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ltc4215-1/ltc4215-3 1 421513fc hot swap controller with i 2 c compatible monitoring n live board insertion n electronic circuit breakers n computers, servers n platform management n allows safe insertion into live backplane n 8-bit adc monitors current and voltage n i 2 c/smbus interface n wide operating voltage range: 2.9v to 15v n di/dt controlled soft-start n circuit breaker timeout: 20s (ltc4215-1) or 420s (ltc4215-3) n three general purpose outputs n high side drive for external n-channel mosfet n no external gate capacitor required n input overvoltage/undervoltage protection n optional latchoff or auto-retry after faults n alerts host after faults n inrush current limit with foldback n available in 24-pin (4mm 5mm) qfn the ltc ? 4215-1/ltc4215-3 hot swap? controllers allow a board to be safely inserted and removed from a live backplane. using an external n-channel pass transistor, board supply voltage and inrush current are ramped up at a n a d j u s t a b l e r a t e . a n i 2 c interface and onboard adc allow for monitoring of load current, voltage and fault status. the device features adjustable foldback current limit and a soft-start pin that sets the di/dt of the inrush current. an i 2 c interface may con? gure the part to latch off or automatically restart after the ltc4215-1/ltc4215-3 detect a current limit fault. the controller has additional features to interrupt the host when a fault has occurred, provide three general purpose outputs, notify when output power is good, detect insertion of a load card, and power-up either automatically upon insertion or wait for an i 2 c command to turn on. the ltc4215-1 has a 20s circuit breaker ? lter for applica- tions that require a fast fault response time. the ltc4215-3 has an extended 420s circuit breaker ? lter for applications where supply transients may exceed 20s. + uv v dd sense + sense C ltc4215-1 gate timer ss on intv cc powergood reset ok led measured voltage gnd en source ov sdai sdao scl adr0 adr1 fb gpio1 gpio2 gpio3 adin 3.4k plug-in card 1.18k p6ke16a 10 0.005 fdc653n 30.1k v out 12v 3.57k 4215 ta01a c l 0.1f connector 2 connector 1 34.8k backplane 68nf 0.1f gnd scl sda 12v 12v application with 5a circuit breaker start-up waveform typical application features applications description v out 10v/div v gpio1 10v/div inrush current 2.5a/div v dd 10v/div 40ms/div 42151 ta01b c l = 12000f 5k pull-up to v dd contact bounce l , lt, ltc, ltm, linear technology and the linear logo are registered trademarks of linear technology corporation. hot swap is a trademark of linear technology corporation. all other trademarks are the property of their respective owners. protected by u.s. patent 7330065.
ltc4215-1/ltc4215-3 2 421513fc supply voltage (v dd ) ................................ C0.3v to 24v supply voltage (intv cc ) .......................... C0.3v to 6.5v input voltages gate-source (note 3) .......................... C0.3v to 5v sense + , sense C ................ v dd C 0.3v to v dd + 0.3v source .................................................... C5v to 24v en , fb, on, ov, uv ................................ C0.3v to 12v adr0, adr1, timer, adin, ss ................................ C0.3v to intv cc + 0.3v gpio2, gpio3, scl, sda, sdai, sdao C0.3v to 6.5v output voltages gate, gpio1 .......................................... C0.3v to 24v gpio2, gpio3 ....................................... C0.3v to 6.5v operating temperature range ltc4215c-1 ............................................. 0c to 70c ltc4215i-1 .......................................... C40c to 85c storage temperature range qfn .................................................... C65c to 125c (notes 1, 2) symbol parameter conditions min typ max units supplies v dd input supply range l 2.9 15 v v ov(vdd) input supply overvoltage threshold l 15 15.6 16.5 v i dd input supply current l 35 ma v dd(uvl) input supply undervoltage lockout v dd rising l 2.75 2.84 2.89 v 8 9 top view 25 ufd package 24-lead (4mm 5mm) plastic qfn 10 11 12 24 23 22 21 20 6 5 4 3 2 1 uv ov ss gnd on en sdao fb gpio1 intv cc timer adin gpio3 adr1 v dd sense + sense C gate source sdai scl gpio2 nc adr0 7 14 15 16 17 18 19 13 t jmax = 125c, ja = 34c/w (exposed pad is soldered) exposed pad (pin 25) pcb gnd connection optional lead free finish tape and reel part marking* package description temperature range ltc4215cufd-1#pbf ltc4215cufd-1#trpbf 42151 24-lead (4mm 5mm) plastic qfn 0c to 70c ltc4215iufd-1#pbf ltc4215iufd-1#trpbf 42151 24-lead (4mm 5mm) plastic qfn C40c to 85c ltc4215cufd-3#pbf ltc4215cufd-3#trpbf 42153 24-lead (4mm 5mm) plastic qfn 0c to 70c ltc4215iufd-3#pbf ltc4215iufd-3#trpbf 42153 24-lead (4mm 5mm) plastic qfn C40c to 85c lead based finish tape and reel part marking* package description temperature range ltc4215cufd-1 ltc4215cufd-1#tr 42151 24-lead (4mm 5mm) plastic qfn 0c to 70c ltc4215iufd-1 ltc4215iufd-1#tr 42151 24-lead (4mm 5mm) plastic qfn C40c to 85c ltc4215cufd-3 ltc4215cufd-3#tr 42153 24-lead (4mm 5mm) plastic qfn 0c to 70c ltc4215iufd-3 ltc4215iufd-3#tr 42153 24-lead (4mm 5mm) plastic qfn C40c to 85c consult ltc marketing for parts speci? ed with wider operating temperature ranges. *the temperature grade is identi? ed by a la bel on the shipping container. for more information on lead free part marking, go to: http://www.linear.com/leadfree/ for more information on tape and reel speci? cations, go to: http://www.linear.com/tapeandreel/ pin configuration absolute maximum ratings order information electrical characteristics the l denotes the speci? cations which apply over the full operating temperature range, otherwise speci? cations are at t a = 25c. v dd = 12v unless otherwise noted.
ltc4215-1/ltc4215-3 3 421513fc the l denotes the speci? cations which apply over the full operating temperature range, otherwise speci? cations are at t a = 25c. v dd = 12v unless otherwise noted. symbol parameter conditions min typ max units v dd(hyst) input supply undervoltage lockout hysteresis l 75 100 125 mv intv cc internal regulator voltage v dd 3.3v l 2.9 3.1 3.4 v intv cc(uvl) intv c undervoltage lockout intv cc rising l 2.55 2.64 2.79 v intv cc(hyst) intv c undervoltage lockout hysteresis l 20 55 75 mv current limit and circuit breaker v sense(th) circuit breaker threshold (v dd C v sense ) l 22.5 25 27.5 mv v sense current limit voltage (v dd C v sense )v fb = 1.3v v fb = 0v start-up timer expired l l l 22 6.5 65 25 10 75 29 13 90 mv mv mv t d(oc) oc fault filter v sense = 50mv (ltc4215-1) v sense = 50mv (ltc4215-3) l l 15 300 20 420 30 600 s s i sense(in) sense pin input current v sense = 12v l 10 20 35 a gate drive v gate external n-channel gate drive (v gate C v source ) (note 3) v dd = 2.9v to 15v l 4.7 5.9 6.5 v i gate(up) external n-channel gate pull-up current gate on, v gate = 0v l C15 C20 C30 a i gate(dn) external n-channel gate pull-down current gate off, v gate = 15v l 0.8 1 1.6 ma i gate(dn) fast pull-down current from gate to source during oc/uvlo v dd C sense = 100mv, v gs = 4v 300 450 700 ma t phl(sense) (v dd C sense) high to gate low v dd C sense = 100mv, c gs = 10nf l 0.5 1 s v gs(powerbad) gate-source voltage for power bad fault v source = 2.9v C 15v l 3.8 4.3 4.7 v comparator inputs v on(th) on pin threshold voltage v on rising l 1.210 1.235 1.26 v v on(hyst) on pin hysteresis l 60 128 180 mv i on(in) on pin input current v on = 1.2v l 01 a v en (th) en input threshold v en = rising l 1.215 1.235 1.255 v v en (hyst) en hysteresis l 50 128 200 mv i en en pin input current en = 3.5v l 01 a v ov(th) ov pin threshold voltage v ov rising l 1.215 1.235 1.255 v v ov(hyst) ov pin hysteresis l 10 30 40 mv i ov(in) ov pin input current v ov = 1.8v l 0.2 1 a v uv(th) uv pin threshold voltage v uv rising l 1.215 1.235 1.255 v v uv(hyst) uv pin hysteresis l 60 80 100 mv i uv(in) uv pin input current v uv = 1.8v l 0.2 1 a v uv(rth) uv pin reset threshold voltage v uv falling l 0.33 0.4 0.47 v v uv(rhyst) uv pin reset threshold hysteresis l 60 125 210 mv v fb foldback pin power good threshold fb rising l 1.215 1.235 1.255 v v fb(hyst) fb pin power good hysteresis l 3 8 15 mv i fb foldback pin input current fb = 1.8v l 0.2 1 a v gpio1(th) gpio1 pin input threshold v gpio1 rising l 0.8 1 1.2 v v gpio2(th) gpio2 pin input threshold v gpio2 rising l 1 1.6 2 v v gpio3(th) gpio3 pin input threshold v gpio3 rising l 1 1.6 2 v electrical characteristics
ltc4215-1/ltc4215-3 4 421513fc the l denotes the speci? cations which apply over the full operating temperature range, otherwise speci? cations are at t a = 25c. v dd = 12v unless otherwise noted. symbol parameter conditions min typ max units other pin functions v gpio1(ol) gpio1 pin output low voltage i gpio1 = 5ma l 0.25 0.4 v v gpio2(ol) gpio2 output low voltage i gpio2 = 3ma l 0.2 0.4 v v gpio3(ol) gpio3 output low voltage i gpio3 = 1ma l 0.2 0.4 v i gpio1-3(oh) gpio1-3 pin input leakage current v gpio1 = 15v, v gpio2-3 = 5v l 01 a i source source pin input current source = 15v l 40 80 120 a t p(gate) input (on, ov, uv, en ) to gate off propagation delay l 35 s t d(gate) turn-on delay on uv, ov, en overcurrent auto-retry l l l 50 2.5 1 100 5 2 150 7.5 s ms s v timerl(th) timer low threshold l 0.17 0.2 0.23 v v timerh(th) timer high threshold l 1.2 1.235 1.26 v i timer(up) timer pin pull-up current l C80 C100 C120 a i timer(down) timer pin pull-down current for oc auto-retry l 1.4 2 2.6 a i timer(up/down) timer current up/down ratio l 40 50 60 i ss soft-start ramp pull-up current ramping waiting for gate to slew l l C7.5 C0.4 C10 C0.7 C12.5 C1.0 a a adc res resolution (no missing codes) l 8 bits inl integral nonlinearity v dd C sense (note 5) source adin l l l C2 C1.25 C1.25 0.5 0.2 0.2 2 1.25 1.25 lsb lsb lsb v os offset error (note 4) v dd C sense source adin l l l 2.0 1.0 1.0 lsb lsb lsb tue total unadjusted error v dd C sense source adin l l l 5.5 5.0 5.0 lsb lsb lsb fse full-scale error v dd C sense source adin l l l 5.5 5.0 5.0 lsb lsb lsb v fs full-scale voltage (255 ? v lsb )v dd C sense source adin l l l 37.625 15.14 1.205 38.45 15.44 1.23 39.275 15.74 1.255 mv v v r adin adin pin sampling resistance v adin = 1.28v l 12 m i adin adin pin input current v adin = 1.28v l 0 0.1 a conversion rate 10 hz i 2 c interface v adr(h) adr0, adr1, input high voltage l intv cc C0.8 intv cc C0.4 intv cc C0.2 v i adr(in,z) adr0, adr1, hi-z input current adr0, adr1= 0.8v adr0, adr1= intv cc C 0.8v l l 3 C3 a a v adr(l) adr0, adr1, input low voltage l 0.2 0.4 0.8 v i adr(in) adr0, adr1, input current adr0, adr1 = 0v, intv cc l C80 80 a electrical characteristics
ltc4215-1/ltc4215-3 5 421513fc note 1: stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. exposure to any absolute maximum rating condition for extended periods may affect device reliability and lifetime. note 2: all currents into pins are positive; all voltages are referenced to gnd unless otherwise speci? ed. note 3: an internal clamp limits the gate pin to a minimum of 5v above source. driving this pin to voltages beyond the clamp may damage the device. note 4: offset error is the offset voltage measured from 1lsb when the output code ? ickers between 0000 0000 and 0000 0001. note 5: integral nonlinearity is de? ned as the deviation of a code from a precise analog input voltage. maximum speci? cations are limited by the lsb step size and the single shot measurement. typical speci? cations are measured from the 1/4, 1/2 and 3/4 areas of the quantization band. note 6: guaranteed by design and not subject to test. symbol parameter conditions min typ max units v sda,scl(th) sda, scl input threshold l 1.3 1.7 1.9 v i sda,scl(oh) sda, scl input current scl, sda = 5v l 1 a v sda(ol) sda output low voltage i sda = 3ma l 0.2 0.4 v i 2 c interface timing f scl(max) scl clock frequency operates with f scl f scl(max) l 400 1000 khz t buf(min) bus free time between stop/start condition l 0.12 1.3 s t hd,sta(min) hold time after (repeated) start condition l 30 600 ns t su,sta(min) repeated start condition set-up time l 30 600 ns t su,sto(min) stop condition set-up time l 140 600 ns t hd,dat(min) data hold time (input) l 30 100 ns t hd,dato data hold time (output) l 300 500 900 ns t su,dat(min) data set-up time l 30 600 ns t sp suppressed spike pulse width l 50 110 250 ns c x scl, sda input capacitance sdai tied to sdao (note 6) l 10 pf the l denotes the speci? cations which apply over the full operating temperature range, otherwise speci? cations are at t a = 25c. v dd = 12v unless otherwise noted. t a = 25c, v dd = 12v unless otherwise noted. i dd vs v dd v dd (v) 0 0 i dd (ma) 2 4 5 4215 g01 1 3 10 25 15 20 intv cc (v) 2.5 v dd (v) 2.5 3.0 4.0 4215 g02 3.0 3.5 4.0 3.5 i load (ma) 0 0 v cc (v) 2 4 4215 g03 1 3 4 10 2 68 v dd = 12v, 5v v dd = 3.3v intv cc vs v dd intv cc vs i load electrical characteristics typical performance characteristics.
ltc4215-1/ltc4215-3 6 421513fc current limit vs v fb temperature (c) C50 C25 70 75 80 85 v hyst(uv) (mv) 90 0 50 4215 g05 25 75 100 v th circuit breaker vs temperature temperature (c) C50 C25 90 i timer (a) 110 0 50 4215 g06 95 105 100 25 75 100 v fb (v) 0 i lim (mv) 20 25 30 1.2 1.4 4215 g07 15 10 0 0.2 0.4 0.6 0.8 1.0 5 temperature (c) C50 C25 22 circuit breaker threshold (mv) 24 27 0 50 75 4215 g08 23 26 25 25 100 v dd = 5v, 12v v dd = 3.3v v gate vs temperature v th(uv) vs temperature i timer vs temperature v hyst(uv) vs temperature i gate (a) 0 5 6 7 20 4215 g10 4 3 51015 25 2 1 0 v gate (v) v dd = 3.3v v dd = 12v v dd = 5v v gate vs i gate i gate pull-up vs temperature temperature (c) C50 C10 i gate (a) C20 C30 C25 0 50 75 4315 g11 C15 C25 25 100 t a = 25c, v dd = 12v unless otherwise noted. v (sense+) C v (senseC) (mv) 0 25 50 75 100 125 150 t phl v (gate) (s) 1 100 4215 g17 10 0.1 t phl(gate) vs sense voltage typical performance characteristics temperature (c) C50 C25 1.230 v th (uv) rising (v) 1.234 1.240 0 50 4215 g04 1.232 1.238 1.236 25 75 100 temperature (c) C50 v gate(source) (v) 5.8 5.9 6.0 75 4215 g09 5.7 5.6 C25 25 0 50 100 5.5 5.4 6.1 v dd = 3.3v v dd = 12v v dd = 5v
ltc4215-1/ltc4215-3 7 421513fc v ol(gpio1) vs i gpio1 total unadjusted error vs code (adin) adc inl vs code (adin) code 0 inl (lsb) 128 192 4215 g14 256 64 0.5 0.4 0.3 0.2 0.1 0 C0.1 C0.2 C0.3 C0.4 C0.5 code 0 64 128 192 0 0.001 0.002 0.003 0.004 0.006 4215 g13 256 0.005 error (mv) i gpio1 (ma) 0 v ol(gpio1) (v) 0.2 0.4 0.6 0.1 0.3 0.5 2468 4215 g12 10 0 v dd = 3.3v, 5v, 12v adc full-scale error vs temperature temperature (c) C50 C25 C1.0 full-scale error (lsb) C0.2 1.0 0 50 4215 g05 C0.6 0.6 0.2 C0.4 0.8 C0.8 0.4 0 25 75 100 t a = 25c, v dd = 12v unless otherwise noted. adc dnl vs code (adin) code 0 C0.5 C0.4 C0.3 dnl (lsb) C0.1 C0.2 0 0.1 0.2 0.5 0.4 128 4215 g15 256 64 192 0.3 typical performance characteristics
ltc4215-1/ltc4215-3 8 421513fc adin: adc input. a voltage between 0v and 1.235v ap- plied to this pin is measured by the onboard adc. tie to ground if unused. adr0, adr1: serial bus address inputs. tying these pins to ground, to the intv cc pin or leaving open con? gures one of 9 possible addresses. see table 1 in applications information. en : enable input. ground this pin to indicate a board is present and enable the n-channel mosfet to turn on. when this pin is high, the mosfet is not allowed to turn on. an internal 10a current source pulls up this pin. transitions on this pin are recorded in the fault register. a high-to-low transition activates the logic to read the state of the on pin and clear faults. see applications information. exposed pad (pin 25): exposed pad may be left open or connected to device ground. fb: foldback current limit and power good input. a resistive divider from the output is tied to this pin. when the voltage at this pin drops below 1.235v, power is not considered good. the power bad condition may result in the gpio1 pin pulling low or going high impedance depending on the con? guration of control register bits a6 and a7. also a power bad fault is logged in this condition if the ltc4215-1/ltc4215-3 have ? nished the start-up cycle and the gate pin is high (see applications information). the start-up current limit folds back from a 25mv sense voltage to 10mv as the fb pin voltage drops from 1.3v to 0v. foldback is not active once the part leaves start-up and the current limit is increased to 75mv. gate: gate drive for external n-channel mosfet. an internal 20a current source charges the gate of the mosfet. no compensation capacitor is required on the gate pin, but a resistor and capacitor network from this pin to ground may be used to set the turn-on output voltage slew rate (see applications information). during turn-off there is a 1ma pull-down current. during a short circuit or undervoltage lockout (v dd or intv cc ), a 450ma pull-down current source between gate and source is activated. gnd: device ground. gpio1: general purpose input/output and signals power good/bad. open drain logic output that is pulled to ground if bit b6 is reset. status register bit c6 indicates if gpio1 is high or low. high impedance output (high) by default. gpio1 may also be con? gured to indicate power-good or power-bad as detected by the fb pin in status bit c3. see applications information. tie to ground if unused. con? gure according to table 2 and 3. gpio2: general purpose input/output and fault alert output. open drain logic output that is pulled to ground when bit d6 is set. status register bit c5 indicates if gpio2 is high or low. gpio2 may be con? gured as an output that is pulled to ground when a fault occurs to alert the host controller. a fault alert is enabled by the alert register. gpio2 is con? gured as a general purpose output (high) with all alerts disabled by default. see applications in- formation. tie to ground if unused. con? gure according to tables 3 and 5. gpio3: general purpose input/output. open drain logic output that is pulled to ground when bit d7 is set. status register bit c2 indicates if gpio3 is high or low. gpio3 is con? gured as output low by default. see applications information. tie to ground if unused. con? gure accord- ing to table 5. intv cc : low voltage supply decoupling output. connect a 0.1f capacitor from this pin to ground. on: on control input. a rising edge turns on the external n-channel mosfet and a falling edge turns it off. this pin also con? gures the state of the fet on bit in the con- trol register (and hence the external mosfet) at power up. for example, if the on pin is tied high, then the fet on bit (a3 in table 2) goes high 100ms after power-up. likewise if the on pin is tied low then the part remains off after power-up until the fet on bit is set high using the i 2 c bus. a high-to-low transition on this pin clears the fault register. pin functions
ltc4215-1/ltc4215-3 9 421513fc ov: overvoltage comparator input. connect this pin to an external resistive divider from v dd . if the voltage at this pin rises above 1.235v, an overvoltage fault is detected and the gate turns off. tie to gnd if unused. scl: serial bus clock input. data at the sda pin is shifted in or out on rising edges of scl. this is a high impedance pin that is generally driven by an open-collector output from a master controller. an external pull-up resistor or current source is required. sdao: serial bus data output. open-drain output for s e n d i n g d a t a b a c k t o t h e m a s t e r c o n t r o l l e r o r a c k n o w l e d g - ing a write operation. normally tied to sdai to form the sda line. an external pull-up resistor or current source is required. sdai: serial bus data input. a high impedance input for shifting in address, command or data bits. normally tied to sdao to form the sda line. sense + : positive current sense input. connect this pin to the input of the current sense resistor. must be connected to the same trace as v dd . sense C : negative current sense input. connect this pin to the output of the current sense resistor. this pin provides sense voltage feedback and monitoring for the current limit, circuit breaker and adc. source: n-channel mosfet source and adc input. connect this pin to the source of the external n-channel mosfet switch for gate drive return. this pin also serves as the adc input to monitor output voltage. the pin pro- vides a return for the gate pull-down circuit. ss: soft start input. sets the inrush current slew rate at start-up. connect a 68nf capacitor to provide 5mv/ms as the slew rate for the sense voltage in start-up. this cor- responds to 1a/ms with a 5m sense resistor. note that a large soft-start capacitor and a small timer capacitor may result in a condition where the timer expires before the inrush current has started. allow an additional 10nf of timer capacitance per 1nf of soft-start capacitor to ensure proper start-up. use 1nf minimum to ensure an accurate inrush current. timer: start-up timer input. connect a capacitor be- tween this pin and ground to set a 12.3ms/f duration for start-up, after which an overcurrent fault is logged if the inrush is still current limited. the duration of the off time is 600ms/f when overcurrent auto retry is enabled, resulting in a 1:50 duty cycle. an internal timer provides a 100ms start-up time and 5 seconds auto-retry time if this pin is tied to intv cc . allow an additional 10nf of timer capacitance per 1nf of soft-start (ss) capacitor to ensure proper start-up. the minimum value for the timer capacitor is 10nf. uv: undervoltage comparator input. connect this pin to an external resistive divider from v dd . if the voltage at this pin falls below 1.155v, an undervoltage fault is detected and the gate turns off. pulling this pin below 0.4v resets all faults and allows the gate to turn back on. tie to intv cc if unused. v dd : supply voltage input. this pin has an undervoltage lockout threshold of 2.84v and overvoltage lockout threshold of 15.6v pin functions
ltc4215-1/ltc4215-3 10 421513fc timing diagram functional diagram 1.235v + C + C + C + C + C + C + C + C + C uv uv + C + C + C pg pwrgd logic fault cb 25mv 75mv cs gate source fet on sense C sense + foldback and di/dt rst uv fb on v dd adin sdai sdao scl alert ov en 0.4v 1.235v 10a intv cc 10a v cc 1.235v 1.235v 2.84v 15.6v 1.235v ss 1.235v 0.6v reset ov1 ov en en on tm1 gp uvlo2 tm2 on ov2 ov2 uvlo1 v dd(uvlo) charge pump and gate driver gpi01 1v timer + C 0.2v 1.235v v dd C v sense i 2 c addr source a/d converter 8 100a 2.64v 3.1v gen 2a + C + C gp gpi02 1.6v + C gp gpi03 1.6v + C adro adr1 4215 bd intv cc + C 5 i 2 c 1 of 9 t su, dat t su, sto t su, sta t buf t hd, sta t sp t sp t hd, dato, t hd, dati t hd, sta start condition stop condition repeated start condition start condition 4215 td01 sdai/sdao scl
ltc4215-1/ltc4215-3 11 421513fc the ltc4215-1/ltc4215-3 are designed to turn a boards supply voltage on and off in a controlled manner, allowing the board to be safely inserted or removed from a live backplane. during normal operation, the charge pump and gate driver turn on an external n-channel mosfets gate to pass power to the load. the gate driver uses a charge pump that derives its power from the v dd pin. also included in the gate driver is an internal 6.5v gate- to-source clamp. during start-up the inrush current is tightly controlled by using current limit foldback, soft start di/dt limiting and output dv/dt limiting. the current sense (cs) ampli? er monitors the load current using the difference between the sense + and sense C pin voltages. the cs ampli? er limits the current in the load by pulling back on the gate-to-source voltage in an active control loop when the sense voltage exceeds the com- manded value. the cs ampli? er requires 20a input bias current from both the sense + and the sense C pins. a short circuit on the output to ground results in excessive power dissipation during active current limiting. to limit this power, the cs ampli? er regulates the voltage between the sense + and sense C pins at 75mv. if an overcurrent condition persists, the internal circuit breaker (cb) registers a fault when the sense voltage exceeds 25mv for more than 20s in the case of the ltc4215-1 or 420s in the case of the ltc4215-3. this indicates to the logic that it is time to turn off the gate to prevent overheating. at this point the start-up timer capacitor voltage ramps down using the 2a current source until the voltage drops below 0.2v (comparator tm1) which tells the logic that the pass transistor has cooled and it is safe to turn it on again if overcurrent auto-retry is enabled. if the timer pin is tied to intv cc , the cool-down time defaults to 5 seconds on an internal system timer in the logic. the output voltage is monitored using the fb pin and the power good (pg) comparator to determine if the power is available for the load. the power good condition can be signaled by the gpio1 pin using an open-drain pull-down transistor. the gpio1 pin may also be con? gured to signal power bad, or as a general purpose input (gp comparator), or a general purpose open drain output. gpio2 and gpio3 may also be con? gured as a general purpose inputs or general purpose open drain outputs. gpio2 may also be con? gured to generate interrupts when faults occur. the functional diagram shows the monitoring blocks of the ltc4215-1/ltc4215-3. the group of comparators on the left side includes the undervoltage (uv), overvoltage (ov), reset (rst), enable ( en ) and (on) comparators. these comparators determine if the external conditions are valid prior to turning on the gate. but ? rst the two undervoltage lockout circuits, uvlo1 and uvlo2, validate the input supply and the internally generated 3.1v supply, intv cc . uvlo2 also generates the power-up initialization to the logic circuits as intv cc crosses this rising threshold. if the ? xed internal overvoltage comparator, ov2, detects that v dd is greater than 15.6v, the part immediately gener- ates an overvoltage fault and turns the gate off. included in the ltc4215-1/ltc4215-3 is an 8-bit a/d converter. the converter has a 3-input multiplexer to select between the adin pin, the source pin and the v dd C sense voltage. an i 2 c interface is provided to read the a/d registers. it also allows the host to poll the device and determine if faults have occurred. if the gpio2 line is con? gured as an alert interrupt, the host is enabled to respond to faults in real time. the typical sda line is divided into an sdai (input) and sdao (output). this simpli? es applications using an optoisolator driven directly from the sdao out- put. an application which uses optoisolation is shown in the typical applications section. the i 2 c device address is decoded using the adr0 and adr1 pins. these inputs have three states each that decode into a total of 9 device addresses. operation
ltc4215-1/ltc4215-3 12 421513fc a typical ltc4215-1/ltc4215-3 application is in a high availability system in which a positive voltage supply is distributed to power individual cards. the device measures card voltages and currents and records past and present fault conditions. the system queries each ltc4215-1/ ltc4215-3 over the i 2 c periodically and reads status and measurement information. a basic ltc4215-1/ltc4215-3 application circuit is shown in figure 1. the following sections cover turn-on, turn-off and various faults that the ltc4215-1/ltc4215-3 detect and act upon. external component selection is discussed in detail in the design example section. turn-on sequence the power supply on a board is controlled by using an external n-channel pass transistor (q1) placed in the power path. note that resistor r s provides current detection. re- sistors r1, r2 and r3 de? ne undervoltage and overvoltage levels. r5 prevents high frequency oscillations in q1, and r6 and c1 form an optional network that may be used to provide an output dv/dt limited start-up. figure 1. typical application several conditions must be present before the external mosfet turns on. first the external supply, v dd , must exceed its 2.84v undervoltage lockout levels. next the internally generated supply, intv cc , must cross its 2.64v undervoltage threshold. this generates a 60s to 120s power-on-reset pulse. during reset the fault registers are cleared and the control registers are set or cleared as described in the register section. after a power-on-reset pulse, the ltc4215-1/ltc4215-3 go through the following turn-on sequence. first the uv and ov comparators indicate that input power is within the ac- ceptable range, which is indicated by bits c0-c1 in table 4. second, the en pin is externally pulled low. finally, all of these conditions must be satis? ed for the duration of 100ms to ensure that any contact bounce during inser- tion has ended. when these initial conditions are satis? ed, the on pin is checked and its state written to bit a3 in table 2. if it is high, the external mosfet is turned on. if the on pin is low, the external mosfet is turned on when the on pin is brought high or if a serial bus turn-on command is sent by setting bit a3. applications information + uv v dd sense + sense C ltc4215-1 gate adr1 adr0 timer ss intv cc gnd en source ov on sdai sda0 scl fb gpio3 gpio2 gpio1 adin r3 3.4k 1% plug-in card r2 1.18k 1% r5 10 rs 0.005 q1 fdc653n r7 30.1k 1% v out 12v r8 3.57k 1% 24k 4215 f01 c l 330f c f 0.1f connector 2 connector 1 r1 34.8k 1% backplane c ss 7.5nf c3 0.1f c timer 0.68f gnd scl sda 12v 24k 24k reset 3.3v z1 p6ke16a r6 15k c1 6.8nf nc
ltc4215-1/ltc4215-3 13 421513fc the mosfet is turned on by charging up the gate with a 20a current source. when the gate voltage reaches the mosfet threshold voltage, the mosfet begins to turn on and the source voltage then follows the gate voltage as it increases. when the mosfet is turning on, it ramps inrush current up linearly at a di/dt rate selected by capacitor c ss . once the inrush current reaches the limit set by the fb pin, the di/dt ramp stops and the inrush current follows the fold- back pro? le as shown in figure 2. the timer capacitor integrates at 100a during start-up and once it reaches its t hr e s h o l d o f 1. 2 3 5 v, t h e p a r t c h e c k s t o s e e i f i t i s i n c ur r e n t limit, which indicates that it has started up into a short- circuit condition. if this is the case, the overcurrent fault bit, d2 in table 5, is set and the part turns off. if the part is not in current limit, the 25mv circuit breaker is armed and the current limit is switched to 75mv. alternately an internal 100ms start-up timer may be selected by tying the timer pin to intv cc . as the source voltage rises, the fb pin follows as set by r7 and r8. once fb crosses its 1.235v threshold, and the start-up timer has expired, the gpio1 pin, if con? gured to indicate power-good, ceases to pull low and indicates that power is now good. alternately bit c3 can be read to check power-good status, where a zero indicates that power is good. figure 2. power-up waveforms if r6 and c1 are employed for a constant current during start-up, which produces a constant dv/dt at the output, a 20a pull-up current from the gate pin slews the gate upwards and the part is not in current limit. the start-up timer may expire in this condition and an overcurrent (oc) fault is not generated even though start-up has not completed. either the sense voltage increases to the 25mv cb threshold and generates an oc fault, or the fb pin voltage crosses its 1.235v power good threshold and is indicated in bit c3 as well as the gpio1 pin if gpio1 is con? gured to do so. gate pin voltage a curve of gate-to-source drive vs v dd is shown in the typical performance characteristics. at minimum input supply voltage of 2.9v, the minimum gate-to-source drive voltage is 4.7v. the gate-to-source voltage is clamped below 6.5v to protect the gates of logic level n-channel mosfets. turn-off sequence the gate is turned off by a variety of conditions. a normal turn-off is initiated by the on pin going low or a serial bus turn-off command. additionally, several fault conditions turn off the gate. these include an input overvoltage applications information v dd + 6v v gate v out gpio1 (power good) i load ? r sense v dd v sense 25mv 10mv ss limited fb limited 4215 f02 timer expires t startup
ltc4215-1/ltc4215-3 14 421513fc (ov pin), input undervoltage (uv pin), overcurrent circuit breaker (sense C pin), or en transitioning high. writing a logic one into the uv, ov or oc fault bits (d0-d2 in table 5) also latches off the gate if their auto-retry bits are set to false. normally the mosfet is turned off with a 1ma current pulling down the gate pin to ground. with the mosfet turned off, the source and fb voltages drop as cl dis- charges. when the fb voltage crosses below its threshold, gpio1 may be con? gured to pull low to indicate that the output power is no longer good. if the v dd pin falls below 2.74v for greater than 2s or intv cc drops below 2.60v for greater than 1s, a fast shut down of the mosfet is initiated. the gate pin is pulled down with a 450ma current to the source pin. overcurrent fault the ltc4215-1/ltc4215-3 feature an adjustable current limit that protects against short circuits or excessive load current. an overcurrent fault occurs when the circuit breaker 25mv threshold has been exceeded for longer than the 20s (ltc4215-1) or 420s (ltc4215-3) time-out delay. current limiting begins immediately when the current sense voltage between the v dd and sense pins reaches 75mv. the gate pin is then brought down and regulated in order to limit the current sense voltage to 75mv. when the 20s (ltc4215-1) or 420s (ltc4215-3) circuit breaker time out has expired, the external mosfet is turned off and the overcurrent fault bit d2 is set. after the mosfet is turned off, the timer capacitor begins discharging with a 2a pull-down current. when the timer pin reaches its 0.2v threshold the mosfet is allowed to turn on again if the overcurrent fault has been cleared. however, if the overcurrent auto-retr y bit, a 2 has been set then the mosfet turns on again automatically without resetting the overcurrent fault. use a minimum value of 10nf for c t . if the timer pin is bypassed by tying it to intv cc , the part is allowed to turn on again after an internal 5 second timer has expired, in the same manner as the timer pin passing its 0.2v threshold. overvoltage fault an overvoltage fault occurs when either the ov pin rises above its 1.235v threshold, or the v dd pin rises above its 15.6v threshold, for more than 2s. this shuts off the gate with a 1ma current to ground and sets the overvoltage present bit c0 and the overvoltage fault bit d0. if the pin subsequently falls back below the threshold for 100ms, the gate is allowed to turn on again unless overvoltage auto-retry has been disabled by clearing bit a0. undervoltage fault an undervoltage fault occurs when the uv pin falls below its 1.235v threshold for more than 2s. this turns off the gate with a 1ma current to ground and sets undervoltage present bit c1 and undervoltage fault bit d1. if the uv pin subsequently rises above the threshold for 100ms, the gate is turned on again unless undervoltage auto-retry has been disabled by clearing bit a1. when power is ap- plied to the device, if uv is below its 1.235v threshold after intv cc crosses its 2.64v undervoltage lockout threshold, an undervoltage fault is logged in the fault register. figure 3. short-circuit waveforms applications information v gate 10v/div v source 10v/div v dd 10v/div i load 10a/div 5s/div 4215 f03 r s = 5m c l = 0 r short = 1 r6 = 30k c1 = 0.1f
ltc4215-1/ltc4215-3 15 421513fc board present change of state whenever the en pin toggles, bit d4 is set to indicate a change of state. when the en pin goes high, indicating board removal, the gate turns off immediately (with a 1ma current to ground) and clears the board present bit, c4. if the en pin is pulled low, indicating a board insertion, all fault bits except d4 are cleared and enable bit, c4, is set. if the en pin remains low for 100ms the state of the on pin is captured in fet on control bit a3. this turns the switch on if the on pin is tied high. there is an internal 10a pull-up current source on the en pin. if the system shuts down due to a fault, it may be desirable to restart the system simply by removing and reinserting a load card. in cases where the ltc4215-1/ltc4215-3 and the switch reside on a backplane or midplane and the load resides on a plug-in card, the en pin detects when the p l u g - i n c a r d i s r e m o v e d . f i g u r e 4 s h o w s a n e x a m p l e w h e r e the en pin is used to detect insertion. once the plug-in card is reinserted the fault register is cleared (except for d4). after 100ms the state of the on pin is latched into bit a3 of the control register. at this point the system starts up again. if a connection sense on the plug-in card is driving the en pin, insertion or removal of the card may cause the pin voltage to bounce. this results in clearing the fault register when the card is removed. the pin may be debounced using a ? lter capacitor, c en , on the en pin as shown in figure 4. the ? lter time is given by: t filter = c en ? 123 [ms/f] fet short fault a fet short fault is reported if the data converter mea- sures a current sense voltage greater than or equal to 1.6mv while the gate is turned off. this condition sets fet short fault bit d5. power bad fault a power bad fault is reported if the fb pin voltage drops below its 1.235v threshold for more than 2s when the gate is high. this pulls the gpio1 pin low immediately when con? gured as power-good, and sets power-bad pres- ent bit, c3, and power bad fault bit d3. a circuit prevents power-bad faults if the gate-to-source voltage is low, eliminating false power-bad faults during power-up or power-down. if the fb pin voltage subsequently rises back above the threshold, a power-good con? gured gpio1 pin returns to a high impedance state and bit c3 is reset. fault alerts when any of the fault bits in fault register d are set, an optional bus alert is generated if the appropriate bit in the alert register b has been set. this allows only selected faults to generate alerts. at power-up the default state is to not alert on faults and the gpio2 pin is high. if an alert is enabled, the corresponding fault causes the gpio2 pin to pull low. after the bus master controller broadcasts the alert response address, the ltc4215-1/ltc4215-3 respond with their addresses on the sda line and releases gpio2 as shown in table 6. if there is a collision between two ltc4215-1/ltc4215-3s responding with their ad- dresses simultaneously, then the device with the lower address wins arbitration and responds ? rst. the gpio2 line is also released if the device is addressed by the bus master if gpio2 is pulled low due to an alert. figure 4. plug-in card insertion/removal applications information C + 1.235v gnd motherboard connector plug-in card source out ltc4215-1 en c en load 4215 f04 10a
ltc4215-1/ltc4215-3 16 421513fc once the gpio2 signal has been released for one fault, it is not pulled low again until the fault register indicates a different fault has occurred or the original fault is cleared and it occur s again. note that this means repeated or con- tinuing faults do not generate alerts until the associated fault register bit has been cleared. the gpio2 pin may also be used as a general purpose output by setting or resetting bit d6. when d6 is set, gpio2 will pull low, and when d6 is reset (default) gpio2 will be high or pulled low due to an alert. the ltc4215-1/ ltc4215-3 will not respond to the alert response address if the gpio2 pin is being pulled low due to bit d6 being set. see figure 12 for a schematic detailing the behavior of the gpio2 pin. resetting faults faults are reset with any of the following conditions. first, a serial bus command writing zeros to the fault register d bits 0-5 clears the associated faults. second, fault register bits 0-5 are cleared when the switch is turned off by the on pin or bit a3 going from high to low, if the uv pin is brought below its 0.4v reset threshold for 2s, or if intv cc falls below its 2.64v undervoltage lockout threshold. finally, when en is brought from high to low, only fault bits d0-d3 and d5 are cleared, and bit d4, w h i c h i n d i c a t e s a e n c h a n g e o f s t a t e , i s s e t . n o t e t h a t f a u l t s that are still present, as indicated in status register c, cannot be cleared. the fault register is not cleared when auto-retrying. when auto-retry is disabled the existence of a d0, d1 or d2 fault keeps the switch off. as soon as the fault is cleared, the switch turns on. if auto-retry is enabled, then a high value in c0 or c1 holds the switch off and the fault register is ignored. subsequently, when bits c0 and c1 are cleared by removal of the fault condition, the switch is allowed to turn on again. the ltc4215-1/ltc4215-3 will set bit d2 and turn off in the event of an overcurrent fault, preventing it from remaining in an overcurrent condition. if con? gured to auto-retry, the ltc4215-1/ltc4215-3 will continually attempt to restart after cool-down cycles until it succeeds in starting up without generating an overcurrent fault. data converter the ltc4215-1/ltc4215-3 incorporate an 8-bit ? a/d converter that continuously monitors three different volt- ages. the ? a r c h i t e c t u r e i n h e r e n t l y a v e r a g e s s i g n a l n o i s e during the measurement period. the source pin has a 1/12.5 resistive divider to monitor a full scale voltage of 15.4v with 60mv resolution. the adin pin is monitored with a 1.235v full scale and 4.82mv resolution, and the voltage between the v dd and sense pins is monitored with a 38.6mv full scale and 151v resolution. results from each conversion are stored in registers e (sense), f (source) and g (adin), as seen in tables 6-8, and are updated 10 times per second. setting control register bit a5 invokes a test mode that halts the data converter so that registers e, f, and g may be written to and read from for software testing. con? guring the gpio pins table 2 describes the possible states of the gpio1 pin using the control register bits a6 and a7. at power-up, the default state is for the gpio1 pin to be a general purpose output with output value set by bit b6 (default 1 = gpio1 hi-z). other applications for the gpio1 pin are to go high impedance when power is good (fb pin greater than 1.235v), pull down when power is good, and a general purpose input. digital input information can be read from bit c6 (table 4). table 3 is used to con? gure the gpio2 pin as a fault alert output (see fault alerts) and also can be used as a general purpose output and a general purpose input. by default the gpio2 pin is a general purpose output in the high-impedance state as set by bit d6 (default 0 = gpio2 hi-z, table 5). digital input information can be read from bit c5 (table 4). the gpio3 pin is a general purpose output/input that defaults to output-low as set by bit d7 (default 1 = gpio3 pulled low, table 5). digital input information can be read from bit c2 (table 4). applications information
ltc4215-1/ltc4215-3 17 421513fc current limit stability for many applications the ltc4215-1/ltc4215-3 current limits will be stable without additional components. how- ever there are certain conditions where additional compo- nents may be needed to improve stability. the dominant pole of the current limit circuit is set by the capacitance and resistance at the gate of the external mosfet, and larger gate capacitance makes the current limit loop more stable. usually a total of 8nf gate to source capacitance is suf? cient for stability and is typically provided by in- herent mosfet c gs , however the stability of the loop is degraded by increasing r sense or by reducing the size of the resistor on a gate rc network if one is used, which may require additional gate to source capacitance. board level short-circuit testing is highly recommended as board layout can also affect transient performance, for stability testing the worst case condition for current limit stabil- ity occurs when the output is shorted to ground after a normal start-up. there are two possible parasitic oscillations when the mosfet operates as a source follower when ramping at power-up or during current limiting. the ? rst type of oscillation occurs at high frequencies, typically above 1mhz. this high frequency oscillation is easily damped with r5 as shown in figure 1. in some applications, one may ? nd that r5 helps in short-circuit transient recovery as well. however, too large of an r5 value will slow down the turn-off time. the recommended r5 range is between 5 and 500. the second type of source follower oscillation occurs at frequencies between 200khz and 800khz due to load capacitance being between 0.2f and 9f, the presence of r5 resistance, the absence of a drain bypass capacitor, a combination of bus wiring inductance and bus supply o u t p u t i m p e d a n c e . to p r e v e n t t h e s e c o n d t y p e o f o s c i l l a t i o n avoid load capacitance below 10f, alternately connect an external capacitor from the mosfet gate to ground with a value greater than 1.5nf. supply transients the ltc4215-1/ltc4215-3 are designed to ride through s u p p l y t r a n s i e n t s c a u s e d b y l o a d s t e p s . i f t h e r e i s a s h o r t e d load and the parasitic inductance back to the supply is greater than 0.5h, there is a chance that the supply col- lapses before the active current limit circuit brings down the gate pin. if this occurs, the undervoltage monitors pull the gate pin low. the undervoltage lockout circuit has a 2s ? lter time after v dd drops below 2.74v. the uv pin reacts in 2s to shut the gate off, but it is recom- mended to add a ? lter capacitor c f to prevent unwanted shutdown caused by a transient. eventually either the uv pin or undervoltage lockout responds to bring the current under control before the supply completely collapses. supply transient protection the ltc4215-1/ltc4215-3 are safe from damage with supply voltages up to 24v. however, spikes above 24v may damage the part. during a short-circuit condition, figure 5. recommended layout applications information uv ov ss gnd on en sdao fb gpio1 intv cc timer adin gpio3 adr1 v dd sense + sense C gate source sdai scl gpio2 nc adr0 r2 r3 c f z1 r1 sense resistor r s c3 ltc4215-1 r8 i load 4215 f05 i load
ltc4215-1/ltc4215-3 18 421513fc large changes in current ? owing through power supply traces may cause inductive voltage spikes which exceed 24v. to minimize such spikes, the power trace inductance should be minimized by using wider traces or heavier trace plating. also, a snubber circuit dampens inductive voltage spikes. build a snubber by using a 100 resistor in series with a 0.1f capacitor between v dd and gnd. a surge suppressor, z1 in figure 1, at the input can also prevent damage from voltage surges. design example as a design example, take the following speci? cations: v in = 12v, i max = 5a, i inrush = 1a, di/dt inrush = 10a/ms, c l = 330f, v uv(on) = 10.75v, v ov(off) = 14.0v, v pwrgd(up) = 11.6v, and i 2 c address = 1001011. this completed design is shown in figure 1. selection of the sense resistor, r s , is set by the overcurrent threshold of 25mv: r s = 25mv i ma x = 0.005 the mosfet is sized to handle the power dissipation dur- ing inrush when output capacitor c l is being charged. a method to determine power dissipation during inrush is based on the principle that: energy in c l = energy in q1 this uses: energy in c l = 1 2 cv 2 = 1 2 0.33mf () 12 () 2 or 0.024 joules. calculate the time it takes to charge up c out : t startup = c l ? v dd i inrus h = 0.33mf ? 12v 1 a = 4ms the power dissipated in the mosfet: p diss = energyin c l t startu p = 6w the soa (safe operating area) curves of candidate mosfets must be evaluated to ensure that the heat capacity of the package tolerates 6w for 4ms. the soa curves of the fairchild fdc653n provide for 2a at 12v (24w) for 10ms, satisfying this requirement. since the fdc653n has less than 8nf of gate capacitance and we are using a gate rc network, the short circuit stability of the current limit should be checked and improved by adding a capacitor from gate to source if needed. the inrush current is set to 1a using c1: c1 = c l ? i gate i inrus h c1 = 0.33mf ? 20a 1 a or c1 = 6.8nf the inrush di/dt is set to 10a/ms using c ss : c ss = i ss di / dt a s ? 0.0375 ? 1 r sens e = 10a 10000 ? 0.0375 ? 1 5m = 7.5nf for a start-up time of 4ms with a 2x safety margin we choose: c timer = 2? t startup 12.3ms/ f + c ss ?10 c timer = 8ms 12.3ms/ f + 7.5nf ? 10 0.68f note the minimum value of c timer is 10nf, and each 1nf of soft-start capacitance needs 10nf of timer capaci- tance/time during start-up. the uv and ov resistor string values can be solved in the following method. first pick r3 based on i string being applications information
ltc4215-1/ltc4215-3 19 421513fc figure 6. data transfer over i 2 c or smbus 1.235v/r3 at the edge of the ov rising threshold, where i string > 40a. then solve the following equations: r2 = v ov(off) v uv(on) ? r3 ? uv th(rising) ov th(falling) ? r3 r1 = v uv(on) ?(r3 + r2) uv th(rising) ?r3?r2 in our case we choose r3 to be 3.4k to give a resistor string currrent below 100a. then solving the equations results in r2 = 1.16k and r1 = 34.6k. the fb divider is solved by picking r8 and solving for r7, choosing 3.57k for r8 we get: r7 = v pwrgd(up) ?r8 fb th(rising) ?r8 resulting in r7 = 30k. a 0.1f capacitor, c f , is placed on the uv pin to prevent supply glitches from turning off the gate via uv or ov. the address is set with the help of table 1, which indicates binary address 1001011 corres ponds to address 4. address 4 is set by setting adr1 open and adr0 high. next the value of r5 and r6 are chosen to be the default values 10 and 15k as discussed previously. in addition a 0.1f ceramic bypass capacitor is placed on the intv cc pin. layout considerations to achieve accurate current sensing, a kelvin connection is required. the minimum trace width for 1oz copper foil is 0.02" per amp to make sure the trace stays at a reasonable temperature. using 0.03" per amp or wider is recommended. note that 1oz copper exhibits a sheet resistance of about 530?. small resistances add up quickly in high current applications. to improve noise immunity, put the resistive dividers to the uv, ov and fb pins close to the device and keep traces to v dd and gnd short. it is also important to put the bypass capacitor for the intv cc pin, c3, as close as possible between intv cc and gnd. a 0.1f capacitor from the uv pin (and ov pin through resistor r2) to gnd also helps reject supply noise. figure 4 shows a layout that addresses these issues. note that a surge suppressor, z1, is placed between supply and ground using wide traces. digital interface the ltc4215-1/ltc4215-3 communicate with a bus mas- ter using a 2-wire interface compatible with i 2 c bus and smbus, an i 2 c extension for low power devices. the ltc4215-1/ltc4215-3 are read-write slave devices and support smbus bus read byte, write byte, read word and write word commands. the second word in a read word command is identical to the ? rst word. the second word in a write word command is ignored. data formats for these commands are shown in figures 6 to 11. start and stop conditions when the bus is idle, both scl and sda are high. a bus master signals the beginning of a transmission with a start condition by transitioning sda from high to low while scl is high, as shown in figure 6. when the master has ? nished communicating with the slave, it issues a stop condition by transitioning sda from low to high while scl is high. the bus is then free for another transmission. applications information scl sda start condition stop condition address r/ w ack data ack data ack 1 - 7 8 9 4215 f06 a6 - a0 b7 - b0 b7 - b0 1 - 7 8 9 1 - 7 8 9 p s
ltc4215-1/ltc4215-3 20 421513fc i 2 c device addressing nine distinct bus addresses are available using two 3- state address pins, adr0 and adr1. table 1 shows the correspondence between pin states and addresses. note that address bits b7 and b6 are internally con? gured to 10. in addition, the ltc4215-1/ltc4215-3 respond to two special addresses. address (1011 111) is a mass write address that writes to all ltc4215-1/ltc4215-3s, regardless of their individual address settings. mass write can be disabled by setting register bit a4 to zero. address (0001 100) is the smbus alert response address. if the ltc4215-1/ltc4215-3 are pulling low on the gpio2 pin due to an alert, it acknowledges this address by broadcasting its address and releasing the gpio2 pin. applications information figure 7. ltc4215-1/ltc4215-3 serial bus sda write byte protocol figure 8. ltc4215-1/ltc4215-3 serial bus sda write word protocol figure 9. ltc4215-1/ltc4215-3 serial bus sda read byte protocol figure 10. ltc4215-1/ltc4215-3 serial bus sda read word protocol figure 11. ltc4215-1/ltc4215-3 serial bus sda alert response protocol s address 1 0 a4:a0 4215 f07 from master to slave from slave to master a: acknowledge (low) a : not acknowledge (high) r: read bit (high) w : write bit (low) s: start condition p: stop condition command data x x x x x b2:b0 0 w 000 b7:b0 a a ap s address 1 0 a4:a0 command data data x x x x x b2:b0 0 w 000 0 4215 f08 x x x x x x x x b7:b0 a a a ap s address 1 0 a4:a0 1 0 a4:a0 1 0 command s address r a b7:b0 1 data x x x x x b2:b0 0 w 00 4215 f10 a a a p s address 1 0 a4:a0 1 0 a4:a0 1 0 command s address r a b7:b0 1 data x x x x x b2:b0 0 w 00 4215 f11 a 0 a b7:b0 data a a p s alert response address 0 0 0 1 1 0 0 device address 1 0 a4:a0 0 1 1 r 0 4215 f11 a a p
ltc4215-1/ltc4215-3 21 421513fc figure 12. control logic for gpio2 pin 4215 ta02 rising edge detect iq rising edge detect iq ? ? ? status bit c0 alert enable bit b0 power on reset i 2 c address ack status bit c5 alert enable bit b5 register bit d6 gpio2 pin s r q applications information acknowledge the acknowledge signal is used in handshaking between transmitter and receiver to indicate that the last byte of data was received. the transmitter always releases the sda line during the acknowledge clock pulse. when the slave is the receiver, it pulls down the sda line so that it remains low during this pulse to acknowledge receipt of the data. if the slave fails to acknowledge by leaving sda high, then the master may abort the transmission by generating a stop condition. when the master is receiv- ing data from the slave, the master pulls down the sda line during the clock pulse to indicate receipt of the data. after the last byte has been received the master leaves the sda line high (not acknowledge) and issues a stop condition to terminate the transmission. write protocol the master begins communication with a start con- dition followed by the seven bit slave address and the r/ w bit set to zero, as shown in figure 7. the addressed ltc4215-1/ltc4215-3 acknowledge this and then the master sends a command byte which indicates which internal register the master wishes to write. the ltc4215- 1/ltc4215-3 acknowledge this and then latch the lower three bits of the command byte into its internal register address pointer. the master then delivers the data byte and the ltc4215-1/ltc4215-3 acknowledge once more and latch the data into its control register. the transmis- sion is ended when the master sends a stop condition. if the master continues sending a second data byte, as in a write word command, the second data byte is ac- knowledged by the ltc4215-1/ltc4215-3 but ignored, as shown in figure 8. read protocol the master begins a read operation with a start condition followed by the seven bit slave address and the r/ w bit set to zero, as shown in figure 9. the addressed ltc4215-1/ ltc4215-3 acknowledge this and then the master sends a command byte which indicates which internal register the master wishes to read. the ltc4215-1/ltc4215-3 acknowledge this and then latch the lower three bits of the command byte into its internal register address pointer. the master then sends a repeated start condition followed by the same seven bit address with the r/ w bit now set to one. the ltc4215-1/ltc4215-3 acknowledge and send the contents of the requested register. the transmission is ended when the master sends a stop condition. if the
ltc4215-1/ltc4215-3 22 421513fc master acknowledges the transmitted data byte, as in a read word command, figure 10, the ltc4215-1/ltc4215-3 repeat the requested register as the second data byte. alert response protocol when any of the fault bits in fault register d are set, an optional bus alert is generated if the appropriate bit in the alert register b is also set. if an alert is enabled, the corresponding fault causes the gpio2 pin to pull low. after the bus master controller broadcasts the alert response address, the ltc4215-1/ltc4215-3 respond with their address on the sda line and then release gpio2 as shown in figure 11. the gpio2 line is also released if the device is addressed by the bus master. the gpio2 signal is not pulled low again until the fault register indicates a differ- ent fault has occurred or the original fault is cleared and it oc cur s again. note tha t this me ans repe a ted or con tinuing faults do not generate alerts until the associated fault register bit has been cleared. applications information table 1. ltc4215-1/ltc4215-3 device addressing description* device address device address ltc4215-1/ltc4215-3 address pins h 76543210 adr1 adr0 mass write be 10111110 x x alert response 19 00011001 x x 8 90 1001000x nc l 9 92 1001001x h nc 10 94 1001010x nc nc 11 96 1001011x nc h 12 98 1001100x l l 13 9a 1001101x h h 14 9c 1001110x l nc 15 9e 1001111x l h 25 b2 1011001x h l *subset of ltc4215 addresses
ltc4215-1/ltc4215-3 23 421513fc table 2. control register a (00h)read/write bit name operation a7:6 gpio1 con? gure function a6 a7 gpio pin power good 0 0 gpio = c3 power good 0 1 gpio = c3 general purpose output (default) 1 0 gpio = b6 general purpose input 1 1 c6 = gpio1 a5 test mode enable enables test mode to disable the adc; 1 = adc disable, 0 = adc enable (default) a4 mass write enable allows mass write addressing; 1 = mass write enabled (default), 0 = mass write disabled a3 fet on control on control bit latches the state of the on pin at the end of the debounce delay; 1 = fet on, 0 = fet off a2 overcurrent auto-retry overcurrent auto-retry bit; 1 = auto-retry after overcurrent, 0 = latch off after overcurrent (default) a1 undervoltage auto-retry undervoltage auto-retry; 1 = auto-retry after undervoltage (default), 0 = latch off after undervoltage a0 overvoltage auto-retry overvoltage auto-retry; 1 = auto-retry after overvoltage (default), 0 = latch off after overvoltage table 3. alert register b (01h)read/write bit name operation b7 reserved not used b6 gpio1 output output data bit to gpio1 pin when con? gured as output. defaults to 1 b5 fet short alert enables alert for fet short condition; 1 = enable alert, 0 = disable alert (default) b4 en state change alert enables alert when en changes state; 1 = enable alert, 0 disable alert (default) b3 power bad alert enables alert when output power is bad; 1 = enable alert, 0 disable alert (default) b2 overcurrent alert enables alert for overcurrent condition; 1 = enable alert, 0 disable alert (default) b1 undervoltage alert enables alert for undervoltage condition; 1 = enable alert, 0 disable alert (default) b0 overvoltage alert enables alert for overvoltage condition; 1 = enable alert, 0 disable alert (default) applications information
ltc4215-1/ltc4215-3 24 421513fc table 4. status register c (02h)read bit name operation c7 fet on 1 = fet on, 0 = fet off c6 gpio1 input reports the state of the gpio1 pin; 1 = gpio1 high, 0 = gpio1 low c5 gpio2 input reports the state of the gpio2 pin; 1 = gpio2 high, 0 = gpio2 low c4 en indicates if the ltc4215 is enabled when en is low; 1 = en pin low, 0 = en pin high c3 power bad indicates power is bad when fb is low; 1 = fb low, 0 = fb high c2 gpio3 input reports the state of the gpio3 pin; 1 = gpio3 high, 0 = gpio3 low c1 undervoltage indicates input undervoltage when uv is low; 1 = uv low, 0 = uv high c0 overvoltage indicates v dd or ov input overvoltage when ov is high; 1 = ov high, 0 = ov low table 5. fault register d (03h)read/write bit name operation d7 gpio3 output sets the state of the gpio3 pin; 1 = gpio3 pulled low (default), 0 = gpio3 high impedance d6 gpio2 output sets the state of the gpio2 pin; 1 = gpio2 pulled low, 0 = gpio2 high impedance (default) d5 fet short fault occurred indicates potential fet short was detected when measured current sense volage exceeded 1mv while fet was off; 1 = fet is shorted, 0 = fet is good d4 en changed state indicates that the ltc4215 was enabled or disabled when en changed state; 1 = en changed state, 0 = en unchanged d3 power bad fault occurred indicates power was bad when fb when low; 1 = fb was low, 0 = fb was high d2 overcurrent fault occurred indicates overcurrent fault occured; 1 = overcurrent fault occured, 0 = not overcurrent faults d1 undervoltage fault occurred indicates input undervoltage fault occured when uv went low; 1 = uv was low, 0 = uv was high d0 overvoltage fault occurred indicates input overvoltage fault occured when ov went high; 1 = ov was high, 0 = ov was low table 6. sense register e (04h)read/write bit name operation e7:0 sense voltage measurement sense voltage data, 8-bit data with 151v lsb and 38.45mv full scale table 7. source register f (05h)read/write bit name operation f7:0 source voltage measurement source voltage data, 8-bit data with 60.5mv lsb and 15.44v full scale table 8. adin register g (06h)read/write bit name operation g7:0 adin voltage measurement adin voltage data, 8-bit data with 4.82mv lsb and 1.23v full scale applications information
ltc4215-1/ltc4215-3 25 421513fc 5v card resident application with inverting led driver and 16.6a circuit breaker typical applications + uv v dd sense ltc4215-1 gate intv cc timer gnd en adr0 adr1 source ov sdai sda0 scl gpio2 on fb gpio1 gpio3 adin ss plug-in card r5 10 r6 15k c1 22nf c ss 68nf r s 0.0015 q1 si7880dp r7 6.98k 1% r8 2.67k 1% r4 24k r9 24k r10 910 4215 ta03 c l 1000f c f 0.1f r1 11.5k 1% r2 1.74k 1% r3 2.67k 1% backplane gnd alert scl sda v in 5v v out 5v c timer 1f c3 0.1f
ltc4215-1/ltc4215-3 26 421513fc 12v application with high current non-inverting led drivers and 8.3a circuit breaker + uv v dd sense + sense C ltc4215-1 gate timer ss on intv cc gnd en source ov sdai sdao scl adr0 adr1 fb gpio3 gpio2 gpio1 adin r3 3.47k 1% plug-in card r2 1.18k 1% p6ke16a r5 10 r s 0.003 q1 q2 q3 r7 30.1k 1% v out 12v r8 3.57k 1% r9 24k 4215 ta04 c l 0.1f connector 2 connector 1 r1 34.8k 1% backplane c ss 68nf c3 0.1f gnd scl sda 12v r10 24k r11 24k r12 220 r13 220 reset led led 3.3v typical applications
ltc4215-1/ltc4215-3 27 421513fc information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. ufd package 24-lead plastic qfn (4mm 5mm) (reference ltc dwg # 05-08-1696 rev a) 4.00 0.10 (2 sides) 5.00 0.10 (2 sides) note: 1. drawing proposed to be made a jedec package outline mo-220 variation (wxxx-x). 2. drawing not to scale 3. all dimensions are in millimeters 4. dimensions of exposed pad on bottom of package do not include mold flash. mold flash, if present, shall not exceed 0.15mm on any side 5. exposed pad shall be solder plated 6. shaded area is only a reference for pin 1 location on the top and bottom of package pin 1 top mark (note 6) 0.40 0.10 23 24 1 2 bottom view?exposed pad 0.75 0.05 r = 0.115 typ r = 0.05 typ pin 1 notch r = 0.20 or c = 0.35 0.25 0.05 0.50 bsc 0.200 ref 0.00 ? 0.05 (ufd24) qfn 0506 rev a recommended solder pad pitch and dimensions apply solder mask to areas that are not soldered 0.70 0.05 0.25 0.05 0.50 bsc 2.65 0.05 2.00 ref 3.00 ref 4.10 0.05 5.50 0.05 3.10 0.05 4.50 0.05 package outline 2.65 0.10 2.00 ref 3.00 ref 3.65 0.10 3.65 0.05 package description
ltc4215-1/ltc4215-3 28 421513fc linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com ? linear technology corporation 2008 lt 0709 rev c ? printed in usa part number description comments ltc1422 single channel, hot swap controller operates from 2.7v to 12v, so-8 ltc1642a single channel, hot swap controller operates from 3v to 16.5v, overvoltage protection up to 33v, ssop-16 ltc1645 dual channel, hot swap controller operates from 3v to 12v, power sequencing, so-8 or so-14 ltc1647 dual channel, hot swap controller operates from 2.7v to 16.5v, so-8 or ssop-16 ltc4210 single channel, hot swap controller operates from 2.7v to 16.5v, active current limiting, sot23-6 ltc4211 single channel, hot swap controller operates from 2.5v to 16.5v, multifunction current control, msop-8 or msop-10 ltc4212 single channel, hot swap controller operates from 2.5v to 16.5v, power-up timeout, msop-10 ltc4215 single channel, hot swap controller with i 2 c, adc operates from 2.9v to 15v, 27 device addresses, fault alert output ltc4216 single channel, hot swap controller operates from 0v to 6v, msop-10 or 12-lead (4mm 3mm) dfn lt4220 positive and negative voltage, dual channel, hot swap controller operates from 2.7v to 16.5v, ssop-16 ltc4221 dual hot swap controller/sequencer operates from 1v to 13.5v, multifunction current control, ssop-16 ltc4230 triple channel, hot swap controller operates from 1.7v to 16.5v, multifunction current control, ssop-20 ltc4260 single channel, hot swap controller with i 2 c, adc adc for board power monitoring, 8.5v to 80v ltc4261 negative voltage, hot swap controller with i 2 c, adc operates from 9.5v to C100v or more (shunt regulated), 24-lead (4mm 5mm) qfn or ssop-28 C12v card resident application with optically isolated i 2 c and 16.6a current limit typical application related parts uv v dd sense + sense C ltc4215-1 gate intv cc adr0 adr1 en gnd source ov sdai sdao scl on fb gpio1 gpio2 gpio3 adin r5 10 r6 15k c1 22nf r s 0.0015 q1 si7880dp C12v C12v r7 30.1k 1% output C12v r8 3.57k 1% 4215 ta05 c3 0.1f d1 5.6v r14 10k r1 34.8k 1% r2 1.18k 1% r12 10k r4 3.3k r10 3.3k C12v r3 3.4k 1% c f 0.1f c l 1000f r13 3.3k hcpl-0300 287 7 C7v 3 6 5 d2 p6ke16a 2 8 C7v 3 6 5 C7v C7v hcpl-0300 68 5 2 3 r9 10k C7v C7v q2 plug-in card backplane gnd 5v sda scl v in C12v timer ss c timer 1f c ss 68nf

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