TMS320DM6443: undershoot spec

Hi Pavel,

Thank you for quick reply.
I could understand it with your answer.

Best Regards,
Shigehiro Tsuda

Hi Pavel,

Thank you for your support.

It is an additional question.
What is the allowable voltage for overshoot / undershoot?
There was your answer of 30% over/undershoot, can you answer specifically with the voltage value?

Best Regards,
Shigehiro Tsuda

Hi Shigehiro,

DM64x datasheet does not provide such info, so I can not guarantee the exact value on 100%. What I was able to find is that on similar devices (DM38x, AM335x), the voltage value for over/undershoot is 25%, this is stated in DM38x/AM335x datasheet. Also in the below e2e thread. For DM64x device, this value should be similar.

e2e.ti.com/.../709992

Regards,
Pavel

Hi Pavel,

Thank you for quick reply.
Which of the following is correct?

Absolute Maximum Ratings Over Operating Case Temperature Range
1.VI I/O, 3.3V -0.5 V to 4.2 V
absolute maximum rating + 30% nom IO select
undershoot -(0.5 +3 .3*0.3) V = -1.49 V
overshoot (4.2+ 3.3*0.3 )V = 5.19 V

Recommended Operating Conditions
2.Supply voltage, I/O, 3.3V (DVDD33, USB_DVDDA3P3) min 3.15 nom 3.3 max 3.45
absolute maximum rating + 30% max IO select
undershoot -( 0.5+3 .45*0.3) V = -1.535 V
overshoot (4.2+ 3.45*0.3 )V = 5.235 V

3.Supply voltage, I/O, 3.3V (DVDD33, USB_DVDDA3P3) min 3.15 nom 3.3 max 3.45
IO:3.3V
max IO or VSS select + 30% max IO select
undershoot -( 0+3 .45*0.3) V = -1.035 V
overshoot (3.45+ 3.45*0.3 )V = 4.485 V

4.other

Best Regards,
Shigehiro Tsuda

Hi Pavel,

Is there the update information?
It is said to respond to our customers as soon as possible.
We appreciate your cooperation so that we can reply to customers.

Best Regards,
Shigehiro Tsuda

Shigehiro,

DM64x datasheet does not provide such info, so I can not guarantee the exact value on 100%. What I was able to find is that on similar devices (DM38x, AM335x), the voltage value for over/undershoot is 25%/30%:

Absolute Maximum Ratings
Input and Output voltage ranges:
V I/O, 1.35-V pins (Transient Overshoot/Undershoot) : 30% of DVDD_DDR[0] for up to 30% of the signal period
V I/O, 1.5-V pins (Transient Overshoot/Undershoot) : 30% of DVDD_DDR[0] for up to 30% of the signal period
V I/O, 1.8-V pins (Transient Overshoot/Undershoot): 25% of DVDDx for up to 30% of the signal period
V I/O, 3.3-V pins (Transient Overshoot/Undershoot): 25% of DVDDx for up to 30% of the signal period

Regards,
Pavel

Hi Pavel,

Thank you for your support.

Case AM335x I/O 3.3V, which of the following is the definition of undershoot / overshoot?

I did not know which voltage is indicated by "corresponding I / O supply voltage" described below.

datasheet: 5.1 Absolute Maximum Ratings
Transient overshoot and undershoot specification at I / O terminal:

25% of corresponding I / O supply voltage for up to 30% of signal period

① 5.1 Absolute Maximum Ratings
overshoot
VDDSHV 1 (Absolute Maximum Ratings: 3.8 V) + VDDSHV 1 x 30%
undershoot
- (VDDSHV 1 (Absolute Maximum Ratings: 0.5 V) + VDDSHV 1 (3.8 V) x 30%)

② 5.5 Recommended Operating Conditions (max)
overshoot
VDDSHV 1 (Absolute Maximum Ratings: 3.8 V) + VDDSHV 1 (3.465 V) x 30%
undershoot
- (VDDSHV 1 (Absolute Maximum Ratings: 0.5 V) + VDDSHV 1 (3.465 V) x 30%)

③ 5.5 Recommended Operating Conditions (nom)
overshoot
VDDSHV1 (Absolute Maximum Ratings: 3.8 V) + VDDSHV 1 (3.3 V) x 30%
undershoot
- (VDDSHV 1 (Absolute Maximum Ratings: 0.5 V) + VDDSHV 1 (3.3 V) x 30%)

④other

Best Regards,
Shigehiro Tsuda

In case of AM335x, the "corresponding IO supply voltage" can be: VDDS_DDR, VDDS, VDDSHV1, VDDSHV2, VDDSHV3, VDDSHV4, VDDSHV5 and VDDSHV6.

Regards,
Pavel

Hi Pavel,

Thank you for your support.

I do not know which voltage specification is 30%.
In the case of 3.3 V, can you tell me which of the following values?
① Absolute Maximum Ratings = 3.8 V x 30%
② Recommended Operating Conditions (nom) = 3.3 V x 30%
③ Recommended Operating Conditions (max) = 3.465 x 30%

Best Regards,
Shigehiro Tsuda

Shigehiro,

The under/overshoot value of 30% is provided in "5.1 Absolute Maximum Ratings", thus should apply to:

① Absolute Maximum Ratings = 3.8 V x 30%

Regards,
Pavel

Hi Pavel,

Thank you for quick reply.
I understand that it will be Absolute Maximum Ratings.

Best Regards,
Shigehiro Tsuda

Hello Pavel, 

I’m sorry for my interrupt. We’d like to re-clarify the fail-safe I/O for DM6443 because Shigehiro was asking this device. I believe you provided AM335x information. According to TMS320DM6443 datasheet, there is no description for undershoot/overshoot/fail-sale I/O.

Due to NOR Flash EOL, customer needs to change it. However, customer observed this undershoot with other NOR Flash.

Could you re-clarify fail-safe I/O capability (Max, period), please?

 

Regarding DM6443, Absolute Maximum Ratings = 1.89 V x 30% = 0.567V , it this correct?

It is really appreciated your quick reply.

Best regards, Miyazaki

Hi Miyazaki,

Takayuki Miyazaki said:

Could you re-clarify fail-safe I/O capability (Max, period), please?

Takayuki Miyazaki said:

Regarding DM6443, Absolute Maximum Ratings = 1.89V x 30% = 0.567V , it this correct?

Regarding AM335x, we have 2.1V x 25% = 0.525V

Regarding DM38x, we have 1.8V x 25% = 0.45V

Regarding DM64x, I think should be similar, but we do not have over/under shoot data in datasheet, thus I can not guarantee on 100%. I will try to check within TI and come back to you if I am able to find something more.

UPDATE

I found one internal e2e thread (link below) that states:

"For non-PCI I/Os, I belive we support 30% over/undershoot for 30% of the cycle time."

Thus we have:   2.5V x 30% = 0.75V

Regards,
Pavel

Hi Pavel,

Thank you for your support.

In the AM437x datasheet, the definition of overshoot / undershoot has the following definition.

Overshoot = 20% of nominal IO supply voltage
Undershoot = 20% of nominal IO supply voltage

It is defined as nominal.

Which one is correct?
I think that this undeshoot/overshoot definition is not device dependent.

①Use the max value of VDDSHV1 of Absolute Maximum Ratings.
② Use the max value of VDDSHV1 of the recommended operating condition.
③ Use the nominal value of VDDSHV1 of Recommended Operating Conditions.

I checked it with AM437x also in the following Sitara forum

e2e.ti.com/.../2663032

Best Regards,
Shigehiro Tsuda

Shigehiro,

I made a double check with Biser, I confirm that recommended nominal value should be used (not absolute max, not recommended max).

Thus for DM64x we should have:

1.8V x 30% = 0.54V


Regards,
Pavel

Hi Pavel,

Thank you for your support.

As a conclusion, is the following understanding correct?
Absolute Maximum Ratings voltage value is not used.
overshoot: 1.89 + 0.54 = 2.43 V
undershoot: 0-0.54 V = -0.54 V

I have to make an official answer to our customer, so I want a reliable answer.

Best Regards,
Shigehiro Tsuda

Shigehiro,

Per mine understanding we have:

overshoot: 1.8 + 0.54 = 2.34 V (we used nominal value, not max recommended)
undershoot: 0 - 0.54 = -0.54V

As we do not have this data (under/overshoot ratings) in DM64x datasheet, I can not guarantee on 100% about these values. These values are based on internal e2e threads (links provided to your TI FAE in this e2e thread) and values provided for other TI devices like DM38x, AM335x, etc

Regards,
Pavel

Hi Pavel,

Thank you for quick reply.

I understood that the undershoot/overshoot voltage is below.

overshoot: 1.8 + 0.54 = 2.34 V 
undershoot: 0 - 0.54 = -0.54V 

I will check with Miyazaki-san for answers to customers.

Best Regards,
Shigehiro Tsuda