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TCAN337: Under what conditions will keep RXD(No.4) terminal to high level?

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Kazuya Nakai59

Replies: 12

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Part Number: TCAN337

Hello guys,

One of our customers is in trouble with TCAN337. Could you please give me your advice or your help?

They are using the deivce for some car system. They sometimes observed RXD(No.4) terminal was kept to high level continuously. They want to know what conditions will keep RXD(No.4) terminal to high level continuously?

Is the phenomenon occured by high level of S(No.8) terminal (Silent mode)? Or is there any other condition?

Your reply would be much appreciated.

Best regards,

Kazuya Nakai.

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Eric Hackett
- Nov 20, 2018 4:06 PM
Kazuya-san,

Silent mode works by disabling the transmit driver, but the RXD pin should still reflect what is happening on the bus (CANH and CANL). When the RXD terminal was kept to a high level continuously, was there any CAN bus activity?

Regards,

Eric Hackett

Texas Instruments | INT-TRX| Applications Engineer
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Kazuya Nakai59
- Nov 20, 2018 11:44 PM
In reply to Eric Hackett:

Hello Eric,
Thank you very much for your reply. I see. I will ask the customer to take CANH/CANL waveform when RXD=H continuously.

Best regards,
Kazuya Nakai.
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Eric Hackett
- Nov 21, 2018 1:03 AM
In reply to Kazuya Nakai59:

Kazuya-san,

Thank you, and if you can find out what the state of pin 8 is while this is happening that would help as well.

Regards,

Eric Hackett

Texas Instruments | INT-TRX| Applications Engineer
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Kazuya Nakai59
- Nov 21, 2018 1:09 AM
In reply to Eric Hackett:

Hello Eric,

I see. I will ask the customer to check "S" terminal (No.8) waveform.

Thank you and best regards,
Kazuya Nakai.
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Kazuya Nakai59
- Nov 26, 2018 10:36 AM
In reply to Kazuya Nakai59:

Hello Eric,

I asked the customer to take CANH, CANL and S terminal waveform. But they couldn't get those waveform because they didin't have any opportunity to measure those on their end customer products.
But they want to get any possible cause that RXD keeps high level though they don't send us any waveform.
I think the following two causes can be considered.
1. V(ID) is less than 0.5V (marginal voltage range is between 0.5V and 0.9V).
2. Dominant time out is occured.

Is my understanding correct? Is there any other cause?

Also I have the following questions. Could you please give me your answers?
Q1. Which is RXD output level(H or L level) when V(ID) is less than 0.1V and CHNH/CHNL voltage are in 0V~0.2V range?
Is RXD output level H level not depend on CHNH/CHNL voltage range?

Q2. If the dominant time out is occured, how can it be cancelled? Is the time out cancelled when V(ID) becomes less than 0.5V?

Thank you very much and best regards,
Kazuya Nakai.
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Eric Hackett
- Nov 27, 2018 10:38 PM
In reply to Kazuya Nakai59:

Kazuya-san,

If there is no traffic on the CAN bus and the device is in Normal mode, the RXD pin is left at recessive, meaning that it stays high in its idle state. Dominant timeout would cause the output driver to be disabled and thus leave RXD at a high level, but unless something is driving a dominant state first for an extended period of time, this won't happen.

Q1. If VID is less than 0.1V, than RXD should be high because that's a recessive bus signal. However, your bus signals shouldn't be at 0-0.2V range, even in silent mode. Are CANH and CANL biased to GND at all times?

Q2. RXD timeout occurs when the bus is in a dominant state for an extended period of time. Once the bus goes recessive again, the RXD timeout is released.

Regards,

Eric Hackett

Texas Instruments | INT-TRX| Applications Engineer
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Kazuya Nakai59
- Nov 28, 2018 1:30 AM
In reply to Eric Hackett:

Hello Eric,
Thank you very much for your reply.
Could I ask you a few additional questions?
Q1. When TCAN337 is in Silent mode, is the dominant time out happened with long dominant state?
Q2. I'm sorry I ask you similar question to the previous. I understood that RXD=H level fixing is not happened as long as VID state is repeated between recessive and dominant on CANH/CANL of TCAN337. Is my understanding correct?

Thank you again and best regards,
Kazuya Nakai.
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Eric Hackett
- Nov 28, 2018 5:24 PM
In reply to Kazuya Nakai59:

Kazuya-san,

Q1. Since the receiver driver is still enabled, the RXD timeout will still occur if the bus is held dominant for too long. However, the TXD timeout is not enabled since the TXD driver is disabled in Silent mode.

Q2. RXD will follow the bus state. So if CANH - CANL (VID) is > 0.9V, the bus is considered dominant, so RXD will be low. If CANH - CANL (VID) is < 0.5V, the bus is considered recessive and RXD will be high.

If no signal is being transmitted on the CAN bus, the RXD state will be a logic high, because the bus is in a recessive state unless a CAN node is driving a dominant signal.

Is the customer seeing the RXD pin stay high even when there are dominant bits driven on the CAN bus?

Regards,

Eric Hackett

Texas Instruments | INT-TRX| Applications Engineer
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Eric Hackett
- Dec 4, 2018 10:13 PM
In reply to Eric Hackett:

Kazuya-san,

Are there any updates from the customer?

Regards,

Eric Hackett

Texas Instruments | INT-TRX| Applications Engineer
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Kazuya Nakai59
- Dec 5, 2018 12:06 AM
In reply to Eric Hackett:

Hello Eric,

Thank you for your remind. I don't have any update. I will check whether the customer problem is solved or not and i will inform you it.

Best regards,
Kazuya Nakai.
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