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| 型号： | LTC3808EDE#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 20/28页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 14-DFN |
| 标准包装： | 91 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 825kHz |
| 占空比： | 100% |
| 电源电压： | 2.75 V ~ 9.8 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | 14-WFDFN 裸露焊盘 |
| 包装： | 管件 |
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LTC3808
APPLICATIO S I FOR ATIO
However, if the controller goes into pulse skipping opera-
tion and halts switching due to a light primary load current,
then V AUX will droop. An external resistor divider from
V AUX to the SYNC/MODE sets a minimum voltage V AUX(MIN) :
460kHz and 635kHz in spread spectrum modulation op-
eration. Figure 9 shows the spectral plots of the output
(V OUT ) noise with/without spread spectrum modulation.
Note the significant reduction in peak output noise
(>20dBm).
V AUX ( MIN ) = 0 . 4 V ? ? 1 +
R 5 ?
?
?
R 6 ?
?
The spread spectrum modulation operation of the LTC3808
is enabled by setting SYNC/MODE pin to a DC voltage
If V AUX drops below this value, the SYNC/MODE voltage
forces temporary continuous switching operation until
V AUX is again above its minimum.
Spread Spectrum Modulation with SYNC/MODE and
PLLLPF Pins
Switching regulators, which operate at fixed frequency,
conduct electromagnetic interference (EMI) to their down-
between 1.35V and several hundred mV below V IN by tying
a resistor between SYNC/MODE and V IN .
Table 3 summarizes the different states in which the
SYNC/MODE Pin can be used.
Table 3. The States of the SYNC/MODE Pin
SYNC/MODE PIN CONDITION
GND (0V to 0.35V) Forced Continuous Mode
Current Reversal Allowed
stream load(s) with high spectral power density at this
fundamental and harmonic frequencies. The peak energy
can be lowered and distributed to other frequencies and
their harmonics by modulating the PWM frequency. The
LTC3808’s switching noise (at 550kHz) is spread between
V OUT Spectrum without Spread Spectrum Modulation
NOISE (dBm)
–10dBm/DIV
V FB (0.45V to 1.2V)
Resistor to V IN
(1.35V to V IN – 0.5V)
V IN
Feedback Resistors
External Clock Signal
Pulse Skipping Mode
No Current Reversal Allowed
Spread Spectrum Modulation
Pulse Skipping at Light Loads
No Current Reversal Allowed
Burst Mode Operation
No Current Reversal Allowed
Regulate an Auxiliary Winding
Enable Phase-Locked Loop
(Synchronize to External Clock)
Pulse Skipping at Light Load
No Current Reversal Allowed
Fault Condition: Short-Circuit and Current Limit
START FREQ: 400kHz
3808 F09a
If the LTC3808’s load current exceeds the short-circuit cur-
RBW: 100Hz
STOP FREQ: 700kHz
V OUT Spectrum with Spread Spectrum Modulation
(C SSM = 2200pF)
NOISE (dBm)
–10dBm/DIV
rent limit (I SC ), which is set by the short-circuit sense thresh-
old ( ? V SC ) and the on resistance (R DS(ON) ) of bottom
N-channel MOSFET, the top P-channel MOSFET is turned
off and will not be turned on at the next clock cycle unless
the load current decreases below I SC . In this case, the
controller ’s switching frequency is decreased and
the output is regulated by short-circuit (current limit)
protection.
In a hard short (V OUT = 0V), the top P-channel MOSFET is
turned off and kept off until the short-circuit condition is
START FREQ: 400kHz
RBW: 100Hz
STOP FREQ: 700kHz
3808 F09b
cleared. In this case, there is no current path from input
supply (V IN ) to either V OUT or GND, which prevents
excessive MOSFET and inductor heating.
Figure 9. Spectral Response of Spread Spectrum Modulation
3808f
20
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| LTC3808EGN#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LTC3808EGN#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LTC3809EDD | 功能描述:IC REG CTRLR BUCK PWM CM 10-DFN RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LTC3809EDD#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 10-DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 特色产品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 标准包装:1 系列:PowerWise® PWM 型:电压模式 输出数:1 频率 - 最大:1MHz 占空比:81% 电源电压:4.5 V ~ 18 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-5°C ~ 125°C 封装/外壳:32-WFQFN 裸露焊盘 包装:Digi-Reel® 产品目录页面:1303 (CN2011-ZH PDF) 其它名称:LM3754SQDKR |
| LTC3809EDD#TR | 功能描述:IC REG CTRLR BUCK PWM CM 10-DFN RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
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