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ISOUSB211: How to set EQxx pins

Part Number: ISOUSB211

Hello TI experts,

My customer considers ISOUSB211 for their new product for USB 2.0 high speed communication.

they just want to isolate function, and don't need noting more, so i suggested the diagram in figure 8.6 in datasheet.

I think it would be a best to change VBUS2 to 5V, cause both sides are USB 5V supply. please give me your opinion about this.

and I cannot find the way to set EQxx pins on the device. is it okay to set exactly same with figure 8.6? (EQ10=GND, EQ11=float, EQ20=3.3V, EQ21=GND)

or is there other options which depends on the situation?

Please check these issues above. Thanks.

Best regards,

Chase 

  • Hi Chase,

    Thank you for reaching out to us!

    The example shows 3.3V on VBUS2 because the MCU needs a 3.3V supply.

    ISOUSB211 VBUS can support 3.3V and 5V, and it is fine to set the VBUS2 to 5V.

    If 3.3V is available in the system, then it is preferred for lower power dissipation.

    If VBUS2 is connected to 5V, V3P3V2 should be left floating and only connects to a bypass capacitor since it will be driven by ISOUSB211 internal LDO.

    To get optimal signal integrity, please refer to this application note to select pre-emphasis and equalizer settings

    based on the trace loss. In general,  EQxx, EQxx pins can be connected to respective GNDx pins for short trace where equalization is not needed..

    Regards,

    Alfred

  • Dear Alfred,

    Thank you for your reply.

    I attach the schematic. could you review it?

    the concerns are ;

    1. Can I use both 5V and 3.3V for VCC2 pin?

    2. is it okay to use 3.3V for CDPENZ1 and CDPENZ2 pins? (we do not use BC 1.2 protocol.)

    Best regards,

    Chase

  • Hi Chase,

    Please see below for my feedback.

    1. Since VBUS is set to 5V, the internal LDO will generate 3.3V for the V3P3V. Hence, no external 3.3V supply is needed. Please keep the capacitor.

    2. It is fine to use either 5V or 3.3V for VCC2 pin. It can take 2.35V to 5.5V as specified in the datasheet.

    3.I recommend not using VBUS1 for VCC1. This is because VBUS1 is provided by the USB host and it might be used to generate isolated power supply for VBUS2. This might affect the power integrity when all components are drawing current at the same time. On top of that, since 3.3V_UD is available, I recommend using it for VCC1.

    4. It is recommend using 3.3V for CDPENZ1 and CDPENZ2 pins. The absolute maximum ratings for these pins are -0.3V to V3P3V+3.3V. 

    5. There are no values for the capacitors in the schematic, please follow the recommendation from the datasheet for their values.

    Regards,

    Alfred

  • Hi Chase,

    To add to Alfred's response, it will be good to know which supplies are externally available on the board on each side.

    1. Is side 1 connected to the USB connector and side 2 connected to the MCU/Controller?

    2. If so, VBUS1 will be available from the USB connector and I would think 3.3V_UD is not separately available externally and has to be generated internally by ISOUSB211. In this case VCC1 should be connected to VBUS1 directly.  (If 3.3V_UD is available externally from a different power source or regulator, then connecting VCC1 to 3.3V_UD is preferred).

    2.  On side 2, is an external 3.3V_DD already available in the system (eg. to power the MCU)? If this is available, and can supply >120mA, then it is preferred to connect VBUS2, V3p3V2 and VCC2 to 3.3V_DD. If 3.3V_DD is not available externally, connect VBUS2 to +5V_ISO, leave V3P3V2 unconnected except for decoupling capacitors, and connect VCC2 to +5V_ISO. 

    Rgds,

    Anant

  • Dear Anant,

    Thank you for your reply.

    Actually both sides of ISOUSB211 would be use 5V supply. in this case i think that it would be good to follow Alfred's advice. what do you think about it?

    1. side 2 also connected USB controller/connector (5V system)

    2. Yes, 3.3V supply is in the system anyway.

    Best regards,

    Chase

  • Chase,

    Thanks for your response. Yes, please follow Alfred's advice. That is, if 3.3V is available externally on both sides, please connect VCC1 and VCC2 to these supplies. Connect VBUS1 and VBUS2 to the USB_5V and +5V_ISO repsectively, and connect only capacitors to the 3P3V pins on ISOUSB211, since 3P3V pins will be driven by ISOUSB211 internal LDOs. 

    Rgds,

    Anant