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general description the max1978/MAX1979 are the smallest, safest, most accurate complete single-chip temperature controllers for peltier thermoelectric cooler (tec) modules. on-chip power fets and thermal control-loop circuitry minimize external components while maintaining high efficiency. selectable 500khz/1mhz switching frequency and a unique ripple-can- cellation scheme optimize component size and efficiency while reducing noise. switching speeds of internal mosfets are optimized to reduce noise and emi. an ultra- low-drift chopper amplifier maintains ?.001? temperature stability. output current, rather than voltage, is directly con- trolled to eliminate current surges. individual heating and cooling current and voltage limits provide the highest level of tec protection. the max1978 operates from a single supply and provides bipolar ?a output by biasing the tec between the outputs of two synchronous buck regulators. true bipolar operation controls temperature without ?ead zones?or other nonlin- earities at low load currents. the control system does not hunt when the set point is very close to the natural operating point, where only a small amount of heating or cooling is needed. an analog control signal precisely sets the tec current. the MAX1979 provides unipolar output up to 6a. a chopper-stabilized instrumentation amplifier and a high- precision integrator amplifier are supplied to create a pro- portional-integral (pi) or proportional-integral-derivative (pid) controller. the instrumentation amplifier can interface to an external ntc or ptc thermistor, thermocouple, or semicon- ductor temperature sensor. analog outputs are provided to monitor tec temperature and current. in addition, separate overtemperature and undertemperature outputs indicate when the tec temperature is out of range. an on-chip volt- age reference provides bias for a thermistor bridge. the max1978/MAX1979 are available in a low-profile 48-lead thin qfn-ep package and is specified over the -40? to +85? temperature range. the thermally enhanced qfn-ep package with exposed metal pad minimizes operating junction temperature. an evaluation 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 features smallest, safest, most accurate complete single-chip controller on-chip power mosfets?o external fets circuit footprint < 0.93in 2 circuit height < 3mm temperature stability to 0.001? integrated precision integrator and chopper stabilized op amps accurate, independent heating and cooling current limits eliminates surges by directly controlling tec current adjustable differential tec voltage limit low-ripple and low-noise design tec current monitor temperature monitor over- and undertemperature alarm bipolar ?a output current (max1978) unipolar +6a output current (MAX1979) max1978/MAX1979 integrated temperature controllers for peltier modules ________________________________________________________________ maxim integrated products 1 ordering information freq n.c. lx1 pgnd1 n.c. lx1 pv dd 1 gnd gnd lx1 pv dd 1 pgnd1 pgnd2 lx2 pgnd2 lx2 pv dd 2 n.c. lx2 n.c. os2 1 2 3 4 5 6 7 8 9 10 11 12 36 35 34 33 32 31 30 29 28 27 26 25 difout fb- fb+ bfb+ aout ain- ain+ gnd int- intout cs ref ctli v dd gnd gnd maxv maxin maxip itec comp os1 qfn-ep max1978 MAX1979 bfb- top view *electrically connected to the underside metal slug. note: gnd is connected to the underside metal slug. 48 47 46 45 44 43 42 41 40 39 38 37 13 14 15 16 17 18 19 20 21 22 23 24 ot pv dd 2 shdn ut pin configuration 19-2490; rev 0; 7/02 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. typical operating circuit appears at end of data sheet. evaluation kit available part temp range pin-package max1978 etm -40 c to +85 c 48 thin qfn-ep* MAX1979 etm -40 c to +85 c 48 thin qfn-ep * ep = exposed pad.
max1978/MAX1979 integrated temperature controllers for peltier modules 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v dd = pv dd 1 = pv dd 2 = shdn = 5v, freq = gnd, ctli = fb+ = fb- = maxv = maxip = maxin = ref, t a = 0 c to +85 c , unless otherwise noted. typical values 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, ot , ut to gnd............................................-0.3v to +6v freq, comp, os1, os2, cs, ref, itec, ain+, ain-, aout, int-, intout, bfb+, bfb-, fb+, fb-, difout to gnd......................................-0.3v to (v dd + 0.3v) pv dd 1, pv dd 2 to v dd ...........................................-0.3v to +0.3v pv dd 1, pv dd 2 to gnd...............................-0.3v to (v dd + 0.3v) pgnd1, pgnd2 to gnd .......................................-0.3v to +0.3v comp, ref, itec, ot , ut , intout, difout, bfb-, bfb+, aout short to gnd .............................indefinite peak lx current (max1978) (note 1).................................4.5a peak lx current (MAX1979) (note 1)....................................+9a continuous power dissipation (t a = +70 c) 48-lead thin qfn-ep (derate 26.3mw/ c above +70 c) (note 2) .................2.105w operating temperature ranges max1978etm ..................................................-40 c to +85 c MAX1979etm ..................................................-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 (max1978) -4.3 +4.3 v dd = 5v, i tec = 0 to 6a, v out = v os1 (MAX1979) 4.3 v dd = 3v, i tec = 0 to 3a, v out = v os1 - v os2 (max1978) -2.3 +2.3 output voltage range v out v dd = 3v, i tec = 0 to 6a, v out = v os1 (MAX1979) 2.3 v max1978 3 maximum tec current i tec ( max ) MAX1979 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 135 150 160 v os1 < v cs v maxi_ = v ref /3 40 50 60 v maxi_ = v ref 135 150 160 current-sense threshold v os1 > v cs v maxi_ = v ref /3 40 50 60 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 not exceed the ic s package power dissipation limits. note 2: solder underside metal slug to pc board ground plane.
max1978/MAX1979 integrated temperature controllers for peltier modules _______________________________________________________________________________________ 3 electrical characteristics (continued) (v dd = pv dd 1 = pv dd 2 = shdn = 5v, freq = gnd, ctli = fb+ = fb- = maxv = maxip = maxin = ref, t a = 0 c to +85 c , unless otherwise noted. typical values at t a = +25 c.) parameter symbol conditions min typ max units v lx = 0, t a = +25 c 0.02 10 pfet leakage i leak(p) v lx = 0, t a = +85 c1 a v dd = 5v 30 50 no-load supply current i dd(no load) v dd = 3.3v 15 30 ma shutdown supply current i dd-sd shdn = gnd, v dd = 5v (note 3) 2 3 ma thermal shutdown t s h u td own 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 freq = gnd 450 500 650 switching frequency internal oscillator f sw-int freq=v dd 800 1000 1200 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 0.25 v dd v shdn , freq input high voltage v ih v dd = 3v to 5.5v 0.75 v dd v v maxv = v ref ? 0.67, v os1 to v os2 = 4v, v dd = 5v -1 +1 maxv threshold accuracy v maxv = v ref ? 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 a ctli v ctli = 0.5v to 2.5v (note 4) 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 s 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 % instrumentation amp input bias current i dif-bias -10 0 +10 na instrumentation amp offset voltage v dif-os v dd = 3v to 5.5v -200 +20 +200 v instrumentation amp offset- voltage drift with temperature v dd = 3v to 5.5v 0.1 v/ c instrumentation amp preset gain a dif r load = 10k ? to ref 45 50 55 v/v
max1978/MAX1979 integrated temperature controllers for peltier modules 4 _______________________________________________________________________________________ electrical characteristics (continued) (v dd = pv dd 1 = pv dd 2 = shdn = 5v, freq = gnd, ctli = fb+ = fb- = maxv = maxip = maxin = ref, t a = 0 c to +85 c , unless otherwise noted. typical values at t a = +25 c.) parameter symbol conditions min typ max units integrator amp open-loop gain a ol-int r load = 10k ? to ref 120 db integrator amp cmrr cmrr int 100 db integrator amp input bias current i int-bias v dd = 3v to 5.5v 1 na integrator amp voltage offset v int-os v dd = 3v to 5.5v -3 +0.1 +3 mv integrator amp gain bandwidth gbw int 100 khz undedicated chopper amp open-loop gain a ol-ain r load = 10k ? to ref 120 db undedicated chopper amp cmrr cmrr ain 85 db undedicated chopper amp input bias current i ain-bias v dd = 3v to 5.5v -10 0 +10 na undedicated chopper amp offset voltage v ain-os v dd = 3v to 5.5v -200 +10 +200 v undedicated chopper amp gain bandwidth gbw ain 100 khz undedicated chopper amp output ripple v ripple a = 5 20 mv bfb_ buffer error c l oa d < 100p f -200 0 +200 v ut and ot leakage current i leak v ut = v ot = 5.5v 1 a ut and ot output low voltage v ol sinking 4ma 50 150 mv ut trip threshold fb+ - fb- (see typical application circuit ) -20 mv ot trip threshold fb+ - fb- (see typical application circuit )20 mv
max1978/MAX1979 integrated temperature controllers for peltier modules _______________________________________________________________________________________ 5 electrical characteristics (v dd = pv dd 1 = pv dd 2 = shdn = 5v, freq = gnd, ctli = fb+ = fb- = maxv = maxip = maxin = ref, t a = -40 c to +85 c , unless otherwise noted.) (note 5) parameter symbol conditions min max units input supply range v dd 3 5.5 v v dd = 5v, i tec = 0 to 3a, v out = v os1 -v os2 (max1978) -4.3 +4.3 v dd = 5v, i tec = 0 to 6a, v out = v os1 (MAX1979) 4.3 v dd = 3v, i tec = 0 to 3a, v out = v os1 - v os2 (max1978) -2.3 +2.3 output voltage range v out v dd = 3v, i tec = 0 to 6a, v out = v os1 (MAX1979) 2.3 v max1978 3 maximum tec current i tec ( max ) MAX1979 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 5mv v maxi_ = v ref 135 160 v os1 < v cs v maxi_ = v ref /3 40 60 v maxi_ = v ref 135 160 current-sense threshold v os1 > v cs v maxi_ = v ref /3 40 60 mv v dd = 5v 50 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 3) 3 ma v dd rising 2.4 2.8 uvlo threshold v uvlo v dd falling 2.25 2.75 v freq = gnd 450 650 switching frequency internal oscillator f sw-int freq = v dd 800 1200 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 f req 0 or v dd -5 +5 a shdn , freq input low voltage v il v dd = 3v to 5.5v 0.25 ? v dd v shdn , freq input high voltage v ih v dd = 3v to 5.5v 0.75 ? v dd v
note 3: includes power fet leakage. note 4: ctli gain is defined as: note 5: specifications to -40 c are guaranteed by design, not production tested. a ctli vv vv ctli ref osi cs = ? () ? () max1978/MAX1979 integrated temperature controllers for peltier modules 6 _______________________________________________________________________________________ electrical characteristics (continued) (v dd = pv dd 1 = pv dd 2 = shdn = 5v, freq = gnd, ctli = fb+ = fb- = maxv = maxip = maxin = ref, t a = -40 c to +85 c , unless otherwise noted.) (note 5) parameter symbol conditions min max units v maxv = v ref ? 0.67, v os1 to v os2 = 4v, v dd = 5v -1 +1 maxv threshold accuracy v maxv = v ref ? 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 a ctli v ctli = 0.5v to 2.5v (note 4) 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 s 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 -0.125 +0.125 % instrumentation amp input bias current i dif-bias -10 +10 na instrumentation amp offset voltage v dif-os v dd = 3v to 5.5v -200 +200 v instrumentation amp preset gain a dif r load = 10k ? to ref 45 55 v/v integrator amp input bias current i int-bias v dd = 3v to 5.5v 1 na integrator amp voltage offset v int-os v dd = 3v to 5.5v -3 +3 mv undedicated chopper amp input bias current i ain-bias v dd = 3v to 5.5v -10 +10 na undedicated chopper amp offset voltage v ain-os v dd = 3v to 5.5v -200 +200 v bfb_ buffer error c load < 100pf -200 +200 v ut and ot leakage current i leak v ut = v ot = 5.5v 1 a ut and ot output low voltage v ol sinking 4ma 150 mv
max1978/MAX1979 integrated temperature controllers for peltier modules _______________________________________________________________________________________ 7 efficiency vs. tec current v dd = 5v max1978 toc01 tec current (a) efficiency (%) 2.0 1.5 1.0 0.5 10 20 30 40 50 60 70 80 90 0 0 2.5 r tec = 1.1 ? efficiency vs. tec current v dd = 3.3v max1978 toc02 tec current (a) 2.0 1.5 0.5 1.0 10 20 30 40 50 60 70 80 0 0 2.5 r tec = 0.855 ? efficiency (%) output-voltage ripple waveforms max1978 toc03 400ns/div v os2 100mv/div ac-coupled v os1 100mv/div ac-coupled v os1 - v os1 50mv/div input supply ripple max1978 toc04 200ns/div v dd 20mv/div ac-coupled tec current vs. ctli voltage max1978 toc05 20ms/div v ctli 1v/div i tec 2a/div -0v -0a zero-crossing tec current max1978 toc06 1ms/div v ctli 200mv/div i tec 500ma/div 1.5v 0a v itec vs. tec current max1978 toc07 tec current (a) v itec (v) 2 1 0 -1 -2 0.5 1.0 1.5 2.0 2.5 3.0 0 -3 3 tec current vs. temperature max1978 toc08 temperature ( c) i tec (a) 80 60 40 20 0 -20 0.995 1.000 1.005 1.010 0.990 -40 i tec = 1a r sense = 0.68 ? switching frequency vs. temperature switching frequency (khz) 494 496 498 500 502 504 506 508 492 max1978 toc09 temperature ( c) 80 60 40 20 0 -20 -40 v ctli = 1.5v r tec = 1 ? typical operating characteristics (v dd = 5v, v ctli = 1v, v freq = gnd, rtec = 1 ? , circuit of figure 1, t a = +25 c, unless otherwise noted.)
max1978/MAX1979 integrated temperature controllers for peltier modules 8 _______________________________________________________________________________________ switching frequency change vs. input supply max1978 toc10 v dd (v) switching frequency change (khz) 5.0 4.5 4.0 3.5 -30 -25 -20 -15 -10 -5 0 5 10 -35 3.0 5.5 reference voltage change vs. input supply reference voltage change (mv) -2.5 -2.0 -1.5 -1.0 -0.5 0 0.5 1.0 -3.0 max1978 toc11 v dd (v) 5.0 4.5 4.0 3.5 3.0 5.5 reference voltage change vs. temperature max1978 toc12 temperature ( c) reference voltage change (mv) 60 40 20 0 -20 -3 -2 -1 0 1 2 3 -4 -40 80 reference load regulation max1978 toc13 reference load current (ma) reference voltage change (mv) 0.8 0.6 -0.2 0 0.2 0.4 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 -1.0 -0.4 1.0 sink source ato voltage vs. thermistor temperature max1978 toc14 thermistor temperature ( c) ato voltage (v) 30 20 010 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 0 -10 40 50 60 ntc, 10k ? thermistor circuit in figures 1 and 2 startup and shutdown waveforms max1978 toc15 100 s/div v shdn 5v/div i tec 500ma/div i dd 200ma/div ctli step response max1978 toc16 1ms/div 1.5v 0a v ctli 1v/div i tec 1a/div input supply step response max1978 toc17 1a 0v v dd 2v/div i tec 20ma/div 10ms/div thermal stability, cooling mode max1978 toc18 4s/div temperature 0.001 c/div i tec = +25 c t a = +45 c typical operating characteristics (continued) (v dd = 5v, v ctli = 1v, v freq = gnd, rtec = 1 ? , circuit of figure 1, t a = +25 c, unless otherwise noted.)
max1978/MAX1979 integrated temperature controllers for peltier modules _______________________________________________________________________________________ 9 pin description thermal stability, room temperature max1978 toc19 4s/div temperature 0.001 c/div i tec = +25 c t a = +25 c thermal stability, heating mode max1978 toc20 4s/div temperature 0.001 c/div t tec = +25 c t a = +5 c temperature error vs. ambient temperature max1978 toc21 ambient temperature ( c) temperature error ( c) 30 40 10 20 0 -10 -0.02 -0.01 0 0.01 0.02 0.03 -0.03 -20 50 typical operating characteristics (continued) (v dd = 5v, v ctli = 1v, v freq = gnd, rtec = 1 ? , circuit of figure 1, t a = +25 c, unless otherwise noted.) pin name function 1 os2 output sense 2. os2 senses one side of the differential tec voltage. os2 is a sense point, not a power output. 2, 8, 29, 35 n.c. not internally connected 3, 5 pgnd2 power ground 2. internal synchronous rectifier ground connections. connect all pgnd pins together at power ground plane. 4, 6, 9 lx2 inductor 2 connection. connect all lx2 pins together. connect lx2 to lx1 when using the MAX1979. 7, 10 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. bypass to pgnd2 with a 10f ceramic capacitor. 11 shdn shutdown control input. active-low shutdown control. 12 ot under-temperature alarm. open-drain output pulls low if temperature feedback falls 20mv (typically +1.5 c) below the set-point voltage. 13 ut under-temperature alarm. open-drain output pulls low if temperature feedback falls 20mv (typically +1.5 c) below the set-point voltage. 14 intout integrator amp output. normally connected to ctli. 15 int- integrator amp inverting input. normally connected to difout through thermal-compensation network. 16, 25, 26, 42, 43 gnd analog ground. connect all gnd pins to analog ground plane. 17 difout chopper-stabilized instrumentation amp output. differential gain is 50 ? (fb+ - fb-). 18 fb- chopper-stabilized instrumentation amp inverting input. connect to thermistor bridge. 19 fb+ chopper-stabilized instrumentation amp noninverting input. connect to thermistor bridge. 20 bfb- chopper-stabilized buffered fb- output. used to monitor thermistor bridge voltage. 21 bfb+ chopper-stabilized buffered fb+ output. used to monitor thermistor bridge voltage. 22 ain+ undedicated chopper-stabilized amplifier noninverting input
max1978/MAX1979 integrated temperature controllers for peltier modules 10 ______________________________________________________________________________________ pin description (continued) pin name function 23 ain- undedicated chopper-stabilized amplifier inverting input 24 aout undedicated chopper-stabilized amplifier output 27, 30 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. bypass to pgnd1 with a 10f ceramic capacitor. 28, 31, 33 lx1 inductor 1 connection. connect all lx1 pins together. connect lx1 to lx2 when using the MAX1979. 32, 34 pgnd1 power ground 1. internal synchronous-rectifier ground connections. connect all pgnd pins together at power ground plane. 36 freq switching-frequency select. low = 500khz, high = 1mhz. 37 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 ) ? 8. 38 comp current-control loop compensation. for most designs, connect a 10nf capacitor from comp to gnd. 39 maxip maximum positive tec current. connect maxip to ref to set default positive current limit +150mv / r sense . 40 maxin maximum negative tec current. connect maxin to ref to set default negative current limit -150mv / r sense . connect maxin to gnd when using the MAX1979. 41 maxv maximum bipolar tec voltage. connect an external resistive divider from ref to gnd to set the maximum voltage across the tec. the maximum tec voltage is 4 ? v maxv . 44 v dd analog supply voltage input. bypass to gnd with a 10f ceramic capacitor. 45 ctli tec current-control input. sets differential current into the tec. center point is 1.50v (no tec current). connect to intout when using the thermal control loop. i tec = (v os1 - v cs ) / r sense = (v ctli - 1.50) / (10 ? r sense ). when (v clti - v ref ) > 0, v os2 > v os1 > v cs . 46 ref 1.5v reference voltage output. bypass ref to gnd with a 1f ceramic capacitor. 47 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 for the max1978. the MAX1979 tec current is unipolar. 48 os1 output sense 1. os1 senses one side of the differential tec voltage. os1 is a sense point, not a power output.
max1978/MAX1979 integrated temperature controllers for peltier modules ______________________________________________________________________________________ 11 max1978 1.5v reference max v tec = v maxv x 4 max i tec = (v maxip / v ref ) x (0.15v/r sense ) max i tec = (v maxin / v ref ) x (0.15v/r sense ) ref maxv maxip maxin itec ctli comp gnd ot ut cs os1 ref ref + 1v ref - 1v r pgnd2 r 50r 50r ref difout ain+ aout fb+ fb- bfb+ bfb- int- ref ain- intout lx2 os2 os1 cs pgnd1 lx1 pv dd 1 v dd pv dd 2 v dd r sense 3v to 5.5v on off shdn freq pwm control and gate drive functional diagram
max1978/MAX1979 detailed description power stage the power stage of the max1978/MAX1979 thermoelectric cooler (tec) temperature controllers consists of two switching buck regulators that operate together to directly control tec current. this configura- tion creates a differential voltage across the tec, allow- ing bidirectional 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. the internal thermal-control loop drives ctli to regulate tec temperature. the on-chip thermal-control circuitry can be configured to achieve temperature control sta- bility of 0.001 c. figure 1 shows a typical tec thermal- control circuit. ripple cancellation switching regulators like those used in the max1978/MAX1979 inherently create ripple voltage on each common-mode output. the regulators in the max1978 switch in phase and provide complementary in-phase duty cycles, so ripple waveforms at the differ- ential tec output are greatly reduced. this feature sup- presses ripple currents and electrical noise at the tec to prevent interference with the laser diode while mini- mizing output capacitor filter size. integrated temperature controllers for peltier modules 12 ______________________________________________________________________________________ tec max1978 10 f 0.01 f v dd v dd shdn pv dd 1pv dd 2 ref ref maxv maxin maxip undertemp alarm comp overtemp alarm dc current monitor ref itec bfb- ain- ain+ ctli freq gnd pgnd2 pgnd1 intout int- difout fb+ fb- lx2 os2 os1 cs lx1 aout 20k ? 1% 69.8k ? 1% 105k ? 1% 1 f thermistor voltage monitor 80.6k ? 100k ? 100k ? 0.068 ? 10k ? 1 f 3 h 3 h 4.7 f 1 f 20k ? 1m ? 10 f 0.047 f 0.47 f ref thermal feedback ut ot 10 f 10 f 1 f figure 1. max1978 typical application circuit
switching frequency freq sets the switching frequency of the internal oscil- lator. the oscillator frequency is 500khz when freq = gnd. the oscillator frequency is 1mhz when freq = v dd . the 1mhz setting allows minimum inductor and fil- ter-capacitor values. efficiency is optimized with the 500khz setting. voltage and current-limit settings the max1978 and MAX1979 provide settings to limit the maximum differential tec voltage. applying a volt- age to maxv limits the maximum voltage across the tec to (4 ? v maxv ). the max1978 also limits the maximum positive and negative tec current. the voltages applied to maxip and maxin independently set the maximum positive and negative output current limits. the MAX1979 con- trols tec current in only one direction, so the maximum current is set only with maxip. maxin must be con- nected to gnd when using the MAX1979. chopper-stabilized instrumentation amplifier the max1978 and MAX1979 include a chopped input instrumentation amplifier with a fixed gain of 50. an external thermal sensor, typically a thermistor, is con- nected to one of the amp s inputs. the other input is connected to a voltage that represents the temperature set point. this set point can be derived from a resistor- divider network or dac. the included instrumentation amplifier provides low offset drift needed to prevent temperature set-point drift with ambient temperature changes. temperature stability of 0.001 c can be achieved over a 0 c to +50 c ambient temperarure range by using the amplifier as in figure 1. difout is the instrumentation amplifier output and is proportional to 50 times the difference between the set-point tem- perature and the tec temperature. this difference is commonly referred to as the error signal . for best temperature stability, derive the set-point voltage from the same reference that drives the thermistor (usually the max1978/MAX1979 ref output). this is called a ratiometric or bridge connection. the bridge con- nection optimizes stability by eliminating ref drift as an error source. errors at ref are nullified because they affect the thermistor and set point equally. the instrumentation amplifier utilizes a chopped input scheme to minimize input offset voltage and drift. this generates output ripple at difout that is equal to the chop frequency. the difout peak-to-peak ripple amplitude is typically 100mv but has no effect on tem- perature stability. difout ripple is filtered by the inte- grator in the following stage. the chopper frequency is derived from, and is synchronized to, the switching fre- quency of the power stage. integrator amplifier an on-chip integrator amplifier is provided on the max1978/MAX1979. the noninverting terminal of the amplifier is connected internally to ref. connect an appropriate network of resistors and capacitors between difout and int-, and connect intout to ctli for typi- cal operation. ctli directly controls the tec current magnitude and polarity. the thermal-control-loop dynam- ics are set by the integrator input and feedback compo- nents. see the applications information section for details on thermal-loop compensation. current monitor output itec provides a voltage output proportional to the tec current, itec (see the functional diagram ): v itec = 1.5v + 8 ? (v os1 - v cs ) over- and under-temperature alarms the max1978/MAX1979 provide open-drain status out- puts that alert a microcontroller when the tec tempera- ture is over or under the set-point temperature. ot and ut pull low when v (fb1+ - fb-) is more than 20mv. for a typical thermistor connection, this translates to approxi- mately 1.5 c error. reference output the max1978/MAX1979 include an on-chip 1.5v volt- age reference accurate to 1% over temperature. bypass ref with 1f to gnd. ref can be used to bias an external thermistor for temperature sensing as shown in figures 1 and 2. note that the 1% accuracy of ref does not limit the temperature stability achievable with the max1978/MAX1979. this is because the ther- mistor and set-point bridge legs are intended to be dri- ven ratiometrically by the same reference source (ref). variations in the bridge-drive voltage then cancel out and do not generate errors. consequently, 0.001 c sta- ble temperature control is achievable with the max1978/MAX1979 reference. an external source can be used to bias the thermistor bridge. for best accuracy, the common-mode voltage applied to fb+ and fb- should be kept between 0.5v and 1v, however the input range can be extended from 0.2v to v dd / 2 if some shift in instrumentation amp offset (approximately -50v/v) can be tolerated. this shift remains constant with temperature and does not con- tribute to set-point drift. max1978/MAX1979 integrated temperature controllers for peltier modules ______________________________________________________________________________________ 13
max1978/MAX1979 buffered outputs, bfb+ and bfb- bfb+ and bfb- output a buffered version of the voltage that appears on fb+ and fb-, respectively. the buffers are typically used in conjunction with the undedicated chopper amplifier to create a monitor for the thermistor voltage/tec temperature (figures 1 and 2). these buffers are unity-gain chopper amplifiers and exhibit output ripple. each output can be either integrated or filtered to remove the ripple content if necessary. undedicated chopper-stabilized amplifier in addition to the chopper amplifiers at difout and bfb_, the max1978/MAX1979 include an additional chopper amplifier at aout. this amplifier is uncommit- ted but is intended to provide a temperature-propor- tional analog output. the thermistor voltage typically is connected to the undedicated chopper amplifier through the included buffers bfb+ and bfb-. figure 3 shows how to configure the undedicated amplifier as a thermistor voltage monitor. the output voltage at aout is not precisely linear, because the thermistor is not lin- ear. aout is also chopper stabilized and exhibits out- put ripple and can be either integrated or filtered to remove the ripple content if necessary. integrated temperature controllers for peltier modules 14 ______________________________________________________________________________________ tec MAX1979 10 f 10 f 10 f 1 f 0.01 f v dd v dd shdn pv dd 1pv dd 2 ref ref maxv maxin maxip undertemp alarm comp overtemp alarm dc current monitor ref itec bfb- ain- ain+ ctli freq gnd pgnd2 pgnd1 intout int- difout fb- fb+ os2 os1 cs lx2 lx1 aout 20k ? 1% 69.8k ? 1% 105k ? 1% 1 f thermistor voltage monitor 80.6k ? 100k ? 100k ? 0.03 ? 10k ? 3 h 4.7 f 1 f 20k ? 1m ? 10 f 0.047 f 0.47 f ref thermal feedback ut ot figure 2. MAX1979 typical application circuit
design procedure inductor selection small surface-mount inductors are ideal for use with the max1978/MAX1979. 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, 3.0h and 1f have a res- onance at 92khz, which is adequate for 500khz operation. where: f lc = resonant frequency of output filter. capacitor selection filter capacitors decouple each power-supply input (v dd , pv dd 1, and pv dd 2) with a 10f ceramic capacitor close to the sup- ply pins. if long supply lines separate the source sup- ply from the max1978/MAX1979, or if the source supply has high output impedance, place an additional 22f to 100f ceramic capacitor between the v dd power plane and power ground. insufficient supply bypassing can result in supply bounce and degraded accuracy. compensation capacitor include a compensation capacitor to ensure current- power control-loop stability. select the capacitor so that the unity-gain bandwidth of the current-control loop is less than or equal to 10% the resonant frequency of the output filter: where: f bw = unity-gain bandwidth frequency 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 consider tec parameters to guarantee a robust design. these parameters include maximum positive current, maximum negative current, and the maximum voltage allowed across the tec. these limits should be used to set 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 itec by the following equations: v maxip = 10 (i tecp(max) ? r sense ) v maxin = 10 (i tecn(max) ? r sense ) where i tecp(max) is the maximum positive tec current and i tecn(max) is the maximum negative tec current. positive tec current occurs when cs is less than os1: i tec ? r sense = cs - os1 when i tec < 0. i tec ? r sense = os1 - cs when i tec > 0. c g f r rr comp m bw sense sense tec ? ? ? ? ? ? + ? ? ? ? ? ? 24 2 ( ) f lc lc = 1 2 max1978/MAX1979 integrated temperature controllers for peltier modules ______________________________________________________________________________________ 15 max1978 MAX1979 x50 fb+ fb- bfb- aout ain+ ain- 10k ? 1 f 20k ? 1% 80.6k ? 1% 69.8k ? 1% 105k ? 1% ref ref v setpoint figure 3. thermistor voltage monitor
max1978/MAX1979 the MAX1979 controls the tec current in only one direction (unipolar). set the maximum unipolar tec cur- rent by applying a voltage to maxip. connect maxin to gnd when using the MAX1979. the equation for set- ting maxip is the same for the max1978 and MAX1979. do not exceed the positive or negative cur- rent-limit specifications on the tec. refer to the tec manufacturer s data sheet for these limits. setting max tec voltage apply a voltage to maxv to control the maximum differ- ential 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 ? v maxv use resistors from 10k ? to 100k ? to form a voltage- divider to set v maxv . thermal-control loop the max1978/MAX1979 provide all the necessary amplifiers needed to create a thermal-control loop. typically, the chopper-stabilized instrumentation ampli- fier generates an error signal and the integrator amplifi- er is used to create a pid controller. figure 4 shows an example of a simple pid implementation. the error sig- nal needed to control the loop is generated from the difference between the set point and the thermistor voltage. the desired set-point voltage can be derived from a potentiometer, dac, or other voltage source. figure 5 details the required connections. connect the output of the pid controller to ctli. for details, see the applications information section. control inputs/outputs tec current control the voltage at ctli directly sets the tec current. ctli typically is driven from the output of a temperature-con- trol circuit c intout . for the purposes of the following equations, it is assumed that positive tec current is heating. the transfer function relating current through the tec (i tec ) and v ctli is given by: i tec = (v ctli - v ref ) / (10 ? r sense ) where v ref is 1.50v and i tec = (v os1 - v cs ) / r sense v ctli is centered around ref (1.50v). i tec is zero when v ctli = 1.50v. when v ctli > 1.50v, the max1978 is heat- ing. current flow is from os2 to os1. the voltages are: v os2 > v os1 > v cs when v ctli < 1.50v, current flows from os1 to os2: v os2 < v os1 < v cs integrated temperature controllers for peltier modules 16 ______________________________________________________________________________________ c3 c2 c1 r3 r2 difout intout ref int- r1 figure 4. proportional integral derivative controller max1978 MAX1979 fb- ref fb+ c ref v setpoint v thermistor max1978 MAX1979 fb- ref fb+ c ref v setpoint v thermistor dac digital input figure 5. the set point can be derived from a potentiometer or a dac
shutdown control drive shdn low to place the max1978/MAX1979 in a power-saving shutdown mode. when the max1978/ MAX1979 are in shutdown, the tec is off (v os1 and v os2 decay to gnd) and input supply current lowers to 2ma (typ). itec output itec is a status output that provides a voltage propor- tional to the actual tec current. itec = ref when tec current is zero. the transfer function for the itec output: v itec = 1.50 + 8 ? (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. applications information the max1978/MAX1979 drive a thermoelectric cooler inside a thermal-control loop. tec drive polarity and power are regulated to maintain a stable control tem- perature based on temperature information read from a thermistor, or from other temperature-measuring devices. carefully selected external components can achieve 0.001 c temperature stability. the max1978/ MAX1979 provide precision amplifiers and an integra- tor amplifier to implement the thermal-control loop (figures 1 and 2). connecting and compensating the thermal-control loop typically, the thermal loop consists of an error amplifier and proportional integral derivative controller (pid) (figure 4). the thermal response of the tec module must be understood before compensating the thermal loop. in particular, tecs generally have stronger heat- ing capacity than cooling capacity because of the effects of waste heat. consider this point when analyz- ing the tec response. analysis of the tec using a signal analyzer can ease compensation calculations. most tecs can be crudely modeled as a two-pole system. the second pole poten- tially creates an oscillatory condition because of the associated 180 phase shift. a dominant pole compen- sation scheme is not practical because the crossover frequency (the point of the bode plot where the gain is zero db) must be below the tec s first pole, often as low as 0.02hz. this requires an excessively large inte- grator capacitor and results in slow loop-transient response. a better approach is to use a pid controller, where two additional zeros are used to cancel the tec and integrator poles. adequate phase margin can be achieved near the frequency of the tec s second pole when using a pid controller. the following is an exam- ple of the compensation procedure using a pid con- troller. figure 6 details a two-pole transfer function of a typical tec module. this bode plot can be generated with a signal analyzer driving the ctli input of the max1978/MAX1979, while plotting the thermistor volt- age from the module. for the example module, the two poles are at 0.02hz and 1hz. the first step in compensating the control loop involves selecting components r3 and c2 for highest dc gain. film capacitors provide the lowest leakage but can be large. ceramic capacitors are a good compromise between low leakage and small size. tantalum and electrolytic capacitors have the highest leakage and generally are not suitable for this application. the inte- grating capacitor, c2, and r3 (figure 4) set the first zero (fz1). the specific application dictates where the first zero should be set. choosing a very low frequency results in a very large value capacitor. set the first zero frequency to no more than 8 times the frequency of the lowest tec pole. setting the frequency more than 8 times the lowest pole results in the phase falling below -135 and may cause instability in the system. for this example, c2 = 10f. resistor r3 then sets the zero at 0.16hz using the following equation: this yields a value of r3 = 99.47k ? . for our example, use 100k ? . next, adjust the gain for a crossover frequency for max- imum phase margin near the tec s second pole. from figure 6, the tec bode plot, approximately 30db of gain is needed to move the 0db crossover point up to 1.5hz. the error amplifier provides a fixed gain of 50, or approximately 34db. therefore, the integrator needs to provide -4db of gain at 1.5hz. c1 and r3 set the gain at the crossover frequency. c a c rf c 1 1 2 23 = + fz cr 1 1 223 = max1978/MAX1979 integrated temperature controllers for peltier modules ______________________________________________________________________________________ 17
max1978/MAX1979 where: a = the gain needed to move the 0db crossover point up to the desired frequency. in this case, a = -4db = 0.6. f c = the desired crossover frequency, 1.5hz in this example. c1 is found to be 0.58f; use 0.47f. next, the second tec pole must be cancelled by adding a zero. canceling the second tec pole pro- vides maximum phase margin by adding positive phase to the circuit. setting a second zero (fz2) to at least 1/5 the crossover frequency (1.5hz/5 = 0.3hz), and a pole (fp1) to 5 times the crossover frequency or higher (5 1.5hz = 7.5hz) ensures good phase margin, while allowing for variation in the location of the tec s second pole. set the zero fz2 to 0.3hz and calculate r2: where fz2 is the second zero. r2 is calculated to be 1.1m ? ; use 1m ? . now pole fp1 is added at least 5 times the crossover frequency to terminate zero fz2. choose fp1 = 15hz, find r1 using the following equation: resistor r1 is found to be 22k ? , use 20k ? the final step is to terminate the first zero by setting the rolloff frequency with a second pole, fp2. a good choice is 2 times fp1. choose fp2 = 30hz, find c3 using the following equation: where c3 is found to be 0.05f, use 0.047f. figure 7 displays the compensated gain and phase plots for the above example. the example given is a good place to start when com- pensating the thermal loop. different tec modules require individual testing to find their optimal compen- sation scheme. other compensation schemes can be used. the above procedure should provide good results for the majority of optical modules. chip information transistor count: 6023 process: bicmos fp cr 2 1 233 = fp cr 1 1 211 = fz cr 2 1 212 = integrated temperature controllers for peltier modules 18 ______________________________________________________________________________________ tec gain and phase frequency (hz) gain (db) phase (degrees) 10 1 0.1 0.01 -70 -60 -50 -40 -30 -20 -10 0 10 20 -135 -90 -45 0 45 30 40 -80 90 -180 0.001 100 figure 6. bode plot of a generic tec module compensated tec gain and phase frequency (hz) gain (db) phase (degrees) 10 1 0.1 0.01 -30 -20 -10 0 10 20 30 40 50 60 -135 -90 -45 0 45 70 80 -80 -40 -50 -60 -70 90 -180 0.001 100 figure 7. compensated thermal-control loop using the tec module in figure 6
max1978/MAX1979 integrated temperature controllers for peltier modules ______________________________________________________________________________________ 19 typical operating circuit max1978 input 3v to 5.5v v dd pv dd- bfb- ain- shdn ot on off overtemp alarm ut undertemp alarm aout temp monitor itec ain+ maxv tec current monitor voltage limit heating current limit cooling current limit maxip maxin ref lx1 pgnd1 cs os1 os2 lx2 pgnd2 fb+ fb- tec i tec = 3a ntc ref dac optional dac
max1978/MAX1979 integrated temperature controllers for peltier 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. 20 ____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 ? 2002 maxim integrated products printed usa is a registered trademark of maxim integrated products. 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 .) 32, 44, 48l qfn .eps proprietary information approval title: document control no. 21-0144 package outline 32, 44, 48l qfn thin, 7x7x0.8 mm 1 a rev. 2 e l e l a1 a a2 e/2 e d/2 d detail a d2/2 d2 b l k e2/2 e2 (ne-1) x e (nd-1) x e e c l c l c l c l k proprietary information document control no. approval title: a rev. 2 2 exposed pad variations 21-0144 package outline 32, 44, 48l qfn thin, 7x7x0.8 mm common dimensions ** note: t4877-1 is a custom 48l pkg. with 4 leads depopulated. total number of leads are 44.

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