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| 型号： | LTC1147CS8-5#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 10/16页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 8-SOIC |
| 标准包装： | 100 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 占空比： | 100% |
| 电源电压： | 3.5 V ~ 14 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： | 0°C ~ 70°C |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 包装： | 管件 |
| 产品目录页面： | 1332 (CN2011-ZH PDF) |
LTC1147-3.3
LTC1147-5/LTC1147L
APPLICATIO S I FOR ATIO
Optimum efficiency is obtained by making the ESR equal
to R SENSE . As the ESR is increased up to 2R SENSE , the
efficiency degrades by less than 1%. If the ESR is greater
than 2R SENSE , the voltage ripple on the output capacitor
will prematurely trigger Burst Mode operation, resulting in
disruption of continuous mode and an efficiency hit which
can be several percent.
Manufacturers such as Nichicon and United Chemicon
should be considered for high performance capacitors.
The OS-CON semiconductor dielectric capacitor available
from Sanyo has the lowest ESR/size ratio of any aluminum
electrolytic at a somewhat higher price. Once the ESR
requirement for C OUT has been met, the RMS current
rating generally far exceeds the I RIPPLE(P-P) requirement.
In surface mount applications multiple capacitors may
have to be paralleled to meet the capacitance, ESR or RMS
current handling requirements of the application. Alumi-
num electrolytic and dry tantalum capacitors are both
available in surface mount configurations. In the case of
tantalum, it is critical that the capacitors are surge tested
for use in switching power supplies. An excellent choice
is the AVX TPS series of surface mount tantalums, avail-
able in case heights ranging from 2mm to 4mm. For
example, if 200 μ F/10V is called for in an application
requiring 3mm height, two AVX 100 μ F/10V (P/N TPSD
107K010) could be used. Consult the manufacturer for
other specific recommendations.
At low supply voltages, a minimum capacitance at C OUT is
needed to prevent an abnormal low frequency operating
mode (see Figure 4). When C OUT is made too small, the
output ripple at low frequencies will be large enough to trip
the voltage comparator. This causes Burst Mode opera-
tion to be activated when the LTC1147 series would
normally be in continuous operation. The effect is most
pronounced with low values of R SENSE and can be im-
proved by operating at higher frequencies with lower
values of L. The output remains in regulation at all times.
Checking Transient Response
The regulator loop response can be checked by looking
at the load transient response. Switching regulators
take several cycles to respond to a step in DC (resistive)
load current. When a load step occurs, V OUT shifts by an
amount equal to ? I LOAD (ESR), where ESR is the effec-
tive series resistance of C OUT . ? I LOAD also begins to
charge or discharge C OUT until the regulator loop adapts
to the current change and returns V OUT to its steady
state value. During this recovery time V OUT can be
monitored for overshoot or ringing which would indi-
cate a stability problem. The external components shown
in the Figure 1 circuit will prove adequate compensation
for most applications.
A second, more severe transient is caused by switching
in loads with large (>1 μ F) supply bypass capacitors. The
discharged bypass capacitors are effectively put in par-
allel with C OUT , causing a rapid drop in V OUT . No regulator
can deliver enough current to prevent this problem if the
load switch resistance is low and it is driven quickly. The
only solution is to limit the rise time of the switch drive so
1000
800
600
400
L = 50 μ H
R SENSE = 0.02 ?
L = 25 μ H
R SENSE = 0.02 ?
that the load rise time is limited to approximately
(25)C LOAD . Thus a 10 μ F capacitor would require a 250 μ s
rise time, limiting the charging current to about 200mA.
Efficiency Considerations
The percent efficiency of a switching regulator is equal to
the output power divided by the input power times 100%.
200
0
0
1
L = 50 μ H
R SENSE = 0.05 ?
2 3
(V IN – V OUT ) VOLTAGE (V)
4
5
It is often useful to analyze individual losses to determine
what is limiting the efficiency and which change would
produce the most improvement. Percent efficiency can be
expressed as:
LTC1147 ? F04
%Efficiency = 100% – (L1 + L2 + L3 + ...)
Figure 4. Minimum Value of C OUT
sn1147 1147fds
10
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| LTC1147HVCS8-3.3 | 功能描述:IC REG CTRLR BUCK PWM CM 8-SOIC RoHS:否 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) |
| LTC1147HVCS8-3.3#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 8-SOIC 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:4,000 系列:- PWM 型:电压模式 输出数:1 频率 - 最大:1.5MHz 占空比:66.7% 电源电压:4.75 V ~ 5.25 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:40-VFQFN 裸露焊盘 包装:带卷 (TR) |
| LTC1147HVCS8-3.3#TR | 功能描述:IC REG CTRLR BUCK PWM CM 8-SOIC RoHS:否 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) |
| LTC1147HVCS8-3.3#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 8-SOIC 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:4,000 系列:- PWM 型:电压模式 输出数:1 频率 - 最大:1.5MHz 占空比:66.7% 电源电压:4.75 V ~ 5.25 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:40-VFQFN 裸露焊盘 包装:带卷 (TR) |
| LTC1147I | 制造商:LINER 制造商全称:Linear Technology 功能描述:High Efficiency Step-Down Switching Regulator Controllers |
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