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参数资料
| 型号： | LTC3709EUH#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 10/24页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 32-QFN |
| 标准包装： | 2,500 |
| 系列： | PolyPhase® |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 200kHz |
| 占空比： | 90% |
| 电源电压： | 5 V ~ 36 V |
| 降压： | 是 |
| 升压： | 无 |
| 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 ~ 85°C |
| 封装/外壳： | 32-WFQFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
LTC3709
OPERATIO
(Refer to Functional Diagram)
MAIN CONTROL LOOP
The LTC3709 is a constant on-time, current mode step-
down controller with two channels operating 180 degrees
out of phase. In normal operation, each top MOSFET is
turned on for a fixed interval determined by its own one-
shot timer OST. When the top MOSFET is turned off, the
bottom MOSFET is turned on until the current comparator
I CMP trips, restarting the one-shot timer and repeating the
cycle. The trip level of the current comparator is set by the
I TH voltage, which is the output of error amplifier EA.
Inductor current is determined by sensing the voltage
between the SENSE – and SENSE + pins using either the
bottom MOSFET on-resistance or a separate sense resis-
tor. At light load, the inductor current can drop to zero and
become negative. This is detected by current reversal
comparator I REV , which then shuts off the bottom MOSFET,
resulting in discontinuous operation. Both switches will
remain off with the output capacitor supplying the load
current until the I TH voltage rises above the zero current
level (0.8V) to initiate another cycle. Discontinuous mode
operation is disabled when the FCB pin is tied to ground,
forcing continuous synchronous operation.
The main control loop is shut down by pulling the RUN/SS
pin low, turning off both top MOSFET and bottom MOSFET.
Releasing the pin allows an internal 1.2 μ A current source
to charge an external soft-start capacitor C SS . When this
voltage reaches 1.4V, the LTC3709 turns on and begins
operating with a clamp on the noninverting input of the
error amplifier. This input is also the reference input of the
error amplifier. As the voltage on RUN/SS continues to
rise, the voltage on the reference input also rises at the
same rate, effectively controlling output voltage slew rate.
Operating Frequency
The operating frequency is determined implicitly by the
top MOSFET on time and the duty cycle required to
maintain regulation. The one-shot timer generates an on-
time that is proportional to the ideal duty cycle, thus
holding the frequency approximately constant with changes
in V IN . The nominal frequency can be adjusted with an
external resistor R ON .
Output Overvoltage Protection
An overvoltage comparator, OV, guards against transient
overshoots (>10%) as well as other more serious condi-
tions that may overvoltage the output. In this condition,
the top MOSFET is turned off and the bottom MOSFET is
turned on and held on until the condition is cleared.
Power Good (PGOOD) Pin
Overvoltage and undervoltage comparators OV and UV
pull the PGOOD output low if the output feedback voltage
exits a ± 10% window around the regulation point. In
addition, the output feedback voltage must be out of this
window for a continuous duration of at least 100 μ s before
the PGOOD is pulled low. This is to prevent any glitch on
the feedback voltage from creating a false power bad
signal. The PGOOD will indicate a good power immediately
when the feedback voltage is in regulation.
Short-Circuit Detection and Protection
After the controller has been started and been given
adequate time to charge the output capacitor, the RUN/SS
capacitor is used in a short-circuit time-out circuit. If the
output voltage falls to less than 67% of its nominal output
voltage, the RUN/SS capacitor begins discharging on the
assumption that the output is in an overcurrent and/or
short-circuit condition. If the condition lasts for a long
enough period, as determined by the size of the RUN/SS
capacitor, the controller will be shut down until the
RUN/SS pin voltage is recycled. This built-in latch off can
be overridden by providing a >5 μ A pull-up at a compli-
ance of 5V to the RUN/SS pin. This current shortens the
soft-start period but also prevents net discharge of the
RUN/SS capacitor during an overcurrent and/or short-
circuit condition.
DRV CC
Power for the top and bottom MOSFET drivers and most
of the internal controller circuitry is derived from the
DRV CC pin. The top MOSFET driver is powered from a
floating bootstrap capacitor C B . This capacitor is normally
recharged from DRV CC through an external Schottky di-
ode D B when the top MOSFET is turned off.
3709fb
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC-3710 | 制造商:LITEON 制造商全称:Lite-On Technology Corporation 功能描述:0.3 FOUR LED CLOCK FREQUENCY DISPLAYS |
| LTC-3710E | 制造商:LITEON 制造商全称:Lite-On Technology Corporation 功能描述:0.3 FOUR LED CLOCK FREQUENCY DISPLAYS |
| LTC-3710G | 功能描述:LED 显示器和配件 4 Digit, Green RoHS:否 制造商:Avago Technologies 显示器类型:7 Segment 数位数量:2 字符大小:7.8 mm x 14.22 mm 照明颜色:Red 波长:628 nm 共用管脚:Common Anode 工作电压:2.05 V 工作电流:20 mA 最大工作温度:+ 85 C 最小工作温度:- 35 C 封装:Tube |
| LTC-3710HR | 功能描述:LED 显示器和配件 4 Digit, Red RoHS:否 制造商:Avago Technologies 显示器类型:7 Segment 数位数量:2 字符大小:7.8 mm x 14.22 mm 照明颜色:Red 波长:628 nm 共用管脚:Common Anode 工作电压:2.05 V 工作电流:20 mA 最大工作温度:+ 85 C 最小工作温度:- 35 C 封装:Tube |
| LTC-3710P | 功能描述:LED 显示器和配件 4 Digit, Red RoHS:否 制造商:Avago Technologies 显示器类型:7 Segment 数位数量:2 字符大小:7.8 mm x 14.22 mm 照明颜色:Red 波长:628 nm 共用管脚:Common Anode 工作电压:2.05 V 工作电流:20 mA 最大工作温度:+ 85 C 最小工作温度:- 35 C 封装:Tube |
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