductor for a given application may differ
from the one indicated by this simple design guide. A
larger value inductor provides a higher maximum load
current, and reduces the output voltage ripple. If your
load is lower than the maximum load current, then you
can relax the value of the inductor and operate with higher
ripple current. This allows you to use a physically smaller
inductor, or one with a lower DCR resulting in higher
ef ?ciency. Be aware that if the inductance differs from
the simple rule above, then the maximum load current
will depend on input voltage. In addition, low inductance
may result in discontinuous mode operation, which further
reduces maximum load current. For details of maximum
output current and discontinuous mode operation, see
Linear Technology’s Application Note 44. Finally, for duty
cycles greater than 50% (V OUT /V IN > 0.5), a minimum
inductance is required to avoid sub-harmonic oscillations.
See Application Note 19.
VALUE
I RMS
DCR
HEIGHT
The current in the inductor is a triangle wave with an average
PART NUMBER
(μH)
(A)
(Ω)
(mm)
value equal to the load current. The peak switch current
Sumida
is equal to the output current plus half the peak-to-peak
CR43-3R3
CR43-4R7
CDRH4D16-3R3
CDRH4D28-3R3
CDRH4D28-4R7
CDRH5D28-100
CDRH5D28-150
CDRH73-100
CDRH73-150
3.3
4.7
3.3
3.3
4.7
10
15
10
15
1.44
1.15
1.1
1.57
1.32
1.3
1.1
1.68
1.33
0.086
0.109
0.063
0.049
0.072
0.048
0.076
0.072
0.13
3.5
3.5
1.8
3
3
3
3
3.4
3.4
inductor ripple current. The LT3474 limits its switch cur-
rent in order to protect itself and the system from overload
faults. Therefore, the maximum output current that the
LT3474 will deliver depends on the switch current limit,
the inductor value, and the input and output voltages.
When the switch is off, the potential across the inductor
is the output voltage plus the catch diode drop. This gives
the peak-to-peak ripple current in the inductor
( ) f ?
Coilcraft
DO1606T-332
DO1606T-472
3.3
4.7
1.3
1.1
0.1
0.12
2
2
Δ I L =
( 1– DC ) ( V OUT + V F )
L
DO1608C-332
DO1608C-472
MOS6020-332
3.3
4.7
3.3
2
1.5
1.8
0.08
0.09
0.046
2.9
2.9
2
where f is the switching frequency of the LT3474 and L
is the value of the inductor. The peak inductor and switch
current is
MOS6020-472
10
1.5
0.05
2
I SW ( PK ) = I L ( PK ) = I OUT +
Δ I L
2
3474fd
11
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