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| 型号： | LT3757MPMSE#PBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING REGULATOR, 1000 kHz SWITCHING FREQ-MAX, PDSO10 |
| 封装： | 3 X 3 MM, LEAD FREE, PLASTIC, MSOP-10 |
| 文件页数： | 36/36页 |
| 文件大小： | 436K |
| 代理商： | LT3757MPMSE#PBF |
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LT3757
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applicaTions inForMaTion
Main Control Loop
The LT3757 uses a fixed frequency, current mode control
scheme to provide excellent line and load regulation. Op-
eration can be best understood by referring to the Block
Diagram in Figure 1.
ThestartofeachoscillatorcyclesetstheSRlatch(SR1)and
turns on the external power MOSFET switch M1 through
driver G2. The switch current flows through the external
current sensing resistor RSENSE and generates a voltage
proportional to the switch current. This current sense
voltage VISENSE (amplified by A5) is added to a stabilizing
slope compensation ramp and the resulting sum (SLOPE)
isfedintothepositiveterminalofthePWMcomparatorA7.
When SLOPE exceeds the level at the negative input of A7
(VC pin), SR1 is reset, turning off the power switch. The
level at the negative input of A7 is set by the error amplifier
A1 (or A2) and is an amplified version of the difference
between the feedback voltage (FBX pin) and the reference
voltage (1.6V or –0.8V, depending on the configuration).
In this manner, the error amplifier sets the correct peak
switch current level to keep the output in regulation.
TheLT3757hasaswitchcurrentlimitfunction.Thecurrent
sense voltage is input to the current limit comparator A6.
If the SENSE pin voltage is higher than the sense current
limit threshold VSENSE(MAX) (110mV, typical), A6 will reset
SR1 and turn off M1 immediately.
The LT3757 is capable of generating either positive or
negative output voltage with a single FBX pin. It can be
configuredasaboost,flybackorSEPICconvertertogener-
ate positive output voltage, or as an inverting converter to
generate negative output voltage. When configured as a
SEPICconverter,asshowninFigure1,theFBXpinispulled
up to the internal bias voltage of 1.6V by a voltage divider
(R1 and R2) connected from VOUTtoGND.ComparatorA2
becomes inactive and comparator A1 performs the invert-
ing amplification from FBX to VC. When the LT3757 is in
an inverting configuration, the FBX pin is pulled down to
–0.8V by a voltage divider connected from VOUT to GND.
Comparator A1 becomes inactive and comparator A2
performs the noninverting amplification from FBX to VC.
The LT3757 has overvoltage protection functions to
protect the converter from excessive output voltage
overshoot during start-up or recovery from a short-circuit
condition. An overvoltage comparator A11 (with 20mV
hysteresis) senses when the FBX pin voltage exceeds the
positive regulated voltage (1.6V) by 8% and provides a
reset pulse. Similarly, an overvoltage comparator A12
(with 10mV hysteresis) senses when the FBX pin voltage
exceeds the negative regulated voltage (–0.8V) by 11%
and provides a reset pulse. Both reset pulses are sent to
the main RS latch (SR1) through G6 and G5. The power
MOSFET switch M1 is actively held off for the duration of
an output overvoltage condition.
Programming Turn-On and Turn-Off Thresholds with
the SHDN/UVLO Pin
The SHDN/UVLO pin controls whether the LT3757 is
enabled or is in shutdown state. A micropower 1.22V
reference, a comparator A10 and a controllable current
source IS1 allow the user to accurately program the sup-
ply voltage at which the IC turns on and off. The falling
value can be accurately set by the resistor dividers R3
and R4. When SHDN/UVLO is above 0.7V, and below the
1.22V threshold, the small pull-down current source IS1
(typical 2A) is active.
The purpose of this current is to allow the user to program
therisinghysteresis.TheBlockDiagramofthecomparator
and the external resistors is shown in Figure 1. The typical
falling threshold voltage and rising threshold voltage can
be calculated by the following equations:
VVIN,FALLING =1.22
(R3
+R4)
R4
VVIN,RISING = 2A R3+ VIN,FALLING
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT3757MPMSE-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Boost, Flyback, SEPIC and Inverting Controller |
| LT3758 | 制造商:LINER 制造商全称:Linear Technology 功能描述:High Input Voltage, Boost, Flyback, SEPIC and Inverting Controller |
| LT3758A | 制造商:LINER 制造商全称:Linear Technology 功能描述:60V Low IQ Inverting DC/DC Controller Wide Operating VIN Range: 3.5V to 60V |
| LT3758AEDD#PBF | 制造商:Linear Technology 功能描述:IC REG CTRLR BST FLYBK INV 10DFN |
| LT3758AEDD#TRPBF | 制造商:Linear Technology 功能描述:IC REG CTRLR BST FLYBK INV 10DFN 制造商:Linear Technology 功能描述:SP-SWREG/Controller, High Input Voltage, Boost, Flyback, SEPIC and Inverting Con |
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