AS1536/AS1537
Datasheet - Detailed Description
8 Detailed Description
The AS1536/AS1537 analog-to-digital converters have two modes of operation:
ꢀ
Normal A/D Conversion Mode – Pulling pin SHDNN high or leaving it open puts the device into normal A/D conver-
sion mode.
ꢀ
Shutdown Mode – Pulling pin SHDNN low shuts the device down and reduces supply current below 2µA (VDD ≤
3.6V).
Note: Pulling pin CSN low starts a conversion. The conversion result is available at pin DOUT in unipolar serial for-
mat (see Timing and Control on page 13).
Figure 23 shows a basic configuration for the AS1536/AS1537. The integrated input track/hold circuitry and a succes-
sive-approximation register (SAR) circuitry convert analog input signals to a digital 12-bit output. No external-hold
capacitor is needed for the track/hold circuit.
The devices convert analog input signals in the 0V to VREF range in 13.7µs (includes track/hold acquisition time).
The AS1536 internal reference is trimmed to 2.5V; the AS1537 requires an external reference. Both devices can
accept external reference voltages from 1.0V to VDD. The serial interface requires only three digital lines (at pins
SCLK, CSN, and DOUT) and provides a simple microprocessor interface.
Figure 23. Operational Diagram
1
8
+2.7V to +5.25V
VDD
SCLK
+
4.7µF
0.1µF
2
7
AIN
CSN
AS1536/
AS1537
3
6
SHDNN
DOUT
Reference Input
Required for AS1537,
Optional for AS1536
4
5
REF
GND
AS1536 – 4.7µF
AS1537 – 0.1µF
Analog Input
Figure 24 illustrates the integrated comparator sampling architecture. The full scale input voltage is set by the voltage
at pin REF.
Figure 24. Equivalent Input Circuit
REF
CHOLD
13pF
+
AIN
–
+
CSWITCH
14pF
Sample
Switch
–
Comparator
CHOLD
13pF
RIN
–
+
GND
S&H and DAC
CSWITCH includes all parasitics
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