AS1537 datasheet(14/21 Pages) AMSCO

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AS1536/AS1537

Datasheet - D e t a i l e d D e s c r i p t i o n

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

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

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.

11...111

11...1110

11....101

00...011

00...010

00...001

00...000

Input Voltage AIN

FS - 3/2LSB

Full Scale (FS)

Transition

Full Scale = VREF

Zero Scale = 0

1LSB = VREF/4096

Complete Conversion Sequence

Conversion 0

Conversion 1

Power-Up

Shutdown

tWAKE

Power-Up

CSN

SHDNN

DOUT

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