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参数资料
| 型号： | LTC3705IGN#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 11/20页 |
| 文件大小： | 0K |
| 描述： | IC CTRLR OCP 16SSOP |
| 标准包装： | 100 |
| 输出隔离： | 隔离 |
| 输入电压： | 18 V ~ 80 V |
| 输出电压： | 11V |
| 工作温度： | -40°C ~ 125°C |
| 封装/外壳： | 16-SSOP（0.154"，3.90mm 宽） |
| 供应商设备封装： | 16-SSOP |
| 包装： | 管件 |
LTC3705
APPLICATIO S I FOR ATIO
UVLO
V IN
R1
completes the soft-start interval. In order to ensure that
control is properly transferred from the LTC3705 (pri-
mary-side) to the LTC3706 (secondary-side), it is neces-
sary to limit the rate of rise on the primary-side soft-start
LTC3705
GND
R2
3705 F02
RUN/STOP
CONTROL
(OPTIONAL)
ramp so that the LTC3706 has adequate time to wake up
and assume control before the output voltage gets too
high. This condition is satisfied for many applications if the
following relationship is maintained:
Figure 2. Resistive Voltage Divider for
UVLO and Optional Run/Stop Control
Linear Regulator
The linear regulator eliminates the long start-up times
associated with a conventional trickle charger by using an
external NMOS to quickly charge the capacitor connected
to the V CC pin.
Note that a trickle charger usually requires a large capaci-
tor to provide holdup for the V CC pin while the converter
attempts to start. The linear regulator in the LTC3705 can
both charge the capacitor connected to the V CC pin and
provide primary-side gate-drive bias current. Therefore,
with the linear regulator, the capacitor need only be large
enough to cope with the ripple current from driving the top
and bottom gates and holdup need not be considered.
The external NMOS for the linear regulator should be a
standard 3V threshold type (i.e. not a logic level thresh-
C SS,SEC ≤ C SS_PRI
However, care should be taken to ensure that soft-start
transfer from primary-side to secondary-side is com-
pleted well before the output voltage reaches its target
value. A good design goal is to have the transfer completed
when the output voltage is less than one-half of its target
value. Note that the fastest output voltage rise time during
primary-side soft-start mode occurs with minimum load
current.
The open-loop start-up frequency on the LTC3705 is set
by placing a resistor R FS(S) from the FS/IN – pin to GND.
Although the exact start-up frequency on the primary side
is not critical, it is generally a good practice to set it
approximately equal to the operating frequency on the
secondary side.
In this mode the start-up frequency of the LTC3705 is
approximately:
old). The rate of charge of V CC from 0V to 8V is controlled
by the LTC3705 to be approximately 45 μ s regardless of
the size of the capacitor connected to the V CC pin. The
f PRI =
34 ? 109
R FS ( S ) + 10 , 000
charging current for this capacitor is approximately:
In the event that the LTC3706 fails to start up properly and
I C =
8 V
45 μ s
C
assume control of switching, there are several fail-safe
mechanisms to help avoid overvoltage conditions. First,
the LTC3705 implements a volt-second clamp that may be
The safe operating area (SOA) for the external NMOS
should be chosen so that capacitor charging does not
damage the NMOS. Excessive values of capacitor are
unnecessary and should be avoided.
Start-Up Considerations
When used in a self-starting converter with the LTC3706,
the LTC3705 initially begins the soft-start of the converter
in an open-loop fashion. After bias is obtained on the
secondary side, the LTC3706 assumes control and
used to keep the primary-side duty cycle at a level that
does not produce an excessive output voltage. Second,
the timeout of the linear regulator (described in the follow-
ing section) means that, unless the LTC3706 starts and
supports the LTC3705’s gate drives through the pulse
transformer and on-chip rectifier, the LTC3705 eventually
suffers a gate drive undervoltage fault. Finally, the LTC3706
has an independent overvoltage detection circuit that
crowbars the output of the DC/DC converter using the
synchronous secondary-side MOSFET switch.
3705fb
11
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相关代理商/技术参数 |
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| LTC3706EGN#PBF | 功能描述:IC SECONDARY SIDE CTRLR 24SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 电源控制器，监视器 系列:PolyPhase® 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:- 应用:多相控制器 输入电压:- 电源电压:9 V ~ 14 V 电流 - 电源:- 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:40-WFQFN 裸露焊盘 供应商设备封装:40-TQFN-EP（5x5） 包装:带卷 (TR) |
| LTC3706EGN#TRPBF | 功能描述:IC SECONDARY SIDE CTRLR 24SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 电源控制器，监视器 系列:PolyPhase® 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:- 应用:多相控制器 输入电压:- 电源电压:9 V ~ 14 V 电流 - 电源:- 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:40-WFQFN 裸露焊盘 供应商设备封装:40-TQFN-EP（5x5） 包装:带卷 (TR) |
| LTC3706IGN | 制造商:Linear Technology 功能描述:Secondary Side PWM Cntrlr POST REGUL 255KHz to 345KHz 24-Pin SSOP N |
| LTC3706IGN#PBF | 功能描述:IC SECONDARY SIDE CTRLR 24SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 电源控制器，监视器 系列:PolyPhase® 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:- 应用:多相控制器 输入电压:- 电源电压:9 V ~ 14 V 电流 - 电源:- 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:40-WFQFN 裸露焊盘 供应商设备封装:40-TQFN-EP（5x5） 包装:带卷 (TR) |
| LTC3706IGN#TRPBF | 功能描述:IC SECONDARY SIDE CTRLR 24SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 电源控制器，监视器 系列:PolyPhase® 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:- 应用:多相控制器 输入电压:- 电源电压:9 V ~ 14 V 电流 - 电源:- 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:40-WFQFN 裸露焊盘 供应商设备封装:40-TQFN-EP（5x5） 包装:带卷 (TR) |
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