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PSoC™ 5, 3 & 1

delfinavelez
Level 1
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Hello,

I'm a PhD researcher in University Nacional of Cordoba, Argentina. As part of my research, I'm investigating the PSoC 5LP CY8C58LP Switched Capacitor and Continuous Time Block and I have some questions regarding the capacitor values in the TRM.

This is the figure 28-1 of the TRM showing the complete block:

delfinavelez_0-1642183988561.png

 

In this diagram, the values the capacitor named “comp” are between 1.24fF and 5pF but in table 28-3 the “comp” capacitor values are between 3pF and 5.1pF.

delfinavelez_4-1642184130250.png

Are the values in the table for all possible configurations of the SC-CT block? Or it can take other values as well?

 

On the other hand, I’m analyzing the variation of the capacitor values between the output driver and the negative input terminal (feedback capacitance) depending on the mode.

For example, if the block is used as Continuous Time Transimpedance Amplifier (TIA), this is the capacitance values table 28-9.

delfinavelez_1-1642183988564.png

Nevertheless, not all those values match the ones in figure 28-1 or combinations among them. Are there any other capacitors than the ones in the figure?

Even more, in the figure 8-13 of the CY8C58LP family datasheet, there’s a C2=1.7pF capacitor that is not in figure 28-1 of the TRM.

 

delfinavelez_2-1642183988571.png

Is the figure 28-1 incomplete? If that´s the case, can you share with me a more complete diagram of SC-CT block where I can see all capacitors?

Thanks in advance.

Best regards,

Delfina Velez

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DennisS_46
Employee
25 likes received 50 replies posted 25 replies posted
Employee

Delfina:

I checked with our legal department. I am not allowed to send you any internal un-published documents. I am
disappointed. I will try to answer your questions.

The structure of the comp cap is not one switch for each of the values, the resulting values are the sum of
various caps, roughly as shown:

 

DennisS_46_4-1642547971864.png

The capacitor values are not binary weighted  (1,2,4,8 times some small value), the specific values don't matter,
the result is the listed values in Table 28-3. The values shown in Fig28-1 are indicative of some of the modes, they are not exact; they indicated values are not complete for all modes.

The structure for the feedback capacitor is similar:

DennisS_46_3-1642547645942.png

The cap values are not binary weighted. They are combined based on control register settings in SC[0:3]_CR0 for operating mode and SC[0:3]_CR1 to achieve the required summed value for each mode.

I hope this provides the answers that you need. If it helps, you can build a project then enter the debug mode and
examine the registers; the register numbers are listed in the Registers TRM 001-82120 which is downloadable. If for physical testing, you can change the register values with direct register writes in your code.

I hope that this helps your efforts. I am happy to TRY to answer  any of your questions. but without violating
company policy regarding disclosure of internal documentation.

---- Dennis

 

 

 

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