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| 1 of 17 051506 features two temperature-controlled 8-bit digital-to- analog converters (dacs) dac settings changeable every 4c access to temperature data and device control through a 2-wire interface operates with +3.3v or +5v supplies packaging: 8-pin tssop operating temperature: -40oc to +95oc programming temperature: 0oc to +70oc ordering information DS1851E-010 8-pin 173mil tssop DS1851E-010+ 8-pin 173mil tssop + denotes lead-free package. pin assignments pin descriptions v cc - +3.3v or +5v power supply input gnd - ground sda - 2-wire serial data input/output scl - 2-wire serial clock input outg - dac output with respect to ground v rg - reference input from ground outv - dac output with respect to v cc v rc - reference input from v cc description the ds1851 dual temperature-contro lled nonvolatile (nv) dacs consis ts of two dacs, two eeprom look-up tables, and a direct-to-digita l temperature sensor. both of th e dacs can be programmed with any temperature coefficient, which mean s that any system temperature eff ects can be corrected without any additional external devices. the ds1851 provides an ideal method for setting and temperature- compensating bias voltages and currents in control applications using a minimal amount of external circuitry. the user-defined settings for both dacs are stored in two eeprom look-up tabl es and can be accessed over the industry-standard 2-wire serial bus, which consists of sda and scl pins. these look-up tables can assign a unique output value to each dac for every 4c increment over the -40c to +95c range. the output of the digital temperature sensor is also available as a 12-bit, two?s complement value over the serial bus. www.maxim-ic.com ds1851 dual temperature-controlled n v di g ital-to- a nalo g converters sda 1 8 v cc scl 2 7 v rc v rg 3 6 outv gnd 4 5 outg 8-pin tssop (173mil)
ds1851 2 of 17 ds1851 block diagram figure 1 sd a scl v cc 2-wire interface digital temperature sensor 8-bit dac-g 8-bit dac-v gnd outg v cc outv table select byte configuration byte temperature msb byte temperature lsb byte address pointer user memory dac-v setting dac-g setting user memory 40x8 bit eeprom look-up table 1 (dac-v) 40x8 bit eeprom look-up table 2 (dac-g) v rc v rg gnd ds1851 3 of 17 pin descriptions name pin description v cc 8 power-supply terminal. the ds1851 will support supply voltages ranging from 3.0v to 5.5v. gnd 4 ground terminal sda 1 2-wire serial data interface. the serial data pin is for serial data transfer to and from the ds1851. th e pin is open drain and may be wire-or?ed with other open-drain or open-collector interfaces. scl 2 2-wire serial clock input. the serial clock input is used to clock data into the ds1851 on rising edges and clock data out on falling edges. outg 5 dac-g output. this calculated output is between v cc and v rg . outv 6 dac-v output. this calculated output is between v cc and v rc . v rg 3 reference input from gnd. this input is used for a reference in dac-g. v rc 7 reference input from v cc . this input is used for a reference in the dac-v. ds1851 4 of 17 memory organization 40x8 bit eeprom look-up table 1 (dac-v) 40x8 bit eeprom look-up table 2 (dac-g) 60h 61h 62h 63h 64h 65h-6fh 70h 71h 72h-7fh table select byte configuration byte temperature msb temperature lsb address pointer user memory dac-v setting dac-g setting user memory 80h a7h read-only memory (tbd) read-only memory (tbd) f8h-ffh ds1851 5 of 17 memory locations memory location name of location function of location 60h table select byte writing to this byte determines which of the two 40x8 eeprom look-up tables is selected for reading or writing. 01h (table 01h selected) 02h (table 02h selected) 61h configuration byte pol ? analog updating tau ? temperature/address update ten ? temperature update enable aen ? address update enable default setting is 0fh, tau = 1, ten = 1, and aen = 1. pol = 1 until power is high enough to guarantee outputs from the analog temperature converter. once pol = 0, automa ted updates will begin. tau becomes a 1 after a temperature and address update has occurred as a result of a temperature conversion. the user can write this bit to 0 and check for a transition from 0 to 1 in order to verify that a conversion has occurred. if ten = 0, the temperature conversion feature is disabled. the user sets the dac in manual mode by writing to addresses 70h and 71h to control dac-v and dac-g, respectively. with aen = 0 the user can operate in a test mode. address updates made from the temperature sensor will cease. the user can load a memory location into 64h and verify that the values in locations 70h and 71h are the expected user-defined values. 62h temperature msb this byte cont ains the msb of the 12-bit 2?s complement temperature output from the temperature sensor. pol tau ten aen s 2 6 2 5 2 4 2 3 2 2 2 1 2 0 ds1851 6 of 17 memory location name of location function of location 63h temperature lsb this byte contains the lsb of the 12-bit 2?s complement temperature output from the temperature sensor. 64h address pointer ca lculated, current dac address (80h?a7h). the user-defined dac setting at this location in the respective look-up table will be loaded into 70h and 71h to set the two dacs. 65h to 6fh user memory general-purpose user memory 70h dac-v setting in the user-contro lled setting mode, this block contains the dac-v setting. 71h dac-g setting in the user-contro lled setting mode, this block contains the dac-g setting. 72h to 7fh user memory general-purpose user memory 80h to a7h user-defined look-up table this bl ock contains the user-defined temperature settings of the dacs. values between 00h and ffh can be written to either table to set the 8-bit dacs. the first address location, 80h, is used to set the dac at -40c. each successive memory location will contain the dac setting for the previous temperature +4c. for example, memory address 81h is th e address that will set the dac in a -36c environment. dac operation one dac performs an 8-bit analog c onversion using the difference between v rc and v cc as the reference. the output values follow the following equation: outv = v rc + (v cc ? v rc ) * dacreg1/255 dacreg1 is the decimal equivalent of the digital value to be converted to analog. the other dac performs an 8-bit analog conversion using the difference between v rg and gnd as the reference. the output values follow the following equation: outg = v rg - (v rg ? gnd) * dacreg2/255 dacreg2 is the decimal equivalent of the digital value to be converted to analog. 2 - 1 2 - 2 2 - 3 2 - 4 x x x x ds1851 7 of 17 temperature conversion the direct-to-digital temperature sensor measures temperature through the use of an on-chip temperature measurement technique with an operating range fro m -40c to +95c. temp erature conversions are initiated upon power-up, and the most recent result is stored in address locations 62h and 63h, which are updated every 10ms. temperature conversion will not occur during an active read or write to memory. the values of the dacs are determined by the temper ature-addressed look-up ta ble that assigns a unique value to both for every 4c increment with a 1c hysteresis at a temperature transition over the operating temperature range. (see figure 2.) memory location over temperature figure 2 4 8 12 temperature ( c) m6 m5 m4 m3 m2 m1 memory location increasing temp decreasing temp ds1851 8 of 17 2-wire operation clock and data transitions the sda pin is normally pulled high with an external resistor or device. data on the sda pin may only change during scl low time periods. data changes during scl high periods will indicate a start or stop conditions depending on the conditions discussed below. refer to the timing diagram in figure 4 for further details. start condition a high-to-low transition of sda with scl high is a start condition that must precede any other command. refer to the timing diagram in figure 4 for further details. stop condition a low-to-high transition of sda with scl high is a stop condition. after a read sequence, the stop command places the ds1851 into a low-power mode. refer to the timing diagram in figure 4 for further details. acknowledge bit all address bytes a nd data bytes are transmitted via a serial protocol. the ds1851 pulls sda low during the ninth clock pulse to acknowledge that it has received each word. standby mode the ds1851 features a low-power m ode that is automatically enabled after power-on, after a stop command, and after the completion of all internal operations. 2-wire interface reset after any interruption in protocol, power loss, or system reset, the following steps reset the ds1851: 1) clock up to nine cycles. 2) look for sda high in each cycle while scl is high. 3) create a start condition while sda is high. device addressing the ds1851 must receive an 8-bit device address word following a start condition to enable a specific device for a read or write operation. the address wo rd is clocked into the ds1851 msb to lsb. the address word consists of ah (1010) followed by 000 then the r/w bit. if the r/w bit is high, a read operation is initiated. the r/w is low, a write operation is initiated. upon a match of the address, the ds1851 will output a zero for one clock cycle as an acknowledge. if the address does not match, the ds1851 ignores the communication. ds1851 9 of 17 write operations after receiving a matching address byte with the r/w bit set low, the device goes into the write mode of operation. the master must transmit an 8-bit eepro m memory address to the device to define the address where the data is to be written. after the byte has been recei ved, the ds1851 will transmit a zero for one clock cycle to acknowledge the receipt of the a ddress. the master must then transmit an 8-bit data word to be written into this address. the ds1851 will again transmit a zero for one clock cycle to acknowledge the receipt of the data. at this point, th e master must terminate the write operation with a stop condition. the ds1851 then enters an internally-timed write process t w to the eeprom memory. all inputs are disabled during this byte write cycle. the ds1851 is capable of an 8-byte page write. a page write is initiated the same way as a byte write, but the master does not send a stop condition after the first byte. instead, after the slave acknowledges receipt of the data byte, the master can send up to se ven more bytes using the same nine-clock sequence. the master must terminate the write cycle with a stop condition or the data clocked into the ds1851 will not be latched into permanent memory. acknowledge polling once the internally-timed write ha s started and the ds1851 inputs are disabled, acknowledge polling can be initiated. the process involves transmitting a star t condition followed by the device address. the r/w bit signifies the type of operation that is desired. the read or write sequence will only be allowed to proceed if the internal write cycle has co mpleted and the ds1851 responds with a zero. read operations after receiving a matching address byte with the r/w bit set high, the device goes into the read mode of operation. there are three read operations: current address read, random rea d, and sequen tial address read. current address read the ds1851 has an internal address register that contai ns the address used during the last read or write operation, incremented by one. this da ta is maintained as long as v cc is valid. if the most recent address was the last byte in memory, then the register resets to the first address. this address stays valid between operations as long as power is available. once the device address is clocked in and acknowledge d by the ds1851 with the r/w bit set to high, the current address data word is clocked out. the master does not respond with a zero, but does generate a stop condition afterwards. random read a random read requires a dummy-byte write-sequence to load in the data word address. once the device and data address bytes are clocke d in by the master and acknowledged by the ds1851, the master must generate another start condition. th e master now initiates a current a ddress read by sending the device address with the r/w bit set hig h. the ds1851 will acknowledge the device address, then serially clocks out the data byte. ds1851 10 of 17 sequential address read sequential reads are initiated by either a current address read or a random address read. after the master receives the first data byte, the master responds w ith an acknowledge. as long as the ds1851 receives this acknowledge after a byte is read, the master may clock out additional data words from the ds1851. after reaching address ffh, it resets to address 00h. the sequential read operation is terminated when th e master initiates a stop condition. the master does not respond with a zero. 2-wire serial port operation the 2-wire serial port interface supports a bidirectional data tr ansmission protocol with device addressing. a device that sends data on the bus is defined as a transmitter, and a device receiving data as a receiver. the device that controls the message is called a ?master.? the devices that are controlled by the master are ?slaves.? the bus must be controlled by a master device that generates the serial clock (scl), controls the bus access, and generates th e start and stop conditions. the ds1851 operates as a slave on the 2-wire bus. connections to the bus are made via the open-drain i/o lines, sda and scl. the following i/o terminals control the 2-wire serial port: sda and scl. timing diagrams for the 2-wire serial port can be found in figures 3 and 4. timing in formation for the 2-wire serial port is provided in the ac electrical characteristics table for 2-wire serial communications. the following bus protocol has been defined: 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. accordingly, the following bus conditions have been defined: bus not busy: both 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. ds1851 11 of 17 data valid: the state of the data line represents valid da ta when, after a start condition, the data line is stable for the duration of the high period of th e clock signal. the data on the line can be changed during the low period of the clock signal. there is one clock pulse per bit of data . figures 3 and 4 detail how data transfer is accomplished on the 2-wire bus. depending upon the state of the r/w bit, two types of data transfer are possible. each data transfer is initiated with a start c ondition 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 transferre d byte-wise and each receiver acknowledges with a ninth bit. within the bus specifications, a regular mode (100kh z clock rate) and a fast mode (400khz clock rate) are defined. the ds1851 works in both modes. acknowledge: each receiving device, when addressed, genera tes an acknowledge after the reception of each byte. the master device must generate an extra cl ock pulse that is associated with this acknowledge 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 a stable low during the high period of the acknowledge-related clock pulse. of course, setup and hold times must be taken into acc ount. 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 lin e high to enable the master to generate the stop condition. 1) data transfer from a master transmitter to a slave receiver. the first byte transmitted by the master is the command/control byte, followed by a number of da ta bytes. the slave returns an acknowledge bit after each received byte. 2) data transfer from a slave transmitter to a master receiver. the master transmits the first byte (the command/control byte) to the slave. the slave th en returns an acknowledge bit. next, follows a number of data bytes 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? can be returned. the master device generates all se rial clock pulses and the start an d stop conditions. a transfer is ended with a stop condition or with a repeated start condition. since a repeated start condition is also the beginning of the next serial transfer, the bus will not be released. ds1851 12 of 17 the ds1851 may operate in the following two modes: 1) slave receiver mode: serial data and clock are received through sda and scl respectively. after each byte is received, an acknowledge bit is tran smitted. 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 (device) address and direction bit. 2) slave transmitter mode: the first byte 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 ds1851 while the seri al clock is input on scl. start and stop conditions are recognized as the beginning and end of a serial transfer. following the start condition, the ds1851 monitors the sda bus checking the device type identifier being transmitted. upon receiving the 1010000 control code and the read/write bit, the slave device outputs an acknowledge signal on the sda line. ds1851 13 of 17 2-wire data transfer protocol figure 3 2-wire timing diagram figure 4 ds1851 14 of 17 absolute maximum ratings* voltage on any pin relative to ground -0.3v to +6.0v operating case temperature ra nge -40c to +95c programming temperature range 0c to +70c storage temperature range -55c to +125c soldering temperature 260c for 10 seconds * this is a stress rating only and f unctional operation of the device at these or any other conditions above those indicated in the operation s ections of this specification is not implied. exposure to absolute maximum rating conditions for extended periods of time may affect reliability. recommended dc operating conditions (-40 c to +95 c) parameter symbol min typ max units notes supply voltage v cc +3.0 +5.5 v 1 dc electrical characteristics (-40c to +95c; v cc = +3.0v to +5.5v) parameter symbol condition min typ max units notes supply active current i cc 0.6 1 ma 8 input leakage i li -1 +1 a input logic 1 v ih 0.7v cc v cc + 0.3 v input logic 0 v il gnd - 0.3 0.3v cc v input current each i/o pin 0.4 ds1851 16 of 17 dac (-40c to +95c; gnd + 0.1 |
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