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参数资料
| 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： | 4/36页 |
| 文件大小： | 436K |
| 代理商： | LT3757MPMSE#PBF |
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LT3757
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3757fc
applicaTions inForMaTion
TheoperatingfrequencyoftheLT3757canbesynchronized
to an external clock source. By providing a digital clock
signal into the SYNC pin, the LT3757 will operate at the
SYNCclockfrequency.Ifthisfeatureisused,anRTresistor
should be chosen to program a switching frequency 20%
slowerthanSYNCpulsefrequency.TheSYNCpulseshould
have a minimum pulse width of 200ns. Tie the SYNC pin
to GND if this feature is not used.
Duty Cycle Consideration
Switching duty cycle is a key variable defining converter
operation.Assuch,itslimitsmustbeconsidered.Minimum
on-time is the smallest time duration that the LT3757 is
capable of turning on the power MOSFET. This time is
generally about 220ns (typical) (see Minimum On-Time
in the Electrical Characteristics table). In each switching
cycle, the LT3757 keeps the power switch off for at least
220ns (typical) (see Minimum Off-Time in the Electrical
Characteristics table).
The minimum on-time and minimum off-time and the
switching frequency define the minimum and maximum
switching duty cycles a converter is able to generate:
Minimum duty cycle = minimum on-time frequency
Maximum duty cycle = 1 – (minimum off-time frequency)
Programming the Output Voltage
The output voltage (VOUT) is set by a resistor divider, as
shown in Figure 1. The positive and negative VOUT are set
by the following equations:
VOUT,POSITIVE =1.6V 1+
R2
R1
VOUT,NEGATIVE = –0.8V 1+
R2
R1
The resistors R1 and R2 are typically chosen so that
the error caused by the current flowing into the FBX pin
during normal operation is less than 1% (this translates
to a maximum value of R1 at about 158k).
Soft-Start
The LT3757 contains several features to limit peak switch
currents and output voltage (VOUT) overshoot during
start-up or recovery from a fault condition. The primary
purpose of these features is to prevent damage to external
components or the load.
High peak switch currents during start-up may occur in
switching regulators. Since VOUT is far from its final value,
the feedback loop is saturated and the regulator tries to
chargetheoutputcapacitorasquicklyaspossible,resulting
in large peak currents. A large surge current may cause
inductor saturation or power switch failure.
The LT3757 addresses this mechanism with the SS pin. As
shown in Figure 1, the SS pin reduces the power MOSFET
current by pulling down the VC pin through Q2. In this
way the SS allows the output capacitor to charge gradu-
ally toward its final value while limiting the start-up peak
currents. The typical start-up waveforms are shown in the
Typical Performance Characteristics section. The inductor
current IL slewing rate is limited by the soft-start function.
Besides start-up, soft-start can also be triggered by the
following faults:
1. INTVCC > 17.5V
2. INTVCC < 2.6V
3. Thermal lockout
Any of these three faults will cause the LT3757 to stop
switching immediately. The SS pin will be discharged by
Q3. When all faults are cleared and the SS pin has been
discharged below 0.2V, a 10A current source IS2 starts
charging the SS pin, initiating a soft-start operation.
The soft-start interval is set by the soft-start capacitor
selection according to the equation:
TSS =CSS
1.25V
10A
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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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