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 www.austriamicrosystems.com 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 www.austriamicrosystems.com 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 Revision 1.03 2 - 20 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 www.austriamicrosystems.com 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 3 - 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 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 www.austriamicrosystems.com PD = 01 Internal Ref. OFF, ADC ON @ 50kSPS Revision 1.03 VDD V 1 GΩ 4 µA 4 - 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 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 www.austriamicrosystems.com 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 www.austriamicrosystems.com tHOLDDATA Repeated START Revision 1.03 6 - 20 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 www.austriamicrosystems.com 0 15 30 45 60 75 90 Temperature (°C) Temperature (°C) Revision 1.03 7 - 20 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) www.austriamicrosystems.com 3.2 3.7 4.2 4.7 5.2 Supply Voltage (V) Revision 1.03 8 - 20 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) www.austriamicrosystems.com 5000 10000 15000 20000 25000 Input Signal Frequency (kHz) Revision 1.03 9 - 20 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 www.austriamicrosystems.com 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 www.austriamicrosystems.com Revision 1.03 11 - 20 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 www.austriamicrosystems.com Revision 1.03 12 - 20 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. www.austriamicrosystems.com Revision 1.03 13 - 20 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) www.austriamicrosystems.com Revision 1.03 14 - 20 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 www.austriamicrosystems.com Revision 1.03 15 - 20 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. www.austriamicrosystems.com Revision 1.03 16 - 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 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 www.austriamicrosystems.com 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. www.austriamicrosystems.com Revision 1.03 18 - 20 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 www.austriamicrosystems.com Revision 1.03 19 - 20 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 personal injury, property damage, loss of profits, loss of use, interruption of business or indirect, special, incidental or 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: http://www.austriamicrosystems.com/contact www.austriamicrosystems.com Revision 1.03 20 - 20