www.austriamicrosystems.com

Revision 1.00

19 - 29

AS1520/AS1521

Figure 26. Two’s Complement Transfer Function for

Figure 27. Two’s Complement Transfer Function for

RANGE = 1 and MODE = 0

RANGE = 0 and MODE = 0

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.

*

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).

Table 12. Software Controlled Power Modes

PD1/PD0

(page 23)

Mode

Total Supply Current

Device Circuits

*

During Conversion

After Conversion

Input

Comparator

Reference

AS1520

AS1521

AS1520

AS1521

00

Full Power-Down Mode

2.8mA

2.2mA

0.5µA

0.5µA

Off

Off

01

Reduced-Power Mode

2.8mA

2.2mA

0.4mA

0.4mA

Reduced

Power

On

10

11

Normal Operation

2.8mA

2.2mA

2.0mA

1.8mA

Full Power

On

011....111

011...110

000...010

000...001

000...000

111...111

111...110

111...101

100...001

100...000

-FS

ZS

Input Voltage AIN+ - AIN- (LSB)

+FS - 1LSB

-Full Scale = 0

011....111

011...110

000...010

000...001

000...000

111...111

111...110

111...101

100...001

100...000

-FS

ZS

Input Voltage AIN+ - AIN- (LSB)

+FS - 1LSB

Zero Scale = 0