3
Operation
3.1
Power On
3.2
Fixed Output TPS714xx Device Configuration
4
Thermal Guidelines
4.1
Thermal Considerations
T = T + P
J
A
D
JA
´ q
(1)
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Operation
Other output voltages can be configured by changing the feedback resistors on the board. The feedback
network is high impedance and sensitive to noise or resistance value changes. The pins of J5 should not
be touched while the device is powered on because the impedance of a human is enough to alter the
output voltage set point. The output voltage may increase or decrease if J5 is touched, which may
damage any load connected to the EVM.
This section discusses the operation of the TPS71401EVM.
Connect the positive input power supply to J1. Connect the input power return (ground) to J3. The
TPS71401EVM has an absolute maximum input voltage of 11.0 V. The recommended maximum operating
voltage is 10 V. The actual highest input voltage may be less than 10 V as a result of thermal conditions.
See the
section of this manual to determine the highest input voltage.
Connect the desired load between J2 (positive lead) and J4 (negative or return lead). Configure jumper J5
for the desired output voltage. The function of J5 is described in the
section of this manual.
The TPS71401 EVM can also be used to evaluate fixed-output voltage versions of the TPS714 LDO. The
board layout and device footprints are the same for both the adjustable and the fixed-output voltage
versions of the TPS714. To evaluate a fixed-output voltage version, the IC on the board must be changed
to the desired fixed output voltage (TPS714xx). Note that R
1
must be removed from the EVM board if a
fixed output voltage version is mounted to the EVM board.
This section presents guidelines for the thermal management of the TPS71401DRVEVM-426 PCB.
Thermal management is a key design component of any power converter application and is especially
important when the power dissipation in the LDO is high. To better help users design the TPS71401 family
into an application, the following formula should be used to approximate the maximum power dissipation
at a particular ambient temperature:
Where:
•
T
J
is the junction temperature
•
T
A
is the ambient temperature
•
P
D
is the power dissipation in the IC
• θ
JA
is the thermal resistance from junction to ambient
All temperatures are in degrees Celsius.
The thermal resistance from junction to ambient for the TPS71401EVM has a typical value of 65
°
C/W. The
recommended maximum operating junction temperature specified in the data sheet for the TPS71401
family is +125
°
C. With these two pieces of information, the maximum power dissipation can be found by
using
.
SBVU013 – January 2009
TPS71401DRVEVM-426
3
