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general description critical loads often employ parallel-connected power supplies with redundancy in order to enhance system reliability. the max8535/max8536/max8585 are highly integrated but inexpensive mosfet controllers that pro- vide isolation and redundant power capability in high-reli- ability systems. the max8535/max8585 are used in 12v systems, and have an internal charge pump to drive the gates of the n-channel pass elements to v cc + 10v. the max8536 is used in 3.3v and 5v systems, with a charge- pump output of v cc + 5v. during startup, the max8535/max8536 /max8585 moni- tor the voltage drop across external mosfets. once v cc approaches or exceeds the bus voltage, the mosfets are turned on. the max8535/max8536/ max8585 feature a dual-purpose timer input. a single external resistor from timer to ground sets the turn-on speed of the external mosfets. optionally, the timer input can be used as a logic-enable pin. once the device is turned on, the max8535/max8536 /max8585 monitor the load, protecting against overvoltage, under- voltage, and reverse-current conditions. overvoltage and undervoltage fault thresholds are adjustable and can be disabled. the current-limit trip points are set by the external mosfets?r ds(on) , reducing component count. an open-drain logic-low fault output indicates if an overvoltage, undervoltage, or reverse-current fault occurs. all devices come in a space-saving 8-pin ?ax package and are specified over the extended -40? to +85? temperature range. ?ax is a registered trademark of maxim integrated products, inc. applications silver box supplies for servers on-board redundant power supplies in blade servers network/telecom power supplies rectifiers redundant power supplies in high-availability systems features ? simple, integrated, and inexpensive oring mosfet controller ? oring mosfet drive for 12v (max8535/max8585) and 3.3v or 5v (max8536) bus ? eliminates oring diode power dissipation and reverse leakage current ? provides n + 1 redundant supply capability for highly reliable systems ? isolates failed supply from output bus in <1? ? reverse-current flow detection ? programmable soft-start ? logic-enable input ? adjustable overvoltage and undervoltage trip points ? fault-indicator output ? space-saving 8-pin ?ax package max8535/max8536/max8585 oring mosfet controllers with fastest fault isolation for redundant power supplies ________________________________________________________________ maxim integrated products 1 max8535 max8536 max8585 gate cs fault uvp ovp gnd timer v cc silver box or rectifiers out+ out- redundant output bus +v o -v o n.c. output: 3.3v/5v (max8536), 12v (max8535) typical operating circuit ordering information 19-2735; rev 1; 3/04 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. part temp range pin-package max8535 eua -40? to +85? 8 ?ax max8535aeua -40? to +85? 8 ?ax max8536 eua -40? to +85? 8 ?ax max8585 eua -40? to +85? 8 ?ax pin configuration, functional diagrams, and typical application circuits appear at end of data sheet. evaluation kit available
max8535/max8536/max8585 oring mosfet controllers with fastest fault isolation for redundant power supplies 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v cc = 12v (max8535/max8535a/max8585), v cc = 5v (max8536), v cs = v cc - 0.1v, r timer = 25k ? , uvp = 2v, ovp = 1v, c gate = 0.01?, t a = 0? to +85? , unless otherwise noted.) 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. gate to gnd (max8535/max8535a/max8585)...-0.3v to +28v v cc to gnd (max8535/max8535a/max8585) .....-0.3v to +18v cs, fault to gnd (max8535/max8535a/max8585) ......................-0.3v to +15v gate to gnd (max8536) ............................ -0.3v to (v cc + 6v) v cc , cs, fault to gnd (max8536) .......................-0.3v to +6v ovp, uvp, timer to gnd........................................-0.3v to +6v continuous power dissipation (t a = +70?) 8-pin ?ax (derate 4.5mw/? above +70?) .............362mw operating temperature range ...........................-40? to +85? storage temperature range .............................-65? to +150? junction temperature .........................................?.+150? lead temperature (soldering, 10s) .................................+300? parameter symbol conditions min typ max units v cc supply v cc = 14v (max8535/ max8535a/max8585) 2 4.5 v cc supply current timer = 2.5v v cc = 6v (max8536) 2 3 ma v cc = 14v (max8535/ max8535a/max8585) 4.5 v cc shutdown current timer = 0v v cc = 6v (max8536) 3 ma max8535/max8535a/ max8585, charge pump on 814 max8536, charge pump on 3.0 5.5 v cc input voltage timer = 2.5v max8535/max8535a/ max8585, charge pump off 17 v cs = 14v (max8535/ max8535a/max8585) 100 cs input current timer = 2.5v cs = 5.5v (max8536) 50 ? cs isolation c s = m ax op er ati ng vol tag e, v c c = 0v , i( v c c ) -0.05 -1 ? max8535/max8535a/max8585, rising threshold 6 6.5 7 v cc undervoltage lockout v ccok max8536, rising threshold 2.5 2.7 2.9 v rising threshold 14 14.5 15 v cc overvoltage internal threshold max8535/ max8535a/ max8585 falling threshold 13.3 13.9 14.5 v charge-pump voltage measured from v gate to v cc , v cc = 3.3v (max8536) 5 5.5 6 v cc = 5v (max8536) 5 5.5 6 gate voltage v gate v c c = 12v ( m ax 8535/m ax 8535a/m ax 8585) 91112 v
max8535/max8536/max8585 oring mosfet controllers with fastest fault isolation for redundant power supplies _______________________________________________________________________________________ 3 electrical characteristics (continued) (v cc = 12v (max8535/max8535a/max8585), v cc = 5v (max8536), v cs = v cc - 0.1v, r timer = 25k ? , uvp = 2v, ovp = 1v, c gate = 0.01?, t a = 0? to +85? , unless otherwise noted.) parameter symbol conditions min typ max units r timer = 20k ? 187 r timer = 125k ? = = timer timer voltage 1.219 1.25 1.281 v timer maximum source current v timer = 1v 80 100 120 ? timer high-input current v timer = 1.5v 10 20 ? max8535/max8535a/max8585 1.5 3.4 timer maximum frequency select voltage input range max8536 1.5 v cc - 0.6 v timer logic high v ih charge pump enabled 1.0 v timer logic low v il charge pump disabled 0.5 v fault fault output low voltage i fault = 0.5ma 0.8 v fault sink current fault = 0.8v 0.5 ma fault = 18v ( max 8535 /max 8535a/max 8585) 5 fault leakage current fault = 6v (max8536) 5 ? gate gate on threshold measured from v cc to cs 0.3 0.4 0.5 v i timer = 0? (max8535/ max8535a/max8585) 35 50 65 v gate = v cc = 12v i timer = 50? (max8535/ max8535a/max8585) 15 25 36 i timer = 0? (max8536) 17 25 33 gate drive current v gate = v cc = 5v i timer = 50? (max8536) 8 12 16 ? gate shutdown delay from fault sense to the start of gate voltage falling, or from timer to the start of gate voltage falling 200 300 ns gate = v cc + 5v (max8535/max8536) 100 200 300 gate discharge current gate = v cc + 5v (max8535a/max8585) 200 300 400 ma g ate vol tag e fal l fr om faul t to v gat e = v c c , c gat e = 0.01f ( 200ns + c v /i = 700ns, typ ) (max8535/max8536) 0.7 gate fall time max8535a/max8585 0.55 ? current sense measured from cs to v cc (max8535/max8535a/max8536) 20 30 40 reverse-current threshold max8585 -3 0 +3 mv
max8535/max8536/max8585 oring mosfet controllers with fastest fault isolation for redundant power supplies 4 _______________________________________________________________________________________ electrical characteristics (v cc = 12v (max8535/max8535a/max8585), v cc = 5v (max8536), v cs = v cc - 0.1v, r timer = 25k ? , uvp = 2v, ovp = 1v, c gate = 0.01?, t a = -40? to +85? , unless otherwise noted.) (note 1) parameter symbol conditions min typ max units v cc supply v cc = 14v (max8535/ max8535a/max8585) 4.5 v cc supply current timer = 2.5v v cc = 6v (max8536) 3 ma v cc = 14v (max8535/ max8535a/max8585) 4.5 v cc shutdown current timer = 0v v cc = 6v (max8536) 3 ma max8535/max8535a/ max8585, charge pump on 814 max8536, charge pump on 3.0 5.5 v cc input voltage timer = 2.5v max8535/max8535a/ max8585, charge pump off 17 v cs isolation c s = m ax op er ati ng vol tag e, v c c = 0v , i( v c c ) -1 ? (max8535/max8535a/max8585) rising threshold 6.0 7.0 v cc undervoltage lockout v ccok (max8536) rising threshold 2.5 2.9 v rising threshold 14 15 v cc overvoltage internal threshold (max8535/ max8535a/ max8585) falling threshold 13.3 14.5 v electrical characteristics (continued) (v cc = 12v (max8535/max8535a/max8585), v cc = 5v (max8536), v cs = v cc - 0.1v, r timer = 25k ? , uvp = 2v, ovp = 1v, c gate = 0.01?, t a = 0? to +85? , unless otherwise noted.) parameter symbol conditions min typ max units timer = open (max8535/max8535a/ max8536) 524 startup reverse-current blank time max8585 32 ms forward-current threshold measured from v cc to cs 5 10 15 mv overvoltage protection ovp rising 1.219 1.25 1.281 ovp fault threshold v ovp ovp falling 1.2 v ovp bias current 0.2 ? undervoltage protection uvp rising threshold 1.219 1.25 1.281 uvp fault voltage v uvp uvp falling threshold 1.119 1.15 1.181 v uvp bias current 0.4 ?
max8535/max8536/max8585 oring mosfet controllers with fastest fault isolation for redundant power supplies _______________________________________________________________________________________ 5 electrical characteristics (continued) (v cc = 12v (max8535/max8535a/max8585), v cc = 5v (max8536), v cs = v cc - 0.1v, r timer = 25k ? , uvp = 2v, ovp = 1v, c gate = 0.01?, t a = -40? to +85? , unless otherwise noted.) (note 1) parameter symbol conditions min typ max units charge-pump voltage measured from v gate to v cc , v cc = 3.3v (max8536) 56 v cc = 5v (max8536) 5 6 gate voltage v gate v c c = 12v ( m ax 8535/m ax 8535a/m ax 8585) 9 12 v timer timer voltage 1.200 1.281 v timer maximum source current v timer = 1.0v 80 120 ? timer high-input current v timer = 1.5v 20 ? max8535/max8535a/max8585 1.5 3.4 timer maximum frequency select voltage input range max8536 1.5 v cc - 0.6 v timer logic high v ih charge pump enabled 1.1 v timer logic low v il charge pump disabled 0.5 v fault fault output low voltage i fault = 0.5ma 0.8 v fault sink current fault = 0.8v 0.5 ma fault = 18v (max8535/ max8535a/max8585) 5 fault leakage current fault = 6v (max8536) 5 ? gate gate on threshold measured from v cc to cs 0.3 0.5 v i timer = 0? (max8535/ max8535a/max8585) 35 65 v gate = v cc = 12v i timer = 50? (max8535/ max8535a/max8585) 15 36 i timer = 0? (max8536) 17 33 gate-drive current v gate = v cc = 5v i timer = 50? (max8536) 8 16 ? gate shutdown delay from fault sense to the start of gate voltage falling, or from timer to the start of gate voltage falling 300 ns gate = v cc + 5v (max8535/max8536) 100 300 gate discharge current max8535a/max8585 200 400 ma current sense measured from cs to v cc (max8535/max8535a/max8586) 20 40 reverse-current threshold max8585 -5 +5 mv forward-current threshold measured from v cc to cs 5 15 mv
max8535/max8536/max8585 oring mosfet controllers with fastest fault isolation for redundant power supplies 6 _______________________________________________________________________________________ electrical characteristics (continued) (v cc = 12v (max8535/max8535a/max8585), v cc = 5v (max8536), v cs = v cc - 0.1v, r timer = 25k ? , uvp = 2v, ovp = 1v, c gate = 0.01?, t a = -40? to +85? , unless otherwise noted.) (note 1) note 1: specifications to -40? are guaranteed by design and not production tested. parameter symbol conditions min typ max units overvoltage protection ovp fault threshold v ovp ovp rising 1.20 1.281 v ovp bias current 0.2 ? undervoltage protection uvp rising threshold 1.200 1.281 uvp fault voltage v uvp uvp falling threshold 1.10 1.19 v uvp bias current 0.4 ?
max8535/max8536/max8585 oring mosfet controllers with fastest fault isolation for redundant power supplies _______________________________________________________________________________________ 7 standby: cpmp: off gate: low wait for v share cs - v cc < 0.4v v share = (cs - v cc ) < 0.4v i forward = (v cc - cs) > 0.01v i reverse = (cs - v cc ) > 0.03v cs - v cc > 0.4v v cc > v ccok on: set v share latch, charge pump on uvp fault uvp = ok cs v cc cs - 0.4v cs + 0.01v v share latch i reverse blanking fault shutdown gate: fault latched fault shutdown gate: fault latched uvp fault shutdown gate: fault not latched i reverse condition detected after 500ms blank time (max8535/max8535a/max8536) (max8585) i reverse after 32ms blank time cs - 0.03v i forward and ovp fault i forward i reverse timer >1v all transitions are asynchronous v cc or timer cycled v cc or timer cycled 500ms fault shutdown gate: not latched ovp ok and i reverse during first 500ms uvp = ok state diagram
max8535 typical operating characteristics (v cc = 12v, r timer = 25k ? , uvp = 2v, ovp = 1v, c gate = 0.01?, bus = 100?, t a = +25 c, unless otherwise specified.) max8535/max8536/max8585 oring mosfet controllers with fastest fault isolation for redundant power supplies 8 _______________________________________________________________________________________ gate-charge current vs. timer resistance (r timer ) max8535/max8536 toc01 resistance (k ? ) gate-charge current ( a) 100 10 20 30 40 50 60 0 10 1000 t a = -40 c t a = +25 c t a = +85 c supply current vs. temperature max8535/max8536 toc02 temperature ( c) supply current (ma) 80 60 40 20 0 -20 2.2 2.4 2.6 2.8 3.0 3.2 3.4 2.0 -40 timer = gnd timer is unconnected max8535 reverse-current threshold vs. temperature max8535/max8536 toc03 temperature ( c) reverse-current threshold (mv) 60 35 10 -15 27 29 31 33 35 34 32 30 28 26 25 -40 85 uvp and ovp leakage current vs. temperature max8535/max8536 toc04 temperature ( c) leakage current (na) 80 60 40 20 0 -20 20 40 60 80 100 120 140 0 -40 uvp ovp power-up waveform (v bus = 0v) max8535/max8536 toc05 i mosfet 10a/div v cs 10v/div v gate 20v/div v cc 10v/div 4ms/div power-up waveform (v bus = 12v) max8535/max8536 toc06 i mosfet 2a/div v cs 10v/div v gate 20v/div v cc 10v/div 4ms/div
max8535 typical operating characteristics (continued) (v cc = 12v, r timer = 25k ? , uvp = 2v, ovp = 1v, c gate = 0.01?, bus = 100?, t a = +25 c, unless otherwise specified.) max8535/max8536/max8585 oring mosfet controllers with fastest fault isolation for redundant power supplies _______________________________________________________________________________________ 9 timer-enabled startup and shutdown waveforms (v cc = 12v, v bus = 12v) max8535/max8536 toc07 i mosfet 50ma/div v cs 10v/div v gate 20v/div v timer 2v/div 4ms/div timer-enabled startup and shutdown waveforms (v cc = 12v, v bus = 0v) max8535/max8536 toc08 i mosfet 10a/div v cs 10v/div v gate 20v/div v timer 1v/div 4ms/div reverse-current fault waveform (r1 = 10 ? ) max8535/max8536 toc09 i mosfet 5a/div v fault 10v/div v gate 20v/div v cs 1v/div 12v 400ns/div uvp fault waveform (r1 = 100 ? ) max8535/max8536 toc10 v fault 10v/div v uvp 1v/div 1 s/div 1.25v v cs 10v/div v gate 20v/div selective ovp shutdown waveform (r1 = 10 ? ) max8535/max8536 toc11 v fault 10v/div v gate1 (ovp unit) 20v/div v gate2 (good unit) 20v/div v cs 1v/div 12v 1 s/div
max8536 typical operating characteristics (v cc = 12v, r timer = 25k ? , uvp = 2v, ovp = 1v, c gate = 0.01?, bus = 100?, t a = +25 c, unless otherwise specified.) max8535/max8536/max8585 oring mosfet controllers with fastest fault isolation for redundant power supplies 10 ______________________________________________________________________________________ gate-charge current vs. timer resistance (r timer ) max8535/max8536 toc12 resistance (k ? ) gate-charge current ( a) 100 5 10 15 20 25 30 0 10 1000 t a = +85 c t a = +25 c t a = -40 c supply current vs. temperature max8535/max8536 toc13 temperature ( c) supply current (ma) 80 60 40 20 0 -20 1.2 1.4 1.6 1.8 2.0 2.2 1.0 -40 timer is unconnected timer = gnd max8536 reverse-current threshold vs. temperature max8535/max8536 toc14 temperature ( c) reverse-current threshold (mv) 60 35 10 -15 -40 85 26 27 28 29 30 31 32 33 34 35 25 uvp and ovp leakage current vs. temperature max8535/max8536 toc15 temperature ( c) leakage current (na) 80 60 40 20 0 -20 20 40 60 80 100 120 140 0 -40 uvp ovp power-up waveform (v bus = 0v) max8535/max8536 toc16 i mosfet 2a/div v cs 5v/div v gate 10v/div v cc 5v/div 4ms/div power-up waveform (v bus = 5v) max8535/max8536 toc17 i mosfet 1a/div v cs 5v/div v gate 10v/div v cc 5v/div 4ms/div
max8536 typical operating characteristics (continued) (v cc = 12v, r timer = 25k ? , uvp = 2v, ovp = 1v, c gate = 0.01?, bus = 100?, t a = +25 c, unless otherwise specified.) max8535/max8536/max8585 oring mosfet controllers with fastest fault isolation for redundant power supplies ______________________________________________________________________________________ 11 timer-enabled startup and shutdown waveforms (v cc = 5v, v bus = 5v) max8535/max8536 toc18 i mosfet 50ma/div v cs 5v/div v gate 10v/div v timer 2v/div 4ms/div timer-enabled startup and shutdown waveforms (v cc = 5v, v bus = 0v) max8535/max8536 toc19 i mosfet 1a/div v cs 5v/div v gate 10v/div v timer 2v/div 10ms/div reverse-current fault waveform (r1 = 10 ? ) max8535/max8536 toc20 i mosfet 5a/div v fault 5v/div v gate 10v/div v cs 1v/div 5v 400ns/div uvp fault waveform (r1 = 100 ? ) max8535/max8536 toc21 v cs 1v/div v fault 5v/div v gate v uvp 2v/div 1 s/div 1.25v selective ovp shutdown waveform (r1 = 10 ? ) max8535/max8536 toc22 v fault 5v/div v gate2 (good unit) 10v/div v gate1 (ovp unit) 10v/div v cs 1v/div 5v 1 s/div
max8535/max8536/max8585 oring mosfet controllers with fastest fault isolation for redundant power supplies 12 ______________________________________________________________________________________ detailed description critical loads often employ parallel-connected power supplies with redundancy to enhance system reliability. the max8535/max8536/max8585 are highly integrated but inexpensive mosfet controllers that provide isolation and redundant power capability in high-reliability sys- tems. the max8535/max8585 is used in 12v systems and has an internal charge pump to drive the gates of the n-channel pass elements to v cc + 10v. the max8536 is used in 3.3v and 5v systems, with a charge pump output of v cc + 5v. during startup, the max8535/max8536 /max8585 moni- tor the voltage drop across external mosfets. once v cc approaches or exceeds the bus voltage, the mosfets are turned on. the max8535/max8536/ max8585 feature a dual-purpose timer input. a single external resistor from timer to ground sets the turn-on speed of the external mosfets. optionally, the timer input can be used as a logic-enable pin. once the device is turned on, the max8535/max8536 /max8585 monitor the load, protecting against overvoltage, under- voltage, and reverse-current conditions. overvoltage and undervoltage fault thresholds are adjustable and can be disabled. the current-limit trip points are set by the external mosfets?r ds(on) , reducing component count. an open-drain logic-low fault output indicates if an overvoltage, undervoltage, or reverse-current fault occurs. v cc v cc is the power-supply input for the max8535/ max8536/max8585 and the input to the internal charge pump that drives the gate of the external mosfets. the max8535/max8536/max8585 monitor v cc at all times. v cc connects directly to the power supply (silver box or dc-dc power modules). during startup, the device turns on when v cc rises above the undervoltage thresh- old v ccok . after v cc exceeds v ccok and v cc is greater than (cs - 0.4v), the charge pump turns on, dri- ving gate high and turning on the external mosfets. timer the max8535/max8536/max8585 provide a program- mable-frequency charge pump and shutdown function through timer. slowing down the charge-pump fre- quency allows a user to program soft-start. connecting a resistor from timer to gnd sets the charge-pump fre- quency from 100khz to 500khz. connecting timer to a logic high sets charge-pump operation to a maximum frequency of 550khz. pulling timer to gnd shuts down the charge pump and turns off the external mosfet. reducing the charge-pump frequency increases the i reverse startup blank time (see the reverse-current fault section). gate gate is the output of the internal charge pump that drives the external mosfets. during startup, the gate voltage ramps up according to the charge-pump fre- quency. at 250khz, the gate drive current for the max8535 /max8585 is 25a and the gate drive current pin description pin name function 1 gate gate drive output. bypass gate with a 0.01? capacitor to ground. 2 gnd ground 3v cc power-supply input. bypass v cc with a 0.1? capacitor to ground. 4 uvp undervoltage input. connect a resistor-divider from the v cc to gnd with the center point connected to uvp. leave high impedance if not used. uvp fault threshold must be set above v ccok threshold. 5 timer timer input. connect a resistor from timer to ground to select the charge-pump operating frequency. the charge-pump frequency is proportional to the timer output current. timer can source up to 100?. if pulled low (<0.5v), the gate drive is disabled. if pulled high (above 1.25v), the charge pump operates at 550khz. 6 ovp overvoltage input. connect a resistor-divider from the cs to gnd with the center point connected to ovp. connect to gnd if not used. 7 fault open-drain fault output. fault is low during a fault, high impedance during normal operation. connect a pullup resistor of 50k ? or higher value to a voltage rail. 8cs current-sensing input. connect cs to the positive side of the system bus. bypass with 1nf capacitor to gnd.
max8535/max8536/max8585 oring mosfet controllers with fastest fault isolation for redundant power supplies ______________________________________________________________________________________ 13 for the max8536 is 12?. increasing the charge-pump frequency increases the gate drive current. adding a resistor from gate to the gate of the external mosfets further increases turn-on and turn-off times. cs the voltage drop across the external mosfets is mea- sured between the v cc and cs inputs. cs connects to the positive side of the system bus. the voltage drop across the cs and v cc determines operation modes. i forward is defined as v cc - cs > 0.01v. i reverse is defined as cs - v cc > 0.03v in all except the max8585. in the max8585, i reverse = 0v. fault conditions the max8535/max8536/max8585 contain a versatile fault output that signals overvoltage, undervoltage, or reverse-current conditions. during a fault condi- tion, the charge pump shuts down and the gate dis- charges to ground. undervoltage fault the max8535/max8536/max8585 turn off the external mosfet if the input voltage falls below the uvp thresh- old. if uvp is left unconnected, the undervoltage input is disabled. set the undervoltage threshold to any value above v ccok . when the input voltage rises above the uvp threshold, fault clears and the mosfet turns back on. overvoltage fault the max8535/max8536/max8585 contain an adjustable ovp feature. a resistor-divider from the cs system bus to the ovp input pin sets the overvoltage threshold. when the ovp level is exceeded and the part is in the i forward condition (defined as v cc > cs + 0.01v), the max8535/max8536/max8585 turn off the external mosfet and a fault is latched. if there is no i forward condition, an ovp detection has no effect. in this way, only the input supply, which is caus- ing the overvoltage condition, is turned off in a redun- dant power system application. an overvoltage fault is a latching fault condition, and requires v cc or timer to be cycled to reset the part. reverse-current fault the max8535/max8536 contain a reverse-current pro- tection feature. if, after the 500ms (typ) startup blank time, an i reverse condition is detected, the max8535/ max8536 turn off the external mosfet and a fault is latched. a reverse-current fault forces the max8535/ max8536 to latch off. cycle v cc or timer to exit a latched fault condition. startup blanking time allows the incoming power supply to connect to the system bus at v bus - 0.4v. reducing charge-pump frequency increases the startup blanking time. the max8585 does not latch this fault. applications information selecting the timer resistor to set the frequency of the internal charge-pump oper- ation, connect a resistor from timer to gnd. determine the frequency by using the equation: pull timer above 1.5v for maximum charge-pump fre- quency. pull timer below 0.5v to disable the charge pump. leave timer unconnected for a 500khz charge-pump frequency. selecting the gate capacitor and gate resistor the charge pump uses an internal monolithic transfer capacitor to charge the external mosfet gates. frequency a v r khz a timer = ? ? ? ? ? ? 5 100 125 ? - . / table 1. max8535/max8536/max8585 fault modes fault mode pin conditions gate pin fault pin latching v cc uvlo v cc < v ccok low high impedance no uvp pin undervoltage protection uvp < 1.25v low low no ovp pin overvoltage protection ovp > 1.25v v cc > cs + 0.01v low low yes reverse-current protection ( m ax 8535/m ax 8536) v cc < cs - 0.03v gate on for t > 0.5s low low yes reverse-current protection ( m ax 8585) v cc < cs gate on for t > 0.032s low low no v c c i nter nal ( m ax 8535/m ax 8585) over vol tag e p r otecti on v cc > 14.5v low low no
max8535/max8536/max8585 oring mosfet controllers with fastest fault isolation for redundant power supplies 14 ______________________________________________________________________________________ normally, the external mosfet? gate capacitance is sufficient to serve as a reservoir capacitor. if the mosfets are located at a significant distance from the max8535/max8536 /max8585, place a local bypass capacitor (0.01?, typ) across gate and gnd. for slower turn-on times, add a small capacitor between gate and gnd and a series resistor between gate and the gate of the mosfets. set the uvp fault threshold to set the undervoltage lockout threshold, use a resistor- divider connected between v cc and gnd, with the center node of the divider connected to uvp. for example, use a 10k ? resistor (r4 in figure 4) from uvp to gnd and calculate the other resistor (r3) using: where v uvlo is the desired undervoltage lockout volt- age and v uvp is the uvp reference threshold specified in the electrical characteristics (1.25v, typ). to defeat the uvp, leave uvp unconnected. set the ovp fault threshold to set the ovp threshold, use a resistor-divider con- nected between cs and gnd, with the center node of the divider connected to ovp. for example, use a 10k ? resistor (r6 in figure 4) from ovp to gnd and calculate the other resistor, r5, using: where v ovlo is the desired overvoltage lockout voltage and v ovp is the ovp reference threshold specified in the electrical characteristics (1.25v, typ). to defeat the ovp, connect the ovp input to gnd. mosfet selection the max8535/max8536/max8585 drive n-channel mosfets. the most important feature of the mosfets is r ds(on) . as load current flows through the external mosfet, a voltage (v ds ) is generated from drain-to- source due to the mosfet? on-resistance, r ds(on) . the max8535/max8536/max8585 monitor v ds of the mosfets at all times. the max8535/max8536/ max8585 determine the state of the monitored power supply by measuring the voltage drop across the exter- nal mosfets. with two external mosfets, the equa- tion becomes: v dstotal = r ds(on)1 x i load + r ds(on)2 x i load selecting a mosfet with a low r ds(on) allows more current to flow through the mosfets before the max8535/max8536/max8585 detect reverse-current (i reverse ) and forward-current (i forward ) conditions. using a single mosfet single mosfets can be used if the ovp function is not needed. connect the source of the mosfet to v cc and the drain of the mosfet to cs. layout guidelines keep all traces as short as possible and maximize the high-current trace width to reduce the effect of undesir- able parasitic inductance. the mosfet generates a fair amount of heat because of the high currents involved. in order to dissipate the heat generated by the mosfet, make the power traces very wide with a large amount of copper area, and place the max8535/ max8536/max8585 as close as possible to the drain of the external mosfet. a more efficient way to achieve good power dissipation on a surface-mount package is to lay out two copper pads directly under the mosfet package on both sides of the board. connect the two pads to the ground plane through vias and use enlarged copper mounting pads on the topside of the board. use a ground plane to minimize impedance and inductance. refer to the max8535 evaluation kit data sheet for an example of a pc board layout. in addition to the usual high-power considerations, bypassing prevent false faults by: 1) bypass v cc with a 0.1? capacitor to ground and bypassing cs with a 1nf capacitor to ground. 2) making the traces connecting uvp and ovp as short as possible. 3) kelvin connecting v cc and cs to the external mosfet. rr v v ovlo ovp 56 1 = ? ? ? ? ? ? - rr v v uvlo uvp 34 1 = ? ? ? ? ? ? -
max8535/max8536/max8585 oring mosfet controllers with fastest fault isolation for redundant power supplies ______________________________________________________________________________________ 15 functional diagrams control logic voltage share reverse current forward current overvoltage internal overvoltage external undervoltage shutdown charge pump v cc clk v cc 1.25v ref i osc enable gnd max8535 max8585 14.5v 1.25v 1.25v 10mv *0mv offset in the max8585 30mv* 400mv fault timer gate v cc cs ovp uvp figure 1. max8535/max8585 functional diagram control logic voltage share reverse current forward current overvoltage external undervoltage shutdown charge pump v cc clk v cc 1.25v ref i osc enable max8536 1.25v 1.25v 10mv 30mv 400mv fault timer gate v cc cs ovp uvp gnd figure 2. max8536 functional diagram
max8535/max8536/max8585 oring mosfet controllers with fastest fault isolation for redundant power supplies 16 ______________________________________________________________________________________ typical application circuits max8535 max8585 gate cs fault ovp enable gnd timer uvp v cc silver box or rectifiers out+ out- output bus +v o -v o output: 12v/20a q1 and q2 2xsub75n03-04 30v/4m ? c3 1nf r5 100k ? r2 51k ? r6 10k ? r7 24.9k ? r1 10 ? c1 0.01 f, 50v c2 0.1 f, 16v r3 53.6k ? r4 10k ? figure 3. typical application circuit for 12v/20a output with ovp and uvp max8536 gate cs fault ovp gnd timer uvp v cc silver box or rectifiers out+ out- output bus +v o -v o output: 3.3v or 5v/20a q1 and q2 2xsub75n03-04 30v/4m ? c3 1nf r5 35.7k ? r2 51k ? r6 10k ? r7 24.9k ? r1 10 ? c1 0.01 f, 50v c2 0.1 f, 16v r3 13.3k ? r4 10k ? figure 4. typical application circuit for 3.3v or 5v/20a output with ovp and uvp
max8535/max8536/max8585 oring mosfet controllers with fastest fault isolation for redundant power supplies ______________________________________________________________________________________ 17 max8535 max8585 gate cs fault uvp ovp gnd timer on off enable v cc silver box or rectifiers out+ out- output bus +v o -v o n.c. output: 12v/20a c1 0.01 f, 50v c2 0.1 f, 16v r3 7.5k ? r4 7.5k ? q1 sub75n03-04 30v/4m ? r1 10 ? c3 1nf r2 51k ? figure 5. typical application circuit for 12v/20a output without ovp and uvp
max8535/max8536/max8585 oring mosfet controllers with fastest fault isolation for redundant power supplies 18 ______________________________________________________________________________________ max8535 max8585 gate cs fault ovp gnd timer timer uvp v cc silver box a out+ out- output bus +v o -v o q1a and q2a 2xsub75n03-04 30v/4m ? c3a 1nf r5a 100k ? r2a 51k ? r6a 10k ? r7a 24.9k ? r1a 10 ? c1a 0.01 f, 50v c2a 0.1 f, 16v r3a 53.6k ? r4a 10k ? max8535 max8585 gate cs fault ovp gnd uvp v cc silver box b out+ out- output bus q1b and q2b 2xsub75n03-04 30v/4m ? c3b 1nf r2b 51k ? r7b 24.9k ? r1b 10 ? c1b 0.01 f, 50v c2b 0.1 f, 16v r3b 53.6k ? r4b 10k ? v+ v cca = 12v/20a v ccb = 12v/20a n + 1 u1 u2 figure 6. n + 1 redundant power system connections
max8535/max8536/max8585 oring mosfet controllers with fastest fault isolation for redundant power supplies ______________________________________________________________________________________ 19 chip information transistor count: 3011 process: bicmos 1 2 3 4 8 7 6 5 cs fault ovp timer uvp v cc gnd gate max8535 max8536 max8585 max top view pin configuration
max8535/max8536/max8585 oring mosfet controllers with fastest fault isolation for redundant power supplies 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 2004 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 .) 8lumaxd.eps package outline, 8l umax/usop 1 1 21-0036 j rev. document control no. approval proprietary information title: max 0.043 0.006 0.014 0.120 0.120 0.198 0.026 0.007 0.037 0.0207 bsc 0.0256 bsc a2 a1 c e b a l front view side view e h 0.60.1 0.60.1 ? 0.500.1 1 top view d 8 a2 0.030 bottom view 1 6 s b l h e d e c 0 0.010 0.116 0.116 0.188 0.016 0.005 8 4x s inches - a1 a min 0.002 0.95 0.75 0.5250 bsc 0.25 0.36 2.95 3.05 2.95 3.05 4.78 0.41 0.65 bsc 5.03 0.66 6 0 0.13 0.18 max min millimeters - 1.10 0.05 0.15 dim

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