Micropower Dual 150mA CMOS RF LDO™ Regulators with 75dB Ripple Rejection
Advance
APPLICATIONS INFORMATION cont.
Thermal Considerations
For optimum Thermal dissipation and device reliability,
devices mounted on conventional FR4 PCB material
should be surrounded and connected to as much ground
copper as possible. In a worse case application with min-
imum trace widths and no ground plane, the MSOP-8
package exhibits a thermal resistance of 200 °C/W. The
risk to the device can be calculated in the following exam-
ples. (An Excel spreadsheet calculator is also available at
the Impala Linear web site: Products/ILC7280.)
Thermal Evaluation Examples
For an ambient temperature of 50°C, the maximum pack-
age power dissipation is:
P D(max) = (125°C - 50°C) / 200°C/W
P D(max) = 375mW
If the intent is to operate from a 4V power source with a
150mA load current from both outputs at a 50°C ambient
temperature, the expected power dissipation is found in
the following calculation:
P
P
P
P
P
D(each regulator) = (V
IN
- V
OUT
) * I
OUT
+ (V
IN
* I
GND
)
D(each regulator) = (4V - 3V) * 150mA + (4V * 0.12mA)
D(each regulator) = 150mW
D(both regulators) = 2 * 150mW
D(both regulators) = 300mW
In this example the total power dissipated is 300mW which
is below the 375mW maximum package consideration and
therefore safe to operate. It should be noted that it is not
always possible to operate both regulators at the maximum
output current. For example in a 5V input and 3V output
application at 50°C, one regulator operating at 150ma
would dissipate 267.5mW. The remaining regulator must
be limited to 375mW - 267.5mW or 107.5mW.
An advantage of the ILC7280 low-dropout voltage charac-
teristic is that using the lowest possible input voltage can
minimize power dissipation.
Impala Linear Corporation
ILC7280 1.8
(408) 574-3939
www.impalalinear.com
May 2000
8
IMPALA [ Impala Linear Corporation ]
