AS1524/AS1525
Datasheet - Detailed Description
Figure 19. Single Conversion – AIN1 vs. GND (AS1525), Unipolar Mode AIN+ vs. AIN- (AS1524)
Sampling Instant
tCONV
tACQ
CNVST
SCLK
DOUT
1
4
8
12
High Z
High Z
B11
MSB
B0
LSB
B10
B9
B8
B7
B6
B5
B4
B3
B2
B1
If AIN2 is selected (see Figure 20), drive CNVST high for at least 30ns. Next, drive CNVST low for at least 30ns, and
then high again. This powers up the AS1525 and places the track/hold circuitry in track mode with AIN2 connected to
the positive input capacitor. Next hold CNVST high for tACQ to fully acquire the signal. Drive CNVST low to place the
track/hold circuitry in hold mode. The AS1525 then performs a conversion and shuts down automatically. The MSB is
available at DOUT after 3.7µs. Data can then be clocked out using SCLK.
Note: If all 12 bits of data are not clocked out before CNVST is driven high, AIN2 is selected for the next conversion.
Selecting Unipolar or Bipolar Conversions (AS1524)
True-differential conversion (with the AS1524 unipolar and bipolar modes) is selected using pin CNVST (see page 3).
AIN+ and AIN- are sampled at the falling edge of CNVST. In unipolar mode, AIN+ can exceed AIN- by up to VREF. The
output format is straight binary. In bipolar mode, either input can exceed the other by up to VREF/2. The output format is
two’s complement. In both modes, the input common mode range can go from GND to VDD.
Figure 20. Single Conversion – AIN2 vs. GND (AS1525), Bipolar Mode AIN+ vs. AIN- (AS1524)
Sampling Instant
tCONV
tACQ
CNVST
SCLK
DOUT
1
4
8
12
High Z
High Z
B11
B0
LSB
B10
B9
B8
B7
B6
B5
B4
B3
B2
B1
MSB
Note: In unipolar and bipolar modes, AIN+ and AIN- must not exceed VDD by more than 50mV or be lower than GND
by more than 50mV.
If unipolar mode is selected (see Figure 19), drive CNVST high to power up the AS1524 and place the track/hold cir-
cuitry in track mode with AIN+ and AIN- connected to the input capacitors. Hold CNVST high for tACQ to fully acquire
the signal. Drive CNVST low to place the track/hold circuitry in hold mode. The AS1524 then performs a conversion
and shutdown automatically. The MSB is available at DOUT after 3.7µs. Data can then be clocked out using SCLK.
Clock out all 12 bits of data before driving CNVST high for the next conversion. If all 12 bits of data are not clocked out
before CNVST is driven high, bipolar mode is selected for the next conversion.
If bipolar mode is selected (see Figure 20), drive CNVST high for at least 30ns. Next, drive CNVST low for at least
30ns and then high again. This places the track/hold circuitry in track mode with AIN+ and AIN- connected to the input
capacitors.
Next hold CNVST high for tACQ to fully acquire the signal. Drive CNVST low to place the track/hold circuitry in hold
mode. The AS1524 then performs a conversion and shuts down automatically. The MSB is available at DOUT after
3.7µs. Data can then be clocked out using SCLK.
Note: If all 12 bits of data are not clocked out before CNVST is driven high, bipolar mode is selected for the next con-
version.
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