hd64338342hw Renesas Electronics Corporation., hd64338342hw Datasheet - Page 465

• Manufacturer Part Number: hd64338342hw
• Description: Renesas 8-bit Single-chip Microcomputer H8 Family/h8/300l Super Low Power Series
• Manufacturer: Renesas Electronics Corporation.

12.6.2
This LSI’s analog input is designed such that conversion precision is guaranteed for an input
signal for which the signal source impedance is 10 k or less. This specification is provided to
enable the A/D converter’s sample-and-hold circuit input capacitance to be charged within the
sampling time; if the sensor output impedance exceeds 10 k , charging may be insufficient and it
may not be possible to guarantee A/D conversion precision. However, a large capacitance
provided externally, the input load will essentially comprise only the internal input resistance of
10 k , and the signal source impedance is ignored. However, as a low-pass filter effect is obtained
in this case, it may not be possible to follow an analog signal with a large differential coefficient
(e.g., 5 mV/ s or greater) (see figure 12.6). When converting a high-speed analog signal, a low-
impedance buffer should be inserted.
12.6.3
Adding capacitance results in coupling with GND, and therefore noise in GND may adversely
affect absolute precision. Be sure to make the connection to an electrically stable GND.
Care is also required to ensure that filter circuits do not interfere with digital signals or act as
antennas on the mounting board.
In active mode or sleep mode, analog power supply current (AI
resistance even when the A/D converter is not operating. Therefore, if the A/D converter is not
used, it is recommended that AV
ADCKSTP (A/D converter module standby mode control) bit be cleared to 0 in clock stop
register 1 (CKSTPR1).
Sensor input
Permissible Signal Source Impedance
Influences on Absolute Precision
Sensor output
impedance
Up to 10 k
Low-pass
filter
C to 0.1 F
Figure 12.6 Analog Input Circuit Example
CC
be connected to the system power supply and the
This LSI
C
15 pF
in
=
Rev. 6.00 Aug 04, 2006 page 429 of 680
A/D converter
equivalent circuit
10 k
STOP1
) flows into the ladder
Section 12 A/D Converter
REJ09B0145-0600
20 pF