TPS65070 PGOOD Function on Power Up

Daniel Acevedo

Other Parts Discussed in Thread: TMS320C6746, TPS65070, TPS65023

Hello Forum,

My circuit has the TMS320C6746 DSP powered from the TPS65070, and my question relates to the function of PGOOD on power up.

My plan is to connect the TPS65070 PGOOD output to the reset input of the DSP to take it out of reset on power up after all the PMIC rails have stabilized. My problem is that, according to my reading of the TPS65070 datasheet, the default values in the PGOODMASK register will prevent me from using PGOOD in this way.

The PGOODMASK Bit 5..0 register default values are 010000. My interpretation of this is that the status of all the outputs, except for VDCDC1 (B4), will be masked on power up and according to the datasheet will therefore "not affect the status of the PGOOD output pin."

It seems from this that the only output that isn't part of the automated sequencing (and coincidentally the only output I'm not using) is the one that will determine if PGOOD is HIGH or not on power up. This seems very odd and arbitrary to me. I would have actually expected the opposite of this, where the power good status of all the enabled outputs would have been OR'd together, even on power up, to yield the PGOOD status (like the function of the INT pin on the TPS65023).

From this, my questions are:

1/ Is my interpretation of the PGOOD and PGOODMASK functions correct?

2/ What was the rationale behind this 010000 default PGOODMASK register settings?

3/ Is there any way for the TPS65070 to have its PGOOD output actually reflect the status of the enabled outputs on power up?

4/ Alternatively, can a variant of the TPS65070 be ordered that would have the PGOOD mask default values be the complement of those that exist now; i.e. 101111 rather than 010000?

Thank you in advance for your help!

Regards

over 14 years ago

0 Daniel Acevedo over 14 years ago

TI__Genius 17240 points

See my comments below

Scott Burton said:

From this, my questions are:

1/ Is my interpretation of the PGOOD and PGOODMASK functions correct? [D.A] yes

2/ What was the rationale behind this 010000 default PGOODMASK register settings?
[D.A] For the -70, the default sequence is DCDC3->DCDC2, then DCDC2 enables DCDC1 (externally though TPS3805 as in figure 49 of the datasheet) so PGOOD only goes high if all three DCDC converters are up.

3/ Is there any way for the TPS65070 to have its PGOOD output actually reflect the status of the enabled outputs on power up? [D.A] You can connect the outputs in series as described in question 2, then/or you could write 1F to PGOODMASK (possibly before the PGOOD delay).

4/ Alternatively, can a variant of the TPS65070 be ordered that would have the PGOOD mask default values be the complement of those that exist now; i.e. 101111 rather than 010000? [D.A] The variants are –73, –731, –732 which have PGOODMASK[4:0]=11100 to drive PGOOD high only when DCDC1,2 and 3 are good by default.

0 Scott Burton over 14 years ago in reply to Daniel Acevedo

Prodigy 230 points

Hi Daniel,

Thank you for your response. My comments follow-up questions below:

1/ Is my interpretation of the PGOOD and PGOODMASK functions correct? [D.A] yes

2/ What was the rationale behind this 010000 default PGOODMASK register settings?
[D.A] For the -70, the default sequence is DCDC3->DCDC2, then DCDC2 enables DCDC1 (externally though TPS3805 as in figure 49 of the datasheet) so PGOOD only goes high if all three DCDC converters are up.

[S.B.] So from what you're saying PGOODMASK is linked to the given sequence of the TPS65070 on the presumption that, if DCDC1 is good, then DCDC2, DCDC3, LDO1 and LDO2 must already also be good. Is this correct?

[S.B.] If so, then in my application where DCDC1 is not used, it seems to me that PGOOD will remain LOW post-power up, at least until the PGOODMASK register contents are changed accordingly. Is this also correct?

3/ Is there any way for the TPS65070 to have its PGOOD output actually reflect the status of the enabled outputs on power up? [D.A] You can connect the outputs in series as described in question 2, then/or you could write 1F to PGOODMASK (possibly before the PGOOD delay).

[S.B.] In our design the outputs are sequenced as described in question 2, except DCDC1 is not used (3.3V not required), so from what you've said PGOOD will remain LOW on power up. Unfortunately the TMS320C6746 is powered by the TPS65070, and is brought out of reset by its PGOOD signal; so its not able to write to PGOODMASK until the PGOOD signal is HIGH. The only solution I see is to use an external voltage supervisor to drive a PGOOD to the TMS320C6746, which would be duplicating what is already in the TPS65070, or to purchase a PGOODMASK variant of the TPS65070 (see 4/ below). Would you have any other suggestions?

4/ Alternatively, can a variant of the TPS65070 be ordered that would have the PGOOD mask default values be the complement of those that exist now; i.e. 101111 rather than 010000? [D.A] The variants are –73, –731, –732 which have PGOODMASK[4:0]=11100 to drive PGOOD high only when DCDC1,2 and 3 are good by default.

[S.B.] Unfortunately the power up sequence associated with these variants isn't suitable for our application. That is why I was asking if we could purchase a variant of the TPS65070 with modified PGOODMASK register contents. I'll follow-up on this with our local TI Sales Representative but, is there any technical reason this could be done?

Thanks Daniel.

Regards,

Scott

0 Daniel Acevedo over 14 years ago in reply to Scott Burton

TI__Genius 17240 points

Scott,

I added more comments below

Scott Burton said:

1/ Is my interpretation of the PGOOD and PGOODMASK functions correct? [D.A] yes

2/ What was the rationale behind this 010000 default PGOODMASK register settings?
[D.A] For the -70, the default sequence is DCDC3->DCDC2, then DCDC2 enables DCDC1 (externally though TPS3805 as in figure 49 of the datasheet) so PGOOD only goes high if all three DCDC converters are up.

[S.B.] So from what you're saying PGOODMASK is linked to the given sequence of the TPS65070 on the presumption that, if DCDC1 is good, then DCDC2, DCDC3, LDO1and LDO2 must already also be good. Is this correct?

[D.A] Yes, that is the intention.

[S.B.] If so, then in my application where DCDC1 is not used, it seems to me that PGOOD will remain LOW post-power up, at least until the PGOODMASK register contents are changed accordingly. Is this also correct?

[D.A] Correct

3/ Is there any way for the TPS65070 to have its PGOOD output actually reflect the status of the enabled outputs on power up? [D.A] You can connect the outputs in series as described in question 2, then/or you could write 1F to PGOODMASK (possibly before the PGOOD delay).

[S.B.] In our design the outputs are sequenced as described in question 2, except DCDC1 is not used (3.3V not required), so from what you've said PGOOD will remain LOW on power up. Unfortunately the TMS320C6746 is powered by the TPS65070, and is brought out of reset by its PGOOD signal; so its not able to write to PGOODMASK until the PGOOD signal is HIGH. The only solution I see is to use an external voltage supervisor to drive a PGOOD to the TMS320C6746, which would be duplicating what is already in the TPS65070, or to purchase a PGOODMASK variant of the TPS65070 (see 4/ below). Would you have any other suggestions?

[D.A] Yes, often there a MCU in the system that is capable of handling some of the I2C reqs.
Instead of using PGOOD to power on your processor you could use /RESET by tying the output of DCDC2 to THRESHOLD with a resistor divider.

4/ Alternatively, can a variant of the TPS65070 be ordered that would have the PGOOD mask default values be the complement of those that exist now; i.e. 101111 rather than 010000? [D.A] The variants are –73, –731, –732 which have PGOODMASK[4:0]=11100 to drive PGOOD high only when DCDC1,2 and 3 are good by default.

[S.B.] Unfortunately the power up sequence associated with these variants isn't suitable for our application. That is why I was asking if we could purchase a variant of the TPS65070 with modified PGOODMASK register contents. I'll follow-up on this with our local TI Sales Representative but, is there any technical reason this could be done?

[D.A] Technically there is no reason that this can't be done; though logistically difficult. The correct avenue is through your local TI Sales Rep.
You may be better off if you pursue the /RESET method I described above.

Power management

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TPS65070 PGOOD Function on Power Up