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| 型号： | LTC3549EDCB#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 12/16页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC ADJ 0.25A 6DFN |
| 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： | 0.61 V ~ 5.5 V |
| 输入电压： | 1.6 V ~ 5.5 V |
| PWM 型： | 电流模式，混合 |
| 频率 - 开关： | 2.25MHz |
| 电流 - 输出： | 250mA |
| 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-WFDFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 6-DFN-EP（2x3） |
LTC3549
APPLICATIO S I FOR ATIO
Thermal Considerations
In most applications the LTC3549 does not dissipate much
heat due to its high ef?ciency. But, in applications where the
LTC3549 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
temperature of the part. If the junction temperature reaches
approximately 150°C, both power switches will be turned
off and the SW node will become high impedance.
To avoid the LTC3549 from exceeding the maximum
junction temperature, the user will need to do a thermal
analysis. The goal of the thermal analysis is to determine
whether the operating conditions exceed the maximum
junction temperature of the part. The temperature rise is
given by:
T R = (P D )( θ JA )
where P D is the power dissipated by the regulator and θ JA
is the thermal resistance from the junction of the die to
the ambient temperature.
The junction temperature, T J , is given by:
T J = T A + T R
where T A is the ambient temperature.
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 load current. When
a load step occurs, V OUT immediately shifts by an amount
equal to ( Δ I LOAD ? ESR), where ESR is the effective series
resistance of C OUT . Δ I LOAD also begins to charge or dis-
charge C OUT , which generates a feedback error signal. The
regulator loop then acts to return V OUT to its steady state
value. During this recovery time V OUT can be monitored
for overshoot or ringing that would indicate a stability
problem. For a detailed explanation of switching control
loop theory, see Application Note 76.
A second, more severe transient is caused by switching
in loads with large (> 1μF) supply bypass capacitors. The
discharged bypass capacitors are effectively put in paral-
lel 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 that the load rise time is limited to approximately (25
? C LOAD ). Thus, a 10μF capacitor charging to 3.3V would
require a 250μs rise time, limiting the charging current
to about 130mA.
As an example, consider the LTC3549 in dropout at an input
voltage of 1.6V, a load current of 250mA and an ambient
temperature of 75°C. In the Switch Resistance graph
shown in the Typical Performance Characteristics, the
R DS(ON) of the P-channel switch at 75°C is approximately
0.8 Ω . Therefore, power dissipated by the part is:
P D = I LOAD2 ? R DS(ON) = 50mW
For the DCB6 package, the θ JA is 64°C/W. Thus, the junc-
tion temperature of the regulator is:
T J = 75°C + (0.05)(64) = 78.2°C
which is well below the maximum junction temperature
of 125°C.
Note that at higher supply voltages, the junction temperature
is lower due to reduced switch resistance (R DS(ON) ).
3549f
12
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| LTC3550EDHC#PBF | 功能描述:IC CHARGER BATT DUAL 16-DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 电池管理 系列:- 标准包装:61 系列:- 功能:电源管理 电池化学:锂离子（Li-Ion）、锂聚合物（Li-Pol） 电源电压:4.35 V ~ 5.5 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:22-WFDFN 裸露焊盘 供应商设备封装:22-DFN（6x3）裸露焊盘 包装:管件 |
| LTC3550EDHC#TRPBF | 功能描述:IC CHARGER BATT DUAL 16-DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 电池管理 系列:- 标准包装:61 系列:- 功能:电源管理 电池化学:锂离子（Li-Ion）、锂聚合物（Li-Pol） 电源电压:4.35 V ~ 5.5 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:22-WFDFN 裸露焊盘 供应商设备封装:22-DFN（6x3）裸露焊盘 包装:管件 |
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