AS1536/AS1537
Datasheet - Detailed Description
Figure 30. Supply Current vs. Sampling Rate
Figure 31. Powerup Time vs. Time in Shutdown
800
10000
Internal Reference
700
1000
600
500
400
300
200
100
0
Internal Reference
100
10
External Reference
5V
5V
3V
1
3V
0.1
0.1
10
1000
100000
0.001
0.01
0.1
1
10
Time in Shutdown (s)
Sampling Rate (sps)
Internal 2.5V Reference (AS1536)
The AS1536 internal 2.5V reference output is connected to pin REF and also drives the internal DAC (see Figure 24
on page 12). REF output can be used as a reference voltage source for other components and can source up to
400µA.
The internal reference is enabled by pulling pin SHDNN high. Letting SHDNN float disables the internal reference,
which allows the use of an external reference (see External Reference on page 16).
Pin REF should be bypassed with a 4.7µF capacitor as shown in Figure 23 on page 12. Larger capacitors increase
wake-up time when the devices exit shutdown mode (see Layout Considerations on page 19)
External Reference
Both devices can operate with an external reference at pin REF. The external reference should be within the +1.0V to
VDD voltage range to achieve specified accuracy. The minimum input impedance is 18kΩ for DC currents.
Note: To use an external reference with the AS1536, disable the internal reference by letting pin SHDNN float.
During conversion, the external reference should be capable of delivering up to 250µA of DC load current and have an
output impedance ≤ 10Ω. The recommended minimum value for the bypass capacitor is 0.1µF. If the reference has
higher output impedance or is noisy, bypass it close to pin REF with a 4.7µF capacitor.
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