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参数资料
| 型号： | LTC3707IGN#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 22/32页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 28-SSOP |
| 标准包装： | 2,500 |
| 系列： | PolyPhase® |
| PWM 型： | 电流模式 |
| 输出数： | 2 |
| 频率 - 最大： | 360kHz |
| 占空比： | 99.4% |
| 电源电压： | 4.5 V ~ 28 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： | 28-SSOP（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
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LTC3707
APPLICATIONS INFORMATION
FCB Pin Operation
The FCB pin can be used to regulate a secondary winding
or as a logic level input. Continuous operation is forced
when the FCB pin drops below 0.8V. During continuous
internal current source pulling the pin high. Include this
current when choosing resistor values R5 and R6.
The following table summarizes the possible states avail-
able on the FCB pin:
mode, current ?ows continuously in the transformer pri-
mary. The secondary winding(s) draw current only when
the bottom, synchronous switch is on. When primary
load currents are low and/or the V IN /V OUT ratio is low,
the synchronous switch may not be on for a suf?cient
amount of time to transfer power from the output capacitor
to the secondary load. Forced continuous operation will
support secondary windings providing there is suf?cient
synchronous switch duty factor. Thus, the FCB input pin
removes the requirement that power must be drawn from
the inductor primary in order to extract power from the
auxiliary windings. With the loop in continuous mode, the
Table 1
FCB Pin
0V to 0.75V
0.85V < V FCB < V INTVCC – 2V
Feedback Resistors
= V INTVCC
Condition
Forced Continuous (Current Reversal
Allowed—Burst Inhibited)
Minimum Peak Current Induces
Burst Mode Operation
No Current Reversal Allowed
Regulating a Secondary Winding
Burst Mode Operation Disabled
Constant Frequency Mode Enabled
No Current Reversal Allowed
No Minimum Peak Current
auxiliary outputs may nominally be loaded without regard
to the primary output load.
The secondary output voltage V SEC is normally set as shown
in Figure 6a by the turns ratio N of the transformer:
V SEC ? (N + 1) V OUT
However, if the controller goes into Burst Mode operation
and halts switching due to a light primary load current, then
V SEC will droop. An external resistive divider from V SEC to
the FCB pin sets a minimum voltage V SEC(MIN) :
Voltage Positioning
Voltage positioning can be used to minimize peak-to-peak
output voltage excursions under worst-case transient
loading conditions. The open-loop DC gain of the control
loop is reduced depending upon the maximum load step
speci?cations. Voltage positioning can easily be added to
the LTC3707 by loading the I TH pin with a resistive divider
having a Thevenin equivalent voltage source equal to the
midpoint operating voltage of the error ampli?er, or 1.2V
(see Figure 8).
V SEC(MIN) ≈ 0.8V ? 1 +
?
?
R6 ?
R5 ? ?
The resistive load reduces the DC loop gain while main-
taining the linear control range of the error ampli?er.
The maximum output voltage deviation can theoretically
If V SEC drops below this level, the FCB voltage forces
temporary continuous switching operation until V SEC is
again above its minimum.
In order to prevent erratic operation if no external connec-
be reduced to half or alternatively the amount of output
capacitance can be reduced for a particular application.
A complete explanation is included in Design Solutions
10. (See www.linear.com)
tions are made to the FCB pin, the FCB pin has a 0.18μA
INTV CC
R T2
I TH
R T1
R C
LTC3707
C C
3707 F08
Figure 8. Active Voltage Positioning Applied to the LTC3707
3707fb
22
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| LTC3708EUH | 功能描述:IC REG CTRLR BUCK PWM CM 32-QFN RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:PolyPhase® 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 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 ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
| LTC3708EUH#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 32-QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:PolyPhase® 特色产品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 标准包装:1 系列:PowerWise® PWM 型:电压模式 输出数:1 频率 - 最大:1MHz 占空比:81% 电源电压:4.5 V ~ 18 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:-5°C ~ 125°C 封装/外壳:32-WFQFN 裸露焊盘 包装:Digi-Reel® 产品目录页面:1303 (CN2011-ZH PDF) 其它名称:LM3754SQDKR |
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| LTC3708EUHPBF | 制造商:Linear Technology 功能描述:LTC3708 dual SD tracking PS controller |
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