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AM623: PMIC and supply rails

FRZE
Intellectual 2225 points

Part Number: AM623
Other Parts Discussed in Thread: SYSCONFIG

My customer has a couple of question on the PMIC and the supply rails.

1. Power supply of MMC1 / SDIO interface (VDDSHV5_MMC1): Can it be connected to DVDD1V8 (VDDSHVy) in our use case?

I assume not but would like to get confirmation.

2. Can VDDA_3P3_USB be connected to VDD_3V3 or USB_VBUS (=3V3)?

I assume not but would like to get confirmation.

3. The PMIC (TPS6521902) already has PowerGood detection. So what would be the advantage of using power supply monitoring by CPU? 

In their case only the 3.3V is directly supplied and not going through the PMIC therefore I guess that is the only one they would monitor using VMON

4. In SysConfig only 1 voltage (1.8 or 3.3V) for both of them can be selected for signals PMIC_LPM_EN0 (VDDSHV_CANUART) and WKUP_CLKOUT0 (VDDSHV_MCU). Are VDDSHV_CANUART and VDDSHV_MCU connected? 

5. USB will only be used with 3V3 --> Do we have to connect VDDA_1P8_USB nevertheless? --> to 1V8 or 3V3?

In SysConfig there is only one voltage to be selected (currently 3V3 selected). According to the e2e and if USB operation is desired, all related signals/rails must be connected as per the datasheet regardless of interface type (USB1.1/USB2.0). Please see Table 6-74 and Section 7.4 of the device datasheet for more information. Can you please confirm if they need to connect to 1.8V or 3.3V?

6. We will supply USB_VBUS (=3V3) externally --> any recommendations on this? Or what about connect USB VBUS to VDD_3V3?

So they will not implement the circuit as described in datasheet 9.2.3. (They know: not being compatible to USB Spec.); The range is 0...3,465 V. BSH is owning the USB_VBUS supply and are supplying it externally with 3.3V. So do they still need the Zener diode to be used to support up to 20V.

BR,

Frank

  • 0
    TI__Guru 64655 points
    1. VDDSHV5 is the IO supply for IOs associated with MMC1. This power rail can be powered with a fixed 1.8V supply, a fixed 3.3V supply, or a supply that begins operation at 3.3V and changes to 1.8V as required when connecting MMC1 to connected to an UHS-I SD Card that begins operating at 3.3V and later changes to 1.8V. VDDSHV5 should be sequenced with all other VDDSHV power rails operating at 1.8V if connected to a fixed 1.8V supply. VDDSHV5 should be sequenced with all other VDDSHV power rails operating at 3.3V if connected to a fixed 3.3V supply. There is no restrictions on the sequencing of VDDSHV5 when the MMC1 IOs are connected to a SD Card and power from a dynamic supply since it must turn on or off at the same time as the attached SD Card 3.3V supply.
    2. I do not understand the USB use case, so it is hard to answer some of your USB questions. The VDDA_3P3_USB and VDDA_1P8_USB power rails are used to power different portions of the USB PHY. Both power rails supply power to analog circuits in the PHY and both must be present if either USB0 or USB1 ports are being used. The USB VBUS signal is defined by the USB specification to 5V, so it is not clear how you plan to use USB with a 3.3V VBUS. Are they planning to operate the AM62x as a USB host or USB device?
    3. It is not clear if you are asking about the VMON_1P8_SOC, VMON_3P3_SOC, or VMON_VSYS inputs. I’m not familiar with the use cases for VMON_1P8_SOC and VMON_3P3_SOC, so not able to comment on the expected use case. I suspect these inputs were required to meet some Functional Safety requirement, so they were included in the entire family of AM62x devices. The VMON_VSYS can be used to monitor the power supply sourcing the entire system, before the PMIC, to provide an early detection warning for software.
    4. I will need to get someone else to answer your SysConfig tool question about it not allowing you to select different voltages for VDDSHV_CANUART and VDDSHV_MCU.
    5. This question was answered above in #2.
    6. The VBUS voltage divider / clamp circuit shown in 9.2.23 is required to reduce the VBUS signal to a level that is acceptable for the AM62x VBUS input. VBUS is not expected to be greater than 5.5V unless the system negotiates a higher voltage on VBUS.  The Zener clamp portion of the circuit was included to protect the device if VBUS was accidently connected to a VBUS power source greater than 5.5V. The clamp function could be removed and the resistor values changed to apply the same voltage to the AM62x VBUS input if VBUS is limited to 3.3V. However, I recommend keeping the bias current through the voltage divider the same with 3.3V as the recommended implementation when 5V is applied.

    Regards,
    Paul

  • 0 in reply to peaves
    TI__Intellectual 2225 points

    Let me clarify a little more:

    2: They would like to have dual rile (host and device). They will go in with 5V and use the resistor divider like described in TRM 9.2.. Only USB2.0  is used and so power delivery therefore zener diode not required. The will provide 3.3V to USB_VBUS datasheet 9.2.3.is showing a maximum  voltage of 3,465 V. What is the minimum voltage (threshold) accepted?  

    Is there an option to directly connect (or perhaps pull-up) to SoC_DVDD3V3 (Ref design) 3.3V?

    BR,

    Frank

  • 0
    TI__Mastermind 30715 points
    FRZE said:
    In SysConfig only 1 voltage (1.8 or 3.3V) for both of them can be selected for signals PMIC_LPM_EN0 (VDDSHV_CANUART) and WKUP_CLKOUT0 (VDDSHV_MCU). Are VDDSHV_CANUART and VDDSHV_MCU connected? 

    Frank

    The datasheet is the authority on this, they are separate rails. 

    The tool has grouped them logically, hence the voltage conflict earing if the power rails are set to different voltages. 

    I'll file a ticket to see if this can be improved. 

    --Paul M

  • 0 in reply to PaulM
    TI__Intellectual 2225 points

    Thanks Paul.

    No2 is still not 100% clear to me.: They would like to have dual role (host and device). They will go in with 5V and use the resistor divider like described in TRM 9.2.. Only USB2.0  is used and so power delivery therefore zener diode not required. The will provide 3.3V to USB_VBUS datasheet 9.2.3.is showing a maximum  voltage of 3,465 V. What is the minimum voltage (threshold) accepted?  

    Is there an option to directly connect (or perhaps pull-up) to SoC_DVDD3V3 (Ref design) 3.3V?

    Best regards,

    Frank

  • 0 in reply to FRZE
    TI__Guru 64655 points

    Frank,

    Your initial question related to the USB VBUS voltage divider / clamp circuit made it sound like the customer was connecting the USB port in question to an on-board USB function that only required a 3.3V VBUS. Your latest description seems to indicate the customer is planning to connect the USB port to a USB connector that is configured to operate as a dual-role device, where it can operate as a USB Host or a USB device. If that is the case, the customer must implement the voltage divider / clamp circuit as shown in the section 9.2.3. No exception.

    The PHY threshold levels are set based on the voltage divider ratio when the USB voltage potential is operating as defined in the USB specification. Therefore, the voltage divider needs to be implemented as shown in the datasheet for VBUS voltage levels to be compatible with the PHY thresholds. The Zener clamp in this circuit protects the AM62x VBUS input from an over-voltage condition. This can occur as discussed before when a power delivery device accidently applies the wrong voltage, but it can also occur when a USB cable is suddenly disconnected under load and the back-EMF from the cable inductance sources a high voltage back into the USB port. The AM62x VBUS input is connected to sensitive analog circuits implemented in an advanced process node and the Zener clamp protects these circuits from these over-voltage conditions.

    Regards,
    Paul

  • 0 in reply to peaves
    TI__Intellectual 2225 points

    Thanks for your detailed answer. In our use case we can ensure, that no Power delivery device will be connected and always only 5V supplied to the voltage resistor ("VBUS signal" in Figure 9-4). Do we have to change the voltage dividor for that use case? What are the PHY threshold voltages, we have to provide through the voltage dividor? Also we would need to specify the minimum voltage for this 5V input supply.
    Or what about connecting VBUS_USB constantly to VDD_3V3 ("DVDD3V3" in EV-Board Design PROC142E1) through a 10k Pull-up resistor? What is the maximum current consumption of USB_VBUS? Would this affect the ability to act as a USB host?

    BR,

    Frank

  • 0 in reply to FRZE
    TI__Guru 64655 points

    The voltage divider / clamp circuit design was provided by the USB PHY design team, and they set the PHY thresholds to operate within the VBUS limits defined in the USB specification when using this circuit. Therefore, the VBUS signal you connect to the voltage divider is expected to operate within the limits defined by the USB specification.

    Pulling up VBUS to an on-board 3.3V supply is not an expected use case defined by the USB specification. A system is expected to source 5V with a min current of 500ma to VBUS via a current limited load switch when operating as a USB host, or the attached host will provide the appropriate 5V VBUS when operating as a USB device.

    You mention your product would support dual-role operation. If so, VBUS would need to be connected to the 5V load switch, a Micro-AB connector, and the AM62x VBUS input via the voltage divider / clamp circuit. Therefore, I do not understand the use case where VBUS would be pulled to 3.3V.

    The design team did not define the PHY input thresholds or input current because they expected customers to use the voltage divider / clamp circuit as designed in a system operating as defined by the USB specification. 

    Regards,
    Paul