DF2211NP24V Renesas Technology / Hitachi Semiconductor, DF2211NP24V Datasheet - Page 602

• Manufacturer Part Number: DF2211NP24V
• Description: H8S/2200 Series, 2212 Group, USB, RTC, HSS TNP-64B; Vcc= 2.7 to 3.6 volts, Temp= -20 to 75 C; Package: PVQN0064LB-A
• Manufacturer: Renesas Technology / Hitachi Semiconductor

15.8
15.8.1
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 20, Power-Down Modes.
15.8.2
This LSI's analog input is designed such that conversion precision is guaranteed for an input signal
for which the signal source impedance is 5 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 5 kΩ, charging may be insufficient and it may not be
possible to guarantee A/D conversion precision. 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 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/Ωs or greater) (see figure 15.9). When converting a high-speed
analog signal, a low-impedance buffer should be inserted.
15.8.3
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 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.7.00 Dec. 24, 2008 Page 548 of 698
REJ09B0074-0700
Usage Notes
Module Stop Mode Setting
Permissible Signal Source Impedance
Influences on Absolute Precision
Sensor input
Low-pass
filter C
to 0.1 μF
Figure 15.9 Example of Analog Input Circuit
Sensor output
impedance
to 5 kΩ
This LSI
C
15 pF
in
=
A/D converter
equivalent circuit
10 kΩ
20 pF