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参数资料
| 型号： | LTC3878IGN#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 9/26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
OPERATION
LTC1778 Compatibility
The LTC3878 is compatible with the LTC1778 in applica-
tions which do not use the EXTV CC function. The LTC3878
offers improved gate drive and reduced dead time, which
allows higher efficiency than the LTC1778. On the LTC1778
Pin 9 is EXTV CC , but on the LTC3878 it is a no connect.
The other notable difference is that the shutdown latch-
off timer is removed. The LTC3878 should be a drop in,
pin-for-pin replacement in most applications that do not
use EXTV CC . The LTC3878 should be tested and verified
in each application without assuming compatibility. Con-
tact a Linear applications expert to answer any questions
regarding LTC3878/LTC1778 compatibility.
Main Control Loop
The LTC3878 is a valley current mode controller IC for
use in DC/DC step-down converters. In normal continu-
ous operation, the top MOSFET is turned on for a fixed
interval determined by a one-shot timer, OST. When the
top MOSFET is turned off, the bottom MOSFET is turned
on until the current comparator, I CMP , trips, restarting
the one-shot timer and initiating the next cycle. Inductor
valley current is measured by sensing the voltage between
the PGND and SW pins using the bottom MOSFET on-
resistance. The voltage on the I TH pin sets the compara-
tor threshold corresponding to inductor valley current.
The error amplifier EA adjusts this voltage by comparing
the feedback signal V FB from the output voltage to the
feedback reference voltage V FBREF . Increasing the load
current causes a drop in the feedback voltage relative
to the reference. The EA senses the feedback voltage
drop and adjusts the I TH voltage higher until the average
inductor current matches the load current.
With DC current loads less than 1/2 of the peak-to-peak
ripple the inductor current can drop to zero or become
negative. In discontinuous operation, negative inductor
current is detected and prevented by the current reversal
comparator I REV , which shuts off MB. Both switches
remain off with the output capacitor supplying the load
current until the EA moves the I TH voltage above the zero
current level (0.8V) to initiate another switching cycle.
When the FCB (forced continuous bar) pin is below the
internal FCB threshold reference, V FCB , the regulator is
forced to operate in continuous mode by disabling reversal
comparator, I REV , thereby allowing the inductor current to
become negative.
The continuous mode operating frequency can be deter-
mined by dividing the calculated duty cycle, V OUT /V IN ,
by the fixed on-time. The OST generates an on-time
proportional to the ideal duty cycle, thus holding the
frequency approximately constant with changes in V IN .
The nominal frequency can be adjusted with an external
resistor, R ON .
Foldback current limiting is provided to protect against
low impedance shorts. If the controller is in current limit
and V OUT drops to less 50% of regulation, the current limit
set-point “folds back” to progressively lower values. To
recover from foldback current limit, the excessive load or
low impedance short needs to be removed.
Pulling the RUN/SS pin low forces the controller into its
shutdown state, turning off both MT and MB. Releasing
the pin allows an internal 1.2μA current source to charge
up an external soft-start capacitor, C SS . When the RUN/
SS pin is less than 0.7V, the device is in the low power
shutdown condition with a nominal bias current of 18μA.
When RUN/SS is greater than 0.7V and less than 1.5V,
INTV CC and all internal circuitry are enabled while MT and
MB are forced off. Current-limited soft-start begins when
RUN/SS exceeds 1.5V. Normal operation at full current
limit is achieved at approximately 3V on RUN/SS. Foldback
current limit is defeated during soft-start.
3878fa
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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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