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參數(shù)資料
| 型號(hào)： | LTC3707IGN-SYNC |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 3 A SWITCHING CONTROLLER, 360 kHz SWITCHING FREQ-MAX, PDSO28 |
| 封裝： | 0.150 INCH, PLASTIC, SSOP-28 |
| 文件頁(yè)數(shù)： | 13/32頁(yè) |
| 文件大?。?/td> | 403K |
| 代理商： | LTC3707IGN-SYNC |
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LTC3707-SYNC
20
3707sfa
This built-in overcurrent latchoff can be overridden by
providing a pull-up resistor to the RUN/SS pin as shown in
Figure 7. This resistance shortens the soft-start period and
prevents the discharge of the RUN/SS capacitor during an
over current condition. Tying this pull-up resistor to VIN as
in Figure 7a, defeats overcurrent latchoff. Diode-connecting
this pull-up resistor to INTVCC, as in Figure 7b, eliminates
any extra supply current during controller shutdown while
eliminating the INTVCC loading from preventing controller
start-up.
Why should you defeat overcurrent latchoff? During the
prototyping stage of a design, there may be a problem
with noise pickup or poor layout causing the protection
circuit to latch off. Defeating this feature will easily allow
troubleshooting of the circuit and PC layout. The internal
short-circuit and foldback current limiting still remains
active, thereby protecting the power supply system from
failure. After the design is complete, a decision can be
made whether to enable the latchoff feature.
The value of the soft-start capacitor CSS may need to
be scaled with output voltage, output capacitance and
load current characteristics. The minimum soft-start
capacitance is given by:
CSS > (COUT )(VOUT) (10–4) (RSENSE)
The minimum recommended soft-start capacitor of CSS =
0.1μF will be sufcient for most applications.
Fault Conditions: Current Limit and Current Foldback
The current comparators have a maximum sense voltage
of 75mV resulting in a maximum MOSFET current of
75mV/RSENSE. The maximum value of current limit
generally occurs with the largest VIN at the highest ambient
temperature, conditions that cause the highest power
dissipation in the top MOSFET.
The IC includes current foldback to help further limit load
current when the output is shorted to ground. The foldback
circuit is active even when the overload shutdown latch
described above is overridden. If the output falls below
70% of its nominal output level, then the maximum sense
voltage is progressively lowered from 75mV to 25mV.
Under short-circuit conditions with very low duty cycles,
the controller will begin cycle skipping in order to limit
APPLICATIONS INFORMATION
the short-circuit current. In this situation the bottom
MOSFET will be dissipating most of the power but less
than in normal operation. The short-circuit ripple current
is determined by the minimum on-time tON(MIN) of the
LTC3707-SYNC (less than 200ns), the input voltage and
inductor value:
ΔIL(SC) = tON(MIN) (VIN/L)
The resulting short-circuit current is:
I
mV
R
I
SC
SENSE
LSC
=+
25
1
2
Δ ()
Fault Conditions: Overvoltage Protection (Crowbar)
The overvoltage crowbar is designed to blow a system
input fuse when the output voltage of the regulator rises
much higher than nominal levels. The crowbar causes huge
currents to ow, that blow the fuse to protect against a
shorted top MOSFET if the short occurs while the controller
is operating.
A comparator monitors the output for overvoltage con-
ditions. The comparator (OV) detects overvoltage faults
greater than 7.5% above the nominal output voltage. When
this condition is sensed, the top MOSFET is turned off and
the bottom MOSFET is turned on until the overvoltage
condition is cleared. The output of this comparator is
only latched by the overvoltage condition itself and will
therefore allow a switching regulator system having a poor
PC layout to function while the design is being debugged.
The bottom MOSFET remains on continuously for as long
as the OV condition persists; if VOUT returns to a safe level,
normal operation automatically resumes. A shorted top
MOSFET will result in a high current condition which will
open the system fuse. The switching regulator will regulate
properly with a leaky top MOSFET by altering the duty
cycle to accommodate the leakage.
Phase-Locked Loop and Frequency Synchronization
The IC has a phase-locked loop comprised of an internal
voltage controlled oscillator and phase detector. This
allows the top MOSFET turn-on to be locked to the rising
edge of an external source. The frequency range of the
voltage controlled oscillator is
±50% around the center
frequency fO. A voltage applied to the PLLFLTR pin of 1.2V
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| LTC3707IGN-SYNC#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 28-SSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:PolyPhase® 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(pán) 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱:LM1771SSDX |
| LTC3707IGN-SYNC#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 28-SSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:PolyPhase® 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(pán) 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱:LM1771SSDX |
| LTC3708EUH | 功能描述:IC REG CTRLR BUCK PWM CM 32-QFN RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:PolyPhase® 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(pán) 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱:LM1771SSDX |
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| LTC3708EUH#TR | 功能描述:IC REG CTRLR BUCK PWM CM 32-QFN RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:PolyPhase® 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(pán) 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱:LM1771SSDX |
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