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"PMDC" on EVMAM1808 and board power consumption measurement
I would like to ask a question on EVMAM1808.
Sheet 32 of EVMAM1808
schematics is titled "PMDC Connector", and contains a header J13 of 100 pins, of which only 28
pins are connected.
Since there is no other textual descriptive documentation
such as a manual on EVMAM1808
Support Home, I was not able to find the purpose of this design. Could
anyone tell me what this header is intended for?
It seems probably that "PM" in "PMDC" might stand for "Power Management". Is it
true? I am using EVMAM1808 as a reference design for an OMAP L138 board, and
since both AM1808 and OMAPL138 are optimized for power, there should then be a way to measure and
monitor its actual power consumption during development period. How is this
achieved? Is this done by using this "PMDC" connector?
However, why there are so many unconnected (100 - 28=72, over half are power or GND)
pins on the header? Those unconnected pins have no electrical connection with
the chip or even power management IC, so I wonder if there is any utility in
these header pins.
Why is this "PMDC" header for? How to measure precisely board power consumption? Could anyone help
PMDC_I2C_SDA and PMDC_I2C_SCL pins are directly connected to INA219A power consumption monitoring IC / device. But this I2c bus is not connected to onboard I2C controller of the board.So we need to read shunt resistance voltage from INA219' internal resister using the I2c protocol. The INA219A is an accuracy of 0.5%.
Logic PD recently released their free Wattson software for the AM1808 EVM which will help you see actual voltage, current, and power consumption across all power rails on the CPU design. The software visually shows you which power rails are consuming the power and when they are switching on and off in your application.
Following links are useful for your query:
http://e2e.ti.com/support/dsp/omap_applications_processors/f/42/t/142711.aspxThere is an adapter 100 PIN required to connect to the PC available from this website:
http://createnewstuff.webs.com/breakoutboardwattson.htmThe PC Application software is available from here: http://www.logicpd.com/wattson
Abhijit Das84416PMDC_I2C_SDA and PMDC_I2C_SCL pins are directly connected to INA219A power consumption monitoring IC / device. But this I2c bus is not connected to onboard I2C controller of the board.
I know that "I2C_SDA and PMDC_I2C_SCL are actually not connected to any pin of the CPU." For reading of the power we need to access to another Microcontroller & display unit . But please confirm PMDC_I2C_SDA and PMDC_I2C_SCL pins are not connected to INA219A power consumption monitoring IC ?
First there need to be some slight correction with the naming: PMDC_I2C_SDA→
PMI2C_SDA, PMDC_I2C_SCL→ PMI2C_SCL
Yes, they are connected to INA219.
I think I got your meaning: use external microcontroller to read INA219 array to get power consumption monitoring?
I wonder if it is also possible to query INA219 array from AM1808/OMAPL138 itself? The disadvantage of this approach seems to be that when the CPU is busy with tasks, it cannot query INA219. However, this corresponds to its peak power consumption (current) which is among the most valuable information INA219 could collect. When CPU is connecting with INA219 via I2C, the I2C speed is much lower (100KHz or 400KHz in fast I2C mode) than CPU speed, and there are multiple INA219's, and CPU actually has to poll the on-chip I2C controller register to determine whether particular data have been sent or received. Basically, this means the CPU has to completely be engaged in I2C communication with INA219 array so what is monitored is NOT the power/current associated the actual tasks we are interested in, but the power/current associated with CPU and INA219 array's I2C communication, and this basically render the monitoring useless.
Because of this, the right way is to monitor current/power with an external processor such as a microcontroller?
Is this the motivation for providing the PMDC connection?
For OMAPL138 it is recommend also looking at the board that seems to be
available from some developers , that will work with the LogicPD EVM,
look at the Wattson Adapter board. The Application software gives to user lots of flexibility to user to measures didderent power parameter. For Details please go to the following link.
For more useful purpose of this board referring the following link
Thanks for recommendation.
Any comments on the discussion above (Why OMAP L138 cannot monitor itself via INA219)?
Your assessment is correct, we used an external uP to monitor the INA219 to not clutter the power readings by OMAPL138 accessing the INA219. Additionally we also wanted to be able to measure and show case power of OMAPL138 when it is lower power modes like Deep Sleep or ARM and DSP Idled/WFI etc, in that situation also you cannot have the current monitoring done by OMAPL138 CPUs
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I see it, thanks for the answer.
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