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参数资料
| 型号： | LT3970HMS-3.3#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 12/22页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK 3.3V 0.35A 10MSOP |
| 标准包装： | 50 |
| 类型： | 降压（降压） |
| 输出类型： | 固定 |
| 输出数： | 1 |
| 输出电压： | 3.3V |
| 输入电压： | 4.2 V ~ 40 V |
| PWM 型： | 电流模式，Burst Mode? |
| 频率 - 开关： | 200kHz ~ 2.25MHz |
| 电流 - 输出： | 350mA |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 10-TFSOP，10-MSOP（0.118"，3.00mm 宽） |
| 包装： | 管件 |
| 供应商设备封装： | 10-MSOP |
LT3970 Series
APPLICATIONS INFORMATION
=
C OUT
V IN = 12V
whenalowerswitchingfrequencyisused(duetolonger
on-times). If the input power source has high impedance, or
there is significant inductance due to long wires or cables,
additional bulk capacitance may be necessary. This can
be provided with a low performance electrolytic 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 at the LT3970 and to force this very high frequency
switching current into a tight local loop, minimizing EMI.
A 1μF capacitor is capable of this task, but only if it is
placed close to the LT3970 (see the PCB Layout section).
A second precaution regarding the ceramic input capacitor
concerns the maximum input voltage rating of the LT3970.
A ceramic input capacitor combined with trace or cable
inductance forms a high quality (under damped) tank
circuit. If the LT3970 circuit is plugged into a live supply,
the input voltage can ring to twice its nominal value, pos-
sibly exceeding the LT3970’s voltage rating. This situation
is easily avoided (see the Hot Plugging Safely section).
Output Capacitor and Output Ripple
The output capacitor has two essential functions. It stores
energy in order to satisfy transient loads and stabilize the
LT3970’s control loop. Ceramic capacitors have very low
equivalent series resistance (ESR) and provide the best
ripple performance. A good starting value is:
50
V OUT ? f SW
where f SW is in MHz and C OUT is the recommended output
capacitance in μF. Use X5R or X7R types. This choice will
provide low output ripple and good transient response.
Transient performance can be improved with a higher value
capacitor if combined with a phase lead capacitor (typically
22pF) between the output and the feedback pin. A lower
value of output capacitor can be used to save space and
cost but transient performance will suffer.
The second function is that the output capacitor, along
with the inductor, filters the square wave generated by the
LT3970 to produce the DC output. In this role it determines
the output ripple, so low impedance (at the switching
12
frequency) is important. The output ripple decreases with
increasing output capacitance, down to approximately
1mV. See Figure 1. Note that a larger phase lead capacitor
should be used with a large output capacitor.
18
FRONT PAGE APPLICATION
16 C LEAD = 47pF FOR C OUT ≥ 47μF
14
12
10
8
6
4 V IN = 24V
2
0
0 20 40 60 80 100
C OUT (μF)
3970 F01
Figure 1. Worst-Case Output Ripple Across Full Load Range
When choosing a capacitor, look carefully through the
data sheet to find out what the actual capacitance is under
operating conditions (applied voltage and temperature).
A physically larger capacitor or one with a higher voltage
rating may be required. Table 3 lists several capacitor
vendors.
Table 3. Recommended Ceramic Capacitor Vendors
MANUFACTURER WEBSITE
AVX www.avxcorp.com
Murata www.murata.com
Taiyo Yuden www.t-yuden.com
Vishay Siliconix www.vishay.com
TDK www.tdk.com
Ceramic Capacitors
Ceramic capacitors are small, robust and have very low
ESR. However, ceramic capacitors can cause problems
when used with the LT3970 due to their piezoelectric nature.
When in Burst Mode operation, the LT3970’s switching
frequency depends on the load current, and at very light
loads the LT3970 can excite the ceramic capacitor at audio
frequencies, generating audible noise. Since the LT3970
operates at a lower current limit during Burst Mode
3970fc
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相关代理商/技术参数 |
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| LT3970HMS-5#PBF | 功能描述:IC REG BUCK 5V 0.35A 10MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V，1.5V，1.8V，2.5V 输入电压:2.7 V ~ 20 V PWM 型:- 频率 - 开关:- 电流 - 输出:50mA 同步整流器:是 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 包装:带卷 (TR) 供应商设备封装:10-MSOP 裸露焊盘 |
| LT3970HMS-5#TRPBF | 功能描述:IC REG BUCK 5V 0.35A 10MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V，1.5V，1.8V，2.5V 输入电压:2.7 V ~ 20 V PWM 型:- 频率 - 开关:- 电流 - 输出:50mA 同步整流器:是 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 包装:带卷 (TR) 供应商设备封装:10-MSOP 裸露焊盘 |
| LT3970HMS-5-PBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:40V, 350mA Step-Down Regulator with 2.5μA Quiescent Current and Integrated Diodes |
| LT3970HMS-5-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:40V, 350mA Step-Down Regulator with 2.5μA Quiescent Current and Integrated Diodes |
| LT3970IDDB#PBF | 制造商:Linear Technology 功能描述:Conv DC-DC Single Step Down 4.2V to 40V 10-Pin DFN EP 制造商:Linear Technology 功能描述:Bulk |
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