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参数资料
| 型号： | LT3688HFE#TRPBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING REGULATOR, PDSO24 |
| 封装： | LEAD FREE, PLASTIC, TSSOP-24 |
| 文件页数： | 13/28页 |
| 文件大小： | 415K |
| 代理商： | LT3688HFE#TRPBF |
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LT3688
20
3688f
will charge these pins to ~2V. The RUN/SS pins provide
a soft-start function that limits peak input current to the
circuit during start-up. This helps to avoid drawing more
current than the input source can supply or glitching the
input supply when the LT3688 is enabled. The RUN/SS pins
do not provide an accurate delay to start or an accurately
controlled ramp at the output voltage, both of which depend
on the output capacitance and the load current.
Synchronization
Synchronizing the LT3688 oscillator to an external fre-
quency can be done by connecting a square wave (with
positive and negative pulse width > 150ns) to the SYNC
pin. The square wave amplitude should have valleys that
are below 0.4V and peaks that are above 1.3V (up to 6V).
The LT3688 may be synchronized over a 350kHz to 2.5MHz
range. The RT resistor should be chosen to set the LT3688
switching frequency 20% below the lowest synchronization
input. For example, if the synchronization signal will be
350kHz and higher, RT should be chosen for 280kHz. To
assure reliable and safe operation, the LT3688 will only
synchronize when the output voltage is above 90% of its
regulated voltage. It is therefore necessary to choose a
large enough inductor value to supply the required output
current at the frequency set by the RT resistor (see the
Inductor Selection section). It is also important to note
that the slope compensation is set by the RT value. When
the sync frequency is much higher than the one set by
RT, the slope compensation will be signicantly reduced,
which may require a larger inductor value to prevent
subharmonic oscillation.
Shutdown and Undervoltage Lockout
Figure 8 shows how to add undervoltage lockout (UVLO)
to the LT3688. Typically, UVLO is used in situations where
the input supply is current limited, or has a relatively high
source resistance. A switching regulator draws constant
power from the source, so source current increases as
source voltage drops. This looks like a negative resistance
load to the source and can cause the source to current limit
or latch low under low source voltage conditions.
UVLO prevents the regulator from operating at source
voltages where the problems might occur. An internal
comparator will force the part into shutdown below the
minimum VIN of 3.5V. This feature can be used to prevent
excessive discharge of battery-operated systems. If an
adjustable UVLO threshold is required, the EN/UVLO pin
can be used. The threshold voltage of the EN/UVLO pin
comparator is 1.25V. Current hysteresis is added above the
EN threshold. This can be used to set voltage hysteresis
of the UVLO using the following:
R3
=
VH –VL
3.7μA
R4
=
R3
1.25V
VH – 1.25V – R3 0.3μA
Example: switching should not start until the input is above
4.40V, and is to stop if the input falls below 4V.
VH = 4.40V, VL = 4V
R3
=
4.40V – 4V
3.7μA
= 107k
R4
=
107k
1.25V
4.40V – 1.25V – 107k
0.3μA
= 43.2k
1.25V
3.7μA
0.3μA
R3
R4
C1
EN/UVLO
LT3688
VIN
RUN/SS
VC
3688 F08
–
+
Figure 8. Undervoltage Lockout
APPLICATIONS INFORMATION
Keep the connection from the resistor to the EN/UVLO pin
short and make sure the interplane or surface capacitance
to switching nodes is minimized. If high resistor values
are used, the EN/UVLO pin should be bypassed with a
1nF capacitor to prevent coupling problems from the
switch node.
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| LT3689EUD-5#TRPBF | 1.95 A SWITCHING REGULATOR, 2160 kHz SWITCHING FREQ-MAX, PQCC16 |
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相关代理商/技术参数 |
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| LT3688IFE#PBF | 功能描述:IC REG BUCK ADJ 0.8A DL 24TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 产品培训模块:MIC23xxx HyperLight Load™ Regulators 标准包装:5,000 系列:HyperLight Load® 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.8V 输入电压:2.7 V ~ 5.5 V PWM 型:混合物 频率 - 开关:4MHz 电流 - 输出:2A 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:8-VFDFN 裸露焊盘，8-MLF? 包装:带卷 (TR) 供应商设备封装:8-MLF?（2x2） 产品目录页面:1094 (CN2011-ZH PDF) 其它名称:576-3303-2 |
| LT3688IFE#TRPBF | 功能描述:IC REG BUCK ADJ 0.8A DL 24TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 设计资源:Design Support Tool 标准包装:1 系列:- 类型:升压（升压） 输出类型:固定 输出数:1 输出电压:3V 输入电压:0.75 V ~ 2 V PWM 型:- 频率 - 开关:- 电流 - 输出:100mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:SOT-23-5 细型，TSOT-23-5 包装:剪切带 (CT) 供应商设备封装:TSOT-23-5 其它名称:AS1323-BTTT-30CT |
| LT3688IFEPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Dual 800mA Step-Down Switching Regulator with Power-On Reset |
| LT3688IUF#PBF | 功能描述:IC REG BUCK ADJ 0.8A DL 24QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 产品培训模块:MIC23xxx HyperLight Load™ Regulators 标准包装:5,000 系列:HyperLight Load® 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.8V 输入电压:2.7 V ~ 5.5 V PWM 型:混合物 频率 - 开关:4MHz 电流 - 输出:2A 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:8-VFDFN 裸露焊盘，8-MLF? 包装:带卷 (TR) 供应商设备封装:8-MLF?（2x2） 产品目录页面:1094 (CN2011-ZH PDF) 其它名称:576-3303-2 |
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