AS1520/AS1521
Data Sheet - Detailed Description
Figure 26. Two’s Complement Transfer Function for
RANGE = 1 and MODE = 0
Figure 27. Two’s Complement Transfer Function for
RANGE = 0 and MODE = 0
Full Scale = VREF
011....111
Full Scale = +VREF/2
011....111
-Full Scale = 0
-Full Scale = -VREF/2
Zero Scale = VREF/2
1LSB = VREF/1024
Zero Scale = 0
1LSB = VREF/1024
011...110
011...110
000...010
000...001
000...000
111...111
111...110
111...101
000...010
000...001
000...000
111...111
111...110
111...101
100...001
100...000
100...001
100...000
-FS
ZS
+FS - 1LSB
-FS
ZS
+FS - 1LSB
Input Voltage AIN+ - AIN- (LSB)
Input Voltage AIN+ - AIN- (LSB)
Power Modes
Power consumption can be reduced by placing the AS1520/AS1521 in reduced power mode or in full power-down
mode between conversions.
The power mode is selected using bits PD1 and PD0 of the 8-bit control byte.
Table 12 lists the three operating modes with the corresponding supply current and active device circuits. For data
rates achievable in full power-down mode see Full Power-Down Mode on page 20.
Table 12. Software Controlled Power Modes
*
Total Supply Current
Device Circuits
PD1/PD0
Mode
During Conversion
After Conversion
Input
(page 23)
Reference
Comparator
AS1520
AS1521
AS1520
AS1521
00
01
10
11
Full Power-Down Mode
Reduced-Power Mode
Normal Operation
2.8mA
2.2mA
0.5µA
0.5µA
Off
Off
On
On
Reduced
Power
2.8mA
2.8mA
2.2mA
2.2mA
0.4mA
2.0mA
0.4mA
1.8mA
Full Power
* Circuit operation between conversions; during conversion all circuits are fully powered up.
The selected power-down mode (as shown in Table 12) is initiated after an analog-to-digital conversion is completed.
In all power modes the serial interface remains active, waiting for a new control byte to start conversion (see Figure 30
on page 21). Once the conversion is completed, the AS1520/AS1521 goes into the selected power mode until a new
control byte is shifted in. In reduced power mode the AS1520/AS1521 will be able to start conversion immediately
when running at decreased clock rates. In full power down mode wait until the internal reference has stabilized (depen-
dant on the values of the capacitance of REF and REFADJ).
During initialization the AS1520/AS1521 immediately go into normal operation mode and are ready to convert after 4µs
when using an external reference. When using the internal reference, wait until the internal reference has stabilized
(dependant on the values of the capacitance of REF and REFADJ).
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