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PSoC™ 5, 3 & 1 Forum Discussions

PaSv_1652016
Level 2
Level 2
10 likes given 5 likes given First like received

Hello

which pins to choose for my project
i have:
CY8C5888LTQ MCU

1x differential Delta sigma ADC 18Bit  with internal vref 1.024
1x diferential SAR adc 12bit  with internal -/+ vref 1.024

In  AN58304 (PSoC 3 and PSoC 5LP Pin Selection for Analog Designs)

the document says:

Of these seven ports, three have a slight analog performance advantage P0[7:0], P3[7:0], and P4[7:0]. These ports reside in the analog upper portion of the chip. The analog globals, AGL[7:4] and AGR[7:4] that connect to these ports, also reside only in the upper analog section of the part, which give these ports a slight signal-to-noise ratio advantage.  

Now i configure pin to next ports and analog rail:

pastedImage_2.png

pastedImage_3.png

1. for best accuracy my pin  position correct  or  can I find a better solution for high accuracy?

2. for best accuracy i need use bypass capasitors 10uF   for  all extRef pin or  only  for selected bypas capasitor port  in deltaSig component  ?  

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1 Solution
odissey1
Level 9
Level 9
First comment on KBA 1000 replies posted 750 replies posted

PaSv,

For high accuracy bypass caps are necessary both on DelSg and SAR ADCs. Importance of the reference can be demonstrated by this App Note from the Linear Technology

https://www.analog.com/media/en/reference-design-documentation/design-notes/dn568f_web.pdf

While  selecting ADCs pins is important, it is also important to bring the signal to the pins undistorted. For that, make sure that there is no high-speed digital pins next to the ADC analog inputs. Best is to set nearest pins to GND.

/odissey1

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3 Replies
odissey1
Level 9
Level 9
First comment on KBA 1000 replies posted 750 replies posted

PaSv,

For high accuracy bypass caps are necessary both on DelSg and SAR ADCs. Importance of the reference can be demonstrated by this App Note from the Linear Technology

https://www.analog.com/media/en/reference-design-documentation/design-notes/dn568f_web.pdf

While  selecting ADCs pins is important, it is also important to bring the signal to the pins undistorted. For that, make sure that there is no high-speed digital pins next to the ADC analog inputs. Best is to set nearest pins to GND.

/odissey1

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For high accuracy bypass caps are necessary both on DelSg and SAR ADCs.

i add 10uF to all  pin50\pin51\pin53\pin31 extref

from AN58304 precision pin  for  qfn68 only P0(7) (pin56 ) and p3(7) (pin37)
But  pin56 + pin37  have inconvenient location for for differential input external layout .

my priority external EMI immunity + max internal accuracy.

pastedImage_2.png

which option is more profitable?

1:
Delta sigma  input_P  P0(7)  PIN_56

Delta sigma  input_N  P3(7)  PIN_37

pastedImage_2.png

or

2:
Delta sigma  input_P  P0(7)  PIN_56

Delta sigma  input_N  P0(6)  PIN_55

pastedImage_3.png

?

0 Likes

1. It is enough to put only one 10u caps on each bypass connector, one for DelSig and one for SAR ADC (total 2 caps)

2. Better choice is to keep input lines on the same port and on adjacent pins

Delta sigma  input_P  P0(7)  PIN_56

Delta sigma  input_N  P0(6)  PIN_55

/odissey1