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| 型号： | LTC3809EMS-1 |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 1 A SWITCHING CONTROLLER, 600 kHz SWITCHING FREQ-MAX, PDSO10 |
| 封装： | PLASTIC, MSOP-10 |
| 文件页数： | 24/24页 |
| 文件大小： | 318K |
| 代理商： | LTC3809EMS-1 |
38091f
LTC3809-1
9
Main Control Loop
The LTC3809-1 uses a constant frequency, current mode
architecture. During normal operation, the top external
P-channel power MOSFET is turned on when the clock
sets the RS latch, and is turned off when the current
comparator (ICMP) resets the latch. The peak inductor
current at which ICMP resets the RS latch is determined by
the voltage on the ITH pin, which is driven by the output of
the error amplifier (EAMP). The VFB pin receives the output
voltage feedback signal from an external resistor divider.
This feedback signal is compared to the internal 0.6V
reference voltage by the EAMP. When the load current
increases, it causes a slight decrease in VFB relative to the
0.6V reference, which in turn causes the ITH voltage to
increase until the average inductor current matches the
new load current. While the top P-channel MOSFET is off,
the bottom N-channel MOSFET is turned on until either the
inductor current starts to reverse, as indicated by the
current reversal comparator IRCMP, or the beginning of
the next cycle.
Shutdown, Soft-Start and Tracking Start-Up
(RUN and TRACK/SS Pins)
The LTC3809-1 is shut down by pulling the RUN pin low.
In shutdown, all controller functions are disabled and the
chip draws only 9
A. The TG output is held high (off) and
the BG output low (off) in shutdown. Releasing the RUN
pin allows an internal 0.7
A current source to pull up the
RUN pin to VIN. The controller is enabled when the RUN pin
reaches 1.1V.
The start-up of VOUT is based on the three different
connections on the TRACK/SS pin. The start-up of VOUT
is controlled by the LTC3809-1’s internal soft-start when
TRACK/SS is connected to VIN. During soft-start, the error
amplifier EAMP compares the feedback signal VFB to the
internal soft-start ramp (instead of the 0.6V reference),
which rises linearly from 0V to 0.6V in about 1ms. This
allows the output voltage to rise smoothly from 0V to its
final value while maintaining control of the inductor
current.
The 1ms soft-start time can be changed by connecting the
optional external soft-start capacitor CSS between the
TRACK/SS and GND pins. When the controller is enabled
by releasing the RUN pin, the TRACK/SS pin is charged up
by an internal 1
A current source and rises linearly from
0V to above 0.6V. The error amplifier EAMP compares the
feedback signal VFB to this ramp instead, and regulates VFB
linearly from 0V to 0.6V.
When the voltage on the TRACK/SS pin is less than the
0.6V internal reference, the LTC3809-1 regulates the VFB
voltage to the TRACK/SS pin instead of the 0.6V reference.
Therefore VOUT of the LTC3809-1 can track an external
voltage VX during start-up. Typically, a resistor divider on
VX is connected to the TRACK/SS pin to allow the start-up
of VOUT to “track” that of VX. For coincident tracking during
start-up, the regulated final value of VX should be larger
than that of VOUT, and the resistor divider on VX has the
same ratio as the divider on VOUT that is connected to VFB.
See detailed discussions in the Run and Soft-Start/
Tracking Functions in the Applications Information
Section.
Light Load Operation (Burst Mode Operation,
Continuous Conduction or Pulse Skipping Mode)
(MODE Pin)
The LTC3809-1 can be programmed for either high effi-
ciency Burst Mode operation, forced continuous conduc-
tion mode or pulse skipping mode at low load currents. To
select Burst Mode operation, tie the MODE pin to VIN. To
select forced continuous operation, tie the MODE pin to a
DC voltage below 0.4V (e.g., GND). Tying the MODE pin to
a DC voltage above 0.4V and below 1.2V (e.g., VFB)
enables pulse skipping mode. The 0.4V threshold between
forced continuous operation and pulse skipping mode can
be used in secondary winding regulation as described in
the Auxiliary Winding Control Using the MODE Pin discus-
sion in the Applications Information section.
When the LTC3809-1 is in Burst Mode operation, the peak
current in the inductor is set to approximately one-fourth
of the maximum sense voltage even though the voltage on
the ITH pin indicates a lower value. If the average inductor
current is higher than the load current, the EAMP will
decrease the voltage on the ITH pin. When the ITH voltage
drops below 0.85V, the internal SLEEP signal goes high
and the external MOSFET is turned off.
(Refer to Functional Diagram)
OPERATIO
U
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相关代理商/技术参数 |
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| LTC3809EMSE | 功能描述:IC REG CTRLR BUCK PWM CM 10-MSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LTC3809EMSE#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 10-MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LTC3809EMSE#TR | 功能描述:IC REG CTRLR BUCK PWM CM 10-MSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LTC3809EMSE#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 10-MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LTC3809EMSE-1 | 功能描述:IC REG CTRLR BUCK PWM CM 10-MSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
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