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Hardware Low Power Design Guidelines
9
SPRAC74A–February 2017–Revised March 2017
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Copyright © 2017, Texas Instruments Incorporated
AM335x Low Power Design Guide
2.5.2 On Board Power Monitoring Devices
The INA226 is a current shunt and power monitoring device with an I2C or PMBus interface. Use of the
INA226 allows for easily automated power monitoring via the I2C interface. If there are many rails that
require continuous power measurement, the INA226 removes the requirement for several multimeters or
sets of probes running all over the board. Using a digitally controlled measurement device can also make
it easier to automate measurements, since the system can be controlled using a script that can collect
power data while cycling the device through different use cases.
One drawback of using an integrated power monitoring solution is that depending on the setup, it may
require additional hardware beyond the power monitoring device. For example, on the AM335x GP EVM,
the integrated INA226 devices sit on an external I2C bus. This allows power consumption to be monitored
when the SOC is in suspend or sleep mode, but requires an additional device to read data from the
monitors. It is relatively trivial to get a USB to I2C adapter, or another development board with I2C to
gather this telemetry, but it is another consideration to be made. One potential compromise would be to
connect the INA device to an AM335x I2C bus and create a multiple master bus.
As a reference, AM335x GP EVM uses two INA devices to monitor power consumption on the
VDD_CORE and VDD_MPU voltage supply rails on an external I2C bus.
2.5.3 Note on Remote Sensing
Remote sensing, also sometimes known as four (4) terminal measurement, is when separate sets of
terminals are used to measure current (I) and voltage(V).
Figure 4. Four-Wire Resistance Measurement Configuration
As opposed to traditional local, or two terminal sensing, in the four terminal example, there is no voltage
drop due to lead resistance since the current through the voltage sense terminals is negligible.
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