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参数资料
| 型号： | LTC3878IGN#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 14/26页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 16-SSOP |
| 标准包装： | 2,500 |
| 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-SSOP（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
LTC3878
APPLICATIONS INFORMATION
V OUT = 0 . 8 V ? 1 + B ?
? R A ?
V OUT 2 ( MIN ) = 0 . 8 V ? 1 +
? R 3 ?
Si4884 V OUT2
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 LTC3878 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:
? R ?
To improve the transient response, a feed-forward ca-
pacitor, C FF , may be used. Great care should be taken to
route the V FB line away from noise sources, such as the
inductor or the SW line.
V OUT
Discontinuous Mode Operation and FCB Pin
The FCB (forced continuous bar) pin determines whether
the LTC3878 operates in forced continuous mode or al-
lows discontinuous conduction 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 currents less than 1/2 the peak-
to-peak ripple current. Tying the FCB 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 FCB pin provides a means to maintain a
fly 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 FCB pin sets a minimum
voltage V OUT2(MIN) below which continuous operation is
forced until V OUT2 has risen above its minimum.
? R 4 ?
V IN
LTC3878 C IN
V IN 1N4148
TG
? C OUT2
LTC3878
V FB
R B
C FF
R4
R3
FCB
SW
BG
Si4874
?
V OUT
C OUT
R A
3878 F05
Figure 5. Setting Output Voltage
SGND PGND
Figure 6. Secondary Output Loop
3878 F06
3878fa
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相关代理商/技术参数 |
参数描述 |
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| LTC3879EMSE#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) |
| LTC3879EMSE#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) |
| LTC3879EUD#PBF | 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) |
| LTC3879EUD#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) |
| 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) |
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