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参数资料
| 型号： | LTC3772EDDB#TRMPBF |
| 厂商： | Linear Technology |
| 文件页数： | 8/20页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 8-DFN |
| 标准包装： | 500 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 650kHz |
| 占空比： | 100% |
| 电源电压： | 2.75 V ~ 9.8 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： | 8-WFDFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
LTC3772
OPERATIO
(Refer to the Functional Diagram)
Main Control Loop (Normal Operation)
The LTC3772 is a constant frequency current mode step-
down switching regulator controller. During normal op-
eration, the external P-channel MOSFET is turned on each
cycle when the oscillator sets the RS latch and turned off
when the current comparator resets the latch. The peak
inductor current at which the current comparator trips is
controlled by the voltage on the I TH /RUN pin, which is the
output of the error amplifier. The negative input to the error
amplifier is the output feedback voltage V FB , which is
generated by an external resistor divider connected be-
tween V OUT and ground. When the load current increases,
it causes a slight decrease in V FB relative to the 0.8V
reference, which in turn causes the I TH /RUN voltage to
increase until the average inductor current matches the
new load current.
The main control loop is shut down by pulling the I TH /RUN
pin to ground. Releasing the I TH /RUN pin allows an
internal 1 μ A current source to charge up the external
compensation network. When the I TH /RUN pin voltage
reaches approximately 0.6V, the main control loop is
enabled and the I TH /RUN voltage is pulled up by a clamp
to its zero current level of approximately one diode
voltage drop (0.7V). As the external compensation net-
work continues to charge up, the corresponding peak
inductor current level follows, allowing normal operation.
The maximum peak inductor current attainable is set by a
clamp on the I TH /RUN pin at 1.2V above the zero current
level (approximately 1.9V).
Burst Mode Operation
The LTC3772 incorporates Burst Mode operation at low
load currents (<10% of I MAX ). In this mode, an internal
clamp sets the peak current of the inductor at a level cor-
responding to an I TH /RUN voltage 0.925V, even though the
actual I TH /RUN voltage is lower. When the inductor’s av-
erage current is greater than the load requirement, the
voltage at the I TH /RUN pin will drop. When the I TH /RUN
voltage falls to 0.85V, the sleep comparator will trip, turn-
ing off the external MOSFET. In sleep, the input DC supply
current to the IC is reduced to 40 μ A from 250 μ A in normal
operation. With the switch held off, average inductor cur-
rent will decay to zero and the load will eventually cause the
error amplifier output to start drifting higher. When the error
amplifier output rises to 0.87V, the sleep comparator will
untrip and normal operation will resume. The next oscilla-
tor cycle will turn the external MOSFET on and the switch-
ing cycle will repeat.
Dropout Operation
When the input supply voltage decreases towards the
output voltage, the rate of change of inductor current
during the on cycle decreases. This reduction means that
at some input-output differential, the external P-channel
MOSFET will remain on for more than one oscillator cycle
(start dropping off-cycles) since the inductor current has
not ramped up to the threshold set by the error amplifier.
Further reduction in input supply voltage will eventually
cause the external P-channel MOSFET to be turned on
100%; i.e., DC. The output voltage will then be determined
by the input voltage minus the voltage drop across the
sense resistor, the MOSFET and the inductor.
Undervoltage Lockout Protection
To prevent operation of the external P-channel MOSFET
with insufficient gate drive, an undervoltage lockout cir-
cuit is incorporated into the LTC3772. When the input
supply voltage drops below approximately 2V, the
P-channel MOSFET and all internal circuitry other than the
undervoltage block itself are turned off. Input supply
current in undervoltage is approximately 1 μ A.
Short-Circuit Protection
If the output is shorted to ground, the frequency of the
oscillator is folded back from 550kHz to approximately
200kHz while maintaining the same minimum on time.
This lower frequency allows the inductor current to safely
discharge, thereby preventing current runaway. After the
short is removed, the oscillator frequency will gradually
increase back to 550kHz as V FB rises through 0.3V on its
way back to 0.8V.
3772f
8
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| LTC3772ETS8 | 制造商:Linear Technology 功能描述:DC DC Cntrlr Single-OUT Step Down 2.75V to 9.8V Input 8-Pin TSOT-23 |
| LTC3772ETS8#PBF | 制造商:Linear Technology 功能描述:DC DC Cntrlr Single-OUT Step Down 2.75V to 9.8V Input 8-Pin TSOT-23 |
| LTC3772ETS8#TR | 制造商:Linear Technology 功能描述:DC DC Cntrlr Single-OUT Step Down 2.75V to 9.8V Input 8-Pin TSOT-23 T/R |
| LTC3772ETS8#TRM | 制造商:Linear Technology 功能描述:DC DC Cntrlr Single-OUT Step Down 2.75V to 9.8V Input 8-Pin TSOT-23 T/R |
| LTC3772ETS8#TRMPBF | 功能描述:IC REG CTRLR BUCK PWM TSOT23-8 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) |
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