Power Supply
25
SPRUIE6 – April 2017
Copyright © 2017, Texas Instruments Incorporated
AMIC110 Industrial Communications Engine (AMIC110 ICE)
For the power dissipation calculations in
was used for the switch mode power
supplies (SMPS) and
for the LDOs.
P
SMPS
= ((V
OUT
× I
OUT
) /
η
) – V
OUT
× I
OUT
(2)
P
LDO
= (V
IN
– V
OUT
) × I
OUT
(3)
Table 17. PMIC Power Dissipation
Rail
TPS650250 Maximum
Current
Topology
Current
Power Dissipation
1.1 V
1600 mA
SMPS
≈
420 mA
0.12 W
1.5 V
800 mA
SMPS
≈
260 mA
0.1 W
1.8 V
400 mA
LDO
≈
33 mA
0.1 W
3.3 V
800 mA
SMPS
≈
331 mA
0.28 W
For the calculations in
, SMPS efficiency was assumed to be 80%.
The total power dissipation of the TPS650250 is 0.6 W.
4.6
Measured Power Consumption of System
The measured power consumption test was performed while running the EtherCAT slave firmware on the
AMIC110 ICE connected to a TwinCAT3 terminal on the PC.
lists the measured system power
consumption.
Table 18. Measured System Power Consumption
Rail
Current Consumption
Power Consumption
1.1 V
349 mA
0.384 W
1.5 V
35.8 mA
0.054 W
1.8 W
26.23 mA
0.047 W
3.3 V
128 mA
0.422 W
The power consumption was measured by removing the 0-
Ω
resistors attached to each power rail and
measuring with a multimeter over the removed resistor. See the
for resistor
details.
A multimeter was connected at the 5-V input to measure the input current.
The total power consumption of the board is 0.907 W. The total supply current from the 5-V system power
supply is 248 mA, giving an input power of 1.240 W from the 5-V rail; this means that the overall efficiency
of the TPS650250 is around 78% for the complete system, with 0.333 W of power dissipation in the
TPS650250 package.
Using the given package thermal performance from the datasheet, use
to calculate the
expected temperature increase of the part.
T
TPS650250
= R
θ
JA
× P
Dissipation
= 34°C/W × 0.333 W
≈
11.7°C
(4)
At 85°C ambient, the estimated junction temperature is 96.7°C.
The maximum operating junction temperature of the TPPS650250 is 125°C. If running the TPS650250 at
85°C ambient temperature, the device could dissipate 1.18 W without forced cooling.
