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| 型号： | LTC1878EMS8#TR |
| 厂商： | Linear Technology |
| 文件页数： | 7/16页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC ADJ 0.6A 8MSOP |
| 标准包装： | 2,500 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 0.8 V ~ 6 V |
| 输入电压： | 2.65 V ~ 6 V |
| PWM 型： | 电流模式，混合 |
| 频率 - 开关： | 550kHz |
| 电流 - 输出： | 600mA |
| 同步整流器： | 是 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-TSSOP，8-MSOP（0.118"，3.00mm 宽） |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 8-MSOP |
| 其它名称： | LTC1878EMS8TR |
LTC1878
OPERATIO
Main Control Loop
The LTC1878 uses a constant frequency, current mode
step-down architecture. Both the main (P-channel
MOSFET) and synchronous (N-channel MOSFET) switches
are internal. During normal operation, the internal top
power MOSFET is turned on each cycle when the oscillator
sets the RS latch, and turned off when the current com-
parator, I COMP , resets the RS latch. The peak inductor
current at which I COMP resets the RS latch is controlled by
the voltage on the I TH pin, which is the output of error
amplifier EA. The V FB pin, described in the Pin Functions
section, allows EA to receive an output feedback voltage
from an external resistive divider. When the load current
increases, it causes a slight decrease in the feedback
voltage relative to the 0.8V reference, which in turn,
causes the I TH voltage to increase until the average induc-
tor current matches the new load current. While the top
MOSFET is off, the bottom MOSFET is turned on until
either the inductor current starts to reverse as indicated by
the current reversal comparator I RCMP , or the beginning of
the next clock cycle.
Comparator OVDET guards against transient overshoots
>6.25% by turning the main switch off and keeping it off
until the fault is removed.
Burst Mode Operation
The LTC1878 is capable of Burst Mode operation in which
the internal power MOSFETs operate intermittently based
on load demand. To enable Burst Mode operation, simply
tie the SYNC/MODE pin to V IN or connect it to a logic high
(V SYNC/MODE > 1.5V). To disable Burst Mode operation and
enable PWM pulse skipping mode, connect the SYNC/
MODE pin to GND. In this mode, the efficiency is lower at
light loads, but becomes comparable to Burst Mode
operation when the output load exceeds 50mA. The ad-
vantage of pulse skipping mode is lower output ripple and
less interference to audio circuitry.
When the converter is in Burst Mode operation, the peak
current of the inductor is set to approximately 250mA,
even though the voltage at the I TH pin indicates a lower
value. The voltage at the I TH pin drops when the inductor’s
average current is greater than the load requirement. As
the I TH voltage drops below approximately 0.55V, the
BURST comparator trips, causing the internal sleep line to
go high and forces off both power MOSFETs. The I TH pin
is then disconnected from the output of the EA amplifier
and parked a diode voltage above ground.
In sleep mode, both power MOSFETs are held off and a
majority of the internal circuitry is partially turned off,
reducing the quiescent current to 10 μ A. The load current
is now being supplied solely from the output capacitor.
When the output voltage drops, the I TH pin reconnects to
the output of the EA amplifier and the top MOSFET is again
turned on and this process repeats.
Short-Circuit Protection
When the output is shorted to ground, the frequency of the
oscillator is reduced to about 80kHz, 1/7 the nominal
frequency. This frequency foldback ensures that the
inductor current has ample time to decay, thereby pre-
venting runaway. The oscillator’s frequency will progres-
sively increase to 550kHz (or the synchronized frequency)
when V FB rises above 0.3V.
Frequency Synchronization
A phase-locked loop (PLL) is available on the LTC1878 to
allow the internal oscillator to be synchronized to an
external source connected to the SYNC/MODE pin. The
output of the phase detector at the PLL LPF pin operates
over a 0V to 2.4V range corresponding to 400kHz to
700kHz. When locked, the PLL aligns the turn-on of the top
MOSFET to the rising edge of the synchronizing signal.
When the LTC1878 is clocked by an external source, Burst
Mode operation is disabled; the LTC1878 then operates in
PWM pulse skipping mode. In this mode, when the output
load is very low, current comparator I COMP may remain
tripped for several cycles and force the main switch to stay
off for the same number of cycles. Increasing the output
load slightly allows constant frequency PWM operation to
resume. This mode exhibits low output ripple as well as
low audio noise and reduced RF interference while provid-
ing reasonable low current efficiency.
Frequency synchronization is inhibited when the feedback
voltage V FB is below 0.6V. This prevents the external clock
from interfering with the frequency foldback for short-
circuit protection.
7
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| LTC1878EMS8TRPBF | 制造商:Linear Technology 功能描述: |
| LTC1879EGN | 功能描述:IC REG BUCK SYNC ADJ 1.2A 16SSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V，1.5V，1.8V，2.5V 输入电压:2.7 V ~ 20 V PWM 型:- 频率 - 开关:- 电流 - 输出:50mA 同步整流器:是 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 包装:带卷 (TR) 供应商设备封装:10-MSOP 裸露焊盘 |
| LTC1879EGN#PBF | 功能描述:IC REG BUCK SYNC ADJ 1.2A 16SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:250 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V 输入电压:2.05 V ~ 6 V PWM 型:电压模式 频率 - 开关:2MHz 电流 - 输出:500mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:6-UFDFN 包装:带卷 (TR) 供应商设备封装:6-SON（1.45x1） 产品目录页面:1032 (CN2011-ZH PDF) 其它名称:296-25628-2 |
| LTC1879EGN#TR | 功能描述:IC REG BUCK SYNC ADJ 1.2A 16SSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V，1.5V，1.8V，2.5V 输入电压:2.7 V ~ 20 V PWM 型:- 频率 - 开关:- 电流 - 输出:50mA 同步整流器:是 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 包装:带卷 (TR) 供应商设备封装:10-MSOP 裸露焊盘 |
| LTC1879EGN#TRPBF | 功能描述:IC REG BUCK SYNC ADJ 1.2A 16SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V，1.5V，1.8V，2.5V 输入电压:2.7 V ~ 20 V PWM 型:- 频率 - 开关:- 电流 - 输出:50mA 同步整流器:是 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 包装:带卷 (TR) 供应商设备封装:10-MSOP 裸露焊盘 |
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