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WICED Studio Bluetooth

TaMi_1708256
New Contributor

Please tell me the impedance(ohm) when Signal of CYW20706 is set to output.

Especially I want to know the value of the following signal.

SPI2_MISO_I2S_SCL

SPI2_MISO_I2S_SDA

Thanks

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1 Solution
AnjanaM_61
Moderator
Moderator

Hi,

can you provide the same FW which you are using for test analysis at our side?  Also any reason for  using 2.2K which seems to bit too strong considering most I2C application is rely on 4.7K pull-up?

Thanks,
Anjana

View solution in original post

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9 Replies
AnjanaM_61
Moderator
Moderator

Hello,

Never seen output impedance specified on digital lines. Can you please let us know what you are trying to achieve with those two pins?  Can you share application details for better understanding?

Thanks & Regards,
Anjana

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TaMi_1708256
New Contributor

Hello

We use these to connect with I2C device. At that time, it seems that GND level is 0.2V.

We want to know what this 0.2V is caused by.  if there is some impedance to these signal lines, it looks to the correct behavior.

If there is no impedance , we need to consider other causes.

Thanks

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TaMi_1708256
New Contributor

Hello

I change the following line.

> if there is some impedance to these signal lines, it looks to the correct behavior.

When considering the conditions of the circuit, we guess the impedance will be around 150 ohm.

if there is this impedance to these signal lines, it looks to the correct behavior.

BTW

I found the following in the data sheet.

3.1.3 Digital I/O Characteristics
Table 12. Digital I/O Characteristics

Output Voltage

Low  0.4V  (MAX)

Output Current

Low 2.0mA (VDDO=3.3V/MAX)

From this figure, I estimated the impedance as follows.

0.4 / 0.002 = 200ohm

Is this correct?

This is similar to the 150 ohm above.

Thanks

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BoonT_56
Employee

This division (voltage/current) may not translate to the port impedance. I haven't come across this concept in SPI. Perhaps can you elaborate what device are you trying to connect? If this device a standard I2C device?

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AnjanaM_61
Moderator
Moderator

Hi ,

Just wanna confirm if you are putting any  loading on these lines? (pull-up resistors).

Thanks,
Anjana

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TaMi_1708256
New Contributor

Hi

Thank you for your reply.

Yes,

            

20706 SCL ----+---- 100 ohm  --- I2C device SCL

                        |

                  2.2K ohm (Pull up)

                        |     

                    3.3 V

Thanks

T.M.

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TaMi_1708256
New Contributor

Hi

It is a continuation of the previous comment.

In this case,  Low level of SCL line make to 0.2V.

Thanks

T.M.

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AnjanaM_61
Moderator
Moderator

Hi,

can you provide the same FW which you are using for test analysis at our side?  Also any reason for  using 2.2K which seems to bit too strong considering most I2C application is rely on 4.7K pull-up?

Thanks,
Anjana

View solution in original post

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BoonT_56
Employee

The recommended pull up resistor is 4.7k Ohm, or at least it is the minimum. But the pull up resistor is not to be confused as output/port impedance.

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