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general description the max1968/max1969 are highly integrated and cost- effective, high-efficiency, switch-mode drivers for peltier thermoelectric cooler (tec) modules. both devices uti- lize direct current control to eliminate current surges in the tec. on-chip fets minimize external components while providing high efficiency. a 500khz/1mhz switch- ing frequency and a unique ripple cancellation scheme reduce component size and noise. the max1968 operates from a single supply and pro- vides bipolar 3a output by biasing the tec between the outputs of two synchronous buck regulators. bipolar operation allows for temperature control without ?ead zones?or other nonlinearities at low load currents. this arrangement ensures that the control system does not hunt when the set point is very close to the natural operating point, requiring a small amount of heating or cooling. an analog control signal precisely sets the tec current. the max1969 provides unipolar output up to 6a. reliability is optimized with settable limits for both tec voltage and current, with independently set limits for heating and cooling current. an analog output also monitors tec current. the max1968/max1969 are available in a low-profile 28-pin tssop-ep package and is specified over the -40 c to +85 c temperature range. the thermally- enhanced tssop-ep package with exposed metal pad minimizes operating junction temperature. an evalua- tion kit is available to speed designs. applications fiber optic laser modules wdm, dwdm laser diode temperature control fiber optic network equipment edfa optical amplifiers telecom fiber interfaces ate biotech lab equipment features direct current control prevents tec current surges on-chip power mosfets high-efficiency switch-mode design ripple cancellation for low noise no dead-zone or hunting at low-output current adjustable tec voltage limit separately adjustable heating and cooling current limits itec output monitors tec current 1% accurate voltage reference 500khz/1mhz switching frequency 3a output current (max1968) 6a output current (max1969) thermally enhanced tssop-ep package max1968/max1969 power drivers for peltier tec modules ________________________________________________________________ maxim integrated products 1 ordering information 19-2447; rev 1; 5/04 for pricing, delivery, and ordering information, please contact maxim/dallas direct! at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. evaluation kit available part temp range pin-package max1968 eui -40 c to +85 c 28 tssop-ep* max1969 eui -40 c to +85 c 28 tssop-ep* typical operating circuit pgnd1 pgnd2 ctli comp lx2 lx1 gnd v dd max1968 pv dd 1pv dd 2 os2 cs os2 tec 3v to 5.5v tec current- control signal pin configuration and functional diagram appear at end of data sheet. * ep = exposed paddle.
max1968/max1969 power drivers for peltier tec modules 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v dd = pv dd 1 = pv dd 2 = shdn = 5v, pgnd1 = pgnd2 = freq = gnd, ctli = maxv = maxip = maxin = ref, c ref = 1f, c comp = 0.1f, l lx_ = 3.3h, c cs = c os2 = 1f, i tec < 3a rms (max1968), i tec < 6a rms (max1969), t a = 0? to +85? , unless otherwise noted. typical values are at t a = +25 c.) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. v dd to gnd ..............................................................-0.3v to +6v shdn , maxv, maxip, maxin, ctli, freq to gnd .......................................................-0.3v to +6v comp, os1, os2, cs, ref, itec to gnd ...........................................-0.3v to (v dd + 0.3v) pv dd 1, pv dd 2 to gnd ...............................-0.3v to (v dd + 0.3v) pv dd 1, pv dd 2 to v dd .................................................. -0.3v to +0.3v pgnd1, pgnd2 to gnd .......................................-0.3v to +0.3v comp, ref, itec short to gnd ...................................indefinite peak lx current (max1968) (note 1).................................4.5a peak lx current (max1969) (note 1)....................................+9a continuous power dissipation (t a = +70 c) 28-pin tssop-ep (derate 23.8mw/ c above +70 c).....1.9w operating temperature range ...........................-40 c to +85 c maximum junction temperature .....................................+150 c storage temperature range .............................-65 c to +150 c lead temperature (soldering 10s) ..................................+300 c parameter symbol conditions min typ max units input supply range v dd 3.0 5.5 v v dd = 5v, i tec = 0 to 3a, v out = v os1 - v os2 (max1968) -4.3 +4.3 v dd = 5v, i tec = 0 to 6a, v out = v os1 (max1969) 4.3 v dd = 3v, i tec = 0 to 3a, v out = v os1 - v os2 (max1968) -2.3 +2.3 output voltage range v out v dd = 3v, i tec = 0 to 6a, v out = v os1 (max1969) 2.3 v max1968 3 maximum tec current i tec ( max ) max1969 6 a reference voltage v ref v dd = 3v to 5.5v, i ref = 150a 1.485 1.500 1.515 v reference load regulation ? v ref v dd = 3v to 5.5v, i ref = +10a to -1ma 1.2 5 mv v maxi_ = v ref 140 150 160 v os1 < v cs v maxi_ = v ref /3 40 50 60 v maxi_ = v ref 140 150 160 current-sense threshold accuracy v os1 > v cs v maxi_ = v ref /3 40 50 60 mv switch-fault reset voltage 50 150 250 mv v dd = 5v, i = 0.5a 0.04 0.07 nfet on-resistance r ds ( on-n ) v dd = 3v, i = 0.5a 0.06 0.08 ? v dd = 5v, i = 0.5a 0.06 0.10 pfet on-resistance r ds ( on-p ) v dd = 3v, i = 0.5a 0.09 0.12 ? v lx = v dd = 5v, t a = +25 c 0.02 10 nfet leakage i leak ( n ) v lx = v dd = 5v, t a = +85 c1 a note 1: lx has internal clamp diodes to pgnd and pv dd_ . applications that forward bias these diodes should take care not to exceed the ic s package power dissipation limits.
max1968/max1969 power drivers for peltier tec modules _______________________________________________________________________________________ 3 electrical characteristics (continued) (v dd = pv dd 1 = pv dd 2 = shdn = 5v, pgnd1 = pgnd2 = freq = gnd, ctli = maxv = maxip = maxin = ref, c ref = 1f, c comp = 0.01f, l lx_ = 3.3h, c cs = c os2 = 1f, i tec < 3a rms (max1968), i tec < 6a rms (max1969), t a = 0 c to +85 c , unless otherwise noted. typical values are at t a = +25 c.) parameter symbol conditions min typ max units v lx = 0, t a = +25 c 0.02 10 v lx = 0, t a = +85 c1 pfet leakage i leak ( p ) a v dd = 5v 32 100 no load supply current i dd ( no load ) v dd = 3.3v 20 30 ma shutdown supply current i dd-sd v dd = 5v (note 2) 2 3 ma thermal shutdown t shutdown hysteresis = 15 c +165 c v dd rising 2.4 2.6 2.8 uvlo threshold v uvlo v dd falling 2.25 2.5 2.75 v switching frequency internal oscillator f sw-int freq = gnd 400 550 650 khz os1, os2, cs input current i os1 , i os2 , i cs 0 or v dd -100 +100 a shdn , freq input current i shdn , i freq 0 or v dd -5 +5 a shdn , freq input low voltage v il v dd = 3v to 5.5v v dd x 0.25 v shdn , freq input high voltage v ih v dd = 3v to 5.5v v dd x 0.75 v v maxv = v ref x 0.67, v os1 to v os2 = 4v, v dd = 5v -2 +2 % maxv threshold accuracy v maxv = v ref x 0.33, v os1 to v os2 = 2v, v dd = 3v -2 +2 % maxv, maxip, maxin input bias current i maxv-bias , i maxi_-bias v maxv = v maxi_ = 0.1v or 1.5v -0.1 +0.1 a ctli gain accuracy a ctli v ctli = 0.5v to 2.5v (note 3) 9.5 10 10.5 v/v ctli input resistance r ctli 1m ? terminated at ref 0.5 1.0 2.0 m ? error-amp transconductance g m 50 100 175 a/v itec accuracy v os1 to v cs = +100mv or -100mv -10 +10 % itec load regulation ? v itec v os1 to v cs = +100mv or -100mv, i itec = 10a -0.1 +0.1 %
max1968/max1969 power drivers for peltier tec modules 4 _______________________________________________________________________________________ electrical characteristics (v dd = pv dd 1 = pv dd 2 = shdn = 5v, pgnd1 = pgnd2 = freq = gnd, ctli = maxv = maxip = maxin = ref, c ref = 1f, c comp = 0.1f, l lx_ = 3.3h, c cs = c os2 = 1f, i tec < 3a rms (max1968), i tec < 6a rms (max1969), t a = -40 c to +85 c , unless otherwise noted.) (note 4) parameter symbol conditions min typ max units input supply range v dd 3.0 5.5 v v dd = 5v, i tec = 0 to 3a, v out = v os1 - v os2 (max1968) -4.3 +4.3 v dd = 5v, i tec = 0 to 6a, v out = v os1 (max1969) 4.3 v dd = 3v, i tec = 0 to 3a, v out = v os1 - v os2 (max1968) -2.3 +2.3 output voltage range v out v dd = 3v, i tec = 0 to 6a, v out = v os1 (max1969) 2.3 v max1968 3 maximum tec current i tec ( max ) max1969 6 a reference voltage v ref v dd = 3v to 5.5v, i ref = 150a 1.475 1.515 v reference load regulation ? v ref v dd = 3v to 5.5v, i ref = +10a to -1ma 5 mv v maxi_ = v ref 135 165 v os1 < v cs v maxi_ = v ref / 3 35 65 v maxi_ = v ref 135 165 current-sense threshold accuracy v os1 > v cs v maxi_ = v ref / 3 35 65 mv switch-fault reset voltage 50 250 mv v dd = 5v, i = 0.5a 0.07 nfet on-resistance r ds ( on-n ) v dd = 3v, i = 0.5a 0.08 ? v dd = 5v, i = 0.5a 0.07 pfet on-resistance r ds ( on-p ) v dd = 3v, i = 0.5a 0.12 ? v lx = v dd = 5v, t a = +25 c10 nfet leakage i leak ( n ) v lx = v dd = 5v, t a = -40 c10 a v lx = 0, t a = +25 c10 pfet leakage i leak ( p ) v lx = 0, t a = -40 c10 a v dd = 5v 100 no load supply current i dd(no load) v dd = 3.3v 30 ma shutdown supply current i dd-sd shdn = gnd, v dd = 5v (note 2) 3 ma v dd rising 2.4 2.8 uvlo threshold v uvlo v dd falling 2.25 2.75 v switching-frequency internal oscillator f sw-int freq = gnd 400 650 khz
max1968/max1969 power drivers for peltier tec modules _______________________________________________________________________________________ 5 electrical characteristics (continued) (v dd = pv dd 1 = pv dd 2 = shdn = 5v, pgnd1 = pgnd2 = freq = gnd, ctli = maxv = maxip = maxin = ref, c ref = 1f, c comp = 0.01f, l lx_ = 3.3h, c cs = c os2 = 1f, i tec < 3a rms (max1968), i tec < 6a rms (max1969), t a = -40 c to +85 c , unless otherwise noted.) (note 4) parameter symbol conditions min typ max units os1, os2, cs input current i os1 , i os2 , i cs 0 or v dd -100 +100 a shdn , freq input current i shdn , i freq 0 or v dd -5 +5 a shdn , freq input low voltage v il v dd = 3v to 5.5v v dd x 0.25 shdn , freq input high voltage v ih v dd = 3v to 5.5v v dd x 0.75 v v maxv = v ref x 0.67, v os1 to v os2 = 4v, v dd = 5v maxv threshold accuracy v maxv = v ref x 0.33, v os1 to v os2 = 2v, v dd = 3v -2 +2 % maxv, maxip, maxin input bias current i maxv-bias , i maxi_-bias v maxv = v maxi_ = 0.1v or 1.5v -0.1 +0.1 a ctli gain accuracy a ctli v ctli = 0.5v to 2.5v (note 3) 9.5 10.5 v/v ctli input resistance r ctli 1m ? terminated at ref 0.5 2.0 m ? error-amp transconductance g m 50 175 a/v itec accuracy v os1 to v cs = +100mv or -100mv -10 +10 % note 2: includes power fet leakage. note 3: ctli gain is defined as: note 4: specifications to -40 c are guaranteed by design, not production tested. a vv vv ctli ctli ref os cs = ? ? () 1
i tec vs. temperature max1968 toc09 temperature ( c) tec current (a) 80 60 20 40 0 -20 0.996 0.998 1.000 1.002 1.004 1.006 1.008 1.010 1.012 1.014 0.994 -40 freq = 500khz v ctli = 1.9v r tec = 1 ? v itec vs. tec current max1968 toc08 tec current (a) v itec (v) 1 -1 0.5 1.0 1.5 2.0 2.5 3.0 0 -3 3 zero-crossing tec current vs. ctli voltage max1968 toc07 1ms/div i tec 500ma/div 1.5v 0a v ctli 100mv/div tec current vs. ctli voltage max1968 toc06 20ms/div i tec 1a/div 0v 0a v ctli 1v/div tec current ripple max1968 toc05 400ns/div i tec 2ma/div dc current = 1a v dd ripple max1968 toc04 200ns/div v dd 100mv/div ac-coupled output voltage ripple max1968 toc03 400ns/div v os2 100mv/div ac-coupled v os1 100mv/div ac-coupled efficiency vs. tec current v dd = 3.3v max1968 toc02 tec current (a) efficiency (%) 2 1 10 20 30 40 50 60 70 80 90 0 03 freq = 500khz r load = 0.85 ? efficiency vs. tec current v dd = 5v max1968 toc01 tec current (a) efficiency (%) 2 1 10 20 30 40 50 60 70 80 90 0 03 freq = 500khz r load = 1 ? max1968/max1969 power drivers for peltier tec modules 6 _______________________________________________________________________________________ typical operating characteristics (v dd = 5v, v ctli = 1v, v freq = gnd, r load = 1 ?, circuit of figure 1, t a = +25 c, unless otherwise noted.)
v dd step response max1968 toc18 10ms/div 1a 0v i tec 20ma/div v dd 2v/div ctli step response max1968 toc17 1ms/div i tec 2a/div 1.5v 0a v ctli 1v/div startup and shutdown waveforms max1968 toc16 2ms/div 0v 0a 0a i tec 500ma/div v ctli = 2v i dd 200ma/div v shdn 5v/div reference load regulation v dd = 5v load current (ma) reference voltage change (mv) 0.8 0.6 0.2 0.4 0 -0.2 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 -0.4 1.0 sink source max1968 toc15 reference load regulation v dd = 3.3v max1968 toc14 load current (ma) reference voltage change (mv) 0.8 0.6 0.2 0.4 0 -0.2 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 -1.4 -0.4 1.0 sink source reference voltage change vs. temperature max1968 toc13 temperature ( c) reference voltage change (mv) 80 40 20 -20 -4 -2 -1 0 1 2 -5 -40 -3 060 reference voltage change vs. v dd max1968 toc12 v dd (v) reference voltage change (mv) 5.0 4.5 4.0 3.5 -3.0 -2.5 -1.5 -1.0 0 0.5 1.0 -3.5 3.0 5.5 -2.0 -0.5 switching frequency change vs. v dd max1968 toc11 v dd (v) switching frequency change (khz) 5.0 4.5 4.0 3.5 5 10 15 20 25 30 35 0 3.0 5.5 freq = 500khz switching frequency vs. temperature max1968 toc10 temperature ( c) switching frequency (khz) 80 60 20 40 0 -20 470 490 510 530 550 570 590 610 630 650 450 -40 freq = 500khz v ctli = 1.5v r tec = 1 ? max1968/max1969 power drivers for peltier tec modules _______________________________________________________________________________________ 7 typical operating characteristics (continued) (v dd = 5v, v ctli = 1v, v freq = gnd, r load = 1 ?, circuit of figure 1, t a = +25 c, unless otherwise noted.)
max1968/max1969 power drivers for peltier tec modules 8 _______________________________________________________________________________________ typical operating characteristics (continued) (v dd = 5v, v ctli = 1v, v freq = gnd, r load = 1 ?, circuit of figure 1, t a = +25 c, unless otherwise noted.) thermal stability, room temperature m ax1968 toc21 4s/div temperature 0.001 c/div t tec = +25 c t a = +25 c thermal stability, cooling m ax 1968 toc20 4s/div temperature 0.001 c/div t tec = +25 c t a = +45 c thermal stability, heating m ax1968 toc19 4s/div temperature 0.001 c/div t tec = +25 c t a = +5 c
max1968/max1969 power drivers for peltier tec modules _______________________________________________________________________________________ 9 pin description pin name function 1 v dd analog supply voltage input 2 gnd analog ground. connect to underside metal slug. 3 ctli tec current control input. sets differential current into the tec. center point is 1.50v (no tec current). the current is given by: i tec = (v os1 - v cs ) / r sense = (v ctli - 1.50) / (10 x r sense ). when (v ctli - v ref ) > 0, v os2 > v os1 > v cs . 4 ref 1.50v reference output. bypass ref to gnd with a 1f ceramic capacitor. 5, 7 pgnd2 power ground 2. internal synchronous rectifier ground connections. connect all pgnd pins together at power ground plane. 6, 8, 10 lx2 inductor connection. connect all lx2 pins together. for max1969, connect lx1 and lx2 pins together. 9, 11 pv dd 2 power 2 inputs. must be same voltage as v dd . connect all pv dd 2 inputs together at the v dd power plane. 12 freq switching frequency select. high = 1mhz, low = 500khz. 13 itec tec current monitor output. the itec output voltage is a function of the voltage across the tec current- sense resistor. v itec = 1.50v + (v os1 - v cs ) x 8. 14 os2 output sense 2. os2 senses one side of the differential tec voltage. os2 is a sense point, not a power output. for max1969, connect os2 to gnd. 15 os1 output sense 1. os1 senses one side of the differential tec voltage. os1 is a sense point, not a power output. 16 cs current-sense input. the current through the tec is monitored between cs and os1. the maximum tec current is given by 150mv / r sense and is bipolar. 17 shdn shutdown control input. active-low shutdown control. 18, 20 pv dd 1 power 1 inputs. must be same voltage as v dd . connect all pv dd 1 inputs together at the v dd power plane. 19, 21, 23 lx1 inductor connection. connect all lx1 pins together. for max1969, connect all lx1 and lx2 pins together. 22, 24 pgnd1 power ground 1. internal synchronous rectifier ground connections. connect all pgnd pins together at power ground plane. 25 comp current control-loop compensation. for most designs connect a 0.01f capacitor from comp to gnd. 26 maxin maximum negative tec current. connect maxin to ref to set default negative current limit -150mv / r sense . for max1969, connect maxin to maxip. 27 maxip m axi m um p osi ti ve te c c ur r ent. c onnect m ax ip to re f to set d efaul t p osi ti ve cur r ent l i m i t + 150m v / r s e n s e . (see the setting max positive and negative tec current section). 28 maxv maximum bipolar tec voltage. connect an external resistive-divider from ref to gnd to set the maximum voltage. the maximum tec voltage is 4 x v maxv .
max1968/max1969 power drivers for peltier tec modules 10 ______________________________________________________________________________________ functional diagram max v tec = v maxv ? 4 gnd comp ctli itec maxip freq pwm control and gate control maxin v dd pv dd 1 pv dd 2 r sense pgnd1 pgnd2 maxv ref max1968 shdn max i tec = (v maxip / v ref ) ? (0.15v / r sense ) max i tec = -(v maxin / v ref ) ? (0.15v / r sense ) ref os1 os2 cs lx1 lx2 on off 3v to 5.5v v dd os1 ref cs
max1968/max1969 power drivers for peltier tec modules ______________________________________________________________________________________ 11 detailed description the max1968/max1969 tec drivers consist of two switching buck regulators that operate together to directly control tec current. this configuration creates a differential voltage across the tec, allowing bidirec- tional tec current for controlled cooling and heating. controlled cooling and heating allow accurate tec temperature control within the tight tolerances of laser driver specifications. the voltage at ctli directly sets the tec current. an external thermal-control loop is typ- ically used to drive ctli. figures 1 and 2 show exam- ples of thermal control-loop circuits. ripple cancellation switching regulators like those used in the max1968/max1969 inherently create ripple voltage on the output. the regulators in the max1968 switch in phase and provide complementary in-phase duty cycles so ripple waveforms at the tec are greatly reduced. this feature suppresses ripple currents and electrical noise at the tec to prevent interference with the laser diode. switching frequency freq sets the switching frequency of the internal oscil- lator. with freq = gnd, the oscillator frequency is set to 500khz. the oscillator frequency is 1mhz when freq = v dd . voltage and current-limit settings both the max1968 and max1969 provide control of the maximum differential tec voltage. applying a voltage to maxv limits the maximum voltage across the tec. the max1968 provides control of the maximum positive and negative tec current. the voltage at maxip and maxin sets the maximum positive and negative current through the tec. these current limits can be indepen- dently controlled. the max1969 only controls tec cur- rent in one direction. the maximum tec current is controlled by maxip. connect maxin to gnd when using the max1969. current monitor output itec provides a voltage output proportional to the tec current (i tec ). see the functional diagram for more detail: v itec = 1.5v + 8 x (v os1 - v cs ) reference output the max1968/max1969 include an on-chip voltage ref- erence. the 1.50v reference is accurate to 1% over temperature. bypass ref with 1f to gnd. ref may be used to bias an external thermistor for temperature sensing as shown in figures 1 and 2. design procedure inductor selection small surface-mount inductors are ideal for use with the max1968/max1969. 3.3h inductors are suitable for most applications. select the output inductors so that the lc resonant frequency of the inductance and the output capacitance is less than 1/5 the selected switch- ing frequency. for example, 3.3h and 1f have a res- onance at 87.6khz, which is adequate for 500khz operation where: f = resonant frequency of output filter. capacitor selection filter capacitors decouple each power-supply input (v dd , pv dd 1, pv dd 2) with a 1f ceramic capacitor close to the supply pins. in some applications with long distances between the source supply and the max1968/max1969, addition- al bypassing may be needed to stabilize the input sup- ply. in such cases, a low-esr electrolytic capacitor of 100f or more at v dd is usually sufficient. compensation capacitor a compensation capacitor is needed to ensure current control-loop stability. select the capacitor so that the unity-gain bandwidth of the current control loop is less than or equal to 1/12th the resonant frequency of the out- put filter: where: f bw = loop unity gain bandwidth g m = loop transconductance, typically 100a/v c comp = value of the compensation capacitor r tec = tec series resistance r sense = sense resistor setting voltage and current limits certain tec parameters must be considered to guaran- tee a robust design. these include maximum positive current, maximum negative current, and the maximum c g f r rr for max c g f r rr for max comp m bw sense sense tec comp m bw sense sense tec ? ? ? ? ? ? + ? ? ? ? ? ? ? ? ? ? ? ? + ? ? ? ? ? ? 24 2 1968 12 2 1969 () () () () f lc = 1 2
max1968/max1969 power drivers for peltier tec modules 12 ______________________________________________________________________________________ voltage allowed across the tec. these limits should be used to set the maxip, maxin, and maxv voltages. setting max positive and negative tec current maxip and maxin set the maximum positive and nega- tive tec currents, respectively. the default current limit is 150mv / r sense when maxip and maxin are con- nected to ref. to set maximum limits other than the defaults, connect a resistor-divider from ref to gnd to set v maxi_ . use resistors in the 10k ? to 100k ? range. v maxi_ is related to i tec by the following equations: v maxip = 10(i tecp(max ) x r sense ) v maxin = 10(i tecn(max ) x r sense ) where i tecp(max) is the maximum positive tec current and i tecn(max) is the negative maximum tec current. positive tec current occurs when cs is less than os1: i tec x r sense = v os1 -v cs when i tec > 0. i tec x r sense = v cs -v os1 when i tec < 0. the max1969 controls the tec current in one direction (unipolar current flow from os1 to cs). set the maxi- mum unipolar tec current by applying a voltage to maxin. connect maxip to maxin. the equation for setting maxin is the same for the max1968 and max1969. take care not to exceed the positive or negative cur- rent limit on the tec. refer to the manufacturer s data sheet for these limits. setting max tec voltage apply a voltage to the maxv pin to control the maxi- mum differential tec voltage. maxv can vary from 0 to ref. the voltage across the tec is four times v maxv and can be positive or negative: |v os1 - v os2 | = 4 x v maxv set v maxv with a resistor-divider between ref and gnd using resistors from 10k ? to 100k ? . v maxv can vary from 0 to ref. control inputs/outputs output current control the voltage at ctli directly sets the tec current. ctli is typically driven from the output of a temperature con- trol loop. for the purposes of the following equations, it is assumed that positive tec current is cooling (see figure 1). the transfer function relating current through the tec (i tec ) and v ctli is given by: i tec = (v ctli - v ref )/(10 x r sense ) where v ref is 1.50v and: i tec = (v os1 - v cs )/r sense ctli is centered around ref (1.50v). i tec is zero when ctli = 1.50v. when vctli > 1.50v the max1968 is cooling. current flow is from os2 to os1. the voltages on the pins relate as follows: v os2 > v os1 > v cs the opposite applies when heating. when v ctli < 1.50v current flows from os1 to os2: v os2 < v os1 < v cs shutdown control the max1968/max1969 can be placed in a power-sav- ing shutdown mode by driving shdn low. when the max1968/max1969 are shut down, the tec is off (os1 and os2 decay to gnd) and supply current is reduced to 2ma (typ). itec output itec is a status output that provides a voltage proportion- al to the actual tec current. itec = ref when tec cur- rent is zero. the transfer function for the itec output is: v itec = 1.50 + 8 x (v os1 - v cs ) use itec to monitor the cooling or heating current through the tec. the maximum capacitance that itec can drive is 100pf.
max1968/max1969 power drivers for peltier tec modules ______________________________________________________________________________________ 13 os2 os1 cs lx1 lx2 comp itec gnd ctli 50m ? 100k ? 50k ? 100k ? 100k ? 1 f 1 f 1 f 1 f 1 f 1 f v dd pv dd 1 pv dd 2 pgnd1 pgnd2 ref maxip freq maxin maxv max1968 3v to 5.5v to ref ntc thermistor 0.01 f 10k ? r therm 3.3 h shdn 3.3 h 10 f on off v dd u3a u3b 510k ? 100k ? 10k ? u2 to ref 10 f 0.022 f 240k ? 10k ? temperature set point* *see figure 2 for temperature set point set by a dac 0.1 f 0.1 f v dd 10k ? 1 f max4477 max4477 max4475 figure 1. typical application circuit for max1968. circuit is configured for both cooling and heating with an ntc thermistor. c urrent flowing from os2 to os1 is cooling.
max1968/max1969 power drivers for peltier tec modules 14 ______________________________________________________________________________________ v dd lx1 lx2 gnd 3v to 5.5v pv dd 1 pv dd 2 pgnd1 pgnd2 ref maxip maxin maxv cs os1 os2 shdn itec comp freq ctli on off max1969 to ref v dd u3a u3b u2 to ref 510k ? 100k ? 10k ? 1 f 50k ? 100k ? 2.5 h 25m ? 100k ? 100k ? 4.7 f 10 f r therm 10k ? 0.01 f 0.1 f 10k ? 1 f v dd 240k ? temperature set point* *see figure 1 for temperature set point set by a potentiometer dac v dd dac inputs 1 f 1 f 1 f 0.1 f 0.022 f 10 f max4475 max4477 max4477 max5144 ntc thermistor figure 2. typical application circuit for max1969. maxin sets the maximum tec current. circuit configured for cooling with ntc thermistor. current always flows from cs to os2.
max1968/max1969 power drivers for peltier tec modules ______________________________________________________________________________________ 15 applications information the max1968/max1969 typically drive a thermoelectric cooler inside a thermal control loop. tec drive polarity and power are regulated based on temperature informa- tion read from a thermistor, or other temperature-mea- suring device to maintain a stable control temperature. temperature stability of 0.01 c can be achieved with carefully selected external components. there are numerous ways to implement the thermal loop. figures 1 and 2 show a design that employs preci- sion op amps, along with a dac or potentiometer to set the control temperature. the loop may also be imple- mented digitally, using a precision a/d to read the ther- mistor or other temperature sensor, a microcontroller to implement the control algorithm, and a dac (or filtered pwm signal) to send the appropriate signal to the max1968/max1969 ctli input. regardless of the form taken by the thermal control circuitry, all designs are similar in that they read temperature, compare it to a set-point signal, and then send an error-correcting sig- nal to the max1968/max1969 that moves the tempera- ture in the appropriate direction. chip information transistor count: 2959 process: bicmos pin configuration 28 27 26 25 24 23 22 21 20 19 18 17 16 15 1 2 3 4 5 6 7 8 9 10 11 12 13 14 maxv maxip maxin comp pgnd1 lx1 os1 pgnd1 lx1 pv dd 1 lx1 pv dd 1 shdn cs os2 itec freq pv dd 2 lx2 pv dd 2 lx2 pgnd2 lx2 pgnd2 ref ctli gnd v dd tssop-ep top view max1968 max1969 note: gnd is connected to the underside metal slug.
max1968/max1969 power drivers for peltier tec modules maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. 16 ____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 ? 2004 maxim integrated products printed usa is a registered trademark of maxim integrated products. tssop 4.4mm body.eps d 1 1 21-0108 package outline, tssop, 4.40 mm body exposed pad package information (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline info rmation, go to www.maxim-ic.com/packages .)

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