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| 型号： | LTC1877EMS8#TR |
| 厂商： | Linear Technology |
| 文件页数： | 12/18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 ~ 10 V |
| 输入电压： | 2.65 V ~ 10 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 |
LTC1877
APPLICATIONS INFORMATION
this stable operating point the phase comparator 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
component’s C LP and R LP determine how fast the loop
acquires lock. Typically R LP = 10k and C LP is 2200pF
to 0.01μF. When not synchronized to an external clock,
the internal connection to the V CO is disconnected. This
disallows setting the internal oscillator frequency by a DC
voltage on the V PLL LPF pin.
Ef?ciency Considerations
The ef?ciency of a switching regulator is equal to the output
power divided by the input power times 100%. It is often
useful to analyze individual losses to determine what is
limiting the ef?ciency and which change would produce
the most improvement. Ef?ciency can be expressed as:
Ef?ciency = 100% – (L1 + L2 + L3 + ...)
where L1, L2, etc. are the individual losses as a percent-
age of input power.
I GATECHG = f(Q T + Q B ) where Q T and Q B are the gate
charges of the internal top and bottom switches. Both
the DC bias and gate charge losses are proportional
to V IN and thus their effects will be more pronounced
at higher supply voltages.
2. I 2 R losses are calculated from the resistances of the
internal switches, R SW , and external inductor R L . In
continuous mode, the average output current ?ow-
ing through inductor L is chopped between the main
switch and the synchronous switch. Thus, the series
resistance looking into the SW pin is a function of both
top and bottom MOSFET R DS(ON) and the duty cycle
(DC) as follows:
R SW = (R DS(ON)TOP )(DC) + (R DS(ON)BOT) (1 – DC)
The R DS(ON) for both the top and bottom MOSFETs can
be obtained from the Typical Performance Character-
istics curves. Thus, to obtain I 2 R losses, simply add
R SW to R L and multiply the result by the square of the
average output current.
Other losses including C IN and C OUT ESR dissipative los-
ses and inductor core losses generally account for less
than 2% total additional loss.
Although all dissipative elements in the circuit produce
losses, two main sources usually account for most of
the losses in LTC1877 circuits: V IN quiescent current and
I 2 R losses. The V IN quiescent current loss dominates the
ef?ciency loss at very low load currents, whereas the
I 2 R loss dominates the ef?ciency loss at medium to high
load currents. In a typical ef?ciency plot, the ef?ciency
curve at very low load currents can be misleading since
the actual power lost is of no consequence, as illustrated
in Figure 6.
1
0.1
0.01
0.001
0.0001
0.00001
V IN = 4.2V
L = 10 μ H
V OUT = 1.5V
V OUT = 2.5V
V OUT = 3.3V
Burst Mode OPERATION
1. The V IN quiescent current is due to two components:
the DC bias current as given in the Electrical Charac-
0.1
1
10 100
LOAD CURRENT (mA)
1000
1877 F06
teristics section and the internal main switch and syn-
chronous switch gate charge currents. The gate charge
current results from switching the gate capacitance
of the internal power MOSFET switches. Each time
the gate is switched from high to low to high again, a
packet of charge dQ moves from V IN to ground. The
resulting dQ/dt is the current out of V IN that is typically
larger than the DC bias current. In continuous mode,
Figure 6. Power Lost vs Load Current
Thermal Considerations
In most applications the LTC1877 does not dissipate much
heat due to its high ef?ciency. But, in applications where the
LTC1877 is running at high ambient temperature with low
supply voltage and high duty cycles, such as in dropout,
the heat dissipated may exceed the maximum junction
1877fb
12
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC1877IMS8#PBF | 功能描述:IC REG BUCK SYNC ADJ 0.6A 8MSOP 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 |
| LTC1877IMS8#TRPBF | 功能描述:IC REG BUCK SYNC ADJ 0.6A 8MSOP 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 |
| LTC1878EMS8 | 功能描述:IC REG BUCK SYNC ADJ 0.6A 8MSOP 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:升压（升压） 输出类型:可调式 输出数:1 输出电压:1.24 V ~ 30 V 输入电压:1.5 V ~ 12 V PWM 型:电流模式，混合 频率 - 开关:600kHz 电流 - 输出:500mA 同步整流器:无 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:8-SOIC（0.154"，3.90mm 宽） 包装:带卷 (TR) 供应商设备封装:8-SOIC |
| LTC1878EMS8#PBF | 功能描述:IC REG BUCK SYNC ADJ 0.6A 8MSOP 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 |
| LTC1878EMS8#TR | 功能描述:IC REG BUCK SYNC ADJ 0.6A 8MSOP 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:升压（升压） 输出类型:可调式 输出数:1 输出电压:1.24 V ~ 30 V 输入电压:1.5 V ~ 12 V PWM 型:电流模式，混合 频率 - 开关:600kHz 电流 - 输出:500mA 同步整流器:无 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:8-SOIC（0.154"，3.90mm 宽） 包装:带卷 (TR) 供应商设备封装:8-SOIC |
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