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参数资料
| 型号： | LTC3879EUD#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 15/28页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 16-QFN |
| 标准包装： | 121 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 2MHz |
| 占空比： | 90% |
| 电源电压： | 4 V ~ 38 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： | 16-WFQFN 裸露焊盘 |
| 包装： | 管件 |
| 产品目录页面： | 1336 (CN2011-ZH PDF) |
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LTC3879
APPLICATIONS INFORMATION
Top MOSFET Driver Supply (C B , D B )
An external bootstrap capacitor, C B , connected to the BOOST
pin supplies the gate drive voltage for the topside MOSFET.
This capacitor is charged through diode D B from INTV CC
when the switch node is low. When the top MOSFET turns
on, the switch node rises to V IN and the BOOST pin rises
to approximately V IN + INTV CC . The boost capacitor needs
to store approximately 100 times the gate charge required
by the top MOSFET. In most applications 0.1μF to 0.47μF,
X5R or X7R dielectric capacitor is adequate.
It is recommended that the BOOST capacitor be no larger
than 10% of the INTV CC capacitor C VCC , to ensure that
the C VCC can supply the upper MOSFET gate charge and
BOOST capacitor under all operating conditions. Variable
frequency in response to load steps offers superior tran-
sient performance but requires higher instantaneous gate
drive. Gate charge demands are greatest in high frequency
low duty factor applications under high dI/dt load steps
and at start-up.
Setting Output Voltage
The LTC3879 output voltage is set by an external feed-
back resistive divider carefully placed across the output,
as shown in Figure 5. The regulated output voltage is
determined by:
Discontinuous Mode Operation and MODE Pin
The MODE pin determines whether the LTC3879 operates in
forced continuous mode or allows discontinuous conduc-
tion mode. Tying this pin above 0.8V enables discontinuous
operation, where the bottom MOSFET turns off when the
inductor current reverses polarity. The load current at
which current reverses and discontinuous operation begins
depends on the amplitude of the inductor ripple current and
will vary with changes in V IN . In steady-state operation,
discontinuous conduction mode occurs for DC load cur-
rents less than 1/2 the peak-to-peak ripple current. Tying
the MODE pin below the 0.8V threshold forces continuous
switching, where inductor current is allowed to reverse at
light loads and maintain synchronous switching.
In addition to providing a logic input to force continuous
operation, the MODE pin provides a means to maintain
a ?y back winding output when the primary is operating
in discontinuous mode. The secondary output V OUT2 is
normally set as shown in Figure 6 by the turns ratio N
of the transformer. However, if the controller goes into
discontinuous mode and halts switching due to a light
primary load current, then V OUT2 will droop. An external
resistor divider from V OUT2 to the MODE pin sets a minimum
voltage V OUT2(MIN) below which continuous operation is
forced until V OUT2 has risen above its minimum.
V OUT = 0 . 6 V ? 1 + B ?
V OUT 2 ( MIN ) = 0 . 8 V ? 1 +
? R ?
? R A ?
?
?
R 4 ?
R 3 ? ?
To improve the transient response, a feed-forward ca-
pacitor, C FF , may be used. Great care should be taken to
LTC3879
C IN
V IN
route the V FB line away from noise sources, such as the
inductor or the SW line.
V OUT
R4
R3
MODE
V IN
TG
SW
BG
Si4884
Si4874
?
1N4148
?
V OUT2
C OUT2
V OUT
C OUT
LTC3879
V FB
R B
C FF
SGND PGND
3879 F06
R A
3879 F05
Figure 6. Secondary Output Loop
Figure 5. Setting Output Voltage
3879f
15
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| LTC3879IMSE#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-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) |
| LTC3879IMSE#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-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) |
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| LTC3879IUD#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-QFN 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) |
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