View DS1841X_9097906.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

ds1841 temperature-controlled, nv, i 2 c, logarithmic resistor rev 2; 5/08 ________________________________________________________________ maxim integrated products 1 for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. general description the ds1841 is a 7-bit, logarithmic, nonvolatile (nv) digi-tal resistor that features an on-chip temperature sensor and associated analog-to-digital converter (adc). the integrated temperature sensor indexes a 72-byte nv lookup table (lut) encompassing a temperature range from -40? to +100?. the lut output can drive the resistor directly or be added to an nv initial-value regis- ter (ivr) to drive the resistor. this flexible lut-based architecture allows the ds1841 to provide a tempera- ture-compensated resistor output with arbitrary slope. programming is accomplished by an i 2 c-compatible interface, which can operate at speeds of up to 400khz. applications optical transceiverslinear and nonlinear compensation instrumentation and industrial controls mechanical potentiometer replacement features ? 22k to 3.7k adjustable logarithmic resistor with a 3.6k fixed resistor ? 128 wiper tap points ? on-chip temperature sensor and adc ? 72-byte lookup table (lut) ? i 2 c-compatible serial interface ? address pins allow up to four ds1841s to sharethe same i 2 c bus ? digital supply of 2.7v to 5.5v ? -40? to +100? operating range ? 3mm x 3mm, 10-pin tdfn package 13 4 10 8 7 scl rh rw sda *ep *exposed pad v cc a1 2 9 n.c. gnd 5 6 rgnd a0 tdfn (3.0mm 3.0mm 0.8mm) top view ds1841 pin configuration ordering information 0.1 f 3.3v apd bias control application v cc v out fb sdascl a1a0 gnd 100pf rw rgnd rh v apd 4.7k 4.7k dc-dc converter ds1841 typical operating circuit + denotes a lead-free package. t&r = tape and reel. * ep = exposed pad. registers and modes are capitalized for clarity. part temp range pin-package ds1841n+ -40c to +100c 10 tdfn-ep* ds1841n+t&r -40c to +100c 10 tdfn-ep* downloaded from: http:///
ds1841 temperature-controlled, nv, i 2 c, logarithmic resistor 2 _______________________________________________________________________________________ recommended operating conditions(t a = -40? to +100?) stresses beyond those listed under ?bsolute maximum ratings?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 the operational sections of the specifications is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. voltage range on sda, scl, and v cc relative to gnd .........................................-0.5v to +6.0v voltage range on rh, rw, a0, and a1 relative to gnd ................................-0.5v to (v cc + 0.5v) operating temperature range .........................-40? to +100? programming temperature range .........................0? to +70? storage temperature range .............................-55? to +125? soldering temperature .....................see ipc/jedec j-std-020 rw current............................................................................3ma parameter symbol conditions min typ max units supply voltage v cc (note 1) +2.7 +5.5 v input logic 1 (scl, sda, a0, a1) v ih 0.7 x v cc v cc + 0.3 v input logic 0 (scl, sda, a0, a1) v il -0.3 0.3 x v cc v resistor inputs (rw, rh) v res -0.3 v cc + 0.5 v wiper current i wiper 2m a dc electrical characteristics(v cc = +2.7v to +5.5v, t a = -40? to +100?, unless otherwise noted.) parameter symbol conditions min typ max units input leakage (sda, scl, a0, a1) i l -1 +1 a v cc supply current i cc2 (note 2) 350 a low-level output voltage (sda) v ol 3ma sink current 0 0.4 v i/o capacitance c i/o 5 10 pf power-on recall voltage v por (note 3) 1.6 2.6 v power-up recall delay t d (note 4) 5 ms series resistance r s 3.6 k minimum resistance (gnd to rw) r min (note 5) 370 end-to-end resistance (gnd to rw) r total 22 k r total tolerance t a = +25c -20 +20 % temp coefficient t cv wr set to 40h 250 ppm/c rh, rw capacitance c pot 10 pf absolute maximum ratings downloaded from: http:///
ds1841 temperature-controlled, nv, i 2 c, logarithmic resistor _______________________________________________________________________________________ 3 temperature sensor characteristics(v cc = +2.7v to +5.5v, t a = -40? to +100?, unless otherwise noted.) parameter symbol conditions min typ max units temperature error 5 c update rate (temperature and supply conversion time) t frame 16 ms analog voltage monitoring characteristics(v cc = +2.7v to +5.5v, t a = -40? to +100?, unless otherwise noted.) parameter symbol conditions min typ max units supply resolution lsb full-scale voltage of 6.5536v 25.6 mv input/supply accuracy a cc at factory setting 0.25 1.0 % fs (full scale) update rate (temperature and supply conversion time) t frame 16 ms i 2 c ac electrical characteristics (see figure 3) (v cc = +2.7v to +5.5v, t a = -40? to +100?, timing referenced to v il(max) and v ih(min) .) parameter symbol conditions min typ max units scl clock frequency f scl (note 6) 0 400 khz bus free time between stop and start conditions t buf 1.3 s hold time (repeated) start conditions t hd:sta 0.6 s low period of scl t low 1.3 s high period of scl t high 0.6 s data hold time t hd:dat 0 0.9 s data setup time t su:dat 100 ns start setup time t su:sta 0.6 s sda and scl rise time t r (note 7) 20 + 0.1c b 300 ns sda and scl fall time t f (note 7) 20 + 0.1c b 300 ns stop setup time t su:sto 0.6 s sda and scl capacitive loading c b (note 7) 400 pf downloaded from: http:///
ds1841 temperature-controlled, nv, i 2 c, logarithmic resistor 4 _______________________________________________________________________________________ note 1: all voltages are referenced to ground. currents entering the ic are specified positive and currents exiting the ic are negative. note 2 :i cc is specified with the following conditions: scl and sda = v cc , rw and rh floating with update mode bit = 1. note 3: this is the minimum v cc voltage that causes nv memory to be recalled. note 4 : this is the time from v cc > v por until initial memory recall is complete. note 5: guaranteed by design. note 6: i 2 c interface timing shown is for fast-mode (400khz) operation. this device is also backward-compatible with i 2 c- standard mode timing. note 7: c b ?otal capacitance of one bus line in picofarads. note 8: eeprom write time begins after a stop condition occurs. note 9: guaranteed by characterization. i 2 c ac electrical characteristics (see figure 3) (continued) (v cc = +2.7v to +5.5v, t a = -40? to +100?, timing referenced to v il(max) and v ih(min) .) parameter symbol conditions min typ max units eeprom write time t w (note 8) 10 20 ms a0, a1 setup time t su:a before start 0.6 s a0, a1 hold time t hd:a after stop 0.6 s input capacitance on a0, a1, sda, or scl c i 5 10 pf startup time t st 2 ms nonvolatile memory characteristics(v cc = +2.7v to +5.5v) parameter symbol conditions min typ max units eeprom write cycles t a = +85c 50,000 writes eeprom write cycles t a = +25c (note 9) 200,000 writes downloaded from: http:///
ds1841 temperature-controlled, nv, i 2 c, logarithmic resistor supply current vs. supply voltage ds1841 toc01 supply voltage (v) supply current ( a) 5.0 4.5 4.0 3.5 3.0 50 100 150 200 250 0 2.5 5.5 sda = scl = vcc rh, rh, rw are floating sda = scl = v cc rgnd, rh, rw are floating update mode bit = 0 update mode bit = 0 lut mode and lut adder mode update mode bit = 1 lut mode and lut adder mode update mode bit = 1 supply current vs. temperature ds1841 toc02 temperature ( c) supply current ( a) 80 60 40 20 0 -20 50 100 150 200 250 0 -40 100 sda = scl = vcc rh, rh, rw are floating sda = scl = v cc = 5v rgnd, rh, rw are floating update mode bit = 0 update mode bit = 0 lut mode and lut adder mode update mode bit = 1 lut mode and lut adder mode update mode bit = 1 supply current vs. scl frequency ds1841 toc03 scl frequency (khz) supply current ( a) 300 200 100 50 100 150 200 250 0 0 400 sda = scl = vcc rh, rh, rw are floating sda = v cc = 5v rgnd, rh, rw are floating update mode bit = 0 update mode bit = 0 lut mode and lut adder mode update mode bit = 1 lut mode and lut adder mode update mode bit = 1 wiper resistance (rw) vs. setting ds1841 toc04 setting (dec) wiper resistance (k ) 125 100 75 50 25 5 10 15 20 25 0 0 sda = scl = v cc = 5v sda = scl = v cc = 5v wiper current vs. wiper setting ds1841 toc05 wipe setting (dec) wiper current (ma) 100 75 50 25 0.4 0.8 1.2 1.6 0 0 125 rgnd = 0vrw open force 1.25v on rh and measure current rgnd = 0vrw open force 1.25v on rh and measure current vcc = 5v sda and scl referenced to 5v v cc = 5v sda and scl referenced to 5v rw to rgnd resistance vs. supply voltage ds1841 toc06 supply voltage (v) resistance at rw (k ) 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 10 20 30 40 0 0 5.5 por occurs por occurs ivr is loaded ivr is loaded conversions complete lut value loaded to wr conversions complete lut value loaded to wr typical operating characteristics (v cc = +2.7v to +5.5v, t a = +25?, unless otherwise noted.) _______________________________________________________________________________________ 5 downloaded from: http:///
ds1841 temperature-controlled, nv, i 2 c, logarithmic resistor 6 _______________________________________________________________________________________ pin description pin name function 1 sda i 2 c serial data. input/output for i 2 c data. 2 gnd ground 3 v cc power supply 4 a1 5 a0 address select inputs. determines i 2 c slave address. device address is 01010a 1 a 0 x (see the slave address bte and address pins sections for more details). 6 rgnd low terminal of resistor. must be connected to gnd. 7 rw wiper terminal 8 rh terminal with fixed resistor added in series with digit al resistor 9 n.c. no connection 10 scl i 2 c serial clock. input for i 2 c clock. ep exposed paddle. must be connected to ground. detailed description the ds1841 operates in one of two modes: lut modeand lut adder mode. in lut mode and lut adder mode, the resistor? wiper position is controlled as a function of the temperature measured by the ds1841? internal temperature sensor. the difference between the two lut modes is the way the resistor? wiper posi- tion is calculated. detailed descriptions of these two modes, as well as additional features of the ds1841, are discussed in subsequent sections. digital resistor description the ds1841? resistor consists of 128 resistive stepsbetween rw and rgnd with a series resistor, r s , between rh and rw. the wiper position and the outputseen on rw are decoded based on the value in the wiper register (wr). the step size of each position is optimized to produce a linear response when used in the feedback network of a dc-dc converter. mode selection the ds1841 mode of operation is determined by theupdate mode bit (control register 1, address 03h, bit 0) and the adder mode bit (control register 1, address 03h, bit 1). table 1 illustrates how the two control bits are used to select the operating mode. when shipped from the factory, the ds1841 is programmed with the update mode and adder mode bits set to 1, hence con- figuring the ds1841 in lut adder mode. see appendix a for a detailed table of the control logic bit functions. table 1. operating modes update mode bit adder mode bit mode 1 0 lut mode 1 1 lut adder mode (default) downloaded from: http:///
ds1841 temperature-controlled, nv, i 2 c, logarithmic resistor _______________________________________________________________________________________ 7 lut adder mode (default) lut adder mode is selected by setting the updatemode bit to 1 and the adder mode bit to 1. this mode operates similar to lut mode with one major difference (see the lut mode and lut adder mode block diagram ). the wr is loaded with the sum of the values of lutval (the value pointed to by the address storedin lutar) and ivr. furthermore, in this mode, the val- ues programmed into the lut are signed two? com- plement. this allows convenient positive or negative offsetting of the nominal ivr value. wr resistance val- ues clamp at 00h and 7fh (the msb is ignored). lut mode lut mode is selected by setting the update mode bit(control register 1, address 03h, bit 0) to a 1 and the adder mode bit (control register 1, address 03h, bit 1) to a 0. an overview of the ds1841 in this mode is illus- trated in the lut mode and lut adder mode block diagram . the memory map for the lut mode and the lut adder mode is shown in table 2. the major differ-ence between the two lut modes is whether the value in the ivr is added to the values stored in the lut. thedashed line/arrow shown in the lut drive mode block diagram is not active in lut mode. when in lut mode, on power-up the ivr value is recalled into the wr. thisvalue remains there until completion of the first temper- ature conversion following power-up. the temperature is measured every t frame . the temperature value is used to calculate an index that points to the corre-sponding value in the lut. this index is referred to as the lut address register (lutar) and is located at address 08h. the value stored in the lut at the loca- tion pointed to by lutar is called lutval, and this value is stored as the wr value (wr) at address 09h when update mode bit = 1. the process then repeats itself, continuously updating the wiper setting in a closed-loop fashion. in this mode the 72-byte lut is populated with wiper settings for each two-degree tem- perature window. valid wiper settings are 00h to 7fh (the msb is ignored). table 3 shows the memory addresses of the lut as well as the corresponding temperature range for each byte in the lut. table 2. lut mode and lut adder mode memory map *in lut mode and lut adder mode, wr is accessed through memory address 09h, while ivr remains at memory address 00h. register name address (hex) volatile/nv factory/power-up default ivr initial value register 00h nv (shadowed) 00h cr0 control register 0 02h volatile 00h cr1 control register 1 03h nv (shadowed) 03h lutar lut address register 08h volatile 00h wr lut value register 09h* volatile 00h cr2 control register 2 0ah volatile 00h temp temperature result 0ch volatile (read only) n/a voltage supply voltage result 0eh volatile n/a lut temperature lookup registers 80hCc7h nv 00h downloaded from: http:///
ds1841 temperature-controlled, nv, i 2 c, logarithmic resistor 8 _______________________________________________________________________________________ temperature conversion and supply voltage monitoring temperature conversion the ds1841 features an internal 8-bit temperature sen-sor that can drive the lut and provide a measurement of the ambient temperature over i 2 c by reading the value stored in address 0ch. the sensor is functionalover the entire operating temperature range and is stored in signed two? complement format with a resolu- tion of 1?/bit. see table 2, register 0ch description for the temperature sensor? bit weights. to calculate the temperature, treat the two? complement binary value as an unsigned binary number, then convert it to decimal. if the result is greater than or equal to 128, subtract 256 from the result. lut the ds1841 monitors the internal temperature byrepeatedly polling the sensor? result with update rate t frame . during each cycle, the ds1841 reads the inter- nal temperature, and, based on that temperature,points to the corresponding lut address. every two degrees of temperature will convert into one tempera- ture address slot. see table 3 for a list of temperatures and their corresponding lut addresses. the lut features one-degree hysteresis to prevent chattering if the measured temperature falls on the boundary between two windows (see figure 1). table 3. lut registers and temperature ranges temperature (c) temperature value for given temperature (hex) corresponding lut address (hex) -40 or less d8 80 -39 to -38 d9 to da 81 -37 to -36 db to dc 82 -35 to -34 dd to de 83 +95 to +96 5f to 60 c4 +97 to +98 61 to 62 c5 +99 to +100 63 to 64 c6 +101 or more 65 c7 lut mode and lut adder mode block diagram (update mode bit = 1) 1 of 128 multiplexers ivr on power-up only when in lut adder mode initial value register (ivr) 00h* control logic/ registers lut address register (lutar) 08h 72-byte lookup table (lut) 80h?7h wiper register (wr) 09h* adc i 2 c interface temp sensor v cc voltage temp 0ch v cc (v) 0eh v cc gnd scl sda a0a1 pos 7fhpos 00h r s rgndrw rh control data *note that when in lut or lut adder mode, wr is accessed through 09h while ivr remains at 00h. lutval lutval or lutval + ivr downloaded from: http:///
ds1841 temperature-controlled, nv, i 2 c, logarithmic resistor _______________________________________________________________________________________ 9 supply voltage monitoring the ds1841 also features an internal 8-bit supply volt-age (v cc ) monitor. a value of the supply voltage mea- surement can be read over i 2 c at the address 0eh. to calculate the supply voltage, simply convert thehexadecimal result into decimal and then multiply it by the lsb as shown in the analog voltage monitoring characteristics electrical table. supply current (i cc ) the ds1841 has two supply current levels of power sup-ply consumption. first, active current during i 2 c com- munications while in the lut-driven mode is the ?orstcase?supply current, i cc . all functionality including i 2 c communication is operating simultaneously. second,active current without i 2 c while in the lut-driven mode is quantified by the supply current, i cc2 . sda and scl are held statically in the high logic level. slave address byte and address pins the slave address byte consists of a 7-bit slaveaddress plus a r/ w bit (see figure 2). the ds1841? slave address is determined by the state of the a0 anda1 address pins. these pins allow up to four devices to reside on the same i 2 c bus. address pins tied to gnd result in a 0 in the corresponding bit position in theslave address. conversely, address pins tied to v cc result in a 1 in the corresponding bit positions. forexample, the ds1841? slave address byte is 50h when a0 and a1 pins are grounded. i 2 c communication is described in detail in the i 2 c serial interface description section. memory location temperature ( c) lut34 decreasing temperature increasing temperature 1 c hysteresis window lut33lut32 lut31 lut30 19 21 23 25 19 27 figure 1. lut hysteresis 01 1 0 r/w a0 a1 0 msb lsb read/write bit slave address* *the slave address is determined by address pins a0, a1. figure 2. slave address byte downloaded from: http:///
ds1841 temperature-controlled, nv, i 2 c, logarithmic resistor 10 ______________________________________________________________________________________ memory description the ds1841? internal memory consists of both volatileand nv registers that are organized into eight byte rows. three control registers as well as specializeddata registers are used to control the wiper and drive the lut. register 00h: initial value register (ivr) factory default (ivr) 00h memory type nv memory type volatile 00h ivr b i t 7 b i t 0 if see bit = 0, an i 2 c read retrieves the ivr value and an i 2 c write sets the wiper position in volatile memory and updates ivr in nv memory with this new value. if see bit = 1, an i 2 c read retrieves the wr value and an i 2 c write sets the wiper position (volatile) and the ivr value is not modifi ed. during power-up, ivrs value is used to set the wiper position. register 02h: control register 0 (cr0) factory default 00h memory type volatile 02h see reserved reserved reserved reserved reserved reserved reserved b i t 7 b i t 0 bit 7 see controls ivr and wr functionality, as well as the memory type for contr ol register 1. 0 = (default) issuing an i 2 c read of the value in address 00h retrieves the ivr value. issuing an i 2 c write to address 00h sets both the wipers position (volatile) and t he ivr value (nonvolatile) to the same value. writes to control register 1 (03h) are stored in shadowed sram and eeprom. 1 = issuing an i 2 c read of the value in address 00h retrieves the wr value. issuing an i 2 c write to address 00h only sets the wipers position (volatile). the ivr va lue is not modified. writes to control register 1 (03h) are stored in shadowed sram only. bits 6 to 0 reserved. control register 0 determines how the wiper position values (v olatile and nv versions) are set, as well as how writes to control register 1 are stored. the ivr is located at memory address 00h and is implemented as ee prom shadowed sram. this register can be visualized as an sram byte (the wr portion) in parallel with an e eprom byte (the ivr portion). the operation of the register is controlled by the shadow eeprom ( see ) bit in control register 0, address 02h, bit 7. when the see bit = 0 (default), data written to memory address 00h by i 2 c actually gets stored in both sram (wr) and eeprom (ivr). when see = 1, only the sram (wr) is written to the new value. the eeprom byte (ivr) continues to store the last value written to it when see was 0. reading memory address 00h reads the value stored in wr. the see bit is volatile and its power-up default state is 0. register descriptions downloaded from: http:///
ds1841 temperature-controlled, nv, i 2 c, logarithmic resistor ______________________________________________________________________________________ 11 register 03h: control register 1 (cr1) factory default 03h memory type shadowed nv 03h reserved reserved reserved reserved reserved reserved adder mode update mode b i t 7 b i t 0 bits 7 to 2 reserved. bit 1 adder mode this bit is valid onl if the update mode bit = 1. 0 = the lutval or ivr value is directly loaded to wr though the mux. 1 = (default) the lutval is summed with the ivr value and is directly loaded to wr though the mux. bit 0 update mode 0 = cr0 is enabled. during power-up the ivr value is loaded into th e wr to set the wiper position. updates to temperature result (0ch) and supply voltage result (0eh) are halted. 1 = (default) the wr is controlled directly by i 2 c communication though registers 08h or 09h, or the wr is controlled by the temperature-compensation/lut circuitry. if temper ature compensation is enabled, one of the 72 temperature slots is selected (by the lutar) and this slot value is copied into the lutval, which in turn sets the wr. updates to temperature resul t (0ch) and supply voltage result (0eh) are enabled. control register 1 controls how the wiper position is determined. th e see bit controls whether the values of this register are stored in eeprom or in shadowed sram. on power-up, the eeprom value is recalled to this register, regardless of the state of see . while the registers other than 00h through 0ah can be read, they are not updated by the adc as the adc is disabled with the update mode bit = 0. register 08h: lut address register (lutar) factory default 00h por default 00h until t frame memory type volatile 08h lutar b i t 7 b i t 0 the lutar register serves as the index pointer to choose the corres ponding temperature slot in the lut based on the internal temperature sensor result. the lutar can be directly read by acessing address 08h; however, to write an new value to lutar (to control wr manually), the lutar mode bit must be s et to a 1. register 09h: lut value register (wr*) factory default 00h memory type volatile 09h wr* b i t 7 b i t 0 wr serves as an intermediate location, which is populated automati cally with the results of the temperature-indexed lookup. the wr can be directly read by acessing address 09h; how ever to write an new value to wr (to control it manually), the wiper access control bit must be set to a 1. wr is an unsigned 7- bit value. *wr is updated every t frame if update mode bit = 1. if update mode bit = 0, wr holds the value stored in r egister 00h. downloaded from: http:///
ds1841 temperature-controlled, nv, i 2 c, logarithmic resistor 12 ______________________________________________________________________________________ register 0ah: control register 2 (cr2) factory default 00h memory type volatile 0ah reserved reserved reserved reserved reserved wiper access control lutar mode reserved b i t 7 b i t 0 bits 7 to 3 reserved. bit 2 wiper access control this bit is valid onl in lut mode and in lut adder mode. 0 = (default) wr is loaded with the value from ivr summed with lutval, or j ust the value of lutval based on the state of the adder mode bit. 1 = the ds1841 is placed in a manual mode, allowing wr (address 09h) to be programmed using i 2 c commands. bit 1 lutar mode this bit is valid onl in lut mode and in lut adder mode. 0 = (default) the lutar value, located in at address 08h, is calculated foll owing each temperature conversion that points to the corresponding location in the lut. 1 = automatic updates of lutar are disabled, allowing the lutar regi ster to be programmed using i 2 c commands. bit 0 reserved. this bit must be set to a 0. control register 2 controls how the wiper position is determined. register 0ch: temperature result (temp) factory default none memory type volatile 0ch sign 2 6 2 5 2 4 2 3 2 2 2 1 2 0 b i t 7 b i t 0 this register holds the current temperature result. it is updated every conver sion time, t frame . to calculate the temperature, treat the twos complement binary value as an unsigned binary number, then convert it to decimal. if the result is greater than or equal to 128, subtract 256 from the result. this r egister is only updated when the update mode bit = 1. when the update mode bit = 0, no adc updates are made to th is register. register 0eh: supply voltage result (voltage) factory default none memory type volatile 0eh supply voltage b i t 7 b i t 0 this register holds the current supply voltage result. i t is updated every conversion time, t frame . see the suppl voltage monitoring section. this register is only updated when the update mode bit = 1. when the update mode bit = 0, no adc updates are made to this register. downloaded from: http:///
ds1841 temperature-controlled, nv, i 2 c, logarithmic resistor ______________________________________________________________________________________ 13 i 2 c serial interface description i 2 c definitions the following terminology is commonly used to describei 2 c data transfers. (see figure 3 and i 2 c ac electrical table for additional information.)master device: the master device controls the slave devices on the bus. the master device generates scl clock pulses and start and stop conditions. slave devices: slave devices send and receive data at the master? request.bus idle or not busy: time between stop and start conditions when both sda and scl are inactive and intheir logic-high states. start condition: a start condition is generated by the master to initiate a new data transfer with a slave.transitioning sda from high to low while scl remains high generates a start condition. stop condition: a stop condition is generated by the master to end a data transfer with a slave.transitioning sda from low to high while scl remains high generates a stop condition. repeated start condition: the master can use a repeated start condition at the end of one data trans- fer to indicate that it will immediately initiate a new data transfer following the current one. repeated starts are commonly used during read operations to identify a spe- cific memory address to begin a data transfer. a repeat- ed start condition is issued identically to a normal start condition. bit write: transitions of sda must occur during the low state of scl. the data on sda must remain valid andunchanged during the entire high pulse of scl plus the setup and hold time requirements. data is shifted into the device during the rising edge of the scl. bit read: at the end of a write operation, the master must release the sda bus line for the proper amount ofsetup time before the next rising edge of scl during a bit read. the device shifts out each bit of data on sda at the falling edge of the previous scl pulse and the data bit is valid at the rising edge of the current scl pulse. remember that the master generates all scl clock pulses, including when it is reading bits from the slave. acknowledge (ack and nack): an acknowledge (ack) or not acknowledge (nack) is always the 9th bittransmitted during a byte transfer. the device receiving data (the master during a read or the slave during a write operation) performs an ack by transmitting a 0 during the 9th bit. a device performs a nack by trans- mitting a 1 during the 9th bit. timing for the ack and nack is identical to all other bit writes. an ack is the acknowledgment that the device is properly receiving data. a nack is used to terminate a read sequence or indicates that the device is not receiving data. byte write: a byte write consists of 8 bits of information transferred from the master to the slave (most signifi-cant bit first) plus a 1-bit acknowledgment from the slave to the master. the 8 bits transmitted by the mas- ter are done according to the bit write definition and the acknowledgment is read using the bit read definition. registers 80h to c7h: temperature lookup register (lut) factory default 00h memory type nv 80h to c7h (see table 3 for settings.) b i t 7 b i t 0 these registers at location 80h to c7h are nv and serve to temperature compens ate rw over the operating temperature range of the ds1841. the lut entries are unsigned 8-bit values if the adder mode bit = 0. if t he adder mode bit = 1, lut entries are twos complement, signed 7-bit values. downloaded from: http:///
ds1841 temperature-controlled, nv, i 2 c, logarithmic resistor 14 ______________________________________________________________________________________ byte read: a byte read is an 8-bit information transfer from the slave to the master plus a 1-bit ack or nackfrom the master to the slave. the 8 bits of information that are transferred (most significant bit first) from the slave to the master are read by the master using the bit read definition, and the master transmits an ack using the bit write definition to receive additional data bytes. the master must nack the last byte read to terminate communication so the slave returns control of sda to the master. slave address byte: each slave on the i 2 c bus responds to a slave address byte sent immediately fol- lowing a start condition. the slave address byte con- tains the slave address in the most significant 7 bits and the r/ w bit in the least significant bit. the ds1841? slave address is determined by the stateof the a0 and a1 address pins as shown in figure 2. address pins tied to gnd result in a 0 in the corre- sponding bit position in the slave address. conversely, address pins tied to v cc result in a 1 in the corre- sponding bit positions.when the r/ w bit is 0 (such as in 50h), the master is indicating that it will write data to the slave. if r/ w = 1 (51h in this case), the master is indicating that it wantsto read from the slave. if an incorrect slave address is written, the ds1841assumes the master is communicating with another i 2 c device and ignores the communication until the next start condition is sent. memory address: during an i 2 c write operation, the master must transmit a memory address to identify thememory location where the slave is to store the data. the memory address is always the second byte trans- mitted during a write operation following the slave address byte. i 2 c communication writing a single byte to a slave: the master must gen- erate a start condition, write the slave address byte (r/ w = 0), write the memory address, write the byte of data, and generate a stop condition. remember the master must read the slave? acknowledgment during all byte write operations. when writing to the ds1841, the potentiometer adjusts to the new setting once it has acknowledged the new data that is being written, and the eeprom is written following the stop condition at the end of the write command. to change the setting without changing the eeprom, termi- nate the write with a repeated start condition before the next stop condition occurs. using a repeated start condition prevents the t w delay required for the eeprom write cycle to finish. sdascl t hd:sta t low t high t r t f t buf t hd:dat t su:dat repeated start t su:sta t hd:sta t su:sto t sp stop note: timing is reference to v il(max) and v ih(min) . start figure 3. i 2 c timing diagram downloaded from: http:///
ds1841 temperature-controlled, nv, i 2 c, logarithmic resistor ______________________________________________________________________________________ 15 writing multiple bytes to a slave: i 2 c write operations of multiple bytes can also be performed. during a sin-gle write sequence, up to 8 bytes in one page can be written at one time. if more than eight bytes are trans- mitted in the sequence, then only the last eight trans- mitted bytes are stored. after the last physical memory location in a particular page (8-byte page write), the address counter automatically wraps back to the first location in the same page for subsequent byte write operations. acknowledge polling: any time a eeprom byte is written, the ds1841 requires the eeprom write time(t w ) after the stop condition to write the contents of the byte to eeprom. during the eeprom write time,the device does not acknowledge its slave address because it is busy. it is possible to take advantage of this phenomenon by repeatedly addressing the ds1841, which allows communication to continue as soon as the ds1841 is ready. the alternative to acknowledge polling is to wait for a maximum period of t w to elapse before attempting to access the device. reading a single byte from a slave: unlike the write operation that uses the specified memory address byteto define where the data is to be written, the read opera- tion occurs at the present value of the memory address counter. to read a single byte from the slave, the master generates a start condition, writes the slave address byte with r/ w = 1, reads the data byte with a nack to indicate the end of the transfer, and generates a stopcondition. however, since requiring the master to keep track of the memory address counter is impractical, the following method should be used to perform reads from a specified memory location. reading multiple bytes from a slave: the read opera- tion can be used to read multiple bytes with a singletransfer. when reading bytes from the slave, the master simply acks the data byte if it desires to read another byte before terminating the transaction. after the master reads the last byte it must nack to indicate the end of the transfer and generates a stop condition. during a single read sequence of multiple bytes, after the last address counter position of ffh is accessed, the address counter automatically wraps back to the first location, 00h. read operations can continue indefinitely. manipulating the address counter for reads: a dummy write cycle can be used to force the addresscounter to a particular value. to do this the master gen- erates a start condition, writes the slave address byte (r/ w = 0), writes the memory address where it desires to read, generates a repeated start condi- slave address* start start 0 1 0 1 0 a1 a0 r/w slave ack slave ack slave ack msb lsb msb lsb msb lsb b7 b6 b5 b4 b3 b2 b1 b0 read/ write register address b7 b6 b5 b4 b3 b2 b1 b0 data stop single-byte write-write control register 0 to 00h single-byte read -read temperature register two-byte write - write lut values for registers 80h and 81h start repeated start 51h data master nack stop 0 1010000 00001 100 0ch 01010 001 0 1010000 00000010 50h 02h stop temp example i 2 c transactions (when a0 and a1 are connected to gnd) typical i 2 c write transaction *the slave address is determined by address pins a0 and a1. 00000 000 50h a)b) c) slave ack slave ack slave ack slave ack slave ack slave ack start 0 1010000 10000 000 50h 80h stop 40h 0 100 0 0 00 slave ack slave ack slave ack 50h 0 101 0 0 00 slave ack two-byte read- read lut registers 80h and 81h d) start 0 1010000 10000 000 50h 80h stop slave ack slave ack slave ack master ack 51h 0 101 0 0 01 data data master ack reg81h reg80h repeated start figure 4. i 2 c communication examples downloaded from: http:///
ds1841 temperature-controlled, nv, i 2 c, logarithmic resistor 16 ______________________________________________________________________________________ tion, writes the slave address byte (r/ w = 1), reads data with ack or nack as applicable, and generates astop condition. see figure 4 for i 2 c communication examples. applications information power-supply decoupling to achieve the best results when using the ds1841,decouple both the power-supply pin and the wiper-bias voltage pin with a 0.01? or 0.1? capacitor. use a high-quality ceramic surface-mount capacitor if possi- ble. surface-mount components minimize lead induc- tance, which improves performance, and ceramiccapacitors tend to have adequate high-frequency response for decoupling applications. sda and scl pullup resistors sda is an i/o with an open-collector output that requires a pullup resistor to realize high-logic levels. a master using either an open-collector output with a pullup resistor or a push-pull output driver can be used for scl. pullup resistor values should be chosen to ensure that the rise and fall times listed in the ac elec- trical characteristics are within specification. a typical value for the pullup resistors is 4.7k . appendix a: control bits logic table lutar mode bit wiper access control bit adder mode bit update mode bit control of wr and register functionality x x x 0 ivr is loaded to wr on power-up. subsequent writes to 00h set the val ue of wr. 0 0 0 1 temperature conversion references the lut, determining lutar value, the lutar determines the lutval value, the unsigned lutval value is then automatically loaded into wr. 0 0 1 1 temperature conversion references the lut, determining lutar value, the lutar sets the lutval value, the signed lutval value is then summed with ivr, and the result is loaded into wr. x 1 0 1 i 2 c write (to 09h): the unsigned value written to wr, register 09h, is loaded into wr. x 1 1 1 i 2 c write (to 09h): the signed value of lutval is summed with ivr, the n loaded into wr, register 09h. 1 0 0 1 i 2 c write (to 08h): lutar references lut address, value at lut addres s location is loaded into lutval, the unsigned lutval value is loaded into wr. 1 0 1 1 i 2 c write (to 08h): lutar references lut address, the signed value at lut address location is loaded into lutval, the signed lutval val ue is summed with ivr value, and the result is loaded into wr. package information for the latest package outline information, go to www.maxim-ic.com/packages . package type package code document no. 10 tdfn-ep t1033+1 21-0137 downloaded from: http:///
ds1841 temperature-controlled, nv, i 2 c, logarithmic resistor maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circuit patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 ____________________ 17 2008 maxim integrated products is a registered trademark of maxim integrated products, inc. revision history revision number revision date description pages changed 0 11/07 initial release. in ordering information table, changed part numbers from ds1841t+/ds1841t+t&r to ds1841n+/ds1841n+t&r. 1 1 3/08 in the typical operating characteristics, corrected the supply current for tocs 1, 2, and 3 from ma to a. 5 2 5/08 in register 03h: control register 1 (cr1), changed the factory default from 0 0h to 03h; removed (default) from the adder mode = 0 and update mode = 0 descriptions and added it to the adder mode = 1 and update mode = 1 descriptions. 11 downloaded from: http:///

▲Up To Search▲

Price & Availability of DS1841X

	To Download DS1841X Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .