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参数资料
| 型号： | LT3507AHUHF#TRPBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING REGULATOR, PQCC38 |
| 封装： | 5 X 7 MM, LEAD FREE, PLASTIC, QFN-38 |
| 文件页数： | 3/28页 |
| 文件大小： | 372K |
| 代理商： | LT3507AHUHF#TRPBF |
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LT3507A
11
3507af
fMAX2 is the frequency at which the maximum duty cycle
is exceeded. If there is sufficient charge on the BOOST
capacitor, the regulator will skip OFF periods to increase
the overall duty cycle at frequencies about fMAX2. It will
continue to regulate but with increased inductor current
and greatly increased output ripple.
Note that the restriction on the operating input voltage
refers to steady-state limits to keep the output in regula-
tion; the circuit will tolerate input voltage transients up to
the absolute maximum rating.
Switching Frequency
Once the upper and lower bounds for the switching
frequency are found from the duty cycle requirements,
the frequency may be set within those bounds. Lower
frequencies result in lower switching losses, but require
larger inductors and capacitors. The user must decide
the best trade-off.
The switching frequency is set by a resistor connected
from the RT/SYNC pin to ground, or by forcing a clock
signal into RT/SYNC. The LT3507A applies a voltage of
~1.25V across this resistor and uses the current to set
the oscillator speed. The switching frequency is given by
the following formula:
fSW =
53.2
RT +12.4
where fSW is in MHz and RT is in kΩ.
The formula will give a frequency value that is accurate to
within ±3%, for better accuracy use Table 1.
Table 1. RT for Common Frequencies
SWITCHING FREQUENCY (MHz)
RT (kΩ)
0.25
203
0.5
93.8
0.75
58.0
1.0
40.2
1.25
30.0
1.5
23.0
1.75
18.0
2.0
14.3
2.25
11.4
2.5
9.17
The frequency sync signal will support VHlogiclevelsfrom
1.8V to 5V CMOS or TTL. The duty cycle is not important,
but it needs a minimum on time of 100ns and a minimum
off time of 100ns. If the sync circuit is to be powered from
oneoftheLT3507Aoutputstheremaybestart-upproblems
if the driving gate is high impedance without a supply or
pulls high or low at some intermediate supply voltage.
The circuit shown in Figure 2 prevents these problems by
isolating the clock sync circuit until the clock is operating.
The Schottky diode should be a low leakage type such as
theBAS70fromOnSemiorCMOD6263fromCentralSemi.
RT should be set to provide a frequency within ±25% of
the final sync frequency.
APPLICATIONS INFORMATION
Figure 2. Clock Powered from LT3507A Output
RT/SYNC
VOUT1
3507A F02
LT3507A
SW1
CLK
CLOCK
SYNC
VCC
RT
BAS70
1k
470pF
Inductor Selection and Maximum Output Current
The current in the inductor is a triangle wave with an
average value equal to the load current. The peak switch
current is equal to the output current plus half the peak-
to-peak inductor ripple current. The LT3507A limits its
switch current in order to protect itself and the system
from overload faults. Therefore, the maximum output
current that the LT3507A will deliver depends on the
switch current limit, the inductor value and the input and
output voltages.
When the switch is off, the potential across the inductor
is the output voltage plus the catch diode drop. This gives
the peak-to-peak ripple current in the inductor:
ΔIL = 1–DC
(
) VOUT + VF
L f
where f is the switching frequency of the LT3507A and L
is the value of the inductor. The peak inductor and switch
current is:
ISWPK =ILPK =IOUT +
ΔIL
2
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相关代理商/技术参数 |
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| LT3507AIFE#PBF | 功能描述:IC REG QD BUCK/LINEAR 38TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 线性 + 切换式 系列:- 标准包装:2,500 系列:- 拓扑:降压（降压）同步（3），线性（LDO）（2） 功能:任何功能 输出数:5 频率 - 开关:300kHz 电压/电流 - 输出 1:控制器 电压/电流 - 输出 2:控制器 电压/电流 - 输出 3:控制器 带 LED 驱动器:无 带监控器:无 带序列发生器:是 电源电压:5.6 V ~ 24 V 工作温度:-40°C ~ 85°C 安装类型:* 封装/外壳:* 供应商设备封装:* 包装:* |
| LT3507AIFE#TRPBF | 功能描述:IC REG QD BUCK/LINEAR 38TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 线性 + 切换式 系列:- 标准包装:2,500 系列:- 拓扑:降压（降压）同步（3），线性（LDO）（2） 功能:任何功能 输出数:5 频率 - 开关:300kHz 电压/电流 - 输出 1:控制器 电压/电流 - 输出 2:控制器 电压/电流 - 输出 3:控制器 带 LED 驱动器:无 带监控器:无 带序列发生器:是 电源电压:5.6 V ~ 24 V 工作温度:-40°C ~ 85°C 安装类型:* 封装/外壳:* 供应商设备封装:* 包装:* |
| LT3507AIUHF#PBF | 功能描述:IC REG QD BUCK/LINEAR 38QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 线性 + 切换式 系列:- 标准包装:2,500 系列:- 拓扑:降压（降压）同步（3），线性（LDO）（2） 功能:任何功能 输出数:5 频率 - 开关:300kHz 电压/电流 - 输出 1:控制器 电压/电流 - 输出 2:控制器 电压/电流 - 输出 3:控制器 带 LED 驱动器:无 带监控器:无 带序列发生器:是 电源电压:5.6 V ~ 24 V 工作温度:-40°C ~ 85°C 安装类型:* 封装/外壳:* 供应商设备封装:* 包装:* |
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| LT3507EUHF#2ESPBF | 制造商:Linear Technology 功能描述:TRIPLE MONOLITHIC STEP-DOWN REGULATOR WITH LDO |
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