US38024-BAG1 Renesas Electronics America, US38024-BAG1 Datasheet - Page 431

• Manufacturer Part Number: US38024-BAG1
• Description: DEV EVALUATION KIT H8/38024
• Manufacturer: Renesas Electronics America
• Series: H8®r
• Type: MCUr

Specifications of US38024-BAG1

• Contents: 2G (Second-generation) Evaluation Board, HEW debugger support, Cable and CD-ROM
• For Use With/related Products: H8/38024
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

12.7
12.7.1
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 kΩ 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 kΩ, 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 kΩ, 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/μs or greater) (see figure 12.8). When converting a high-speed analog signal, a low-
impedance buffer should be inserted.
12.7.2
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.
Sensor input
Application Notes
Permissible Signal Source Impedance
Influences on Absolute Precision
Sensor output
impedance
Up to 10 kΩ
Low-pass
filter
C to 0.1 μF
Figure 12.8 Analog Input Circuit Example
This LSI
C
15 pF
in
=
Rev. 8.00 Mar. 09, 2010 Page 409 of 658
A/D converter
equivalent circuit
10 kΩ
Section 12 A/D Converter
REJ09B0042-0800
20 pF