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參數(shù)資料
| 型號： | LT1307IS8#TR |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 1.25 A SWITCHING REGULATOR, 750 kHz SWITCHING FREQ-MAX, PDSO8 |
| 封裝： | 0.150 INCH, PLASTIC, SO-8 |
| 文件頁數(shù)： | 20/20頁 |
| 文件大?。?/td> | 369K |
| 代理商： | LT1307IS8#TR |
9
LT1307/LT1307B
1307fa
quite evident, as is this particular device’s 575kHz switch-
ing frequency (nominal switching frequency is 600kHz).
Note, however, the absence of significant energy at 455kHz.
Figure 7’s plot reduces the frequency span from 255kHz to
655kHz with a 455kHz center. Burst Mode low frequency
ripple creates sidebands around the 575kHz switching
fundamental. These sidebands have low signal amplitude
at 455kHz, measuring – 55dBmVRMS. As load current is
further reduced, the Burst Mode frequency decreases.
This spaces the sidebands around the switching fre-
quency closer together, moving spectral energy further
Trace B. Similarly, Figure 4 details the two circuits with a
load step from 5mA to 45mA with a 1.5V input.
The LT1307B also can be used in lower current applica-
tions where a clean, low ripple output is needed. Figure 5
details transient response of a single cell to 3.3V con-
verter, using an inductor value of 100
H. This high induc-
tance minimizes ripple current, allowing the LT1307B to
regulate without skipping cycles. As the load current is
stepped from 5mA to 10mA, the output voltage responds
cleanly. Note that the VC pin loop compensation has been
made more conservative (increased C, decreased R).
Figure 5. Increasing L to 100
H, Along with RC = 36k,
CC = 20nF and COUT = 10F, Low Noise Performance of
LT1307B Can Be Realized at Light Loads of 5mA to 10mA
10mA
5mA
IL
VIN = 1.25V
1ms/DIV
1307 F05
VOUT = 3.3V
IL
20mA/DIV
VOUT
100mV/DIV
AC COUPLED
At light loads, the LT1307B will begin to skip alternate
cycles. The load point at which this occurs can be de-
creased by increasing the inductor value. However, output
ripple will continue to be significantly less than the LT1307
output ripple. Further, the LT1307B can be forced into
micropower mode, where IQ falls from 1mA to 50A by
pulling down VC to 0.3V or less externally.
DC/DC CONVERTER NOISE CONSIDERATIONS
Switching regulator noise is a significant concern in many
communications systems. The LT1307 is designed to
keep noise energy out of the sensitive 455kHz band at all
load levels while consuming only 60
W to 100W at no
load. At light load levels, the device is in Burst Mode,
causing low frequency ripple to appear at the output.
Figure 6 details spectral noise directly at the output of
Figure 1’s circuit in a 1kHz to 1MHz bandwidth. The
converter supplies a 5mA load from a 1.25V input. The
Burst Mode fundamental at 5.1kHz and its harmonics are
FREQUENCY (kHz)
1
OUTPUT
NOISE
VOLTAGE
(dBmV
RMS
)
40
30
20
10
0
–10
–20
–30
–40
–50
–60
10
100
1000
1307 F06
RBW = 100Hz
Figure 6. Spectral Noise Plot of 3.3V Converter Delivering
5mA Load. Burst Mode Fundamental at 5.1kHz is 23dBmVRMS
or 14mVRMS
FREQUENCY (kHz)
255
OUTPUT
NOISE
VOLTAGE
(dBmV
RMS
)
–20
–25
–30
–35
–40
–45
–50
–55
–60
–65
–70
455
1307 F07
655
RBW = 100Hz
Figure 7. Span Centered at 455kHz Shows – 55dBmVRMS
(1.8
VRMS) at 455kHz. Burst Mode Creates Sidebands 5.1kHz
Apart Around the Switching Frequency Fundamental of 575kHz
APPLICATIO S I FOR ATIO
WU
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| LT1308ACF | 功能描述:IC REG BOOST 5V 1A 14TSSOP RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關穩(wěn)壓器 系列:- 標準包裝:20 系列:SIMPLE SWITCHER® 類型:降壓（降壓） 輸出類型:固定 輸出數(shù):1 輸出電壓:12V 輸入電壓:4 V ~ 60 V PWM 型:電壓模式 頻率 - 開關:52kHz 電流 - 輸出:1A 同步整流器:無 工作溫度:-40°C ~ 125°C 安裝類型:通孔 封裝/外殼:16-DIP（0.300"，7.62mm） 包裝:管件 供應商設備封裝:16-DIP 其它名稱:*LM2575HVN-12LM2575HVN-12 |
| LT1308ACF#PBF | 功能描述:IC REG BOOST 5V 1A 14TSSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關穩(wěn)壓器 系列:- 標準包裝:20 系列:SIMPLE SWITCHER® 類型:降壓（降壓） 輸出類型:固定 輸出數(shù):1 輸出電壓:12V 輸入電壓:4 V ~ 60 V PWM 型:電壓模式 頻率 - 開關:52kHz 電流 - 輸出:1A 同步整流器:無 工作溫度:-40°C ~ 125°C 安裝類型:通孔 封裝/外殼:16-DIP（0.300"，7.62mm） 包裝:管件 供應商設備封裝:16-DIP 其它名稱:*LM2575HVN-12LM2575HVN-12 |
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