Published On: October, 24, 2017 By: Neeraj Dantu | Updated: September 10, 2020 by Greg Sheridan
This application note is intended for engineers to understand the power management system of OSD335x-SM, the the AM335x System in Package. It is also intended to aid in power budgeting for systems using the OSD335x-SM. It provides an overview of the power management system inside the OSD335x-SM and runs through an example application power budgeting procedure.
A PDF of this Application Note can be found here.
The OSD335x-SM, the AM335x System in Package contains the TPS65217C Power Management Integrated Circuit(PMIC) and the TL5209 Low Drop-Out(LDO) regulator as well as all associated passives for power management. The PMIC is responsible for powering the AM335x processor and the DDR3 as well as provide output power for other system needs. It provides configurable power-up and power-down sequencing required by the processor and monitors the processor input voltage levels. The PMIC contains 3 DC-DC power converters, 2 LDOs and 2 load switches that can be configured as LDOs that can be used as power supplies. It can be powered by any combination of a 5V AC adapter, USB port, or Single Cell Li-Ion battery. Figure 1 shows the power system of OSD335x-SM including connections between the PMIC and various power domains of the processor.
Table 1 shows the voltage output levels of each of the voltage sources. Each of the output voltages can be changed dynamically using I2C commands when the PMIC is in active mode.
TPS65217C Voltage Source | OSD335x Voltage rail | Voltage (V) |
DCDC1 | VDDS_DDR | 1.5 |
DCDC2 | VDD_MPU | 1.1 |
DCDC3 | VDD_CORE | 1.1 |
LDO1 | SYS_RTC_1P8V | 1.8 |
LDO2 | SYS_VDD2_3P3V | 3.3 |
LDO3 | SYS_VDD_1P8V | 1.8 |
LDO4 | SYS_VDD3_3P3V | 3.3 |
The power-up sequence of the processor is shown below in Figure 2, with the numbers in red representing the order in which they come up, and the main power up events are described below:
This power up sequence and delays between each step of the sequence are already programmed into the PMIC inside the OSD335x so you don’t need to worry about it. The power-down sequence follows the reverse order of the power-up sequence.
The PMIC also performs some tertiary functions. A few of the key functions are listed below. For a complete explanation of all the functions provided by the TPS65217C PMIC refer to the datasheet.
Now that the function and of the PMIC and its relationship with the processor is clear, the process of power budgeting discussed below can be better understood.
It is a good practice to make a power budget for your product/design at the beginning of the project. Good power budgeting contributes to circuit robustness, increased product life and reduced cost of the product. A power budget should include the availability of power, operating temperature, amount of data collected, communication, and operation modes of the processor.
The first step in making a power budget is to have a power diagram that shows all the power paths of the system. Start with all the available power sources for the system. For OSD335x, this would include power rails that are described in the datasheet as output power supplies. There are six output power rails on the OSD335x including a 2.75V – 5.5 output (SYS_VOUT), three 3.3V outputs (SYS_VDD1_3P3V, SYS_VDD2_3P3V and SYS_VDD3_3P3V) and three 1.8V outputs (SYS_RTC_1P8V, SYS_VDD_1P8V and SYS_ADC_1P8V).
Next, put in the power consuming components and connect them to the appropriate power rail. The connection should be based on the voltage input level for the component. Current supply capacities of the power rails and ease of use can also be factors for choosing the best power rail for the component. In order to understand this process, let us use the OSD3358-SM-RED Platform. The board provides access to many peripherals of OSD335x-SM and has a number of external components powered by the OSD335x-SM. Figure 3 shows the completed power system diagram for the design. It shows most of the components that draw at least a nominal amount of power.
The diagram not only shows the power rail for a particular component but also lists all the components that are being powered by a power rail. In addition to helping with the power budgeting, this allows you to identify power issues early in the design process and make necessary adjustments.
The next step involves making a power budget to estimate power consumption of each component and thus the total power consumption of the board.
There are several challenges involved in accurately estimating the power consumption of each component. For example, it is difficult to estimate how much current, the AM3358 processor and the DDR Memory draw since that is highly application specific. Power consumption will also depend on the presence of a USB device or a Micro SD card. To account for all situations, we can start out by assuming maximum power consumption for all the components. Table 2 shows the power budget table for OSD3358-SM-RED assuming maximum power consumption for each component.
Part Name | Part Number | Max Current (mA) | Supply voltage | rail Voltage (V) | Max Power (mW) |
AM3358 | U1 | 307.8 | Internal | 5 | 1539 |
TPS65217C | U1 | < 1 | Internal | 5 | <5 |
TL5209 | U1 | 25 | Internal | 5 | 125 |
DDR RAM | U1 | 339 | Internal | 1.5 | 508.5 |
TPS2051 | U15 | < 1 | SYS_VOUT | 5 | < 5 |
USB Connectors | X4, X5 | < 500 | SYS_VOUT | 5 | < 2500 |
24LC32AT | U1 | 3 | Internal | 3.3 | 15 |
APX811 | U4 | 20 | SYS_VDD1_3P3V | 3.3 | 66 |
USB2534-1080AEN | U8 | 80 | SYS_VDD1_3P3V | 3.3 | 264 |
ASDMB-12.000MHZ | Y3 | 15 | SYS_VDD1_3P3V | 3.3 | 49.5 |
ASDMB-24.576MHz | Y5 | 15 | SYS_VDD1_3P3V | 3.3 | 75 |
DM3BT-DSF-PEJS | X3 | 200 | SYS_VDD1_3P3V | 3.3 | 1000 |
SDIN8DE2-16G | U7 | 80 | SYS_VDD1_3P3V | 3.3 | 400 |
SN74LVC1G07DCK | U3 | 24 | SYS_VDD1_3P3V | 3.3 | 120 |
SN74LVC2G241DCUR | U6 | 24 | SYS_VDD1_3P3V | 3.3 | 120 |
AR8035-AL1A | U9 | 128 | SYS_VDD1_3P3V | 3.3 | 422.4 |
TDA19988BHN | U10 | 77 | SYS_VDD_1P8V | 1.8 | 385 |
MPU-9250 | U23 | 3.7 | SYS_VDD1_3P3V | 3.3 | 12.21 |
TMP468 | U17 | 10 | SYS_VDD1_3P3V | 3.3 | 33 |
BMP280 | U22 | 1 | SYS_VDD1_3P3V | 3.3 | 3.3 |
S25FL127S | U21 | 50 | SYS_VDD1_3P3V | 3.3 | 165 |
AT97SC3205T | U16 | 25 | SYS_VDD1_3p3V | 3.3 | 82.5 |
Total | ~7895 |
**SDIN8DE2-16G datasheet is not available on the internet. So, an equivalent datasheet was used to determine current consumption
**AT97SC3205T datasheet does not specify current consumption. So, an equivalent datasheet was used
Maximum current consumption values can be found from the component datasheets for most devices. However, there is no deterministic way of calculating the current consumed by the AM335x and the DDR3 as they are highly application specific. The next two sections will explore how to use tools provided by TI and Micron to estimate the max power used by the AM335x and DDR.
Texas Instruments provides access to a power estimation tool that can calculate the internal power consumption of AM3358 including individual power domains of the processor. The process involves filling out a spreadsheet and submitting it to a webpage. The detailed procedure is described in the wiki page “AM335x Power Estimation Tool”. A short overview of the process with notes on usage with the OSD335x is given below. The inputs shown in the screenshots were put in to calculate the maximum power consumption of AM335x.
The worst-case current consumption can be obtained by maximizing the inputs to the spreadsheet. Other relevant resources that help estimation of AM335x power usage are given below:
Like the AM335x spreadsheet, Micron provides a spreadsheet to estimate DDR3L power consumption. Though the exact power consumption depends on the part number of the memory, the spreadsheet serves as a ball park estimation tool. A brief use case of the spreadsheet is shown below.
From the results, the worst case current consumption was calculated to be 339 mA with 1.5 V input.
Some of the current consumption numbers are highly unrealistic. No system uses all the processor cores and peripherals at a 100% utilization. The DDR current consumption is calculated assuming 100% of the time is spent writing to the memory with lowest ACT command interval. So, while it is safe to use these figures to assume worst case load, the system would be vastly over-designed. It is better to build a second power budget table with typical current consumptions and a more application specific scenario while keeping the previous version in mind.
Part Name | Part Number | Max Current (mA) | Supply voltage | rail Voltage (V) | Max Power (mW) |
AM3358 | U1 | 186.4 | Internal | 5 | 932 |
TPS65217C | U1 | < 1 | Internal | 5 | <5 |
TL5209 | U1 | 8 | Internal | 5 | 125 |
DDR RAM | U1 | 206 | Internal | 1.5 | 309 |
TPS2051 | U8 | < 1 | SYS_VOUT | 5 | < 5 |
USB2534-1080AEN | U8 | 45 | SYS_VDD1_3P3V | 3.3 | 148.5 |
USB Connector | X4, X5 | < 500 | SYS_VOUT | 5 | < 2500 |
24LC32AT | U1 | 1 | Intenal | 3.3 | 5 |
DM3BT-DSF-PEJS | X3 | 100 | SYS_VDD1_3P3V | 3.3 | 500 |
SDIN8DE2-16G | U7 | 80 | SYS_VDD1_3P3V | 3.3 | 400 |
SN74LVC1G07DCK | U3 | 16 | SYS_VDD1_3P3V | 3.3 | 80 |
SN74LVC2G241DCUR | U6 | 16 | SYS_VDD1_3P3V | 3.3 | 80 |
AR8035-AL1A | U9 | 33.9 | SYS_VDD1_3P3V | 3.3 | 111.8 |
MPU-9250 | U23 | 3.2 | SYS_VDD1_3P3V | 3.3 | 10.6 |
S25FL127S | U21 | 24 | SYS_VDD1_3P3V | 3.3 | 79.2 |
Total | 5291 |
Table 3 shows an application specific power budget table in which the processor is operated in conditions described in Table 4. All the other peripherals and features are assumed to be disabled in this scenario and ‘typical’ current consumption values from component datasheets are used rather than ‘maximum’ current consumption values.
Feature/peripheral | Utilization (%) |
Cortex A8 | 70 |
Cortex A8 NEON | 70 |
CORE OPP | OPP100 |
MPU OPP | NITRO |
MPU Frequency | 1 GHz |
EMIF | 70 |
OCMC RAM | 70 |
USB | 70 |
Ethernet MAC | 70 |
MMC1 | 70 |
Miscellaneous Peripherals | 50 |
ADC | OFF |
Note that the utilization percentages of each feature/peripheral of the AM335x processor are still high. This is done to leave ourselves some head room if the board runs into an unexpected scenario. Similarly, the RAM usage is also safely assumed to have a 20% page hit rate, a 10ns interval between ACT commands, 30% of the time spent reading from RAM and 30% of the time writing to the RAM. Also, observe that several components of the board are not in use and so are left out of Table 3.
Thus, we have an extreme scenario and an application specific application scenario for our power budget. The usage scenarios should now be stacked up to the supply capacities of output power rails of OSD335x that we outlined in step 1 to make sure everything checks out. Given below are the conditions that need to be verified and corresponding usage on the OSD3358 SBC reference design from the datasheet:
Condition | Limitation | Extreme | Application |
VIN_AC input current | 2.0 A | 1.58 A | 1.05 A |
VIN_USB input current* (See below) | 1.3 A | 1.58 A | 1.05 A |
VIN_BAT input current (5V battery) | 2.0 A | 1.58 A | 1.05 A |
SYS_VOUT output current | 500 mA | 500mA | 500mA |
SYS_VDD1_3P3V (VDD_3V3B) output current | 500 mA | 752.7mA | 318.1mA |
SYS_VDD2_3P3V (VDD_3V3AUX) output current | 150 mA | – | – |
SYS_RTC_1P8V (VDD_RTC) output current | 100 mA | – | – |
SYS_VDD_1P8V (VDD_1V8) output current | 250 mA | 77mA | – |
SYS_ADC_1P8V (VDD_ADC) output current | 25 mA | – | – |
From Table 5, although SYS_VOUT current consumption looks like it touches the maximum recommended output current, it is highly unlikely to have a USB device that would draw 500mA in the application. The extreme condition input current exceeds the USB input current limit. But, there are alternative input power paths(AC and BAT) that can mitigate this issue even though the scenario will never occur. The load current for the SYS_VDD1_3P3V voltage rail also exceeds the output current limit in the extreme scenario. So, that voltage rail may fail if components begin to draw maximum specified currents. But, the application specific current draws taken into account while designing the board are significantly lower than the limits. More weight was placed on the application scenario vs theoretical maximum current consumptions during the design. As can be seen from Table 5, there is enough room for the board to be able to deal with most unexpected situations of high current consumption in an application scenario.
While this board presents no problems in power analysis for an application, there might be situations where the current draws are close or exceed the power rail limits in a design. In this case, alternative approaches to design can solve the problem. The OSD335x has multiple rails of 1.8V and 3.3V. So, spreading out the total current consumption of all the parts among the available power rails can be a first approach. If that does not resolve the issue, alternative power paths need to be designed. This might involve using more regulators and/or using AC/BAT input instead of the current limiting USB input.
This document discussed the power management system of OSD335x-SM and presented a power budgeting procedure that helps in efficient product design. Most of the above discussion centers around hardware. However, software also plays an important role in power management. Some aspects of software power management and a case study on its advantages are presented in the application note: Software Power Management with the OSD335x Family.
Octavo Systems LLC all rights reserved
OCTAVO is registered in the U.S. Patent and Trademark Office. OSD, C-SiP, and the Octavo Logo are trademarks of Octavo Systems LLC.
"*" indicates required fields
"*" indicates required fields
"*" indicates required fields
"*" indicates required fields