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| 型号： | LTC3809EDD#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 17/24页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 10-DFN |
| 标准包装： | 121 |
| 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： | 10-WFDFN 裸露焊盘 |
| 包装： | 管件 |
| 产品目录页面： | 1336 (CN2011-ZH PDF) |
LTC3809
APPLICATIONS INFORMATION
If the external clock frequency is greater than the internal
oscillator’s frequency, f OSC , then current is sourced con-
tinuously from the phase detector output, pulling up the
PLLLPF pin. When the external clock frequency is less
than f OSC , current is sunk continuously, pulling down
the PLLLPF pin. If the external and internal frequencies
are the same but exhibit a phase difference, the current
sources turn on for an amount of time corresponding to
the phase difference. The voltage on the PLLLPF pin is
adjusted until the phase and frequency of the internal and
external oscillators are identical. At the stable operating
point, the phase detector output is high impedance and
the ?lter capacitor C LP holds the voltage.
The loop ?lter components, C LP and R LP , smooth out
the current pulses from the phase detector and provide a
stable input to the voltage-controlled oscillator. The ?lter
components C LP and R LP determine how fast the loop
acquires lock. Typically R LP = 10k and C LP is 2200pF to
0.01μF.
and/or the V IN /V OUT ratio is close to unity, the synchro-
nous MOSFET may not be on for a suf ?cient amount of
time to transfer power from the output capacitor to the
auxiliary load. Forced continuous operation will sup-
port an auxiliary winding as long as there is a suf ?cient
synchronous MOSFET duty factor. The SYNC/MODE
input pin removes the requirement that power must be
drawn from the transformer primary side in order to
extract power from the auxiliary winding. With the loop
in continuous mode, the auxiliary output may nominally
be loaded without regard to the primary output load.
The auxiliary output voltage V AUX is normally set, as shown
in Figure 7, by the turns ratio N of the transformer:
V AUX = (N + 1) ? V OUT
However, if the controller goes into pulse-skipping operation
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) :
V AUX ( MIN ) = 0 . 4 V ? ? 1 +
?
Typically, the external clock (on SYNC/MODE pin) input
high level is 1.6V, while the input low level is 1.2V.
?
?
R 6 ?
R 5 ?
Table 1 summarizes the different states in which the
PLLLPF pin can be used.
Table 1. The States of the PLLLPF Pin
If V AUX drops below this value, the SYNC/MODE voltage
forces temporary continuous switching operation until
V AUX is again above its minimum.
PLLLPF PIN
SYNC/MODE PIN
FREQUENCY
0V
Floating
V IN
DC Voltage (<1.2V or V IN )
DC Voltage (<1.2V or V IN )
DC Voltage (<1.2V or V IN )
300kHz
550kHz
750kHz
R6
LTC3809
TG
V IN
L1
1:N
+
V AUX
1μF
V OUT
RC Loop Filter
Clock Signal
Phase-Locked to
SYNC/MODE
Filter Caps
External Clock
DC Voltage (>1.35V and <V IN – 0.5V) Spread Spectrum
460kHz to 635kHz
R5
SW
BG
+
C OUT
3809 F07
Auxiliary Winding Control Using SYNC/MODE Pin
The SYNC/MODE pin can be used as an auxiliary feedback
to provide a means of regulating a ?yback winding output.
When this pin drops below its ground-referenced 0.4V
threshold, continuous mode operation is forced.
During continuous mode, current ?ows continuously in
the transformer primary side. The auxiliary winding draws
current only when the bottom synchronous N-channel
MOSFET is on. When primary load currents are low
Figure 7. Auxilliary Output Loop Connection
Spread Spectrum Modulation with SYNC/MODE and
PLLLPF Pins
Switching regulators, which operate at ?xed frequency,
conduct electromagnetic interference (EMI) to their down-
stream load(s) with high spectral power density at this
fundamental and harmonic frequencies. The peak energy
3809fc
17
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相关代理商/技术参数 |
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| LTC3809EMSE | 功能描述:IC REG CTRLR BUCK PWM CM 10-MSOP 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) |
| LTC3809EMSE#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 10-MSOP 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) |
| LTC3809EMSE#TR | 功能描述:IC REG CTRLR BUCK PWM CM 10-MSOP 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) |
| LTC3809EMSE#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 10-MSOP 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) |
| LTC3809EMSE-1 | 功能描述:IC REG CTRLR BUCK PWM CM 10-MSOP 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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