TMS320F28388D: VSSOSC, ERRORSTS and VDD pin issue in F28388

Hi,

1. The ERRORSTS pin. The datasheet said this signal requires an external pulldown, but the controlCARD SCH shows the pin is left unconnected. I see in F2837x datasheet the ERRORSTS have internal pulldown, so no such external pulldown is required, is there any change for F2838x? 

It is same as F2837x device. Please refer "Table 4-6. Pins With Internal Pullup and Pulldown" which mention that it has internal pull down. If this signal is not used in application then this can be left unconnected (refer "Table 4-12. Connections for Unused Pins") but if this pin is used in application then user should use external pull down to have this pin pull low by default (in-active state). We'll plan to fix it on controlCard in next revision.

2. The VSSOSC pin. Datasheet said when using an external crystal do not connect this pin to the board ground, instead, connect it to the ground reference of the external crystal oscillator circuit. I see F2837x ref design do as this requirement, but in F28388 controlCARD, the VSSOSC connect direct to GND. Do we need to connect the VSSOSC and crystal ground together to the board GND?

Yes, our recommendation is to connect the VSSOSC to the ground reference of the external crystal oscillator circuit though otherwise also it would work but may have some jitter. Again, we'll review the controlCard and if needed, fix it in next rev.

3. VDD pin. Datasheet said a single 56Ω resistor (10% tolerance) should be placed between between VDD and VSS, this resistor provides a load to consume an internal VDD3VFL to VDD current source and avoid VDD voltage rising during low power device condition. But in controlCARD, we cannot see this resistor. Do we need this resistor?

Yes, this resistor is needed. Again, we'll review the controlCard and fix it in next rev.

Thank you so much for your feedback. Really appreciate it.

Regards,

Vivek Singh

All,

Vivek Singh said:

2. The VSSOSC pin. Datasheet said when using an external crystal do not connect this pin to the board ground, instead, connect it to the ground reference of the external crystal oscillator circuit. I see F2837x ref design do as this requirement, but in F28388 controlCARD, the VSSOSC connect direct to GND. Do we need to connect the VSSOSC and crystal ground together to the board GND?

Yes, our recommendation is to connect the VSSOSC to the ground reference of the external crystal oscillator circuit though otherwise also it would work but may have some jitter. Again, we'll review the controlCard and if needed, fix it in next rev.

This is not an error. A single pin oscillator, not a crystal, is used on this controlCARD. Therefore, these pins should be connected to the board ground. If you use a crystal these are intended to act as a kelvin ground.

Regards,
Cody