UPD78F0078GK-9ET-A Renesas Electronics America, UPD78F0078GK-9ET-A Datasheet - Page 248

• Manufacturer Part Number: UPD78F0078GK-9ET-A
• Manufacturer: Renesas Electronics America

Specifications of UPD78F0078GK-9ET-A

• Lead Free Status / Rohs Status: Supplier Unconfirmed

246
(14) Internal equivalent circuit of ANI0 to ANI7 pins and permissible signal source impedance
Output impedance
of sensor
Remark n = 0 to 7
To complete sampling within the sampling time with sufficient A/D conversion accuracy, the impedance of the
signal source such as a sensor must be sufficiently low. Figure 13-21 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 the ANI0 to ANI7
pins. An example of this is shown in Figure 13-22. 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.
<Sensor internal circuit>
Table 13-4. Resistances and Capacitances of Equivalent Circuit (Reference Values)
Figure 13-22. Example of Connection When Signal Source Impedance Is High
Caution
Lowpass filter
is created.
AV
2.7 V
4.5 V
R0
Figure 13-21. Internal Equivalent Circuit of Pins ANI0 to ANI7
ANIn
REF
C0
The resistances and capacitances in Table 13-4 are not guaranteed values.
0.1 F
Reference
voltage input
12 k
4 k
R1
C0
C1
CHAPTER 13 A/D CONVERTER
User’s Manual U14260EJ4V0UD
R1
2.7 k
8 k
R2
AV
ANIn
REF
<Microcontroller internal circuit>
If a noise of AV
may be generated, clamp using a diode with
a low V
8 pF
8 pF
C1
C2
C1
F
(0.3 V or lower).
R1
REF
R2
1.4 pF
3 pF
or higher or AV
C2
C2
2 pF
2 pF
C3
SS
C3
or lower
R2
C3