OSD335x BAS/IND to OSD335x-SM Migration Guide

Published On: July, 20, 2022 By: Eshtaartha Basu

This application note will help facilitate the migration of your product from the OSD335x (OSD3358-512M-BAS or OSD3358-512M-IND) to the OSD335x-SM (OSD3358-512M-BSM, OSD3358-512M-ISM, or OSD3358-1G-ISM), highlighting the differences between the two devices. Please refer to the linked documentation in this application note for more detailed information.

Notice: The information provided within this document is for informational use only. Octavo Systems provides no guarantees or warranty to the information contained.

Differences between the OSD335x and the OSD335x-SM

Understanding the major differences between the OSD335x and the OSD335x-SM is critical before starting the migration work. Even though the OSD335x-SM has fewer pins and a smaller footprint, it provides access to a superset of the AM335x pins and has increased functionality. The below tables list the hardware differences between the OSD335x and the OSD335x-SM:

Migrating from the OSD335x to the OSD335x-SM

The following sections describe the procedure to convert OSD335x based hardware designs to the OSD335x-SM.

Power System Changes

There are some minor differences in the power system. The OSD335x-SM provides access to additional functionality and must be connected properly to function the same as the OSD335x.

PMIC_NRESET

PMIC_NRESET is the reset pin for the TPS65217C PMIC integrated inside the OSD335x family. PMIC_NRESET is not accessible in the OSD335x, but is accessible externally for the OSD335x-SM. The following options are available:

1. Leave pin unconnected (Same Functionality as the OSD335x)
2. Bring pin out to a test point / header for debug visibility (Recommended if PCB area available)

If during the migration, you wish to change the reset configuration of your design, please refer to the documentation in the TPS65217 Datasheet on “nRESET”.

VDDSHVx

The VDDSHVx signals (i.e. VDDSHV1 to VDDSHV6) are inputs to the AM335x which set the I/O voltage level of different I/O pin groups. There are six VDDSHV pins corresponding to each of the six IO voltage domains. These pins are not accessible on the OSD335x, but are accessible on the OSD335x-SM.

In the OSD335x all six VDDSHV pins are connected to the 3.3V output of the TPS65217C LDO4. This voltage rail is named VDDSHV_3P3V in the OSD335x documentation (See Section 7.3.1 of the OSD335x Datasheet). To have the same functionality on the OSD335x-SM, all VDDSHVx pins should be connected to SYS_VDD3_3P3V (i.e. the OSD335x-SM name for the TPS65217C LDO4 output).

For more information, see I/O Voltages section of OSD335x-SM datasheet and I/O Voltage Connections section of OSD335x-SM Layout Guide.

Signal Name Changes

The following table shows the power system pin name changes between the OSD335x and the OSD335x-SM:

EEPROM

The OSD335x-SM incorporates an EEPROM within the SiP for non-volatile storage of product configuration information or other useful identifiers like a unique serial number. You can learn more about it under the EEPROM section of OSD335x-SM datasheet. The following options are available:

1. If you do not have an EEPROM on your existing OSD335x based design, please check the I2C0 bus for any devices at the 7-bit I2C address 0x50.If there are no devices, you can leave the design as is and not utilize the EEPROM provided in OSD335x-SM.If there is a different device at address 0x50, then there are two options:
   1. Change the I2C address of the device, if possible
   2. Move the device to a different I2C bus
2. If you have an EERPOM on your existing OSD335x based design, there are a couple of options:
   1. If the EEPROM is 4KB and at address 0x50 on I2C0, then you must remove the existing EEPROM and use the OSD335x-SM EEPROM. No software changes should be required (may need to update device tree compatibility parameter).
   2. If the EEPROM is not at address 0x50 on I2C0, then evaluate if you want to use the OSD335x-SM EEPROM. If no, then you can leave the design as is. If yes, then software should be updated to comprehend this change.
   3. If the EEPROM is larger than 4KB and at address 0x50 on I2C0, then evaluate if 4KB is enough storage space for the necessary configuration information. If yes, then use the OSD335x-SM EEPROM. If no, then the existing EEPROM should be relocated to a different I2C bus or address and software should be updated to comprehend this change.

Please note that you will need to make adjustments to your software based any changes to the devices on the I2C0 bus.

Additionally, if you plan to use the OSD335x-SM EERPOM, the EEPROM_WP signal should be connected so that it can be grounded to allow the EEPROM to be programmed. By default, EEPROM_WP is pulled high, i.e. the EEPROM is write protected.

IO Pins

VREFN

The Analog Negative Reference Input (VREFN) is the negative reference for Analog-to-Digital (ADC) sub system of the AM335x. In the OSD335x, VREFN is internally connected to VSSA_ADC (Analog Ground). In the OSD335x-SM, VREFN is externally accessible. The following options are available:

1. If you are not using ADC functionality of AM335x, connect this pin to GND.
2. If you are using the ADC functionality of AM335x, you can connect this pin to AGND_ADC to have the same functionality as the OSD335x.

If during the migration, you wish to change the ADC functionality, you can connect VREFN to the required reference voltage and update your software appropriately.

EEPROM_WP

EEPROM_WP is the write protect pin for the internal EEPROM inside the OSD335x-SM. By default, EEPROM_WP is pulled high (i.e. the EEPROM is write protected by default) and must be pulled or driven to a logic low to be programmed. See the above section on the EEPROM for more information. The following options are available:

1. If you are not using the internal EEPROM in the OSD335x-SM, then this pin can be left unconnected.
2. If you are using the internal EEPROM in the OSD335x-SM, this pin should be connected appropriately for your design (e.g. the signal can be brought to a test point, header, or driven by another source) so that the EEPROM can be programed as required by your application.

Signal Name Changes

The following table shows the I/O pin name changes between the OSD335x and the OSD335x-SM:

PMIC_MUX_IN / PMIC_MUX_OUT

The TPS65217C PMIC has an analog multiplexer (MUX) that provides a way to access critical internal PMIC voltages (VBAT, VSYS, VTS, etc.). The output of this analog multiplexer, i.e. PMIC_MUX_OUT, has a voltage range of 1.8V and can be monitored using one of the ADC inputs of the AM335x. Additionally, to not lose one of the ADC inputs of the AM335x, PMIC_MUX_IN can be used as a pass through for any signal that was previously being monitored by the AM335x. To learn more about PMIC’s MUX pins and their usage, see Analog Multiplexer section of TPS65217 Datasheet.

In the OSD335x, these pins are not available and have been left unconnected within the SiP. The following options are available:

1. If you do not want to add this functionality, both pins can be left unconnected.
2. If you would like to add this functionality, connect PMIC_MUX_OUT to one of the AM335x ADC inputs. If all ADC inputs are currently in use, then one input can be daisy chained using PMIC_MUX_IN. Please see Sheet 2 of the OSD3358-SM-RED schematics for more information.

Please note that the voltage being monitored on PMIC_MUX_IN must be less than or equal to 1.8V.

Internal Passive Component Configuration Differences

Besides major components like the CPU, high-speed memory, and power management, the OSD335x Family of System-in-Package devices integrate a wide range of passive components like pull-up / pull-down resistors, capacitors, inductors, etc. The following tables shows the differences in passive components between the OSD335x and the OSD335x-SM:

Package and Ball Mapping Differences

The OSD335x-SM is about 40% smaller than the OSD335x while retaining the same BGA pitch and overall functionality as indicated in Table 1. However, the BGA ball mapping has been modified to facilitate a low layer count PCB design. You can learn more about pin/ball mapping between the OSD335x and the OSD335x-SM through the OSD335x Pin Mapping Guide. Further, the OSD335x-SM Layout Guide will provide important guidelines on PCB layout strategy when using the OSD335x-SM.

Software Compatibility

Depending on the design migration choices made in the previous sections, the new OSD335x-SM based design should be able to run the same software images as the existing OSD335x based design. Any alterations to the software are only needed if additional functionality is added or if any configuration around the EEPROM has changed. Please take a look at the EEPROM during Boot application note to understand what role the EEPROM plays in a software image.

Other Considerations

We strongly urge customers to read the following application notes and documentation when migrating between the OSD335x and the OSD335x-SM. These capture design considerations that might not have been comprehended during the existing design and you may want to take this opportunity to address some of them:

• Powering the OSD335x family with LiPo and Li-Ion Batteries
• Designing Robust TPS65217 Systems for VIN Brownout
• OSD335x-SM Thermal Guide

Conclusion

Using this application note as a guideline, you should be able to easily migrate from the OSD335x to the OSD335x-SM.  If you run into any problems or have any questions please contact us directly through our forums or our sales team here.

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