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| 型号： | LT3689IMSE-5#TRPBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 1.95 A SWITCHING REGULATOR, 2160 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封装： | LEAD FREE, PLASTIC, MSOP-16 |
| 文件页数： | 4/32页 |
| 文件大小： | 2188K |
| 代理商： | LT3689IMSE-5#TRPBF |
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LT3689/LT3689-5
12
3689fd
OPERATION
The LT3689 is a constant-frequency, current mode step-
down regulator with a watchdog and a reset timer that
allows microprocessor supervisory functions. Operation
can be best understood by referring to the Block Diagram.
Keeping the EN/UVLO pin at ground completely shuts off
the part drawing minimal current from the VIN source. To
turn on the internal bandgap and the rest of the logic cir-
cuitry, raise the EN/UVLO pin above the accurate threshold
of 1.26V. Also, VIN needs to be higher than 3.7V for the
part to start switching.
Switching Regulator Operation
An oscillator, with frequency set by RT, enables an RS flip-
flop, turning on the internal power switch. An amplifier
and comparator monitor the current flowing between the
VIN and SW pins, turning the switch off when this current
reaches a level determined by the voltage at VC. An error
amplifiermeasurestheoutputvoltagethroughtheresistor
divider tied to the FB pin and servos the VC voltage. If the
erroramplifier’soutputincreases,morecurrentisdelivered
to the output; if it decreases, less current is delivered.
An active clamp on the VC voltage provides current limit.
Aninternalregulatorprovidespowertothecontrolcircuitry.
The bias regulator normally draws current from the VIN
pin, but if the OUT pin is connected to an external volt-
age higher than 3V, bias current will be drawn from the
external source (typically the regulated output voltage).
This improves efficiency. The OUT pin also provides a cur-
rent path to the internal boost diode that charges up the
boost capacitor. The switch driver operates either from the
VIN or from the BST pin. An external capacitor is used to
generate a voltage at the BST pin that is higher than the VIN
supply. This allows the driver to fully saturate the internal
bipolarNPNpowerswitchforefficientoperation.Tofurther
optimize efficiency, the LT3689 automatically switches to
Burst Mode operation in light load situations. Between
bursts, all circuitry associated with controlling the output
switch is shut down, reducing the input supply current to
85A in a typical application. The oscillator reduces the
LT3689’s operating frequency when the voltage at the FB
pin is low. This frequency foldback helps to control the
output current during start-up and overload conditions.
A comparator monitors the current flowing through the
catch diode via the DA pin. This comparator delays switch-
ing if the diode current goes higher than 1.2A (typical)
during a fault condition such as a shorted output with
high input voltage. The switching will only resume once
the diode current has fallen below the 1.2A limit. This
way the DA comparator regulates the valley current of the
inductor to 1.2A during a short-circuit.
The LT3689 has an overvoltage protection feature which
disables switching when the VIN goes above 38V (typical)
during transients. When switching is disabled, the LT3689
can safely sustain transient input voltages up to 60V.
Power-On Reset and Watchdog Timer Operation
The LT3689 has a power-on reset (POR) comparator that
monitors the regulated output voltage. If the output volt-
age is below 10% of the regulation value, the RST pin is
pulled low. Once the output voltage crosses over 90% of
the regulation value, a reset timer is started and RST is
released after the programmed reset delay time. The reset
delay is programmable through the CPOR pin.
Thewatchdogtypicallymonitorsamicroprocessor’sactiv-
ity. The watchdog can be enabled or disabled by applying
a logic signal to the WDE pin. The watchdog can be oper-
ated in either timeout or window mode by applying a logic
signaltotheW/Tpin.Intimeoutmode,themicroprocessor
is required to change the logic state of the WDI pin on a
periodic basis in order to clear the watchdog timer and to
prevent the WDO from going low. In window mode, the
watchdogtimerrequiressuccessivenegativeedgesonthe
WDI pin to come within a programmed time window to
keep WDO from going low. Therefore, in window mode, if
the time between the two negative WDI edges is too short
or too long, then the WDO pin will be pulled low. When the
WDO pin goes low, either in timeout or in window mode,
the reset timer turns on and keeps the WDO pin low. The
WDO pin will go high again once the reset timer expires or
the RST pin goes low when the output voltage falls 10%
below the regulation value. Both the timeout and window
periods can be set through the CWDT pin.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT3689IMSE-PBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:700mA Step-Down Regulator with Power-On Reset and Watchdog Timer |
| LT3689IMSE-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:700mA Step-Down Regulator with Power-On Reset and Watchdog Timer |
| LT3689IUD#PBF | 功能描述:IC REG BUCK ADJ 0.7A 16QFN 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 |
| LT3689IUD#TRPBF | 功能描述:IC REG BUCK ADJ 0.7A 16QFN 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 |
| LT3689IUD-5#PBF | 功能描述:IC REG BUCK 5V 0.7A 16QFN 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 |
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