®
®
ADS-325A
As stated before, the five lower bits of the output data will
remain constant for 4 clock cycles with every generation of the
calibration pulse. Since the auto calibration pulses are
generated asynchronously, this may create problems in certain
applications.
External Calibration Function
To avoid the asynchronous data fixation due to the calibration
process, you can disable the internal auto calibration function
and use an external calibration pulse which is synchronized
with the analog input. Input the external calibration pulse to the
CAL pin (pin 14) and tie the SEL pin (pin 17) to AGND. When
digitizing a video signal, for example, you can synchronize the
external calibration pulses with the V-sync or H-sync cycles of
the video signal to avoid losing any data during the video signal
cycles. See figure 6a. and 6b.
ANALOG INPUT
A/D CLOCK
RESET
CAL
Figure 6a. Applying CAL Pulse Every H Sync.
ANALOG INPUT
A/D CLOCK
RESET
CAL
Figure 6b. Applying CAL Pulse Every V Sync.
+AV
S
10µF
+
V
RT
(+4V)
0.1µF
0.1µF
0.1µF
0.1µF
V
RB
(+2V)
0.1µF
NOTES:
1. For using Start-up calibration and
External CAL Pulse Mode, close
JP1 and JP4, and open JP2 and
JP3.
2. For using Start-up calibration and
Internal Auto-calibration Mode, close
JP2 and JP3, and open JP1 and
JP3.
3. For using Start-up calibration Mode
only, close JP2 and JP4, and open
JP1 and JP3.
+AV
S
36
37
38
35 34
V
RB
33
32
31 30
V
RT
29
28 27
AGND
26 25
CE 24
OE 23
CLK 22
MINV 21
LINV 20
ANALOG IN
(+2V to +4V)
EXT. CAL.
PULSE IN
JP1
39 V
IN
40
41 CAL
A/D
CLOCK IN
JP2
42
43
AGND
44
ADS-325A
MODE 19
JP3
+AV
S
18
SEL 17
0.1µF
45 +DV
S
46
47
48 DGND
1
2
3
4
5
6
7
8
9
10
11
13
12
DGND 16
RESET 15
JP4
JP5
10µF
+
JP6
0.1µF
RESET
IN
4. RESET pin (Pin 15) should normally
be connected to +AV
S
(close JP5).
To re-initiate the start-up calibration
after power-up, close JP6 to apply
external RESET pulse.
0.1µF
BIT 10
(LSB)
BIT 1
(MSB)
Figure 7. Typical ADS-325A Connection Diagram
6
MURATA-PS [ MURATA POWER SOLUTIONS INC. ]
