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| 型号： | LTC1876EG |
| 厂商： | Linear Technology |
| 文件页数： | 21/36页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BST PWM CM 36-SSOP |
| 标准包装： | 37 |
| 系列： | PolyPhase® |
| PWM 型： | 电流模式 |
| 输出数： | 3 |
| 频率 - 最大： | 360kHz |
| 占空比： | 99.4% |
| 电源电压： | 3.5 V ~ 36 V |
| 降压： | 是 |
| 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 ~ 85°C |
| 封装/外壳： | 36-SSOP（0.209"，5.30mm 宽） |
| 包装： | 管件 |
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LTC1876
APPLICATIO S I FOR ATIO
Soft-Start/Run Function
The RUN/SS1 and RUN/SS2 pins are multipurpose pins
that provide a soft-start function and a means to shut
down the LTC1876 step-down controllers. Soft-start re-
duces the input power source’s surge currents by gradu-
ally increasing the controller’s current limit (proportional
to V ITH ). This pin can also be used for power supply
sequencing.
An internal 1.2 μ A current source charges up the C SS
capacitor . When the voltage on RUN/SS1 (RUN/SS2)
reaches 1.5V, the particular controller is permitted to start
operating. As the voltage on RUN/SS increases from 1.3V
to 3.0V, the internal current limit is increased from 25mV/
R SENSE to 75mV/R SENSE . The output current limit ramps
up slowly, taking an additional 1.2s/ μ F to reach full cur-
rent. The output current thus ramps up slowly, reducing
the starting surge current required from the input power
supply. If RUN/SS has been pulled all the way to ground
there is a delay before starting of approximately:
Fault Conditions: Overcurrent Latchoff
The RUN/SS pins also provide the ability to latch off the
controller(s) when an overcurrent condition is detected.
The RUN/SS capacitor, C SS , is used initially to turn on and
limit the inrush current of the controller. After the control-
ler has been started and been given adequate time to
charge up the output capacitor and provide full load
current, the RUN/SS capacitor is used for a short-circuit
timer. If the regulator’s output voltage falls to less than
70% of its nominal value after C SS reaches 4.1V, C SS
begins discharging on the assumption that the output is in
an overcurrent condition. If the condition lasts for a long
enough period as determined by the size of the C SS and the
specified discharge current, the controller will be shut
down until the RUN/SS pin voltage is recycled. If the
overload occurs during start-up, the time can be approxi-
mated by:
T LO1 ? [C SS (4.1 – 1.5 + 4.1 – 3.5)]/(1.2 μ A)
= 2.7 ? 10 6 (C SS )
( )
= 1 . 25 s / μ F C
1 . 2 μ A
( )
= 1 . 25 s / μ F C
1 . 2 μ A
t DELAY =
t IRAMP =
1 . 5 V
C SS SS
3V ? 1 .5V
C SS SS
If the overload occurs after start-up the voltage on C SS will
begin discharging from the zener clamp voltage:
T LO2 ? [C SS (6 – 3.5)]/(1.2 μ A) = 2.1 ? 10 6 (C SS )
If an overload occurs on one channel, it will also latch off
the other channel. This built-in overcurrent latchoff can be
By pulling both RUN/SS pins below 1.0V and/or pulling the
STBYMD pin below 0.2V, the controllers are put into low
current shutdown (I Q = 20 μ A). The RUN/SS pins can be
driven directly from logic as shown in Figure 7. Diode D1
in Figure 7 reduces the start delay but allows C SS to ramp
up slowly providing the soft-start function. Each RUN/SS
pin has an internal 6V Zener clamp (See Functional Dia-
gram).
overridden by providing a pull-up resistor to the RUN/SS
pin as shown in Figure 7. This resistance shortens the soft-
start period and prevents the discharge of the RUN/SS
capacitor during an over current condition. Tying this pull-
up resistor to V IN as in Figure 7a, defeats overcurrent
latchoff. Diode-connecting this pull-up resistor to INTV CC ,
as in Figure 7b, eliminates any extra supply current during
controller shutdown while eliminating the INTV CC loading
from preventing controller start-up.
3.3V OR 5V
D1
V IN
RUN/SS
R SS *
INTV CC
R SS *
Why should you defeat overcurrent latchoff? During the
prototype stage of a design, there may be a problem with
C SS
RUN/SS
C SS
noise pickup or poor layout causing the protection circuit
to latch off. Defeating this feature will easily allow trouble-
shooting of the circuit and PC layout. The internal short-
*OPTIONAL TO DEFEAT OVERCURRENT LATCHOFF
(a)
Figure 7. RUN/SS Pin Interfacing
(b)
1876 F07
circuit and foldback current limiting still remains active,
thereby protecting the power supply system from failure.
After the design is complete, a decision can be made
whether to enable the latchoff feature.
1876fa
21
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| LTC1876EG#PBF | 功能描述:IC REG CTRLR BST PWM CM 36-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:PolyPhase® 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 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 ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
| LTC1876EG#TR | 功能描述:IC REG CTRLR BST PWM CM 36-SSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:PolyPhase® 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 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 ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
| LTC1876EG#TRPBF | 功能描述:IC REG CTRLR BST PWM CM 36-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:PolyPhase® 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 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 ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
| LTC1877EMS8 | 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: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 |
| LTC1877EMS8#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 |
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