Analog Input Pins - Cypress FR81S CY91F52 Series Recommendation For Hardware Setup

2.5

Analog Input Pins

Because the ADC works with an internal sample capacitor (Cadc) you must be aware of the time needed to fully charge
this capacitor to the corresponding analog signal source voltage level by the end of the sample time.
When the external impedance is too high, the sampling period for analog voltages may not be sufficient. In this case, it
is recommended to connect an external capacitor (Cext, approx. 0.1 μF) to the analog input pin.
An input impedance maximum (Rext) 15k Ohm is recommended. So, an appropriate sample time has to be selected
depending on the impedance Rext and the capacitance Cext.
Please refer to Datasheet "A/D Converter" chapter for further information.
Analog
Signal
Source #1
Analog
Signal
Source #2
Analog
Signal
Source #n
Component
Cadc
Cadc
Radc
Radc
Cpin
www.cypress.com
Figure 2. Analog Input Circuit Model
MCU
AN1 pin
Rext
Cext
AN2 pin
Rext
Cext
ANn pin
Rext
Cext
Table 1. Reference Values
Value
8.30 pF (Max)
8.30 pF (Max)
1.9K (Max)
4.3K (Max)
5pF..15pF
Document No. 002-09375 Rev. *B
Recommendation for Hardware Setup 32-Bit FR81S Family
Analog SW (Closed during sample)
Cpad
Analog SW
Radc
Cpad
Analog SW
Cpad
ADC
Cadc
AVcc
4.5 V... 5.5 V
3 V... 3.6 V
4.5 V... 5.5 V
3 V... 3.6 V
3