h8s-2628 Renesas Electronics Corporation., h8s-2628 Datasheet - Page 502

• Manufacturer Part Number: h8s-2628
• Description: Renesas 16-bit Single-chip Microcomputer H8s Family/h8s/2600 Series
• Manufacturer: Renesas Electronics Corporation.

Section 17 A/D Converter
17.7
17.7.1
Operation of the A/D converter can be disabled or enabled using the module stop control register.
The initial setting is for operation of the A/D converter to be halted. Register access is enabled by
clearing module stop mode. For details, refer to section 21, Power-Down Modes.
17.7.2
This LSI’s analog input is designed such that conversion accuracy is guaranteed for an input signal
for which the signal source impedance is 5 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 5 k , charging may be insufficient and it may not be
possible to guarantee A/D conversion accuracy. However, for A/D conversion in single mode with
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 17.6). When converting a high-speed
analog signal or converting in scan mode, a low-impedance buffer should be inserted.
17.7.3
Adding capacitance results in coupling with GND, and therefore noise in GND may adversely
affect absolute accuracy. Be sure to make the connection to an electrically stable GND such as
AVss.
Care is also required to insure that filter circuits do not communicate with digital signals on the
mounting board (i.e., acting as antennas).
Rev. 3.00 Oct 04, 2005 page 462 of 598
REJ09B0155-0300
Usage Notes
Module Stop Mode Setting
Permissible Signal Source Impedance
Influences on Absolute Accuracy
Sensor input
Sensor output
impedance
to 5 kΩ
Low-pass
filter C
to 0.1 µF
Figure 17.6 Example of Analog Input Circuit
This LSI
C
15 pF
in
=
A/D converter
equivalent circuit
10 kΩ
20 pF