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TMS320C6746 Powering

Scott Burton
Prodigy 230 points
Other Parts Discussed in Thread: TMS320C6746, TMS320C6748, TPS65070

Hi Forum,

I'm confused by some conflicts within and between the TMS320C6746 datasheet and various TMS320C6746 powering application notes (e.g. SLVA341A, SLVA342A, SLVA343A, SLVA371A, SLVA371A ). I hope you can help!

In this application we're NOT using the USB function on the TMS320C6746.

1/ The datasheet (6.3.1)  indicates that, if RTC is not used then RTC_CVDD should be connected to CVDD (dynamic 1.2V). Could you please confirm this is correct?

2/ The TMS320C6748 datasheet (5.2) indicates that the static rail supplying RVDD is required to be 1.3V for the 456MHz version of the DSP and 1.2V for the 375MHz version. The datasheet also groups RVDD with PLL0_VDDA, PLL1_VDDA and USB_CVDD (6.3.1), which are 1.2V rated. This being the case, is it acceptable with the 456MHz version for these other DSP voltage rails to also operate at 1.3V, or does RVDD need to be supplied from its own separate power rail?

3/ The TMS320C6746 power spreadsheet indicates that the RVDD and the static 1.2V power requirements are only 4mW and 13mW respectively at a 456MHz clock frequency. Is such a low level in line with expectations?

4/ The datasheet (6.3.1) indicates that all static 1.8V I/O supplies (e.g. DVDD18, DDR_DVDD18) can be powered up at the same time as any of the LVCMOS I/O supply groups used at 1.8V (e.g. DVDD3318_A). Could you please confirm this is correct, and that the same rail can be used for both groups?

5/ The TPS65070 PMIC Application Report SLVA371A further states that if DVDD3318n is 3.3V powered then static 1.2V (LDO2) and static 1.8V (LDO1) can ramp up together. If this is true for DVDD3318n being 3.3V, why would it not also be true for DVDD3318n being 1.8V? That is, can the static 1.2V rail and the 1.8V I/O and the 1.8V LVCMOS rails all ramp up together?

6/ Is there a PMIC recommended for us with the TMS320C6746 that will satisfy the power up sequence and RVDD requirements without the need for additional external components such as voltage supervisors, LDOs and MOSFET switches?

Your responses to these questions would be greatly appreciated.

Thank you!

Scott