adc150 Rhopoint Components, adc150 Datasheet - Page 4

• Manufacturer Part Number: adc150
• Description: Programmable Integrating A/d Converter
• Manufacturer: Rhopoint Components

FIGURE 1. BLOCK DIAGRAM
and V
into a differential, voltage controlled, single output
current source.
reference current at the input of the op amp
integrator. The output of the integrator is fed into
a Schmitt trigger, which in turn, is fed into the
ADC's timing control circuitry.
integrator output actuates the Schmitt trigger, the
timing circuit changes the direction of the
reference current source and the integrator
begins integrating in the opposite direction. This
continues until the Schmitt trigger is actuated
again by the integrator and reverses the direction
of the reference current.
The equation for integration times are:
In the ADC150 block diagram (see Figure 1), V
Resolving these equations produces:
V = Voltage
C= Integration Capacitor Value
I
I
ref =
inp =
T
T
Output
T
Data
p =
m =
low
p
=
I
Reference Current
V
Input Current
Time Positive
V
are the inputs. Both are buffered and fed
inp
Time Negative
low
I
hi
ref
V X C
= I
+ I
ref
Switch
Auto
Zero
inp
Output Enable
T
This current is added to the
T
p
p
+ T
- T
Output
Buffer
m
m
T
m
THEORY OF OPERATION
=
-I
V X C
ref
Voltage Controlled
+ I
Current Source
When the
inp
Differential
Auto
Zero
Microprocessor
Convert
hi
Current Source
Bidirectional
Reference
measure the integration time in both directions.
calculate the results of the integration equation and
perform error corrections.
automatically performs an auto zero function at start-
up, but it is recommended to achieve maximum
accuracy, that an auto zero be performed again after
the ADC150 is fully warmed up.
status lines to indicate that the ADC is involved in a
conversion.
direction, the µP will collect the counts for the
integration time. When sufficient counts have been
collected, the µP performs the calculations described
above.
the most significant byte in the output buffer and
raises the S
the convert line, the middle byte is placed on the
output, the S
When the last pulse is placed in the convert line, the
least significant byte is placed in the output buffer and
both status flags are high indicating that the ADC150
is ready for another conversion.
Status line summary:
The timing control circuitry governs the counters that
The ADC150's on-board microprocessor is used to
When the µP detects a convert signal, it lowers the
When the calculations are complete, the µP places
S
0
0
1
1
1
Status
Lines
S
0
1
0
1
0
Conversion in progress.
Conversion complete. MSB in output.
Middle byte in output register.
LSB in output. Ready for next conversion.
0
0
flag. When another pulse is placed on
flag is lowered and the S
When it detects a change in slope
Directional
Current
Counter
Control
Switch
Timing
and
Note that the µP
+15V
-15V
Schmitt
Trigger
1
ADC150DS REV. F MAR 00
flag raised.
Clock