ISOUSB211-Q1: Design Review

Hi Krishna,

The schematic mostly looks good with just one major issue.

1. From the ISOUSB211 functional block diagram in datasheet (also copied below), you can see that there are 4 LDOs inside device, 2 on each side of isolation barrier.
2. VBUS1 is input supply, V3P3V1 is the 3.3V output generated by the LDO. Similarly, VCC1 is input supply, V1P8V1 is the 1.8V output generated by the LDO.
3. Therefore, you have to apply input supply to both VBUS1 and VCC1 for the respective output voltages to be generated.
4. In your schematic, VCC1 is not supplied with any voltage. Therefore, I recommend you to connect it to either V3P3V1 (for 3.3V) or VBUS1 (for 5V) so that the VCC1 input receives supply voltage.
5. This does mean there is going to be a lot of power dissipation in the LDOs inside device. If you do not require wide temperature range operation, then the thermals can be manageable. But if you need the solution to support a wider operating temperature range, then you would have use external LDOs so that the internal heat is now dissipated in external LDOs, thereby, cooling ISOUSB211.
6. To use external supply rails, simply short the input and output pins of internal LDO and connect them both to external supply rail. This bypasses internal LDOs. For example, short VCC1 and V1P8V1 and connect them to external 1.8V.
7. This external 1.8V can be generated using an external LDO drawing power from 5V of VBUS.
8. Follow the same approach to address issue with VCC2 and V1P8V2.

Let us know if anything is not clear, thanks.

Regards,
Koteshwar Rao

Hi Krishna,

The current consumption numbers are [provided in the datasheet itself in Electrical Characteristics:

You can select the max numbers based on the mode of operation in your application.

Also to expand on what Koteshwar mentioned above, I recommend you go through the following section in datasheet as well:

1.  7.3.1 Power Supply Options
2. 8.1 Typical Application and it's subsections along with following figures
   1. Figure 8-1. Isolated Host or Hub With ISOUSB211
   2. Isolated Self-Powered Peripheral With ISOUSB211
   3. Figure 8-3. Isolated Bus-Powered Peripheral Using ISOUSB211

Let us know if you still have any questions after going through the references shared above.

Regards
Varun

Hi Krishna,

Thanks for confirming that you got what you needed.

Also, the datasheet sections mentioned above is what Koteshwar elaborated on -> so whichever explanation suits better, you can consider that for your reference.

Regards
Varun

Hi Krishna,

Yes, this is good to go.

Just make sure to have the J1, J2, J11 and J12 shorted all the time during device's operation.

Regards
Varun