SN74AVC24T245 strange function

NAOKI AOYAMA

Guru 11215 points

Other Parts Discussed in Thread: SN74AVC24T245, SN74AVCH24T245

Hello,

My customer uses the SN74AVC24T245.

He uses the device to translate a signal from CPU(1.8V) to SoC(3.3V).

It is occurred a strange function at one of a channel that drive a LED.

I attach the file of timing chart and block diagram.

8508.SN74AVC24T245timing .pdf

After the CPU initialize time, right operation B-port is Low, but B-port
is High level actually.

The A-port voltage is less than 150mV, there is no noize.

But when he uses a pull-down at A-port by 10kohrm, it is a normal operation.

A strange function occur using another channel or another sample.

Could you tell me the cause of the strange function?

Is it too long CPU initialize time?

Regards,

Naoki Aoyama

over 9 years ago

0 Wei Lang over 9 years ago

TI__Expert 6430 points

Hi,

When CPU is in initialization, the CPU I/O could be on hihg-Z. For translation device, if input is high-Z or floating, output could be low or high.

Please give fixed low by pull down resistor when CPU I/O is floating.

Thanks

Wei

0 NAOKI AOYAMA over 9 years ago in reply to Wei Lang

Guru 11215 points

Hi Wei,

Thank you for your fast reply.

I checked my customer about a condition of CPU I/O in initialization.

He said that the condition is high output, not high-Z....

If a condition is high-Z, is it continued incorrect logic after initialization finished?

(When CPU finish initialization, OE and A-port drive low at same time.)

Regards,

Naoki Aoyama

0 Wei Lang over 9 years ago in reply to NAOKI AOYAMA

TI__Expert 6430 points

Hi,

If input is fixed status (high or low), output should be follow the input logic. If input is floating during initialization and input will be fixed status after initialization, output will follow input logic after initialization.

Thanks

Wei

0 NAOKI AOYAMA over 9 years ago in reply to Wei Lang

Guru 11215 points

Hi Wei,

Please check the attach file, this is an evaluation results.

2476.SN74AVC24T245_evaluation_results.pdf

When OE and A-bus operate High to Low, B-bus operate Low to High.

It is an unusual operation.

My customer check the CPU specification, I/O pin is not High-Z during initialization, it outputs High.

What is the cause of this unusual operation?

Regards,

Naoki Aoyama

0 NAOKI AOYAMA over 9 years ago in reply to NAOKI AOYAMA

Guru 11215 points

Hello,

Is there anyone has been a similar experience like an attach file?

7128.SN74AVC24T245_evaluation_results.pdf

Regards,

Naoki Aoyama

0 Wei Lang over 9 years ago in reply to NAOKI AOYAMA

TI__Expert 6430 points

Hi,

If input is connectted by pull-down resistor, device can work normally. Could the pull-down resistor add on A side input and test again?

I think the CPU I/O status is not stable.

I did not see any similiar result.

Thanks

Wei

0 NAOKI AOYAMA over 9 years ago in reply to Wei Lang

Guru 11215 points

Hi Wei,

Thank you for your reply.

My customer tried to add the pull-down resistor on A side. Then the device work normally.

He is reluctant to add resistor, because it is too many bits to add.

But there is no answer except adding a pull-down resistor.

I will ask customer to add resistor.

Thanks.

Naoki Aoyama

0 Wei Lang over 9 years ago in reply to NAOKI AOYAMA

TI__Expert 6430 points

Could customer try SN74AVCH24T245? This device has bus-hold function.

I think this device can work normallly in customer application.

Thanks

Wei

0 NAOKI AOYAMA over 9 years ago in reply to Wei Lang

Guru 11215 points

Hi Wei,

Thank you for your suggestion.

I will advise customer to try the SN74AVCH24T245.

Thanks.

Naoki Aoyama

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SN74AVC24T245 strange function