PIC14000T-04/SS View Datasheet(PDF) - Microchip Technology
Part Name
Description
MFG CO.
'PIC14000T-04/SS' PDF : 153 Pages View PDF
8.6 Programmable Current Source
Four configuration bits (ADCON1<7:4>) are used to
control a programmable current source for generating
the ramp voltage to the A/D comparator. It allows com-
pensation for full-scale input voltage, clock frequency
and CDAC capacitor tolerance variations. The current
values range from 0 to 33.75 µA (nominal) in 2.25 µA
increments. The intermediate values of the current
source are as follows:
TABLE 8-2: PROGRAMMABLE CURRENT
SOURCE SELECTION
ADCON1<7:4>
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
Current Source
Output
OFF - all current
sources disabled
2.25 µA
4.5 µA
6.75 µA
9 µA
11.25 µA
13.5 µA
15.75 µA
18 µA
20.25 µA
22.5 µA
24.75 µA
27 µA
29.25 µA
31.5 µA
33.75 µA
PIC14000
The programmable current source output is tied to the
CDAC pin and is used to charge an external capacitor
to generate the ramp voltage for the A/D comparator.
(Refer to Figure 8-1.) This capacitor should have a low
voltage-coefficient as found in teflon, polypropylene, or
polystyrene capacitors, for optimum results. The
capacitor must be discharged at the beginning of each
conversion cycle by asserting ADRST (ADCON0<1>)
for at least 200 µs to allow a complete discharge.
Asserting ADRST disables the current sources inter-
nally. Current flow begins when ADRST is cleared.
© 1996 Microchip Technology Inc.
Preliminary
DS40122B-page 61
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