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Part Number: TRS3232
Our customer would like to ask the value of absolute maximum rating for terminals C1 +, C1-, C2 +, C2-.
However, I could not confirm the these value in datasheet.
Could you tell me the maximum rating values for these four terminals?
We will work to confirm these values, but due to some critical team members' absences it may take a little longer than usual. We should be able to provide an update by the end of the week. Thank you for your patience.
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In reply to Max Robertson:
Thank you for your reply.
The customer is urged to answer quickly.
I would appreciate it if you could get back to me right away.
In reply to Y.Ottey:
There is no official document about the abs max values of these pins connecting external capacitors. However after some investigation, I think you can treat C1N, C1P and C2P as V+ (7V abs max), C2N as V- (-7V abs max). Please let me know if you have more questions.
In reply to Hao L:
I recognized from the following MAX3232 posts that the absolute maximum rating of these pins is ± 2 x Vcc,
but can I think that is not the case?
It's a good question. Theoretically the output voltage of the charge pump could reach 2x Vcc. However, it's common to limit the voltage range below the abs max, while the voltage level still meets the ±5V minimum of RS-232 standard. You can refer to this post for some detail of the circuit operation.
I am very grateful to you for the materials.
I would like to ask more question.
If SW3 and SW4 are switched from this state in the red frame of the circuit in the document (Figure.1),
is it possible that SW4 becomes V + and SW3 becomes V- due to the difference between the two SWs?
If this is possible, are the absolute ratings for C2 + and C2− + 7V and -7V, respectively, okay?
Your understanding is correct, which is aligned with my assessment in the first reply. Please let me know if you have more questions.
When our customer used Vcc at 5V, we were informed that a voltage of 7.3V was observed at the C1 + terminal.
This is a value that exceeds the absolute rating you noted earlier.
The capacities of the capacitors C1 to C4 at that time are described below.
(In two cases, C1 + terminal voltage was observed at 7.3V)
1. C1 = C2 = 1μF, C3 = C4 = 10μF
2. C1 = 0.047μF, C2 = 0.33μF, C3 = C4 = 10μF
Can you give me advice if there is a way to reduce the voltage of the C1 + pin?
The suggested cap value for Vcc=5V in the data sheet is:
Please make the C1 peak voltage smaller, you can try make the C1/C3 ratio smaller than 0.047/0.33~=0.14 and keep C2 and C4 same value. 1uF or 10uF could work but you might see longer charging time driving a load. Another note is that you can check the peak voltage of C1+, V+ and an output to see if they are aligned.
Our customer measured again with the following values you suggested,
but the C1 + terminal voltage was 7.2V and the situation remained the same.
Is there any other action to take to make the voltage at C1 + terminal lower than 7V?
Please give me good advice.
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