AM1808 Silicon Errata : DVDD18 Can Pull Up to 2.7V When Using Dual-Voltage IOs at 3.3V

uhtis

Other Parts Discussed in Thread: TPS65023, AM1808

3377.AM1808 Schematics.docWe are using TPS65023 PMIC to power an AM1808 processor. On some of the boards, the 1.8V (DDR Power) rail is acting strangely. It measures upto 2.7V. We have tried out the workaround in AM1808 silicon errata. But still the issue exists.

As per the workaround we have 44.9uF bulk capacitance. We have increased the load upto 90uF. But still we have issues in the 1.8V and 3.3V supply. Schematics attached.

Please advice.

over 13 years ago

0 Michael Green over 13 years ago

TI__Genius 16870 points

Hi,

I am sorry but, the schematics attached are blurry and illegible. Have you tried the other work-arounds listed in the errata? I typically recommend the resistor-transistor solution.

0 Michael Green over 13 years ago in reply to Michael Green

TI__Genius 16870 points

Also, what is ramp rate of your 3.3V rail?

0 uhtis over 13 years ago in reply to Michael Green

Expert 1110 points

8446.AM1808 Schematics.doc

3.3V ramp rate : 720us

0 uhtis over 13 years ago in reply to uhtis

Expert 1110 points

Does this supply ramp up issue cause permanent silicon damage ???

If not, why doesnt it work when we increased the load upto 390mA ????

0 Michael Green over 13 years ago in reply to uhtis

TI__Genius 16870 points

As I understand you are placing bulk capacitance on the 1.8V rail near the AM1808.
Adding an additional load resistor to the 1.8V rail, somewhere in the ballpark of 4.5 Ohms.

If this is not what you are doing, please try this and report the results. I calculate that you will need at least 30.5 uF for the bulk cap solution. How did you increase the load to 390mA? If you did not load the converter like mentioned in point #2, can you try placing a 10 Ohm resistor on the 1.8V rail? This will insure that if loaded the leakage current will be sink and DCDC2 will regulate to 1.8V.

0 uhtis over 13 years ago in reply to Michael Green

Expert 1110 points

We have a total capacitance of 44.9uF for 1.8V rail of AM1808. This capacitance is increased to 88.9uF by adding two 22uF bulk capacitors across 1.8V rail of AM1808 which gives a current of 390mA. This is what we have done. Hope it is clear now.

0 Michael Green over 13 years ago in reply to uhtis

TI__Genius 16870 points

Sorry for the misunderstanding. I recommend the resistor-transistor solution over the others mentioned in the errata. You have to sink current only during the leakage period thus, the use of a transistor makes this solution a preferable one.

0 Sudarshan KR over 9 years ago in reply to Michael Green

Intellectual 840 points

Hi,

is there any recommended circuit which is implemented and tested for the above fix. So that it will help us in implementing the same.

Regards,

Sudarshan

0 Michael Green over 9 years ago in reply to Sudarshan KR

TI__Genius 16870 points

Sudarshan,

Do you want help picking a transistor and resistor leakage pull down or will forcing PWM mode be suitable for you? This of course assumes that your issue is the leakage current from the 3.3V IO.

How about the BSS138 with a 50kohm for starts? It depends on the amount of leakage that you have.

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AM1808 Silicon Errata : DVDD18 Can Pull Up to 2.7V When Using Dual-Voltage IOs at 3.3V