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參數(shù)資料
| 型號(hào)： | LTC1435ACG#TRPBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | High Efficiency Low Noise Synchronous Step-Down Switching Regulator |
| 中文描述： | 2 A SWITCHING CONTROLLER, 138 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封裝： | PLASTIC, SSOP-16 |
| 文件頁(yè)數(shù)： | 4/20頁(yè) |
| 文件大?。?/td> | 355K |
| 代理商： | LTC1435ACG#TRPBF |
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12
LTC1435A
APPLICATIONS INFORMATION
WU
U
The external resistive divider is connected to the output as
shown in Figure 5 allowing remote voltage sensing.
VOSENSE
LTC1435A
R1
R2
1435A F05
100pF
1.19V
≤ VOUT ≤ 9V
SGND
Figure 5. Setting the LTC1435A Output Voltage
Run/ Soft Start Function
The RUN/SS pin is a dual purpose pin that provides the soft
start function and a means to shut down the LTC1435A. Soft
start reduces surge currents from VIN by gradually increas-
ing the internal current limit.
Power supply sequencing can
also be accomplished using this pin.
An internal 3
A current source charges up an external
capacitor CSS. When the voltage on RUN/SS reaches 1.3V
the LTC1435A begins operating. As the voltage on RUN/SS
continues to ramp from 1.3V to 2.4V, the internal current
limit is also ramped at a proportional linear rate. The cur-
rent limit begins at approximately 50mV/RSENSE (at VRUN/
SS = 1.3V) and ends at 150mV/RSENSE (VRUN/SS > 2.7V). The
output current thus ramps up slowly, charging the output
capacitor. If RUN/SS has been pulled all the way to ground
there is a delay before starting of approximately 500ms/
F,
followed by an additional 500ms/
F to reach full current.
tDELAY = 5(10 5)CSS Seconds
Pulling the RUN/SS pin below 1.3V puts the LTC1435A into
a low quiescent current shutdown (IQ < 25A). This pin can
be driven directly from logic as shown in Figure 6. Diode
D1 in Figure 6 reduces the start delay but allows CSS toramp
up slowly for the soft start function; this diode and CSS can
be deleted if soft start is not needed. The RUN/SS pin has
an internal 6V Zener clamp (See Functional Diagram).
Foldback Current Limiting
As described in Power MOSFET and D1 Selection, the worst-
case dissipation for either MOSFET occurs with a short-
circuited output, when the synchronous MOSFET conducts
the current limit value almost continuously. In most appli-
cations this will not cause excessive heating, even for
extended fault intervals. However, when heat sinking is at
a premium or higher RDS(ON) MOSFETs are being used,
foldback current limiting should be added to reduce the
current in proportion to the severity of the fault.
Foldback current limiting is implemented by adding diode
DFB between the output and the ITH pin as shown in the
Functional Diagram. In a hard short (VOUT = 0V) the cur-
rent will be reduced to approximately 25% of the maximum
output current. This technique may be used for all applica-
tions with regulated output voltages of 1.8V or greater.
SFB Pin Operation
When the SFB pin drops below its ground referenced 1.19V
threshold, continuous mode operation is forced. In continu-
ous mode, the large N-channel main and synchronous
switches are used regardless of the load on the main output.
In addition to providing a logic input to force continuous
synchronous operation, the SFB pin provides a means to
regulate a flyback winding output. Continuous synchronous
operation allows power to be drawn from the auxiliary
windings without regard to the primary output load. The SFB
pin provides a way to force continuous synchronous op-
eration as needed by the flyback winding.
The secondary output voltage is set by the turns ratio of the
transformer in conjunction with a pair of external resistors
returned to the SFB pin as shown in Figure 4a. The second-
ary regulated voltage, VSEC, in Figure 4a is given by:
VN
V
R
SEC
OUT
≈+
()
>+
1
1 19 1
6
5
.
where N is the turns ratio of the transformer and VOUT is
the main output voltage sensed by VOSENSE.
Minimum On-Time Considerations
Minimum on-time, tON(MIN), is the smallest amount of time
that the LTC1435A is capable of turning the top MOSFET
1435 F06
CSS
D1
3.3V OR 5V
RUN/SS
CSS
RUN/SS
Figure 6. RUN/SS Pin Interfacing
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| LTC1435ACS | 功能描述:IC REG CTRLR BUCK PWM CM 16-SOIC RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:4,500 系列:PowerWise® PWM 型:控制器 輸出數(shù):1 頻率 - 最大:1MHz 占空比:95% 電源電壓:2.8 V ~ 5.5 V 降壓:是 升壓:無(wú) 回掃:無(wú) 反相:無(wú) 倍增器:無(wú) 除法器:無(wú) Cuk:無(wú) 隔離:無(wú) 工作溫度:-40°C ~ 125°C 封裝/外殼:6-WDFN 裸露焊盤 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱:LM1771SSDX |
| LTC1435ACS#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-SOIC RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 特色產(chǎn)品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 標(biāo)準(zhǔn)包裝:1 系列:PowerWise® PWM 型:電壓模式 輸出數(shù):1 頻率 - 最大:1MHz 占空比:81% 電源電壓:4.5 V ~ 18 V 降壓:是 升壓:無(wú) 回掃:無(wú) 反相:無(wú) 倍增器:無(wú) 除法器:無(wú) Cuk:無(wú) 隔離:無(wú) 工作溫度:-5°C ~ 125°C 封裝/外殼:32-WFQFN 裸露焊盤 包裝:Digi-Reel® 產(chǎn)品目錄頁(yè)面:1303 (CN2011-ZH PDF) 其它名稱:LM3754SQDKR |
| LTC1435ACS#TR | 功能描述:IC REG CTRLR BUCK PWM CM 16-SOIC RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:4,500 系列:PowerWise® PWM 型:控制器 輸出數(shù):1 頻率 - 最大:1MHz 占空比:95% 電源電壓:2.8 V ~ 5.5 V 降壓:是 升壓:無(wú) 回掃:無(wú) 反相:無(wú) 倍增器:無(wú) 除法器:無(wú) Cuk:無(wú) 隔離:無(wú) 工作溫度:-40°C ~ 125°C 封裝/外殼:6-WDFN 裸露焊盤 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱:LM1771SSDX |
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