AS1536/AS1537
Datasheet - Detailed Description
Transfer Function
The data output from the AS1536/AS1537 is binary (unipolar), and Figure 28 depicts the nominal transfer function.
Code transitions occur midway between successive integer LSB values.
Note: If VREF = +2.50V, then 1 LSB = 610µV (2.50V/4096).
Figure 28. Unipolar Transfer Function
11...111
Full Scale (FS)
Transition
11...1110
Full Scale = VREF
Zero Scale = 0
11....101
1LSB = VREF/4096
00...011
00...010
00...001
00...000
0
1
2
3
FS - 3/2LSB
Input Voltage AIN
Reducing Supply Current
Power consumption can be reduced significantly by powering down the devices between conversions. Figure 30
shows a plot of an average supply current versus sampling rate.
Wake-up time (tWAKE) can also factor into reduced power consumption. tWAKE is defined as the time from when pin
SHDNN is deasserted to the time when a conversion may be initiated (see Figure 29).
Figure 29. Shutdown Sequence Timing Diagram
Complete Conversion Sequence
CSN
tWAKE
SHDNN
DOUT
Conversion 0
Power-Up
Conversion 1
Power-Up
Shutdown
For the AS1536 using the internal reference, tWAKE depends on the time in shutdown mode (see Figure 31) since the
external 4.7µF reference bypass capacitor slowly loses charge during shutdown. The wakeup time for AS1536 and
AS1537 using an internal reference are largely dependent on the external reference’s power-up time. The wakeup time
for the ADC itself from shutdown mode is approximately 4µs.
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