PIC18C242 MICROCHIP [Microchip Technology], PIC18C242 Datasheet - Page 171

• Manufacturer Part Number: PIC18C242
• Description: High-Performance Microcontrollers with 10-Bit A/D
• Manufacturer: MICROCHIP [Microchip Technology]

To
Equation 16-1 may be used. This equation assumes
that 1/2 LSb error is used (1024 steps for the A/D). The
1/2 LSb error is the maximum error allowed for the A/D
to meet its specified resolution.
Equation 16-1: Acquisition Time
Equation 16-2: A/D Minimum Charging Time
Example 16-3 shows the calculation of the minimum
required acquisition time T
based on the following application system assump-
tions:
C
Rs
Conversion Error
V
Temperature
V
EXAMPLE 16-3: CALCULATING THE MINIMUM REQUIRED ACQUISITION TIME
T
T
Temperature coefficient is only required for temperatures > 25 C.
T
T
T
DD
HOLD
HOLD
ACQ
V
or
Tc
ACQ
ACQ
ACQ
7/99 Microchip Technology Inc.
C
HOLD
=
calculate
=
=
=
=
=
=
=
Amplifier Settling Time +
Holding Capacitor Charging Time +
Temperature Coefficient
T
T
2 s + Tc + [(Temp - 25 C)(0.05 s/ C)]
-C
-120 pF (1 k + 7 k + 2.5 k ) ln(0.0004885)
-120 pF (10.5 k ) ln(0.0004885)
-1.26 s (-7.6241)
9.61 s
2 s + 9.61 s + [(50 C - 25 C)(0.05 s/ C)]
11.61 s + 1.25 s
12.86 s
AMP
AMP
HOLD
the
(V
-(120 pF)(1 k + R
+ T
+ T
REF
(R
C
=
=
=
=
=
C
minimum
IC
+ T
- (V
+ T
+ R
COFF
REF
COFF
120 pF
2.5 k
1/2 LSb
5V
50 C (system max.)
0V @ time = 0
ACQ
SS
/2048)) • (1 - e
. This calculation is
+ R
Rss = 7 k
acquisition
SS
S
) ln(1/2047)
+ R
S
) ln(1/2047)
(-Tc/C
time,
Preliminary
HOLD
(R
IC
+ R
SS
+ R
S
))
)
PIC18CXX2
DS39026B-page 171