_______________general description the max727/MAX728/max729 are monolithic, bipolar, pulse-width modulation (pwm), switch-mode, step-down dc-dc regulators. each is rated at 2a. very few external components are needed for standard operation because the power switch, oscillator, feedback, and control circuitry are all on-chip. employing a classic buck topology, these regulators perform high-current step-down functions. these regulators have excellent dynamic and transient response characteristics, while featuring cycle-by-cycle cur- rent limiting to protect against overcurrent faults and short- circuit output faults. they also have a wide 8v to 40v input range. each regulator is available in a 5-pin to-220 package. these devices have a preset 100khz oscillator frequency and a preset current limit of 2.6a. see the max724/ max726 data sheet for more applications information. _______________________applications distributed power from high-voltage buses high-current, high-voltage step-down applications multiple-output buck converter max727/MAX728/max729 5v/3.3v/3v 2a step-down, pwm, switch-mode dc-dc regulators ________________________________________________________________ maxim integrated products 1 v in v sw gnd v c sense case is connected to ground. standard package has staggered leads.
contact factory for straight leads.
5-pin to-220 front view max727
MAX728
max729 1 2 3 4 5 __________________pin configuration v in v c v sw 220 m f gnd 2.7k 0.01 m f output
5v at 2a sense 100 m h mbr745 470 m f input
8v to 40v
max727
step-down converter __________typical operating circuit call toll free 1-800-998-8800 for free samples or literature. 19-0149; rev 2; 9/95 ___________________________features ? input range: up to 40v ? 2a on-chip power switch ? fixed outputs: 5v (max727) 3.3v (MAX728) 3v (max729) ? 100khz switching frequency ? excellent dynamic characteristics ? few external components ? 8.5ma quiescent current ? to-220 package ______________ordering information part max727 cck max727eck -40? to +85? 0? to +70? temp. range pin-package 5 to-220 5 to-220 MAX728 cck MAX728eck -40? to +85? 0? to +70? 5 to-220 5 to-220 max729 cck max729eck -40? to +85? 0? to +70? 5 to-220 5 to-220
max727/MAX728/max729 5v/3.3v/3v 2a step-down, pwm, switch-mode dc-dc regulators 2 _______________________________________________________________________________________ input voltage ..................................................45v switch voltage with respect to input voltage ................50v switch voltage with respect to gnd pin (v sw negative) (note 1) .....................................................35v sense pin voltage ................................... -0.3v, +10v operating temperature ranges max72_cck ..................................... 0? to +70? max72_eck ....................................-40 c to +85? junction temperature ranges: max72_cck ....................................0 c to +125? max72_eck ..................................-40 c to +125? storage temperature range ...................-65 c to +160? lead temperature (soldering, 10sec) .................... +300? electrical characteristics (v in = 25v, t j = t min to t max , unless otherwise noted.) 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. absolute maximum ratings ma 3.5 4.8 start-up mode (note 4) v 7.3 8.0 normal mode minimum supply voltage 8.5 11 v in 40v, v sense = 5.5v t j = +25? ? 250 t j = +25? t j = +25? v in = 40v, v sw = 0v switch-off leakage t j = +25? t j = +25? ma t j +125? 150 0.6 1.0 1.7 v sense = v out + 10% v in = 25v, v sw = 0v error-amplifier sink current ? t j = +25? 100 140 225 v sense = v out - 10% error-amplifier source current ?ho 1.7 3000 5000 9000 i sw = 2a error-amplifier transconductance v/v v 1.2 2000 1v v c 4v i sw = 0.5a error-amplifier voltage gain switch-on voltage (note 2) %/v 0.03 0.10 khz switching frequency 20 v out = v sense = 0v (note 5) 85 120 t j = +25? 90 100 110 t j = +25? % 85 90 maximum duty cycle 8v v in 40v switching frequency line regulation units min typ max 3.5 5.0 conditions parameter supply current (note 3) 2.0 2.6 3.2 a switch-current limit (note 5) v 8.0 40.0 input supply voltage range t j 3 0? t j < 0?
max727/MAX728/max729 5v/3.3v/3v 2a step-down, pwm, switch-mode dc-dc regulators _______________________________________________________________________________________ 3 electrical characteristics (continued) (v in = 25v, t j = t min to t max , unless otherwise noted.) note 1: do not exceed switch-to-input voltage limitation. note 2: for switch currents between 1a and 2a, maximum switch-on voltage can be calculated via linear interpolation. note 3: by setting the sense pin to 5.5v, the v c pin is forced to its low clamp level and the switch duty cycle is forced to zero, approximating the zero load condition. note 4: for proper regulation, total voltage from v in to gnd must be 3 8v after start-up. note 5: to avoid extremely short switch-on times, the switch frequency is internally scaled down when v sense is less than 2.6v (max727), 2.0v (MAX728), or 1.8v (max729). switch current limit is tested with v sense adjusted to give a 1? minimum switch-on time. note 6: guaranteed, not production tested. 0% duty cycle 0% duty cycle v c voltage temperature coefficient mv/? thermal resistance junction to case (note 6) ?/w 4.0 v -4 t j = t min to t max v c voltage 1.5 t j = +25? output voltage line regulation %/v 0.005 0.020 8v v in 40v ?.0 ?.0 t j = t min to t max v out (nominal) = 5v (max727), 3.3v (MAX728), or 3v (max729); all conditions of input voltage, output voltage, and load current output voltage tolerance % ?.5 ?.0 t j = +25? max729 MAX728 max727 max729 MAX728 max727 conditions 2.2 3.8 6.5 t j = +25? sense pin divider resistance 2.5 4.2 7.0 k 3.0 5.0 8.0 2.90 3.00 3.10 v c = 2v sense voltage 3.20 3.30 3.40 v 4.85 5.00 5.15 units min typ max parameter ______________________________________________________________pin description 5 v in supplies power to the internal circuitry and also connects to the collector of the internal power switch. v in must be bypassed with a low-esr capacitor, typically 200? or 220?. internal power switch output. the s witch output can swing 35v below ground and is rated for 2a. ground requires a short, low-noise connection to ensure good load regulation. the internal refer- ence is referred to gnd, so errors at this pin are multiplied by the error amplifier. error-amplifier output. a series rc network connected to this pin compensates the max727/MAX728/max729. output swing is limited to about 5.8v in the positive direction and -0.7v in the negative direction. v c can also synchronize the max727/MAX728/max729 to an external ttl clock in the 115khz to 170khz range. see max724/max726 data sheet. sense input is the internal error amplifier's input, and should be directly connected to v out . sense also aids current limiting by reducing oscillator frequency when v out is low. 4 3 2 1 pin v in v sw gnd v c sense function name
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. 4 ___________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 (408) 737-7600 1995 maxim integrated products printed usa is a registered trademark of maxim integrated products. max727/MAX728/max729 5v/3.3v/3v 2a step-down, pwm, switch-mode dc-dc regulators 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. 4 ___________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 (408) 737-7600 1995 maxim integrated products printed usa is a registered trademark of maxim integrated products. e f b dim
a
b
c1
d
e
e
f
h1
j1
l
f p
q min
0.140
0.015
0.014
0.560
0.380
0.045
0.230
0.080
0.500
0.139
0.100 max
0.190
0.040
0.022
0.650
0.420
0.055
0.270
0.115
0.580
0.161
0.120 min
3.56
0.38
0.41
14.23
9.66
1.14
5.85
2.04
12.70
3.54
2.54 max
4.82
1.01
0.50
16.51
10.66
1.39
6.85
2.92
14.73
4.08
3.04 inches millimeters e 21-4737- 5-pin to-220
(straight lead)
package 1.70 bsc 0.067 bsc f p h1 q d a j1 c1 l ________________________________________________________package information e j3 f b dim
a
b
c1
d
e
e
f
h1
j1
j2
j3
l
l1
l2
f p
q min
0.140
0.015
0.014
0.560
0.380
0.045
0.230
0.080
0.170
0.327
0.170
0.260
0.700
0.139
0.100 max
0.190
0.040
0.022
0.650
0.420
0.055
0.270
0.115
0.185
0.335
0.200
0.340
0.720
0.161
0.120 min
3.56
0.38
0.41
14.23
9.66
1.14
5.85
2.04
4.32
8.31
4.32
6.60
17.78
3.54
2.54 max
4.82
1.01
0.50
16.51
10.66
1.39
6.85
2.92
4.70
8.51
5.08
8.64
18.29
4.08
3.04 inches millimeters e 21-005- 5-pin to-220
(staggered lead)
package 1.70 bsc 0.067 bsc f p h1 q d a l2 j1 l1 l c1 j2 contact factory for availability
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