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参数资料
| 型号： | LT3474IFE-1#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 12/20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
To maintain output regulation, this peak current must be
less than the LT3474’s switch current limit I LIM . For SW1,
I LIM is at least 1.6A (1.5A at 125°C) at low duty cycles and
decreases linearly to 1.15A (1.08A at 125°C) at DC = 0.8.
The maximum output current is a function of the chosen
at the LT3474 input and to force this switching current into
a tight local loop, minnimizing EMI. The input capacitor
must have low impedance at the switching frequency to
do this effectively, and it must have an adequate ripple
current rating. The RMS input is:
V OUT ( IN OUT
inductor value:
I OUT ( MAX ) = I LIM –
Δ I L
2
C INRMS = I OUT ?
V – V
V IN
) < I OUT
2
= 1.6A ? ( ) –
1– 0.35?DC
Δ I L
2
and is largest when V IN = 2V OUT (50% duty cycle). Con-
sidering that the maximum load current is 1A, RMS ripple
Choosing an inductor value so that the ripple current is
small will allow a maximum output current near the switch
current limit.
One approach to choosing the inductor is to start with the
simple rule given above, look at the available inductors,
and choose one to meet cost or space goals. Then use
these equations to check that the LT3474 will be able to
deliver the required output current. Note again that these
equations assume that the inductor current is continuous.
Discontinuous operation occurs when I OUT is less than
ΔI L /2.
Input Capacitor Selection
Bypass the input of the LT3474 circuit with a 2.2μF or
higher ceramic capacitor of X7R or X5R type. A lower
value or a less expensive Y5V type will work if there is
additional bypassing provided by bulk electrolytic capaci-
tors or if the input source impedance is low. The following
paragraphs describe the input capacitor considerations in
more detail.
current will always be less than 0.5A
The high switching frequency of the LT3474 reduces the
energy storage requirements of the input capacitor, so that
the capacitance required is less than 10μF. The combination
of small size and low impedance (low equivalent series
resistance or ESR) of ceramic capacitors makes them the
preferred choice. The low ESR results in very low voltage
ripple. Ceramic capacitors can handle larger magnitudes
of ripple current than other capacitor types of the same
value. Use X5R and X7R types.
An alternative to a high value ceramic capacitor is a lower
value ceramic along with a larger electrolytic capaci-
tor. The electrolytic capacitor likely needs to be greater
than 10μF in order to meet the ESR and ripple current
requirements. The input capacitor is likely to see high
surge currents when the input source is applied. Tanta-
lum capacitors can fail due to an over-surge of current.
Only use tantalum capacitors with the appropriate surge
current rating. The manufacturer may also recommend
operation below the rated voltage of the capacitor.
Step-down regulators draw current from the input sup-
ply in pulses with very fast rise and fall times. The input
capacitor is required to reduce the resulting voltage ripple
3474fd
12
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相关代理商/技术参数 |
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|---|---|
| LT3474IFE-PBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Step-Down 1A LED Driver |
| LT3474IFE-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Step-Down 1A LED Driver |
| LT3475 | 制造商:LINER 制造商全称:Linear Technology 功能描述:Dual Step-Down l 1.5A LED Driver |
| LT3475-1 | 制造商:LINER 制造商全称:Linear Technology 功能描述:Dual Step-Down l 1.5A LED Driver |
| LT3475EFE | 制造商:Linear Technology 功能描述:LED DRVR 2Segment 5V/9V/12V/15V/18V/24V 20-Pin TSSOP EP |
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