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| 型号： | MIC2846A-PPYMT TR |
| 厂商： | Micrel Inc |
| 文件页数： | 16/19页 |
| 文件大小： | 0K |
| 描述： | IC LED DRIVR WHITE BCKLGT 14TMLF |
| 标准包装： | 1 |
| 拓扑： | 线性（LDO） |
| 输出数： | 6 |
| 内部驱动器： | 是 |
| 类型 - 主要： | 背光，闪灯/白光 |
| 类型 - 次要： | 白色 LED |
| 电源电压： | 3 V ~ 5.5 V |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 14-UFQFN 裸露焊盘，14-TMLF? |
| 供应商设备封装： | 14-TMLF?（2.5x2.5） |
| 包装： | 标准包装 |
| 工作温度： | -40°C ~ 125°C |
| 产品目录页面： | 1082 (CN2011-ZH PDF) |
| 其它名称： | 576-3480-6 |
? ?
P TOTAL(max) = ? ?
Micrel Inc.
LDO
MIC2846A LDOs are low noise 150mA LDOs. The
MIC2846A LDO regulator is fully protected from damage
due to fault conditions, offering linear current limiting and
thermal shutdown.
Input Capacitor
The MIC2846A stability can be maintained using a
ceramic input capacitor of 1μF. Low-ESR ceramic
capacitors provide optimal performance at a minimum
amount of space. Additional high-frequency capacitors,
such as small-valued NPO dielectric-type capacitors,
help filter out high-frequency noise and are good
practice in any noise sensitive circuit. X5R or X7R
dielectrics are recommended for the input capacitor. Y5V
dielectrics lose most of their capacitance over
temperature and are therefore, not recommended.
Output Capacitor
The MIC2846A LDOs require an output capacitor of at
least 1μF or greater to maintain stability, however, the
output capacitor can be increased to 2.2μF to reduce
output noise without increasing package size. The
design is optimized for use with low-ESR ceramic chip
capacitors. High ESR capacitors are not recommended
because they may cause high frequency oscillation.
X7R/X5R dielectric-type ceramic capacitors are
recommended due to their improved temperature
performance compared to Z5U and Y5V capacitors.
X7R-type capacitors change capacitance by 15% over
their operating temperature range and are the most
stable type of ceramic capacitors. Z5U and Y5V
dielectric capacitors change value by as much as 50%
and 60%, respectively, over their operating temperature
ranges. To use a ceramic chip capacitor with Y5V
dielectric, the value must be much higher than an X7R
ceramic capacitor to ensure the same minimum
capacitance over the equivalent operating temperature
range.
No-Load Stability
Unlike many other voltage regulators, the MIC2846A
LDOs will remain stable and in regulation with no load.
Thermal Considerations
The MIC2846A LDOs are each designed to provide
150mA of continuous current. Maximum ambient
operating temperature can be calculated based on the
MIC2846A
output current and the voltage drop across the part. For
example if the input voltage is 3.6V, the output voltage is
2.8V, and the output current = 150mA. The actual power
dissipation of the regulator circuit can be determined
using the equation:
P LDO1 = (V IN – V OUT1 ) I OUT + V IN I GND
Because this device is CMOS and the ground current
(I GND ) is typically <100μA over the load range, the power
dissipation contributed by the ground current is < 1% and
can be ignored for this calculation.
P LDO1 = (3.6V – 2.8V) × 150mA
P LDO1 = 0.120W
Since there are two LDOs in the same package, the
power dissipation must be calculated individually and
then summed together to arrive at the total power
dissipation.
P TOTAL = P LDO1 + P LDO2
To determine the maximum ambient operating
temperature of the package, use the junction-to-ambient
thermal resistance ( θ JA = 60°C/W) of the device and the
following basic equation:
? T J(max) ? T A ?
? θ JA ?
T J(max) = 125°C, is the maximum junction temperature of
the die and θ JA, is the thermal resistance = 60°C/W.
Substituting P TOTAL for P TOTAL(max) and solving for the
ambient operating temperature will give the maximum
operating conditions for the regulator circuit.
For example, when operating the MIC2846A LDOs
(LDO1=2.8V and LDO2=1.5V) at an input voltage of
3.6V with 150mA load on each, the maximum ambient
operating temperature T A can be determined as follows:
P LDO1 = (3.6V – 2.8V) × 150mA = 0.120W
P LDO2 = (3.6V – 1.5V) × 150mA = 0.315W
P TOTAL =0.120W+ 0.315W = 0.435W
= (125°C – T A )/(60°C/W)
T A = 125°C – 0.435W × 60°C/W
T A = 98.9°C
Therefore, under the above conditions, the maximum
ambient operating temperature of 98.9°C is allowed.
April 2010
16
M9999-041210-D
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