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3710EFE 参数 Datasheet PDF下载

3710EFE图片预览
型号: 3710EFE
PDF下载: 下载PDF文件 查看货源
内容描述: 次级侧同步后稳压器 [Secondary Side Synchronous Post Regulator]
分类和应用: 稳压器
文件页数/大小: 12 页 / 220 K
品牌: Linear [ Linear ]
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LT3710  
U
W U U  
APPLICATIO S I FOR ATIO  
Output N-Channel MOSFET Drivers  
discharging the output, which would cause the output to  
undershoot below ground.  
The LT3710 employs high speed N-channel MOSFET  
synchronous drivers to achieve high system efficiency.  
GBIAS is the 8V regulator output to bias and supply the  
drivers and should be properly bypassed with a low ESR  
capacitor to ground plane. A Schottky catch diode is  
required on the switch node.  
Layout Considerations  
For maximum efficiency, the switching rise and fall times  
are less than 20ns. To prevent radiation, the power  
MOSFETs,SWpinandinputbypasscapacitorleadsshould  
be kept as short as possible. A ground plane should be  
used under the switching circuitry to prevent interplane  
coupling and to act as a thermal spreading path. Note that  
the bottom metal of the package is the heat sink, as well as  
the IC signal ground, and must be soldered to the ground  
plane.  
Light Load Operation  
IftheBGSpinisgrounded,theLT3710staysincontinuous  
mode independent of load condition except in soft-start  
operation (see Soft-Start section). If the BGS pin is left  
open, under light load and VRS1 drops below 8mV, BGATE  
will be turned off(see comparator CA2 of Block Diagram)  
and the LT3710 goes into discontinous mode operation.  
Output Voltage Programming  
Thefeedbackreferencevoltageis0.8V. Theoutputvoltage  
can be easily programmed by the resistor divider, R3 and  
R4, as shown in the Block Diagram.  
Current Limit  
Current limit is set by the 70mV threshold across CL+ and  
CL, the inputs of the amplifier CA1. By connecting an  
external resistor RS1(see Block Diagram), the current  
limit is set for 70mV/RS1. R6 and C6 stablize the current  
limit loop. If current limit is not used, both CL+ and CL–  
should be grounded and the BGS pin should also be  
grounded to disable comparator CA2.  
R3  
VOUT2 = 0.8• 1+  
R4  
Filtering on the SYNC Input  
It is necessary to add RC filtering on the SYNC input of the  
LT3710toeliminatethenegativeglitchattheturnonofthe  
top MOSFET. When the top MOSFET M1 turns on, the  
transformersecondarycurrentinstantlychangesfromthe  
original first output inductor current to the sum of two  
output inductor currents. The high di/dt on the trans-  
former leakage inductance causes the transformer sec-  
ondaryvoltageVS todropforashortinterval.Iftheleakage  
inductance is large enough, the VS dip will be lower than  
the synchronization threshold (about 2.5V), falsely trig-  
gering the synchronization. The top MOSFET is turned off  
immediately. As a result, the output voltage will not be  
regulated properly.  
Soft-Start and Shutdown  
Duringsoft-start,VSS isthereferencevoltagethatcontrols  
the output voltage and the output ramps up following VSS.  
The effective range of VSS is from 0V to VREF. The typical  
time for the output to reach the programmed level is  
(C • 0.8V)/10µA.  
During start up, BGATE will stay off until VSS gets up to  
1.6V. This prevents the bottom MOSFET from turning on  
if the output is precharged.  
To shut down the LT3710, the SS pin should be pulled  
below 50mV by a VN2222 type N-channel transistor. Note  
that during shutdown BGATE will be locked off when VSS  
dropsbelow0.6V.ThispreventsthebottomMOSFETfrom  
A filter circuit is needed to ensure proper operation. A  
small RC filter with RS = 10k and CS = 10pF are typical.  
3710f  
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