M16C65 Datasheet, PDF (714/829 Pages) Renesas Technology Corp – RENESAS MCU M16C FAMILY / M16C/60

Under development
M16C/65 Group
Preliminary Specification
This is a preliminary specification and is subject to change.
27. A/D Converter
27.5 External Sensor
Figure 27.13 shows Analog Input Pin and External Sensor Equivalent Circuit. R₁ in Figure 27.13 is
obtained by the following formulas.
I₂
=
----------^C-----²---⁽--^E-----^x---–-----^V----^s---^a---^m----^p---⁾----------
C_in × R₁ + C₂(R₁ + R₂)
exp
----------------------–----^t--^s--^a---^m----^p-----------------------
C_in × R₁ + C₂(R₁ + R₂)
Time required to charge C₂:
Sampling time –t_samp > C_in × R₁ + C₂(R₁ + R₂)
R1
<
-^t-^s---^a---^m----^p----–-----^C----²-----^×----^R-----²-
C_in + C₂
t_samp = _φ---¹-_A---⁵-_D---
Sensor equivalent
circuit
R₁
I₂
Ex
MCU
V_ref
C_in ^R2 ^(10kΩ)
(15pF)
C₂ (10pF)
V_samp
Sampling time
15
φAD
Figure 27.13 Analog Input Pin and External Sensor Equivalent Circuit
C_in : Input pin capacity
C₂ : Sampling capacity
R₁ : Sensor output resistance
R₂ : Selector resistance
E_x : Sensor output voltage
V_samp: Sampled voltage
V_ref : A/D converter reference voltage
REJ09B0484-0030 Rev.0.30 Sep 09, 2008
Page 679 of 791