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| 型号： | LTC3808EDE#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 17/28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
satisfied, the capacitance is adequate for filtering. The
3.3V OR 5V
output ripple ( ? V OUT ) is approximated by:
LTC3808
RUN
LTC3808
RUN
? V OUT ≈ I RIPPLE ? ? ESR +
8 ? f ? C OUT ?
?
?
1 ?
?
3808 F04
V OUT = 0 . 6 V ? ? 1 + B ?
where f is the operating frequency, C OUT is the output
capacitance and I RIPPLE is the ripple current in the induc-
tor. The output ripple is highest at maximum input voltage
since I RIPPLE increase with input voltage.
Setting Output Voltage
The LTC3808 output voltage is set by an external feedback
resistor divider carefully placed across the output, as
shown in Figure 3. The regulated output voltage is deter-
mined by:
? R ?
? R A ?
For most applications, a 59k resistor is suggested for R A .
In applications where minimizing the quiescent current is
critical, R A should be made bigger to limit the feedback
divider current. If R B then results in very high impedance,
it may be beneficial to bypass R B with a 50pF to 100pF
capacitor C FF .
V OUT
Figure 4. RUN Pin Interfacing
Once the controller is enabled, the start-up of V OUT is
controlled by the state of the TRACK/SS pin. If the TRACK/
SS pin is connected to V IN , the start-up of V OUT is con-
trolled by internal soft-start, which slowly ramps the
positive reference to the error amplifier from 0V to 0.6V,
allowing V OUT to rise smoothly from 0V to its final value.
The default internal soft-start time is around 1ms. The
soft-start time can be changed by placing a capacitor
between the TRACK/SS pin and GND. In this case, the soft-
start time will be approximately:
600mV
t SS = C SS ?
1 μ A
where 1 μ A is an internal current source which is always
on.
When the voltage on the TRACK/SS pin is less than the
internal 0.6V reference, the LTC3808 regulates the V FB
voltage to the TRACK/SS pin voltage instead of 0.6V.
Therefore the start-up of V OUT can ratiometrically track an
LTC3808
V FB
R B
R A
C FF
external voltage V X , according to a ratio set by a resistor
divider at TRACK/SS pin (Figure 5a). The ratiometric
relation between V OUT and V X is (Figure 5c):
= TA ?
3808 F03
Figure 3. Setting Output Voltage
Run and Soft-Start/Tracking Functions
V OUT
V X
R
R A
R A + R B
R TA + R TB
V X
V OUT
The LTC3808 has a low power shutdown mode which is
controlled by the RUN pin. Pulling the RUN pin below 1.1V
puts the LTC3808 into a low quiescent current shutdown
mode (I Q = 9 μ A). Releasing the RUN pin, an internal 0.7 μ A
R TB
R TA
LTC3808
V FB
TRACK/SS
3808 F5a
R B
R A
(at V IN = 4.2V) current source will pull the RUN pin up to
V IN , which enables the controller. The RUN pin can be
Figure 5a. Using the TRACK/SS Pin to Track V X
driven directly from logic as showed in Figure 4.
3808f
17
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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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