How to measure power consumption in i.MX applications
This post is intended to show a method to determine the power consumption in i.MX boards and to share some relevant information about this topic, such as operating points of each SoC.
Operating points
The i.MX processors have several internal power supply domains. As an example, the connectivity of the supply rails and the distribution of the internal power domains for the i.MX 6Dual/6Quad SoC can be seen in the image below1:
The power measurements are taken mainly for the following power supply domains, which consume the majority of the internal power of the processor:
- VDDARM_IN: ARM platform’s supply;
- VDDSOC_IN: peripheral supply;
- VDDHIGH_IN: source of PLLs, DDR pre-drivers, PHYs, and some other circuitries.
Each power rail has a current sense resistor that allows the current to be measured. These resistors can be found by analyzing the boards schematics. Each sense resistor is usually placed between the PMIC output and the corresponding VDD rail, in the i.MX6Q Sabre-SD case it is the R27 resistor for the ARM current and the R21 resistor for SOC current.
To determine the power consumed on each power rail it is necessary to calculate the current that flows through these sense resistors and then multiply it by the power rail’s voltage.
The probe points for some of the NXP’s i.MX6x and i.MX7x boards can be found at the table below2:
| Boards | ARM Current | ARMCAP Voltage | SOC Current | SOCCAP Voltage | VDDHIGH Current | VDDHIGH Voltage |
|---|---|---|---|---|---|---|
| i.MX6Q Sabre-SD | R27 | C679 C669 | R21 | C682 C667 | SH17 | C654 |
| i.MX6QP Sabre-SD | SH5 | C679 C669 | R27 | C682 C667 | SH17 | C654 |
| i.MX6QP Sabre-AI | SH502 | C620 C653 | SH4 | C691 | - | C57 |
| i.MX6SL EVK | SH2 | C75 | SH3 | C390 C79 | SH4 | C405 |
| i.MX6SX Sabre-SD | SH10 (lumped) | C243 C242 | SH10 (lumped) | C261 C260 | R375 | C265 |
| i.MX6UL EVK | R729 (lumped) | C106 | R729 (lumped) | C116 | R730 | C120 |
| i.MX7D Sabre-SD | R20 | - | R24 | - | - | - |
Sensor board
The Hi-Lo Current Sensor Combo Board is a component that eases the process of measuring power consumption. This board is intended to facilitate the current sensing and can measure currents up to 3A.
The sensor board enables the measurement of the voltage drop over the sense resistor and with this information it is possible to calculate the current flowing through the resistor using Ohm’s Law:
I_rail = V_drop / R_sense
This board also allows to measure the power supply rail voltage. With these values, it is possible to calculate the power consumption on each power rail.
P_rail = V_rail * I_rail
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Picture from the i.MX 6Dual/Quad Power Consumption Measurement App Note. ↩
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Information from the Measuring Current in i.MX Applications App Note. ↩