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| 型号： | LTC1877IMS8#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 9/18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
OPERATION
Dropout Operation
When the input supply voltage decreases toward the output
voltage, the duty cycle increases toward the maximum
on-time. Further reduction of the supply voltage forces the
main switch to remain on for more than one cycle until it
reaches 100% duty cycle. The output voltage will then be
determined by the input voltage minus the voltage drop
across the internal P-channel MOSFET and the inductor.
Low Supply Operation
The LTC1877 is designed to operate down to an input supply
voltage of 2.65V although the maximum allowable output
current is reduced at this low voltage. Figure 1 shows the
reduction in the maximum output current as a function of
input voltage for various output voltages.
Another important detail to remember is that at low input
supply voltages, the R DS(ON) of the P-channel switch in-
creases. Therefore, the user should calculate the power
dissipation when the LTC1877 is used at 100% duty cycle
with a low input voltage (see Thermal Considerations in
the Applications Information section).
Slope Compensation and Inductor Peak Current
Slope compensation provides stability in constant-fre-
quency architectures by preventing subharmonic oscilla-
tions at high duty cycles. It is accomplished internally by
adding a compensating ramp to the inductor current signal
at duty cycles in excess of 40%. As a result, the maximum
inductor peak current is reduced for duty cycles >40%.
This is shown in the decrease of the inductor peak current
as a function of duty cycle graph in Figure 2.
1200
V OUT = 2.5V
1100
V IN = 5V
1000
800
V OUT = 1.5V
1000
600
V OUT = 5V
900
400
200
V OUT = 3.3V
L = 10μH
800
700
0
0
2
4
6
8
10
12
600
0
20
40
60
80
100
VIN (V)
1877 F01
DUTY CYCLE (%)
1877 F02
V OUT ? 1 ? OUT ?
( f ) ( L ) ? V IN ?
Figure 1. Maximum Output Current vs Input Voltage
APPLICATIONS INFORMATION
The basic LTC1877 application circuit is shown on the ?rst
page. External component selection is driven by the load
requirement and begins with the selection of L followed
by C IN and C OUT .
Inductor Value Calculation
The inductor selection will depend on the operating fre-
quency of the LTC1877. The internal nominal frequency is
550kHz, but can be externally synchronized from 400kHz
to 700kHz.
Figure 2. Maximum Inductor Peak Current vs Duty Cycle
The operating frequency and inductor selection are inter-
related in that higher operating frequencies allow the use of
smaller inductor and capacitor values. However, operating
at a higher frequency generally results in lower ef?ciency
because of increased internal gate charge losses.
The inductor value has a direct effect on ripple current.
The ripple current ΔI L decreases with higher inductance
or frequency and increases with higher V IN or V OUT .
1 ? V ?
Δ I L =
(1)
1877fb
9
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| 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 |
| LTC1878EMS8#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: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 |
| LTC1878EMS8PBF | 制造商:Linear Technology 功能描述: 制造商:Linear Technology 功能描述:DC-DC Converter Step-Down 2.65-6V MSOP8 |
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