UPD78F0988AGC-8BS Renesas Electronics America, UPD78F0988AGC-8BS Datasheet - Page 219

• Manufacturer Part Number: UPD78F0988AGC-8BS
• Manufacturer: Renesas Electronics America

Specifications of UPD78F0988AGC-8BS

• Lead Free Status / Rohs Status: Supplier Unconfirmed

(15) Internal equivalent circuit of ANI0 to ANI7 pins and permissible signal source impedance
(13) Notes on board design
(14) AV
Remark C1: 4.7 F to 10 F (reference value)
To complete sampling within the sampling time with sufficient A/D conversion accuracy, the impedance of the
sensor or other signal source must be sufficiently low. Figure 11-15 shows the internal equivalent circuit of
the ANI0 to ANI7 pins.
If the impedance of the signal source is high, connect capacitors with a high capacitance to pins ANI0 to ANI7.
An example of this is shown in Figure 11-16. In this case, however, the microcontroller cannot follow an analog
signal with a high differential coefficient because a lowpass filter is created.
To convert a high-speed analog signal or to convert an analog signal in the scan mode, insert a low-impedance
buffer.
Locate analog circuits as far away from digital circuits as possible on the board because the analog circuits
may be affected by the noise of the digital circuits. In particular, do not cross an analog signal line with a digital
signal line, or wire an analog signal line in the vicinity of a digital signal line. Otherwise, the A/D conversion
characteristics may be affected by the noise of the digital line.
Connect AV
Connect a capacitor to the AV
has been stopped and is then started, the voltage applied to the AV
accuracy of the A/D conversion to drop. To prevent this, also connect a capacitor to the AV
Figure 11-14 shows an example of connecting a capacitor.
REF
pin
C2: 0.01 F to 0.1 F (reference value)
Connect C2 as close to the pin as possible.
SS0
and V
Figure 11-14. Example of Connecting Capacitor to AV
C
SS0
1
at one location on the board where the voltages are stable.
REF
pin to minimize conversion errors due to noise. If an A/D conversion operation
CHAPTER 11 A/D CONVERTER
User’s Manual U13029EJ7V1UD
C
2
AV
AV
REF
SS
REF
pin becomes unstable, causing the
REF
Pin
REF
pin.
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