AN1740 Freescale Semiconductor / Motorola, AN1740 Datasheet - Page 49

• Manufacturer Part Number: AN1740
• Description: Applications Using the Analog Subsystem on MC68HC05JJ/JP Series Microcontrollers
• Manufacturer: Freescale Semiconductor / Motorola

AN1740
MOTOROLA
Name
V
V
C
I
t
f
CHG
I
CHG
t
OSC
1. Limited for C
V
MAX
DIS
DIS
CAP
EXT
N
P
X
Unknown voltage on channel selection bus
Charging voltage on external capacitor
Maximum charging voltage on external capacitor
Charging current on external ramping capacitor
Discharge current on external ramping capacitor
Time to charge external capacitor
(100 kHz < f
Time to discharge external capacitor, C
Capacitance of external ramping capacitor
Number of counts for I
Prescaler into timing function ( P)
Clock source frequency (excluding any prescaling)
4-bit result
6-bit result
8-bit result
10-bit result
12-bit result
Using core timer
Using 16-bit programmable timer
Using software loops
V
V
V
V
V
V
DD
DD
DD
DD
DD
DD
EXT
= 3 Vdc
= 5 Vdc
= 3 Vdc
= 5 Vdc
= 3 Vdc
= 5 Vdc
to be less than 2.0 F.
OSC
< 4.0 MHz)
The last variable is the external capacitor size. But, capacitors come in
finite sizes, so there is a trade-off in operating frequency, prescaler, and
capacitor size that yields the desired count resolution for a given full-
scale voltage range. There is no quick rule to select the best
combination, as there are obviously several considerations.
The typical range of single slope A/D performance using the
MC68HC05JJ/JP series MCUs is given in
selecting a starting point.
Function
CHG
Freescale Semiconductor, Inc.
Table 6. A/D Conversion Parameters
For More Information On This Product,
to charge C
Go to: www.freescale.com
EXT
EXT
to V
X
0.0001
0.032
0.128
0.512
2.048
8.192
Min
V
V
1.0
1.1
75
85
28
—
—
—
—
1
8
8
SS
SS
user defined
Table 6
32.768
0.128
0.512
2.048
8.196
1024
Typ
100
0.1
90
—
—
—
—
—
—
—
5
8
8
Analog-to-Digital Conversion
as a guide to
user defined
V
V
V
DD
DD
DD
65536
120
120
10.24
40.96
Max
2.56
104
113
2.0
2.1
4.2
10
—
—
8
8
Application Note
–1.5
–1.5
–1.5
(1)
(1)
counts
ms F
Units
MHz
mA
ms
V
V
v
A
F
P
49