M16C65 Datasheet, PDF (715/829 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
When capacitor C₁ is connected, C₁ is obtained by the following formulas. Figure 27.14 shows Analog
Input Pin and External Sensor Equivalent Circuit (Capacitor is Connected).
If R₁ is infinite, C₂ is charged from C₁.
When the difference of voltages generated by divided capacitor, C₁ and C₂ is V_P:
V_P
=
-------^C-----²--------
C₁ + C₂
×
(E_x
–
V_samp)…(1)
When the difference generated by the conversion is V_p1:
V_P
=
V_P
1
×
-1--
2ⁱ
<
-^V----^R-----^E----^F--
A × 2^x
…
(
2
)
X = 10 (bits)
A: V_P1=
-1--
A
LSB (e.g. when V_P1 = 0.1 LSB, A = 10)
From (1) and (2)
C₁
=
C₂
×
⎛
⎝
E_{-----x----–----}V_----2-
V_P1
–
1_⎠⎞
…(3)
∴C₁
>
C _{2 ⎝⎛} A
×
2^x
-1--
2ⁱ
–
1_⎠⎞
…(4)
In 10-bit resolution A/D converter, C₁ is 0.21 μF or more when C₂ = 10 pF.
Sensor equivalent
circuit
R₁
l₁
Ex
l₂
I_i
C₁
MCU
V_ref
C_in ^{R2 (10kΩ)}
(15pF)
C₂ (10pF)
V_samp
Sampling time
15
φAD
Figure 27.14 Analog Input Pin and External Sensor Equivalent Circuit (Capacitor is Connected)
C₁ : Board parasitic capacitance
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 680 of 791