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AMS1503CD-2.5 参数 Datasheet PDF下载

AMS1503CD-2.5图片预览
型号: AMS1503CD-2.5
PDF下载: 下载PDF文件 查看货源
内容描述: 3A低压差稳压器 [3A LOW DROPOUT VOLTAGE REGULATORS]
分类和应用: 稳压器调节器输出元件
文件页数/大小: 9 页 / 239 K
品牌: ADMOS [ ADVANCED MONOLITHIC SYSTEMS ]
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AMS1503  
APPLICATION HINTS  
Thermal resistance specification for both the Control Section and  
the Power Transistor are given in the electrical characteristics.  
The thermal resistance of the Control section is given as  
0.65°C/W and junction temperature of the Control section can run  
up to 125°C. The thermal resistance of the Power section is given  
as 2.7°C/W and junction temperature of the Power section can run  
up to 150°C. Due to the thermal gradients between the power  
transistor and the control circuitry there is a significant difference  
in thermal resistance between the Control and Power sections.  
Virtually all the power dissipated by the device is dissipated in the  
power transistor. The temperature rise in the power transistor will  
be greater than the temperature rise in the Control section making  
the thermal resistance lower in the Control section. At power  
levels below 12W the temperature gradient will be less than 25°C  
and the maximum ambient temperature will be determined by the  
junction temperature of the Control section. This is due to the  
lower maximum junction temperature in the Control section. At  
power levels above 12W the temperature gradient will be greater  
than 25°C and the maximum ambient temperature will be  
determined by the Power section. In both cases the junction  
temperature is determined by the total power dissipated in the  
device. For most low dropout applications the power dissipation  
will be less than 12W.  
Protection Diodes  
Unlike older regulators, the AMS1503 family does not need any  
protection diodes between the adjustment pin and the output and  
from the output to the input to prevent die over-stress. Internal  
resistors are limiting the internal current paths on the AMS1503  
adjustment pin, therefore even with bypass capacitors on the  
adjust pin no protection diode is needed to ensure device safety  
under short-circuit conditions. The Adjust pin can be driven on a  
transient basis ±7V with respect to the output without any device  
degradation.  
Diodes between the Output pin and VPOWER pin are not usually  
needed. Microsecond surge currents of 25A to50A can be handled  
by the internal diode between the Output pin and VPOWER pin of  
the device. In normal operations it is difficult to get those values  
of surge currents even with the use of large output capacitances. If  
high value output capacitors are used, such as 1000µF to 5000µF  
and the VPOWER pin is instantaneously shorted to ground, damage  
can occur. A diode from output to input is recommended, when a  
crowbar circuit at the input of the AMS1503 is used (Figure 6).  
Normal power supply cycling or even plugging and unplugging in  
the system will not generate current large enough to do any  
damage.  
The power in the device is made up of two components: the power  
in the output transistor and the power in the drive circuit. The  
power in the control circuit is negligible.  
VCONTROL  
The power in the drive circuit is equal to:  
+
D1*  
CONTROL  
POWER OUTPUT  
D2*  
P
DRIVE = (VCONTROL - VOUT)(ICONTROL  
where ICONTROL is equal to between IOUT/100(typ) and  
OUT/58(max).  
The power in the output transistor is equal to:  
OUTPUT = (VPOWER -VOUT)(IOUT  
)
VOUT  
VPOWER  
+
+
AMS1503  
SENSE  
I
ADJ  
R1  
R2  
P
)
The total power is equal to:  
PTOTAL = PDRIVE + POUTPUT  
Figure 6. Optional Clamp Diodes Protect Against  
Input Crowbar Circuits  
Junction-to-case thermal resistance is specified from the IC  
junction to the bottom of the case directly below the die. This is  
the lowest resistance path for the heat flow. In order to ensure the  
best possible thermal flow from this area of the package to the  
heat sink proper mounting is required. Thermal compound at the  
If the AMS1503 is connected as a single supply device with the  
control and power input pins shorted together the internal diode  
between the output and the power input pin will protect the control  
input pin. As with any IC regulator, none the protection circuitry  
will be functional and the internal transistors will break down if  
the maximum input to output voltage differential is exceeded.  
case-to-heat sink interface is recommended.  
A thermally  
conductive spacer can be used, if the case of the device must be  
electrically isolated, but its added contribution to thermal  
resistance has to be considered.  
Thermal Considerations  
The AMS1503 series have internal power and thermal limiting  
circuitry designed to protect the device under overload conditions.  
However maximum junction temperature ratings should not be  
exceeded under continuous normal load conditions. Careful  
consideration must be given to all sources of thermal resistance  
from junction to ambient, including junction-to-case, case-to-heat  
sink interface and heat sink resistance itself.  
Advanced Monolithic Systems, Inc. www.advanced-monolithic.com Phone (925) 443-0722 Fax (925) 443-0723