ams AS1538 8/4-channel, 12-bit i2c analog-to-digital converter Datasheet

AS1538/AS1540
D a ta S he e t
8 / 4 - C h a n n e l , 1 2 - B i t I ² C A n a l o g - t o - D i g i ta l C o n v e r t e r
1 General Description
2 Key Features
Single Supply: 2.7 to 5.25V
The AS1538/AS1540 are single-supply, low-power, 12bit data acquisition devices featuring a serial I²C interface and an 8-channel (AS1538) or 4-channel (AS1540)
multiplexer.
!
!
8-Channel Multiplexer (AS1538)
The analog-to-digital (A/D) converters features a sample-and-hold amplifier an internal asynchronous clock
and an internal reference.
!
4-Channel Multiplexer (AS1540)
!
Sampling Rate: 50kSPS
!
No Missing Codes
!
Internal Reference: 2.5V
!
High Speed I C Interface at 3.4MHz
!
<1.5µA Full Shutdown Current
!
TSSOP-16 or TQFN 4x4 16-pin Package
2
The combination of an I C serial, 2-wire interface and
micropower consumption makes the AS1538 and
AS1540 ideal for applications requiring the A/D converter to be close to the input source in remote locations
and for applications requiring isolation.
The device is available in a TSSOP-16 or TQFN 4x4 16pin package.
2
3 Applications
The device is ideal for voltage-supply monitoring, isolated data acquisition, transducer interfaces, batteryoperated systems, remote data acquisition or any other
analog-to-digital conversion application.
Figure 1. Block Diagram
CH0
SDA
Successive Approximation Register
CH1
Serial
Interface
CH2
CH3
AS1538/AS1540
CH5
AS1538 only
A0
8-Channel
MUX
CH4
SCL
A1
Sample/
Hold
Amp
CDAC
Comparator
CH6
CH7
COM
Buffer
REFIN/OUT
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Revision 1.03
Internal
2.5V
Reference
GND
1 - 20
AS1538/AS1540
Data Sheet - P i n o u t
4 Pinout
Pin Assignments
Figure 2. Pin Assignments (Top View)
CH0 1
16 +VDD
CH0
+VDD
N/C
SDA
CH1 2
15 SDA
16
15
14
13
CH2 3
14 SCL
CH3 4
AS1538
13 A1
CH1
1
CH2
2
12 SCL
11 A1
AS1540
10 A0
CH5 6
11 COM
N/C
4
9
CH6 7
10 REFIN/OUT
CH7 8
9 GND
5
6
7
8
COM
3
REFIN/OUT
CH3
GND
12 A0
N/C
CH4 5
N/C
Pin Descriptions
Table 1. Pin Descriptions
AS1538
1:8
9
10
11
12
13
14
15
16
-
AS1540
1:3,16
6
7
8
10
11
12
13
15
4, 5, 9, 14
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Pin Name
CH0:CH3
CH0:CH7
GND
REFIN/OUT
COM
A0
A1
SCL
SDA
+VDD
NC
Description
Analog Input Channels 0 to 3
Analog Input Channels 0 to 7
Analog Ground
Internal Reference/External Reference Input
Analog Input Channel Common
Slave Address Bit 0
Slave Address Bit 1
Serial Clock
Serial Data
Power Supply Input. 2.7 to 5.25V.
Not Connected
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AS1538/AS1540
Data Sheet - A b s o l u t e M a x i m u m R a t i n g s
5 Absolute Maximum Ratings
Stresses beyond those listed in Table 2 may cause permanent damage to the device. These are stress ratings only,
and functional operation of the device at these or any other conditions beyond those indicated in Electrical Characteristics on page 4 is not implied. Exposure to absolute maximum rating conditions for extended periods may affect
device reliability.
Table 2. Absolute Maximum Ratings
Parameter
Min
Max
Units
+VDD to GND
-0.3
+6
V
Digital Input Voltage to GND
-0.3
+VDD +
0.3
V
100
°C/W
Thermal Resistance θJA
Operating Temperature Range
-40
+85
ºC
Storage Temperature Range
-65
+150
ºC
150
ºC
Junction Temperature (TJMAX)
ESD
Package Body Temperature
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1.5
+260
Comments
on PCB
kV
HBM MIL-Std. 883E 3015.7 methods
ºC
The reflow peak soldering temperature (body
temperature) specified is in accordance with
IPC/JEDEC J-STD-020C “Moisture/Reflow
Sensitivity Classification for Non-Hermetic
Solid State Surface Mount Devices”.
The lead finish for Pb-free leaded packages is
matte tin (100% Sn).
Revision 1.03
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AS1538/AS1540
Data Sheet - E l e c t r i c a l C h a r a c t e r i s t i c s
6 Electrical Characteristics
Electrical Characteristics
+VDD = +2.7 to +5.25V, VREF = +2.5V external, SCL = 3.4MHz, TAMB = -40 to +85ºC (unless otherwise specified).
Table 3. Electrical Characteristics
Symbol
Analog Input
Parameter
Condition
Min
Fullscale Input Span
Positive input, negative input
Typ
Max
Unit
0
VREF
V
Positive input
-0.3
+VDD
+ 0.3
V
Negative Input
-0.3
+VDD
+ 0.3
V
Absolute Input Range
Capacitance
Track Mode
15
Hold Mode
8
ILEAK
Leakage Current
Static Performance
pF
±0.1
±1
µA
±0.75
±1.5
LSB
Differential Linearity Error
±0.5
±1
LSB
Offset Error
±0.5
±6
LSB
±0.2
±1
LSB
±1
±6
LSB
±0.2
±1
LSB
No Missing Codes
12
Integral Linearity Error
Offset Error Match
VREF = 2.5V, 1 LSB = 610µV
1
Gain Error
Gain Error Match
1
Power Supply Rejection
Dynamic Performance
Bits
1
mV
Throughput Frequency
50
kHz
Conversion Time
6.67
µs
AC Accuracy
THD
2
VIN = 2.5VP-P @ 10kHz
-75
dB
Signal-to-Noise Ratio
VIN = 2.5VP-P @ 10kHz
72
dB
Signal-to-Noise (+ Distortion)
Ratio
VIN = 2.5VP-P @ 10kHz
69.5
dB
VIN = 2.5VP-P @ 10kHz
75
dB
Total Harmonic Distortion
Spurious-Free Dynamic Range
Voltage Reference Output
Range
2.475
2.5
2.525
V
Internal Reference Drift
30
ppm/ºC
Output Impedance
30
Ω
Quiescent Current
Voltage Reference Input
440
µA
Range
1
Input Resistance
Reference Input Current
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PD = 01 Internal Ref. OFF, ADC ON
@ 50kSPS
Revision 1.03
VDD
V
1
GΩ
4
µA
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AS1538/AS1540
Data Sheet - E l e c t r i c a l C h a r a c t e r i s t i c s
Table 3. Electrical Characteristics
Symbol
Parameter
Condition
Min
Typ
Max
Unit
CMOS Digital I/O
VIH
Input High Logic Level
+VDD
x 0.7
+VDD
+ 0.5
V
VIL
Input Low Logic Level
-0.3
+VDD
x 0.3
V
VOL
Output Low Logic Level
3mA sink current
0.4
V
IIH
Input High Leakage Current
VIH = +VDD
1
µA
IIL
Input Low Leakage Current
Data Format
Power Supply Requirements
+VDD
VIL = GND
-1
µA
Straight binary
Power Supply Voltage
Specified performance
PD = 00 Full Power-Down
0.04
1.2
Analog Current in Static Mode,
3.6V
PD = 01 Internal Ref. OFF, ADC ON
400
500
PD = 10 Internal Ref. ON, ADC OFF
500
600
PD = 11 Internal Ref. ON, ADC ON
800
900
PD = 00 Full Power-Down
0.04
1.5
IQSTAT
Analog Current in Static Mode,
5.25V
2.7
5.25
PD = 01 Internal Ref. OFF, ADC ON
450
550
PD = 10 Internal Ref. ON, ADC OFF
550
650
PD = 11 Internal Ref. ON, ADC ON
850
950
Quiescent Current at Full
Speed, 3.6V
PD = 01 Internal Ref. OFF, ADC ON
500
600
PD = 11 Internal Ref. ON, ADC ON
850
950
Quiescent Current at Full
Speed, 5.25V
PD = 01 Internal Ref. OFF, ADC ON
650
800
PD = 11 Internal Ref. ON, ADC ON
915
1150
IQ
V
µA
µA
µA
µA
1. Guaranteed by design and characterized on sample base.
2. THD measure out to 5th harmonic.
Timing Characteristics
+VDD = +2.7 to 5.25V, TAMB = -40 to +85ºC (unless otherwise specified). All values referenced to VIHMIN and VILMAX
levels.
Table 4. Timing Characteristics
Symbol
fSCL
tBUF
THOLDSTART
tLOW
tHIGH
TSETUPSTART
TSETUPDATA
THOLDDATA
TRISESCLK
Parameter
SCL Frequency
Bus Free Time Between
STOP and START Conditions
Hold Time for Repeated
START Condition
SCL Low Period
SCL High Period
Setup Time for Repeated
START Condition
Data Setup Time
Data Hold Time
Condition
Min
0.1
Typ
Max
3.4
Unit
MHz
1.3
µs
160
ns
50
50
75
75
100
ns
ns
ns
10
70
ns
ns
1
SCL Rise Time
10
40
ns
1
SCL Rise Time after
Repeated START Condition
and After an ACK Bit
10
80
ns
TRISESCLK1
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Revision 1.03
5 - 20
AS1538/AS1540
Data Sheet - E l e c t r i c a l C h a r a c t e r i s t i c s
Table 4. Timing Characteristics
Symbol
Parameter
Max
Unit
1
TFALLSCLK
1
TRISESDA
1
TFALLSDA
SCL Fall Time
Condition
Min
10
Typ
40
ns
SDA Fall Time
20
80
ns
SDA Fall Time
20
80
ns
TSETUPSTOP
STOP Condition Setup Time
160
ns
1. Guaranteed by design and characterized on sample base.
Figure 3. Timing Diagram
SDA
tBUF
tHOLDSTART
tHIGH
tHOLDSTART
tR
tLOW
tSPIKESUP
tSETUPDATA
tF
tSETUPSTOP
tSETUPSTART
SCL
START STOP
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tHOLDDATA
Repeated
START
Revision 1.03
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AS1538/AS1540
Data Sheet - Ty p i c a l O p e r a t i n g C h a r a c t e r i s t i c s
7 Typical Operating Characteristics
VDD = 3.6V; VREF = 2.5V (internal), fSCL = 3.4MHz, CREF = 4.7µF, TAMB = +25ºC (unless otherwise specified).
Figure 4. DNL vs. Digital Output Code, Int. Reference
Figure 5. INL vs. Digital Output Code, Int. Reference
1
1.2
fSAMPLE = 50ksps
fSAMPLE = 50ksps
0.8
0.8
0.4
INL (LSB) .
DNL (LSB) .
0.6
0.2
0
-0.2
-0.4
-0.6
0.4
0
-0.4
-0.8
-0.8
-1.2
-1
0
1024
2048
3072
0
4096
Figure 6. DNL vs. Digital Output Code, Ext. Reference
1
1024
2048
3072
4096
Digital Output Code
Digital Output Code
Figure 7. INL vs. Digital Output Code, Ext. Reference
1.2
fSAMPLE = 50ksps
fSAMPLE = 50ksps
0.8
0.8
0.4
INL (LSB) .
DNL (LSB) .
0.6
0.2
0
-0.2
-0.4
-0.6
0.4
0
-0.4
-0.8
-0.8
-1
-1.2
0
1024
2048
3072
4096
0
Digital Output Code
1024
2048
3072
4096
Digital Output Code
Figure 8. Offset Error vs. Temperature
Figure 9. Offset Matching vs. Temperature
1
6
0.8
0.6
Offset (LSB) .
Offset (LSB) .
4
2
0
-2
0.4
0.2
0
-0.2
-0.4
-0.6
-4
-0.8
-6
-45 -30 -15
0
15 30
45
60 75
90
-1
-45 -30 -15
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0
15 30 45 60 75 90
Temperature (°C)
Temperature (°C)
Revision 1.03
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AS1538/AS1540
Data Sheet - Ty p i c a l O p e r a t i n g C h a r a c t e r i s t i c s
Figure 10. Offset Error vs. Supply Voltage
Figure 11. Offset Matching vs. Supply Voltage
6
1
0.8
.
Offset Error (LSB)
Offset Error (LSB)
.
4
2
0
-2
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-4
-0.8
-6
-1
2.7
3.2
3.7
4.2
4.7
5.2
2.7
3.2
Supply Voltage (V)
3.7
4.2
4.7
5.2
Supply Voltage (V)
Figure 12. Gain Error vs. Temperature
Figure 13. Gain Matching vs. Temperature
6
1
0.8
Gain Error (LSB) .
Gain Error (LSB) .
4
2
0
-2
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-4
-0.8
-6
-45 -30 -15
0
15 30
45
60 75
-1
-45 -30 -15
90
Temperature (°C)
0
15 30 45 60 75 90
Temperature (°C)
Figure 14. Gain Error vs. Supply Voltage
Figure 15. Gain Matching vs. Supply Voltage
6
1
0.8
Gain Error (LSB) .
Gain Error (LSB) .
4
2
0
-2
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-4
-0.8
-6
-1
2.7
3.2
3.7
4.2
4.7
5.2
2.7
Supply Voltage (V)
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3.2
3.7
4.2
4.7
5.2
Supply Voltage (V)
Revision 1.03
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AS1538/AS1540
Data Sheet - Ty p i c a l O p e r a t i n g C h a r a c t e r i s t i c s
Figure 16. Supply Current vs. Supply Voltage, PD=00
Figure 17. Supply Current vs. Supply Voltage, PD=01
1000
250
Supply Current (µA) .
Supply Current (nA) .
300
200
150
100
50
800
600
400
200
0
0
2.7
3.2
3.7
4.2
4.7
5.2
2.7
3.2
Supply Voltage (V)
Figure 18. Supply Current vs. Supply Voltage, PD=11
4.7
5.2
1200
Supply Current (µA) .
Supply Current (µA) .
4.2
Figure 19. Supply Current vs. Sampling Rate, PD = 11
1000
800
600
400
200
1000
800
600
400
200
0
0
2.7
3.2
3.7
4.2
4.7
0
5.2
Figure 20. FFT, Int. Reference
0
-40
0
-80
-100
-120
-40
40
50
-60
-80
-100
-120
-140
-140
-160
-160
-180
30
fSAMPLE = 50ksps
NFFT = 32768
SNR=72.7dB
THD = -74.7dB
SFDR = 76.5dB
-20
FFT (dBC) .
-60
20
Figure 21. FFT, Ext. Reference
fSAMPLE = 50ksps
NFFT = 32768
SNR=72.7dB
THD = -74.3dB
SFDR = 76.3dB
-20
10
Sampling Rate (ksps)
Supply Voltage (V)
FFT (dBC) .
3.7
Supply Voltage (V)
-180
0
5000
10000 15000 20000 25000
0
Input Signal Frequency (kHz)
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5000
10000 15000 20000 25000
Input Signal Frequency (kHz)
Revision 1.03
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AS1538/AS1540
Data Sheet - D e t a i l e d D e s c r i p t i o n
8 Detailed Description
The AS1538/AS1540 successive approximation register (SAR) A/D converter architecture is based on capacitive
redistribution which inherently includes a sample-and- hold function.
The AS1538/AS1540 core is controlled by an internally generated free-running clock. When the device is not performing conversions or being addressed, the A/D converter-core and internal clock are powered off.
Figure 22. Simplified I/O Diagram
+2.7 to
+5.25V
0.1 to
10µF
CH0
VDD
CH1
+
0.1 to
10µF
+
2kΩ
CH2
CH3
SDA
AS1538/
AS1540
CH4
Microcontroller
SCL
AS1538 only
CH5
CH6
A0
CH7
A1
COM
1µF
GND
REFIN/OUT
Analog Input
When the converter enters the hold mode, the voltage on the selected CHx pin is captured on the internal capacitor
array. The input current on the analog inputs depends on the conversion rate of the device. During the sample period,
the source must charge the internal sampling capacitor (typically 15pF). After the capacitor has been fully charged,
there is no further input current. The amount of charge transfer from the analog source to the converter is a function of
conversion rate.
Figure 23. Reference circuit
VIN
+
+2.7 to
+5.25V
10Ω
CH0:CH7
-
VDD
1nF
+
0.1 to
10µF
2kΩ
AS1538
1µF
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REFIN/OUT
Revision 1.03
SDA
10 - 20
AS1538/AS1540
Data Sheet - D e t a i l e d D e s c r i p t i o n
Reference Voltage
The AS1538/AS1540 can operate with an internal 2.5V reference or an external reference. If a +5V supply is used, an
external +5V reference is required in order to provide full dynamic range for a 0V to +VDD analog input. The external
reference can be as low as 1V. When using a +2.7V supply, the internal +2.5V reference will provide full dynamic range
for a 0V to +2.5V analog input.
As the reference voltage is reduced, the analog voltage weight of each digital output code is reduced. This is often
referred to as the LSB (least significant bit) size and is equal to the reference voltage divided by 4096. This means that
any offset or gain error inherent in the A/D converter will appear to increase, in terms of LSB size, as the reference voltage is reduced.
Digital Interface
2
The AS1538/AS1540 supports the I C serial bus and data transmission protocol in high-speed mode at 3.4MHz. The
2
AS1538/AS1540 operates as a slave on the I C bus. The bus must be controlled by a master device that generates the
serial clock (SCL), controls the bus access, and generates the START and STOP conditions. Connections to the bus
are made via the open-drain I/O pins SCL and SDA.
Figure 24. Bus Protocol
MSB
SDA
ACK from
Receiver
Slave Address
R/W
Direction Bit
ACK from
Receiver
1
SCL
2
6
7
8
9
ACK
1
2
3-8
8
9
ACK
Repeat if More Bytes Transferred
START
STOP or
Repeated
START
The bus protocol (as shown in Figure 24) is defined as:
- Data transfer may be initiated only when the bus is not busy.
- During data transfer, the data line must remain stable whenever the clock line is HIGH. Changes in the data line
while the clock line is HIGH will be interpreted as control signals.
The bus conditions are defined as:
- Bus Not Busy. Data and clock lines remain HIGH.
- Start Data Transfer. A change in the state of the data line, from HIGH to LOW, while the clock is HIGH, defines a
START condition.
- Stop Data Transfer. A change in the state of the data line, from LOW to HIGH, while the clock line is HIGH,
defines the STOP condition.
- Data Valid. The state of the data line represents valid data, when, after a START condition, the data line is stable
for the duration of the HIGH period of the clock signal. There is one clock pulse per bit of data.
Each data transfer is initiated with a START condition and terminated with a STOP condition. The number of data
bytes transferred between START and STOP conditions is not limited and is determined by the master device.
The information is transferred byte-wise and each receiver acknowledges with a ninth-bit.
2
Within the I C bus specifications a high-speed mode (3.4MHz clock rate) is defined.
- Acknowledge: Each receiving device, when addressed, is obliged to generate an acknowledge after the reception of each byte. The master device must generate an extra clock pulse that is associated with this acknowledge
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AS1538/AS1540
Data Sheet - D e t a i l e d D e s c r i p t i o n
bit. A device that acknowledges must pull down the SDA line during the acknowledge clock pulse in such a way
that the SDA line is stable LOW during the HIGH period of the acknowledge clock pulse. Of course, setup and
hold times must be taken into account. A master must signal an end of data to the slave by not generating an
acknowledge bit on the last byte that has been clocked out of the slave. In this case, the slave must leave the
data line HIGH to enable the master to generate the STOP condition.
2
Figure 24 on page 11 details how data transfer is accomplished on the I C bus. Depending upon the state of the R/W
bit, two types of data transfer are possible:
- Master Transmitter to Slave Receiver. The first byte transmitted by the master is the slave address, followed by
a number of data bytes. The slave returns an acknowledge bit after the slave address and each received byte.
- Slave Transmitter to Master Receiver. The first byte, the slave address, is transmitted by the master. The slave
then returns an acknowledge bit. Next, a number of data bytes are transmitted by the slave to the master. The
master returns an acknowledge bit after all received bytes other than the last byte. At the end of the last received
byte, a not-acknowledge is returned. The master device generates all of the serial clock pulses and the START
and STOP conditions. A transfer is ended with a STOP condition or a repeated START condition. Since a
repeated START condition is also the beginning of the next serial transfer, the bus will not be released.
The AS1538 can operate in the following slave modes:
- Slave Receiver Mode. Serial data and clock are received through SDA and SCL. After each byte is received, an
acknowledge bit is transmitted. START and STOP conditions are recognized as the beginning and end of a serial
transfer. Address recognition is performed by hardware after reception of the slave address and direction bit.
- Slave Transmitter Mode. The first byte (the slave address) is received and handled as in the slave receiver
mode. However, in this mode the direction bit will indicate that the transfer direction is reversed. Serial data is
transmitted on SDA by the AS1538 while the serial clock is input on SCL. START and STOP conditions are recognized as the beginning and end of a serial transfer.
Address Byte
The address byte (see Figure 25) is the first byte received following the START condition from the master device.
Figure 25. Address Byte
MSB
6
5
4
3
2
1
LSB
1
0
0
1
0
A1
A0
R/W
- The first five bits (MSBs) of the slave address are factory-set to 10010.
- The next two bits of the address byte are the device select bits, A1 and A0, which are set by the state of pins A1
and A0 at startup. A maximum of four devices with the same pre-set code can therefore be connected on the
same bus at one time. Pins A1/A0 can be connected to +VDD or digital ground.
- The last bit of the address byte (R/W) define the operation to be performed. When set to a 1 a read operation is
selected; when set to a 0 a write operation is selected.
Following the START condition, the AS1538 monitors the SDA bus, checking the device type identifier being transmitted. Upon receiving the 10010 code, the appropriate device select bits, and the R/W bit, the slave device outputs an
acknowledge signal on the SDA line.
Command Byte
The AS1538/AS1540 operation, including powerdown (see Table 5) and channel selection (see Table 6) is determined
by a command byte (see Figure 26).
Figure 26. Command Byte
MSB
6
5
4
3
2
1
LSB
SD
C2
C1
C0
PD1
PD0
X
X
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Revision 1.03
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AS1538/AS1540
Data Sheet - D e t a i l e d D e s c r i p t i o n
Where:
SD: Single-Ended/Differential Inputs
0: Differential Inputs
1: Single-Ended Inputs
C2, C1, C0: Channel Selections
PD1, PD0: Power-Down Selection
X: Unused
Powerdown Selection
Powerdown modes for the AS1538/AS1540 are selected by setting bits PD0 and PD1 of a command byte (see Command Byte on page 12).
Table 5. Powerdown Mode Bit Settings
PD1
PD0
Description
0
0
Powerdown between A/D converter conversions.
0
1
Internal reference off and A/D converter on.
1
0
Internal reference on and A/D converter off.
1
1
Internal reference on and A/D converter on.
Channel Selection
Channel selection for the AS1538/AS1540 is made using a command byte (see Command Byte on page 12).
AS1538
only
AS1538
only
AS1538
only
AS1538
only
Table 6. Channel Selection Bit Settings
1
SD
C2
C1
C0
CH0
CH1
CH2
CH3
CH4
CH5
CH6
CH7
COM
0
0
0
0
+IN
–IN
-
-
-
-
-
-
-
0
0
0
1
-
-
+IN
–IN
-
-
-
-
-
0
0
1
0
-
-
-
-
+IN
–IN
-
-
-
0
0
1
1
-
-
-
-
-
-
+IN
–IN
-
0
1
0
0
–IN
+IN
-
-
-
-
-
-
-
0
1
0
1
-
-
–IN
+IN
-
-
-
-
-
0
1
1
0
-
-
-
-
–IN
+IN
-
-
-
0
1
1
1
-
-
-
-
-
-
–IN
+IN
-
1
0
0
0
+IN
-
-
-
-
-
-
-
–IN
1
0
0
1
-
-
+IN
-
-
-
-
-
–IN
1
0
1
0
-
-
-
-
+IN
-
-
-
–IN
1
0
1
1
-
-
-
-
-
-
+IN
-
–IN
1
1
0
0
-
+IN
-
-
-
-
-
-
–IN
1
1
0
1
-
-
-
+IN
-
-
-
-
–IN
1
1
1
0
-
-
-
-
-
+IN
-
-
–IN
1
1
1
1
-
-
-
-
-
-
-
+IN
–IN
1. For the 4-channel AS1540 only combinations of CH0:CH3 applies.
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AS1538/AS1540
Data Sheet - A p p l i c a t i o n I n f o r m a t i o n
9 Application Information
Initiating a Conversion
After the AS1538/AS1540 has been write-addressed by the bus master, the A/D converter circuitry is powered on, and
conversions will begin when a command byte bit C0 (see Command Byte on page 12) is received. If the address byte
is valid, the AS1538/AS1540 will return an ACK.
Reading Data
Data can be read from the AS1538/AS1540 by read-addressing the device (LSB of address byte set to 1 (see Command Byte on page 12)) and receiving the transmitted bytes. Converted data can only be read from the AS1538/
AS1540 once a conversion has been initiated as described in Initiating a Conversion.
Each 12-bit data word (see Figure 27) is returned in two bytes, where D11 is the MSB of the data word, and D0 is the
LSB. Byte 0 is sent first, followed by Byte 1.
Figure 27. Data Word
MSB
6
5
4
3
2
1
LSB
Byte 0
0
0
0
0
D11
D10
D9
D8
Byte 1
D7
D6
D5
D4
D3
D2
D1
D0
Figure 28 illustrates the interaction between the master and the slave AS1538/AS1540.
The most efficient way to perform continuous conversions is to issue repeated STARTs to the AS1538/AS1540 (to
secure the bus for subsequent ADC conversions) after reading each conversion. It is recommended that during the
conversion mode no data is clocked into the ADC to prevent internal noise. Therefore, after the repeated start commend it is recommanded not to clock in or out any data from the converter for 3.7µs. The ADC powers up after the PD0
bit is clocked in and it takes 1.4µs to fully power up. At a clock frequency of 3.4MHz this time is automatically achieved
and no extra delay should be included.
Figure 28. Read Sequence
ADC Powerdown Mode
S
1
0
0
1
0
A1
A0
W
A
ADC Sampling Mode
SD C2 C1 C0 PD1 PD0 X
Write-Addressing Byte
Sampling
Instance
1
3.7µs
0
A
Command Byte
ADC Conversion Mode
Sr
X
ADC Powerdown Mode *
0
1
0
A1
A0
R
A
0
0
0
0
D11 D10 D9 D8
A
D7 D6 ... D1 D0
N
P
Read-Addressing Byte
From Master to Slave
* Dependant on powerdown selection bits PD0 and PD1
From Slave to Master
Use repeated STARTs to secure the
bus operation and loop back to the
stage of write-addressing for the
next conversion.
Where:
A: Acknowledge (SDA Low)
N: Not Acknowledge (SDA High)
S: START Condition
P: STOP Condition
Sr: Repeated START Condition
W: 0 (Write)
R: 1 (Read)
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Revision 1.03
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AS1538/AS1540
Data Sheet - A p p l i c a t i o n I n f o r m a t i o n
Reading with Internal Reference On/Off
The internal reference defaults to off when the AS1538/AS1540 power is on. If the reference (internal or external) is
continuously turned on and off, a proper amount of settling time must be added before a normal conversion cycle can
be started. The exact amount of settling time needed varies depending on the reference capacitor. For example for a
reference capacitor of 4.7µF and considering the output impedance of the internal reference of 30Ω and the amount of
time to fully charge the capacitor will be 1.4ms. If the reference capacitor is not fully discharged this time can be
reduced greatly.
Figure 29 shows the correct internal reference enable sequence before issuing the typical read sequences required for
the mode when an internal reference is used.
Note: Typical read sequences can be re-used once the internal reference has settled.
Figure 29. Internal Reference Enable Sequence and Typical Read Sequence
Internal-Reference
Enable Settling Time
Internal-Reference Enable Sequence
S
1
0
0
1
0
A1
A0
W
A
X
X
Write-Addressing Byte
X
X
1
X
X
X
A
P
Wait until required settling time reached
Command Byte
Typical Mode Read Sequence
Settled Internal Reference
ADC Powerdown Mode
Sr
1
0
0
1
0
A1
A0
W
A
ADC Sampling Mode
SD C2 C1 C0
Write-Addressing Byte
1
PD0 X
X
A
Command Byte
Settled Internal Reference
ADC Conversion Mode
Sampling
Instance
Sr
1
0
0
1
0
A1
A0
Read-Addressing Byte
ADC Powerdown Mode *
R
A
0
0
0
0
D11 D10 D9 D8
A
D7 D6 ... D1 D0
N
P
**
2 x (8-bits +ACK/NACK
From Master to Slave
* Dependant on powerdown selection
bits PD0 and PD1.
From Slave to Master
** To remain in HS mode, use repeated
STARTs instead of STOPs
Where:
A: Acknowledge (SDA Low)
N: Not Acknowledge (SDA High)
S: START Condition
P: STOP Condition
Sr: Repeated START Condition
W: 0 (Write)
R: 1 (Read)
X: Dont Care
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Revision 1.03
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AS1538/AS1540
Data Sheet - A p p l i c a t i o n I n f o r m a t i o n
When using the internal reference:
1. Bit PD1 off the command byte must always be set to logic 1 for each sample conversion that is issued by the
sequence, as shown in Figure 28 on page 14.
2. In order to achieve 12-bit accuracy conversion when using the internal reference, the internal reference settling time must be considered.
If bit PD1 has been set to logic 0 while using the AS1538/AS1540, then the settling time must be reconsidered
after PD1 is set to logic 1 (i.e., whenever the internal reference is turned on after it has been turned off, the settling time must be long enough to get 12-bit accuracy conversion).
3. When the internal reference is off, it is not turned on until both the first command byte with PD1 = 1 is sent and
then a STOP condition or repeated START condition is issued. (The actual turn-on time occurs once the STOP
or repeated START condition is issued.) Any command byte with PD1 = 1 issued after the internal reference is
turned on serves only to keep the internal reference on. Otherwise, the internal reference would be turned off
by any command byte with PD1 = 0.
The example in Figure 29 can be generalized for a conversion cycle by simply swapping the timing of the conversion
cycle.
Note: If an external reference is used, PD1 must be set to 0, and the external reference must be settled. The typical
sequence in Figure 28 on page 14 or Figure 29 on page 15 can then be used.
Layout
For optimum performance, care should be taken with the physical layout of the AS1538/AS1540 circuitry. The basic
SAR architecture is sensitive to glitches or sudden changes on the power supply, reference, ground connections, and
digital inputs that occur just prior to latching the output of the analog comparator. Therefore, during any single conversion for an n-bit SAR converter, there are n windows in which large external transient voltages can easily affect the
conversion result. Such glitches might originate from switching power supplies, nearby digital logic, and high-power
devices.
- Power to the AS1538/AS1540 should be clean and well-bypassed. A 0.1µF ceramic bypass capacitor should be
placed as close to the device as possible. A 1 to 10µF capacitor may also be needed if the impedance of the connection between +VDD and the power supply is high.
- The AS1538/AS1540 architecture offers no inherent rejection of noise or voltage variation in regards to using an
external reference input. This is of particular concern when the reference input is tied to the power supply. Any
noise and ripple from the supply will appear directly in the digital results.
- While high-frequency noise can be filtered out, voltage variation due to line frequency (50 or 60Hz) can be difficult
to remove.
- The GND pin should be connected to a clean ground point. In many cases, this will be the analog ground. Avoid
connections that are too near the grounding point of a microcontroller or digital signal processor.
- The ideal layout will include an analog ground plane dedicated to the converter and associated analog circuitry.
Note:
For additional information download the evaluation board application note on our website.
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Revision 1.03
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AS1538/AS1540
Data Sheet - P a c k a g e D r a w i n g s a n d M a r k i n g s
10 Package Drawings and Markings
Figure 30. TSSOP-16 Package
Notes:
1. All dimensions are in millimeters; angles in degrees.
2. Dimensioning and tolerancing per ASME Y14.5M – 1994.
3. Dimension D does not include mold flash, protrusions, or gate
burrs. Mold flash, protrusions, and gate burrs shall not exceed
0.15mm per side.
4. Dimension E1 does not include interlead flash or protrusion.
Interlead flash or protrusions shall not exceed 0.25mm per
side.
5. Dimension b does not include dambar protrusion. Allowable
dambar protrusion shall be 0.08mm total in excess of the b
dimension at maximum material condition. Dambar cannot be
located on the lower radius of the foot.
6. Terminal numbers are for reference only.
7. Datums A and B to be determined at datum plane H.
8. Dimensions D and E1 are to be determined at datum plane H.
9. This dimension applies only to variations with an even number
of leads per side.
10. Cross section A-A to be determined at 0.10 to 0.25mm from
the leadtip.
Symbol
A
A1
A2
L
R
R1
b
b1
c
c1
θ1
L1
aaa
bbb
ccc
ddd
e
θ2
θ3
D
E1
E
e
N
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Revision 1.03
Min
0.05
0.85
0.50
0.09
0.09
0.19
0.19
0.09
0.09
0º
Typ
0.90
0.60
0.22
1.0REF
0.10
0.10
0.05
0.20
0.65BSC
12ºREF
12ºREF
Variations
4.90
5.00
4.30
4.40
6.4BSC
0.65BSC
16
Max
1.10
0.15
0.95
0.75
0.30
0.25
0.20
0.16
8º
Notes
1,2
1,2
1,2
1,2
1,2
1,2
1,2,5
1,2
1,2
1,2
1,2
1,2
1,2
1,2
1,2
1,2
1,2
1,2
1,2
5.10
4.50
1,2,3,8
1,2,4,8
1,2
1,2
1,2,6
17 - 20
AS1538/AS1540
Data Sheet - P a c k a g e D r a w i n g s a n d M a r k i n g s
Figure 31. TQFN 4x4 16-pin Package
Symbol
A
A1
L
L1
K
aaa
bbb
ccc
ddd
Min
0.70
0.00
0.45
0.03
0.20
Typ
0.75
0.02
0.55
0.10
0.10
0.10
0.05
Max
0.80
0.05
0.65
0.15
Notes
1, 2
1, 2
1, 2
1, 2
1, 2
1, 2
1, 2
1, 2
1, 2
Symbol
D BSC
E BSC
D2
E2
b
e
N
ND
Min
2.00
2.00
0.25
Typ
4.00
4.00
2.15
2.15
0.30
0.65
16
4
Max
2.25
2.25
0.35
Notes
1, 2
1, 2
1, 2
1, 2
1, 2, 5
1, 2
1, 2, 5
Notes:
1.
2.
3.
4.
Dimensioning and tolerancing conform to ASME Y14.5M-1994.
All dimensions are in millimeters, angle is in degrees.
N is the total number of terminals.
Terminal #1 identifier and terminal numbering convention shall conform to JESD 95-1 SPP-012. Details of terminal #1 identifier are optional, but must be located within the area indicated. The terminal #1 identifier may be
either a mold, embedded metal or mark feature.
5. Dimension b applies to metallized terminal and is measured between 0.15 and 0.30mm from terminal tip.
6. ND refers to the maximum number of terminals on D side.
7. Unilateral coplanarity zone applies to the exposed heat sink slug as well as the terminals.
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AS1538/AS1540
Data Sheet - O r d e r i n g I n f o r m a t i o n
11 Ordering Information
The device is available as the standard products shown in Table 7.
Table 7. Ordering Information
Model
Marking
Description
Delivery Form
Package
AS1538-BTST
AS1538
8-Channel, 12-Bit I²C Analog-to-Digital Converter
Tape and Reel
TSSOP-16
AS1538-BTSU
AS1538
8-Channel, 12-Bit I²C Analog-to-Digital Converter
Tubes
TSSOP-16
AS1540-BQFT
AS1540
4-Channel, 12-Bit I²C Analog-to-Digital Converter
Tape and Reel
TQFN 4x4
16-pin
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Revision 1.03
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AS1538/AS1540
Data Sheet
Copyrights
Copyright © 1997-2007, austriamicrosystems AG, Schloss Premstaetten, 8141 Unterpremstaetten, Austria-Europe.
Trademarks Registered ®. All rights reserved. The material herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner.
All products and companies mentioned are trademarks or registered trademarks of their respective companies.
Disclaimer
Devices sold by austriamicrosystems AG are covered by the warranty and patent indemnification provisions appearing
in its Term of Sale. austriamicrosystems AG makes no warranty, express, statutory, implied, or by description regarding
the information set forth herein or regarding the freedom of the described devices from patent infringement. austriamicrosystems AG reserves the right to change specifications and prices at any time and without notice. Therefore,
prior to designing this product into a system, it is necessary to check with austriamicrosystems AG for current information. This product is intended for use in normal commercial applications. Applications requiring extended temperature
range, unusual environmental requirements, or high reliability applications, such as military, medical life-support or lifesustaining equipment are specifically not recommended without additional processing by austriamicrosystems AG for
each application. For shipments of less than 100 parts the manufacturing flow might show deviations from the standard
production flow, such as test flow or test location.
The information furnished here by austriamicrosystems AG is believed to be correct and accurate. However,
austriamicrosystems AG shall not be liable to recipient or any third party for any damages, including but not limited to
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consequential damages, of any kind, in connection with or arising out of the furnishing, performance or use of the technical data herein. No obligation or liability to recipient or any third party shall arise or flow out of
austriamicrosystems AG rendering of technical or other services.
Contact Information
Headquarters
austriamicrosystems AG
A-8141 Schloss Premstaetten, Austria
Tel: +43 (0) 3136 500 0
Fax: +43 (0) 3136 525 01
For Sales Offices, Distributors and Representatives, please visit:
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