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lm34919b lm34919b-q1 www.ti.com snvs623b ? may 2010 ? revised july 2013 lm34919b ultra-small 40-v 600-ma constant on-time buck switching regulator check for samples: lm34919b , lm34919b-q1 1 features typical applications 2 ? aec-q100 grade 1 qualified (-40 c to 125 c) ? automotive safety and infotainment ? maximum switching frequency: 2.6 mhz ? high efficiency point-of-load (pol) regulator (v in =14v,v o =3.3v) ? non-isolated telecommunication buck ? input voltage range: 6v to 40v regulator ? integrated n-channel buck switch ? secondary high voltage post regulator ? integrated startup regulator description ? no loop compensation required the lm34919b step-down switching regulator ? ultra-fast transient response features all of the functions needed to implement a ? operating frequency remains constant with low cost, efficient, buck bias regulator capable of load current and input voltage supplying 0.6a to the load. this buck regulator contains an n-channel buck switch, and is available ? maximum duty cycle limited during startup in a 10-pin dsbga package. the constant on-time ? adjustable output voltage feedback regulation scheme requires no loop ? valley current limit at 0.64a compensation, results in fast load transient response, and simplifies circuit implementation. the operating ? precision internal reference frequency remains constant with line and load ? low bias current variations due to the inverse relationship between the ? highly efficient operation input voltage and the on-time. the valley current limit results in a smooth transition from constant voltage to ? thermal shutdown constant current mode when current limit is detected, ? 10-pin dsbga package reducing the frequency and output voltage, without the use of foldback. additional features include: vcc under-voltage lockout, thermal shutdown, gate drive under-voltage lockout, and maximum duty cycle limiter. basic step-down regulator 1 please be aware that an important notice concerning availability, standard warranty, and use in critical applications of texas instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. 2 all trademarks are the property of their respective owners. production data information is current as of publication date. copyright ? 2010 ? 2013, texas instruments incorporated products conform to specifications per the terms of the texas instruments standard warranty. production processing does not necessarily include testing of all parameters. vin sw bst lm34919b vcc ss ron/sd 6v - 40v input c1 r on r2 r1 c2 v out l1 c3 c4 d1 c6 rtn isen sgnd fb shutdown r3
lm34919b lm34919b-q1 snvs623b ? may 2010 ? revised july 2013 www.ti.com connection diagram figure 1. bump side figure 2. top view pin descriptions pin no. name description application information a1 ron/sd on-time control and an external resistor from vin to this pin sets the buck switch on-time. shutdown grounding this pin shuts down the regulator. a2 rtn circuit ground ground for all internal circuitry other than the current limit detection. a3 fb feedback input from internally connected to the regulation and over-voltage comparators. the the regulated output regulation level is 2.5v. b1 sgnd sense ground re-circulating current flows into this pin to the current sense resistor. b3 ss softstart an internal current source charges an external capacitor to 2.5v, providing the softstart function. c1 isen current sense the re-circulating current flows through the internal sense resistor, and out of this pin to the free-wheeling diode. current limit is nominally set at 0.64a. c3 vcc output from the startup nominally regulated at 7.0v. an external voltage (7v-14v) can be applied to regulator this pin to reduce internal dissipation. an internal diode connects vcc to vin. d1 vin input supply voltage nominal input range is 6.0v to 40v. d2 sw switching node internally connected to the buck switch source. connect to the inductor, free- wheeling diode, and bootstrap capacitor. d3 bst boost pin for bootstrap connect a 0.022 f capacitor from sw to this pin. the capacitor is charged capacitor from v cc via an internal diode during each off-time. this integrated circuit can be damaged by esd. texas instruments recommends that all integrated circuits be handled with appropriate precautions. failure to observe proper handling and installation procedures can cause damage. esd damage can range from subtle performance degradation to complete device failure. precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications. 2 submit documentation feedback copyright ? 2010 ? 2013, texas instruments incorporated product folder links: lm34919b lm34919b-q1 d3 d2 d1 c3 c1 b3 b1 a3 a2 a1 sw rtn bst vcc ss fb vin isen sgnd ron/sd d1 d2 d3 c1 c3 b1 b3 a1 a2 a3
lm34919b lm34919b-q1 www.ti.com snvs623b ? may 2010 ? revised july 2013 absolute maximum ratings (1) vin to rtn 44v bst to rtn 52v sw to rtn (steady state) -1.5v to 44v esd rating, human body model (2) 2kv bst to vcc 44v bst to sw 14v vcc to rtn 14v sgnd to rtn -0.3v to +0.3v ss, ron/sd to rtn -0.3v to 4v fb to rtn -0.3 to 7v storage temperature range -65 c to +150 c for soldering specs see: junction temperature 150 c (1) absolute maximum ratings are limits beyond which damage to the device may occur. operating ratings are conditions under which operation of the device is intended to be functional. for specifications and test conditions, see the electrical characteristics. (2) the human body model is a 100 pf capacitor discharged through a 1.5k ? resistor into each pin. operating ratings (1) vin 6.0v to 40v junction temperature ? 40 c to + 125 c (1) absolute maximum ratings are limits beyond which damage to the device may occur. operating ratings are conditions under which operation of the device is intended to be functional. for specifications and test conditions, see the electrical characteristics. copyright ? 2010 ? 2013, texas instruments incorporated submit documentation feedback 3 product folder links: lm34919b lm34919b-q1
lm34919b lm34919b-q1 snvs623b ? may 2010 ? revised july 2013 www.ti.com electrical characteristics specifications with standard type are for t j = 25 c only; limits in boldface type apply over the full operating junction temperature (t j ) range. minimum and maximum limits are specified through test, design, or statistical correlation. typical values represent the most likely parametric norm at t j = 25 c, and are provided for reference purposes only. unless otherwise stated the following conditions apply: v in = 12v, r on = 20 k ? . see (1) . symbol parameter conditions min typ max units startup regulator, v cc v cc reg v cc regulated output v in = 12v 6.6 7 7.4 v v in =6v, i cc = 3 ma, 5.3 5.91 v in -v cc dropout voltage i cc = 0 ma, non-switching 20 mv v cc = uvlo vcc + 250 mv v cc output impedance 0 ma i cc 5 ma, v in = 6v 24 ? 0 ma i cc 5 ma, v in = 8v 12 v cc current limit (2) v cc = 0v 15 ma uvlo vcc v cc under-voltage lockout threshold v cc increasing 5.25 v measured at v cc v cc decreasing 5.1 5.25 v uvlo vcc hysteresis, at v cc 150 mv v cc under-voltage lock-out threshold v in increasing, i cc = 3 ma 5.25 5.6 v measured at v in v in decreasing, i cc = 3 ma 5.1 5.4 v uvlo vcc filter delay 100 mv overdrive 3 s i q i in operating current non-switching, fb = 3v, sw = open 0.78 1.0 ma i sd i in shutdown current ron/sd = 0v, sw = open 215 330 a switch characteristics rds(on) buck switch rds(on) i test = 200 ma 0.5 1.0 ? uvlo gd gate drive uvlo v bst - v sw increasing 2.65 3.6 4.40 v v bst - v sw decreasing 3.2 uvlo gd hysteresis 400 mv softstart pin v ss pull-up voltage 2.5 v internal current source v ss = 1v 10.5 a current limit i lim threshold current out of isen 0.52 0.64 0.76 a resistance from isen to sgnd 135 m ? response time 50 ns on timer t on - 1 on-time v in = 12v, r on = 20k ? 127 170 213 ns t on - 2 on-time v in = 24v, r on = 20 k ? 110 ns t on - 3 on-time v in = 6v, r on = 20 k ? 335 ns shutdown threshold voltage at ron/sd rising 0.4 0.74 1.2 v threshold hysteresis voltage at ron/sd 40 mv off timer t off minimum off-time v in = 6v, i cc = 3ma 60 88 120 ns v in = 8v, i cc = 3ma 58 82 118 regulation and over-voltage comparators (fb pin) v ref fb regulation threshold ss pin = steady state 2.440 2.5 2.550 v fb over-voltage threshold 2.9 v fb bias current fb = 3v 1 na (1) typical specifications represent the most likely parametric norm at 25 c operation. (2) v cc provides self bias for the internal gate drive and control circuits. device thermal limitations limit external loading 4 submit documentation feedback copyright ? 2010 ? 2013, texas instruments incorporated product folder links: lm34919b lm34919b-q1
lm34919b lm34919b-q1 www.ti.com snvs623b ? may 2010 ? revised july 2013 electrical characteristics (continued) specifications with standard type are for t j = 25 c only; limits in boldface type apply over the full operating junction temperature (t j ) range. minimum and maximum limits are specified through test, design, or statistical correlation. typical values represent the most likely parametric norm at t j = 25 c, and are provided for reference purposes only. unless otherwise stated the following conditions apply: v in = 12v, r on = 20 k ? . see (1) . symbol parameter conditions min typ max units thermal shutdown t sd thermal shutdown temperature 175 c thermal shutdown hysteresis 20 c thermal resistance ja junction to ambient 61 c/w 0 lfpm air flow copyright ? 2010 ? 2013, texas instruments incorporated submit documentation feedback 5 product folder links: lm34919b lm34919b-q1
lm34919b lm34919b-q1 snvs623b ? may 2010 ? revised july 2013 www.ti.com typical performance characteristics efficiency at 2.1 mhz, 3.3v efficiency at 250 khz, 3.3v figure 3. figure 4. efficiency at 2.1 mhz, 5v v cc vs. v in figure 5. figure 6. v cc vs. i cc i cc vs. externally applied v cc figure 7. figure 8. 6 submit documentation feedback copyright ? 2010 ? 2013, texas instruments incorporated product folder links: lm34919b lm34919b-q1
lm34919b lm34919b-q1 www.ti.com snvs623b ? may 2010 ? revised july 2013 typical performance characteristics (continued) on-time vs. v in and r on voltage at the r on /sd pin figure 9. figure 10. operating current into v in shutdown current into v in figure 11. figure 12. v cc uvlo at vin vs. temperature gate drive uvlo vs. temperature figure 13. figure 14. copyright ? 2010 ? 2013, texas instruments incorporated submit documentation feedback 7 product folder links: lm34919b lm34919b-q1
lm34919b lm34919b-q1 snvs623b ? may 2010 ? revised july 2013 www.ti.com typical performance characteristics (continued) v cc voltage vs. temperature v cc output impedance vs. temperature figure 15. figure 16. v cc current limit vs. temperature reference voltage vs. temperature figure 17. figure 18. soft-start current vs. temperature on-time vs. temperature figure 19. figure 20. 8 submit documentation feedback copyright ? 2010 ? 2013, texas instruments incorporated product folder links: lm34919b lm34919b-q1
lm34919b lm34919b-q1 www.ti.com snvs623b ? may 2010 ? revised july 2013 typical performance characteristics (continued) minimum off-time vs. temperature current limit threshold vs. temperature figure 21. figure 22. operating & shutdown current vs. temperature ron pin shutdown threshold vs. temperature figure 23. figure 24. copyright ? 2010 ? 2013, texas instruments incorporated submit documentation feedback 9 product folder links: lm34919b lm34919b-q1
lm34919b lm34919b-q1 snvs623b ? may 2010 ? revised july 2013 www.ti.com block diagram 10 submit documentation feedback copyright ? 2010 ? 2013, texas instruments incorporated product folder links: lm34919b lm34919b-q1 v out fb vin vcc sw rtn v in bst 2.5v 64 mv ss l1 c2 r1 r2 lm34919b r3 2.9v sd 7v series regulator 100 m : + - sgnd isen c6 gnd r on ron/sd over - voltage comparator regulation comparator level shift current limit comparator + - 10.5 p a vcc uvlo on timer finish start r on logic 0.8v driver gate drive uvlo finish start off timer thermal shutdown 6v to 40v input c1 c3 c4 d1 r sense c5 gnd
lm34919b lm34919b-q1 www.ti.com snvs623b ? may 2010 ? revised july 2013 figure 25. startup sequence copyright ? 2010 ? 2013, texas instruments incorporated submit documentation feedback 11 product folder links: lm34919b lm34919b-q1 uvlo vin vcc sw pin inductor current ss pin t2 v out 7.0v 2.5v t1
lm34919b lm34919b-q1 snvs623b ? may 2010 ? revised july 2013 www.ti.com functional description the lm34919b step down switching regulator features all the functions needed to implement a low-cost, efficient buck bias power converter capable of supplying at least 0.6a to the load. this high voltage regulator contains an n-channel buck switch, is easy to implement, and is available in a dsbga package. the regulator ? s operation is based on a constant on-time control scheme, where the on-time is determined by v in . this feature allows the operating frequency to remain relatively constant with load and input voltage variations. the feedback control requires no loop compensation resulting in very fast load transient response. the valley current limit detection circuit, internally set at 0.64a, holds the buck switch off until the high current level subsides. this scheme protects against excessively high current if the output is short-circuited when v in is high. the lm34919b can be applied in numerous applications to efficiently regulate down higher voltages. additional features include: thermal shutdown, v cc under-voltage lockout, gate drive under-voltage lockout, and maximum duty cycle limiter. control circuit overview the lm34919b buck dc-dc regulator employs a control scheme based on a comparator and a one-shot on- timer, with the output voltage feedback (fb) compared to an internal reference (2.5v). if the fb voltage is below the reference the buck switch is turned on for a time period determined by the input voltage and a programming resistor (r on ). following the on-time the switch remains off until the fb voltage falls below the reference but not less than the minimum off-time. the buck switch then turns on for another on-time period. typically, during start- up, or when the load current increases suddenly, the off-times are at the minimum. once regulation is established, the off-times are longer. when in regulation, the lm34919b operates in continuous conduction mode at heavy load currents and discontinuous conduction mode at light load currents. in continuous conduction mode current always flows through the inductor, never reaching zero during the off-time. in this mode the operating frequency remains relatively constant with load and line variations. the minimum load current for continuous conduction mode is one-half the inductor ? s ripple current amplitude. the operating frequency is approximately: (1) the buck switch duty cycle is approximately equal to: (2) in discontinuous conduction mode current through the inductor ramps up from zero to a peak during the on-time, then ramps back to zero before the end of the off-time. the next on-time period starts when the voltage at fb falls below the reference - until then the inductor current remains zero, and the load current is supplied by the output capacitor. in this mode the operating frequency is lower than in continuous conduction mode, and varies with load current. conversion efficiency is maintained at light loads since the switching losses decrease with the reduction in load and frequency. the approximate discontinuous operating frequency can be calculated as follows: (3) where r l = the load resistance. the output voltage is set by two external resistors (r1, r2). the regulated output voltage is calculated as follows: v out = 2.5 x (r1 + r2) / r2 (4) output voltage regulation is based on ripple voltage at the feedback input, normally obtained from the output voltage ripple through the feedback resistors. the lm34919b requires a minimum of 25 mv of ripple voltage at the fb pin. in cases where the capacitor ? s esr is insufficient additional series resistance may be required (r3). 12 submit documentation feedback copyright ? 2010 ? 2013, texas instruments incorporated product folder links: lm34919b lm34919b-q1 f s = v out 2 x l1 x 6.27 x 10 20 r l x (r on ) 2 dc = t on t on + t off = v out v in f s = v out x (v in 1.5v) 0.565 x 10 -10 x (r on + 1.4 k : ) x v in
lm34919b lm34919b-q1 www.ti.com snvs623b ? may 2010 ? revised july 2013 startup regulator, v cc the start-up regulator is integral to the lm34919b. the input pin (vin) can be connected directly to line voltage up to 40v, with transient capability to 44v. the v cc output regulates at 7.0v, and is current limited at 15 ma. upon power up, the regulator sources current into the external capacitor at vcc (c3). when the voltage on the vcc pin reaches the under-voltage lockout threshold of 5.25v, the buck switch is enabled and the softstart pin is released to allow the softstart capacitor (c6) to charge up. the minimum input voltage is determined by the v cc uvlo falling threshold ( ? 5.1v). when v cc falls below the falling threshold the v cc uvlo activates to shut off the output. if v cc is externally loaded, the minimum input voltage increases. to reduce power dissipation in the startup regulator, an auxiliary voltage can be diode connected to the v cc pin. setting the auxiliary voltage to between 7v and 14v shuts off the internal regulator, reducing internal power dissipation. the sum of the auxiliary voltage and the input voltage (v cc + v in ) cannot exceed 52v. internally, a diode connects vcc to vin (see figure 26 ). figure 26. self biased configuration regulation comparator the feedback voltage at fb is compared to the voltage at the softstart pin (2.5v). in normal operation (the output voltage is regulated), an on-time period is initiated when the voltage at fb falls below 2.5v. the buck switch stays on for the programmed on-time, causing the fb voltage to rise above 2.5v. after the on-time period, the buck switch stays off until the fb voltage falls below 2.5v. input bias current at the fb pin is less than 100 na over temperature. over-voltage comparator the voltage at fb is compared to an internal 2.9v reference. if the voltage at fb rises above 2.9v the on-time pulse is immediately terminated. this condition can occur if the input voltage or the output load changes suddenly, or if the inductor (l1) saturates. the buck switch remains off until the voltage at fb falls below 2.5v. on-time timer, and shutdown the on-time is determined by the r on resistor and the input voltage (v in ), and is calculated from: (5) the inverse relationship with v in results in a nearly constant frequency as v in is varied. to set a specific continuous conduction mode switching frequency (f s ), the r on resistor is determined from the following: copyright ? 2010 ? 2013, texas instruments incorporated submit documentation feedback 13 product folder links: lm34919b lm34919b-q1 t on = v in - 1.5v 0.565 x 10 -10 x(r on + 1.4 k : ) + 55 ns fb sw l1 c2 r1 r2 r3 lm34919b bst vcc d2 c3 c4 d1 isen sgnd v out
lm34919b lm34919b-q1 snvs623b ? may 2010 ? revised july 2013 www.ti.com (6) in high frequency applications the minimum value for t on is limited by the maximum duty cycle required for regulation and the minimum off-time. the minimum off-time limits the maximum duty cycle achievable with a low voltage at v in . at high values of vin, the minimum on-time is limited to ? 90 ns. the lm34919b can be remotely shut down by taking the ron/sd pin low (see figure 27 ). in this mode the ss pin is internally grounded, the on-timer is disabled, and bias currents are reduced. releasing the ron/sd pin allows normal operation to resume. the voltage at the ron/sd pin is between 1.4v and 5.0v, depending on v in and the r on resistor. figure 27. shutdown implementation current limit current limit detection occurs during the off-time by monitoring the recirculating current through the free-wheeling diode (d1). referring to the block diagram, when the buck switch is turned off the inductor current flows through the load, into sgnd, through the sense resistor, out of isen and through d1. if that current exceeds 0.64a the current limit comparator output switches to delay the start of the next on-time period. the next on-time starts when the current out of isen is below 0.64a and the voltage at fb is below 2.5v. if the overload condition persists causing the inductor current to exceed 0.64a during each on-time, that is detected at the beginning of each off-time. the operating frequency is lower due to longer-than-normal off-times. figure 28 shows the inductor current waveform. during normal operation the load current is io, the average of the ripple waveform. when the load resistance decreases the current ratchets up until the lower peak reaches 0.64a. during the current limited portion of figure 28 , the current ramps down to 0.64a during each off-time, initiating the next on-time (assuming the voltage at fb is < 2.5v). during each on-time the current ramps up an amount equal to: i = (v in - v out ) x t on / l1 (7) during this time the lm34919b is in a constant current mode, with an average load current (i ocl ) equal to 0.64a + i/2. generally, in applications where the switching frequency is higher than ? 300 khz and uses a small value inductor, the higher dl/dt of the inductor's ripple current results in an effectively lower valley current limit threshold due to the response time of the current limit detection circuit. however, since the small value inductor results in a relatively high ripple current amplitude ( i in figure 28 ), the load current (i ocl ) at current limit is typically in excess of 640 ma. 14 submit documentation feedback copyright ? 2010 ? 2013, texas instruments incorporated product folder links: lm34919b lm34919b-q1 stop run ron/sd input voltage lm34919b vin r on r on = v out x (v in - 1.5v) f s x 0.565 x 10 -10 x v in - 1.4 k :
lm34919b lm34919b-q1 www.ti.com snvs623b ? may 2010 ? revised july 2013 figure 28. inductor current - current limit operation n-channel buck switch and driver the lm34919b integrates an n-channel buck switch and associated floating high voltage gate driver. the peak current allowed through the buck switch is 1.5a, and the maximum allowed average current is 1a. the gate driver circuit works in conjunction with an external bootstrap capacitor and an internal high voltage diode. a 0.022 f capacitor (c4) connected between bst and sw provides the voltage to the driver during the on-time. during each off-time, the sw pin is at approximately -1v, and c4 charges from v cc through the internal diode. the minimum off-time forced by the lm34919b ensures a minimum time each cycle to recharge the bootstrap capacitor. softstart the softstart feature allows the converter to gradually reach a steady state operating point, thereby reducing start-up stresses and current surges. upon turn-on, after v cc reaches the under-voltage threshold, an internal 10.5 a current source charges up the external capacitor at the ss pin to 2.5v. the ramping voltage at ss (and the non-inverting input of the regulation comparator) ramps up the output voltage in a controlled manner. an internal switch grounds the ss pin if v cc is below the under-voltage lockout threshold, or if the ron/sd pin is grounded. thermal shutdown the lm34919b should be operated so the junction temperature does not exceed 125 c. if the junction temperature increases, an internal thermal shutdown circuit, which activates (typically) at 175 c, takes the controller to a low power reset state by disabling the buck switch. this feature helps prevent catastrophic failures from accidental device overheating. when the junction temperature reduces below 155 c (typical hysteresis = 20 c) normal operation resumes. copyright ? 2010 ? 2013, texas instruments incorporated submit documentation feedback 15 product folder links: lm34919b lm34919b-q1 0.64a load current increases i pk i ocl i o ' i normal operation current limited inductor current
lm34919b lm34919b-q1 snvs623b ? may 2010 ? revised july 2013 www.ti.com applications information external components the procedure for calculating the external components is illustrated with the following design example. referring to the block diagram, the circuit is to be configured for the following specifications: - v out = 3.3v - v in = 6v to 24v - minimum load current = 200 ma - maximum load current = 600 ma - switching frequency = 1.5 mhz - soft-start time = 5 ms r1 and r2: these resistors set the output voltage. the ratio of the feedback resistors is calculated from: r1/r2 = (v out /2.5v) - 1 (8) for this example, r1/r2 = 0.32. r1 and r2 should be chosen from standard value resistors in the range of 1.0 k ? - 10 k ? which satisfy the above ratio. for this example, 2.49k ? is chosen for r2 and 787 ? for r1. r on : this resistor sets the on-time, and (by default) the switching frequency. the switching frequency must be less than 1.53 mhz to ensure the minimum forced on-time does not interfere with the circuit's proper operation at the maximum input voltage. the r on resistor is calculated from the following equation, using the minimum input voltage. (9) check that this value resistor does not set an on-time less than 90 ns at maximum v in . a standard value 28 k ? resistor is used, resulting in a nominal frequency of 1.49 mhz. the minimum on-time is ? 129 ns at vin = 24v, and the maximum on-time is ? 424 ns at vin = 6v. alternately, r on can be determined using equation 5 if a specific on-time is required. l1: the main parameter affected by the inductor is the inductor current ripple amplitude (i or ). the minimum load current is used to determine the maximum allowable ripple in order to maintain continuous conduction mode, where the lower peak does not reach 0 ma. this is not a requirement of the lm34919b, but serves as a guideline for selecting l1. for this case the maximum ripple current is: i or(max) = 2 x i out(min) = 400 ma (10) if the minimum load current is zero, use 20% of i out(max) for i out(min) in equation 10 . the ripple calculated in equation 10 is then used in the following equation: (11) a standard value 8.2 h inductor is selected. the maximum ripple amplitude, which occurs at maximum v in , calculates to 325 ma p-p, and the peak current is 763 ma at maximum load current. ensure the selected inductor is rated for this peak current. c2 and r3: since the lm34919b requires a minimum of 25 mvpp ripple at the fb pin for proper operation, the required ripple at v out is increased by r1 and r2. this necessary ripple is created by the inductor ripple current flowing through r3, and to a lesser extent by c2 and its esr. the minimum inductor ripple current is calculated using equation 11 , rearranged to solve for i or at minimum v in . (12) the minimum value for r3 is equal to: (13) 16 submit documentation feedback copyright ? 2010 ? 2013, texas instruments incorporated product folder links: lm34919b lm34919b-q1 r3 (min) = 25 mv x (r1 + r2) r2 x i or (min) = 0.24 : (v in(min) v out ) x t on(max) l1 = 140 ma i or(min) = l1 = (v in(max) v out ) x t on(min ) i or(max) = 6.67 p h r on = v out x (v in(min) - 1.5v) f s x 0.565 x 10 -10 x v in(min) -1.4 k : = 27.8 k :
lm34919b lm34919b-q1 www.ti.com snvs623b ? may 2010 ? revised july 2013 a standard value 0.27 ? resistor is used for r3 to allow for tolerances. c2 should generally be no smaller than 3.3 f, although that is dependent on the frequency and the desired output characteristics. c2 should be a low esr good quality ceramic capacitor. experimentation is usually necessary to determine the minimum value for c2, as the nature of the load may require a larger value. a load which creates significant transients requires a larger value for c2 than a non-varying load. c1 and c5: c1 ? s purpose is to supply most of the switch current during the on-time, and limit the voltage ripple at v in , on the assumption that the voltage source feeding v in has an output impedance greater than zero. at maximum load current, when the buck switch turns on, the current into v in suddenly increases to the lower peak of the inductor ? s ripple current, ramps up to the upper peak, then drops to zero at turn-off. the average current during the on-time is the load current. for a worst case calculation, c1 must supply this average load current during the maximum on-time, without letting the voltage at v in drop more than 0.5v. the minimum value for c1 is calculated from: (14) where t on is the maximum on-time, and v is the allowable ripple voltage (0.5v). c5 ? s purpose is to minimize transients and ringing due to long lead inductance leading to the vin pin. a low esr, 0.1 f ceramic chip capacitor must be located close to the vin and rtn pins. c3: the capacitor at the vcc pin provides noise filtering and stability for the vcc regulator. c3 should be no smaller than 0.1 f, and should be a good quality, low esr, ceramic capacitor. c3 ? s value, and the v cc current limit, determine a portion of the turn-on-time (t 1 in figure 25 ). c4: the recommended value for c4 is 0.022 f. a high quality ceramic capacitor with low esr is recommended as c4 supplies a surge current to charge the buck switch gate at each turn-on. a low esr also helps ensure a complete recharge during each off-time. c6: the capacitor at the ss pin determines the softstart time, i.e. the time for the output voltage, to reach its final value (t 2 in figure 25 ). the capacitor value is determined from the following: (15) d1: a schottky diode is recommended. ultra-fast recovery diodes are not recommended as the high speed transitions at the sw pin may inadvertently affect the ic ? s operation through external or internal emi. the diode should be rated for the maximum input voltage, the maximum load current, and the peak current which occurs when the current limit and maximum ripple current are reached simultaneously. the diode ? s average power dissipation is calculated from: p d1 = v f x i out x (1-d) (16) where v f is the diode ? s forward voltage drop, and d is the on-time duty cycle. final circuit the final circuit is shown in figure 29 , and its performance is shown in figure 30 and figure 31 . current limit measured approximately 780 ma at 6v, and 812 ma at 24v. copyright ? 2010 ? 2013, texas instruments incorporated submit documentation feedback 17 product folder links: lm34919b lm34919b-q1 c6 = t 2 x 10.5 p a 2.5v = 0.021 p f c1 = i out (max) x t on ' v = 0.5 p f
lm34919b lm34919b-q1 snvs623b ? may 2010 ? revised july 2013 www.ti.com figure 29. example circuit figure 30. efficiency (circuit of figure 29 ) figure 31. frequency vs. v in (circuit of figure 29 ) low-output ripple configurations for applications where lower ripple at v out is required, the following options can be used to reduce or nearly eliminate the ripple. a) reduced ripple configuration: in figure 32 , cff is added across r1 to ac-couple the ripple at v out directly to the fb pin. this allows the ripple at v out to be reduced to a minimum of 25 mvpp by reducing r3, since the ripple at v out is not attenuated by the feedback resistors. the minimum value for cff is determined from: (17) where t on(max) is the maximum on-time, which occurs at v in(min) . the next larger standard value capacitor should be used for cff. r1 and r2 should each be towards the upper end of the 2 k ? to 10 k ? range. 18 submit documentation feedback copyright ? 2010 ? 2013, texas instruments incorporated product folder links: lm34919b lm34919b-q1 cff = t on (max) x 3 (r1//r2) fb sw lm34919b bst vcc d1 isen ron/sd vin 6v - 24v input ss rtn sgnd v out 3.3v c1 2.2 p f shutdown c6 0.022 p f c5 0.1 p f r on 28 k : c3 0.1 p f c4 0.022 p f l1 8.2 p h r3 0.27 : c2 22 p f r1 787 : r2 2.49 k :
lm34919b lm34919b-q1 www.ti.com snvs623b ? may 2010 ? revised july 2013 figure 32. reduced ripple configuration b) minimum ripple configuration: the circuit of figure 33 provides minimum ripple at v out , determined primarily by c2 ? s characteristics and the inductor ? s ripple current since r3 is removed. ra and ca are chosen to generate a sawtooth waveform at their junction, and that voltage is ac-coupled to the fb pin via cb. to determine the values for ra, ca and cb, use the following procedure: calculate v a = v out - (v sw x (1 - (v out /v in(min) ))) (18) where v sw is the absolute value of the voltage at the sw pin during the off-time (typically 1v). v a is the dc voltage at the ra/ca junction, and is used in the next equation. (19) where t on is the maximum on-time (at minimum input voltage), and v is the desired ripple amplitude at the ra/ca junction, typically 50 mv. ra and ca are then chosen from standard value components to satisfy the above product. typically ca is 3000 pf to 5000 pf, and ra is 10 k ? to 300 k ? . cb is then chosen large compared to ca, typically 0.1 f. r1 and r2 should each be towards the upper end of the 2 k ? to 10 k ? range. figure 33. minimum output ripple using ripple injection c) alternate minimum ripple configuration: the circuit in figure 34 is the same as that in figure 29 , except the output voltage is taken from the junction of r3 and c2. the ripple at v out is determined by the inductor ? s ripple current and c2 ? s characteristics. however, r3 slightly degrades the load regulation. this circuit may be suitable if the load current is fairly constant. copyright ? 2010 ? 2013, texas instruments incorporated submit documentation feedback 19 product folder links: lm34919b lm34919b-q1 sw fb lm34919b l1 r1 r2 c2 cb ca ra v out ra x ca = (v in(min) - v a ) x t on ' v fb sw l1 lm34919b cff r1 r3 r2 c2 v out
lm34919b lm34919b-q1 snvs623b ? may 2010 ? revised july 2013 www.ti.com figure 34. alternate minimum output ripple configuration minimum load current the lm34919b requires a minimum load current of 1 ma. if the load current falls below that level, the bootstrap capacitor (c4) may discharge during the long off-time, and the circuit will either shutdown, or cycle on and off at a low frequency. if the load current is expected to drop below 1 ma in the application, r1 and r2 should be chosen low enough in value so they provide the minimum required current at nominal v out . pc board layout refer to application note an-1112 for pc board guidelines for the dsbga package. the lm34919b regulation, over-voltage, and current limit comparators are very fast, and respond to short duration noise pulses. layout considerations are therefore critical for optimum performance. the layout must be as neat and compact as possible, and all of the components must be as close as possible to their associated pins. the two major current loops have currents which switch very fast, and so the loops should be as small as possible to minimize conducted and radiated emi. the first loop is that formed by c1, through the vin to sw pins, l1, c2, and back to c1.the second current loop is formed by d1, l1, c2 and the sgnd and isen pins. the power dissipation within the lm34919b can be approximated by determining the total conversion loss (p in - p out ), and then subtracting the power losses in the free-wheeling diode and the inductor. the power loss in the diode is approximately: p d1 = iout x v f x (1-d) (20) where iout is the load current, v f is the diode ? s forward voltage drop, and d is the on-time duty cycle. the power loss in the inductor is approximately: p l1 = iout 2 x r l x 1.1 (21) where r l is the inductor ? s dc resistance, and the 1.1 factor is an approximation for the ac losses. if it is expected that the internal dissipation of the lm34919b will produce excessive junction temperatures during normal operation, good use of the pc board ? s ground plane can help to dissipate heat. additionally the use of wide pc board traces, where possible, can help conduct heat away from the ic. judicious positioning of the pc board within the end product, along with the use of any available air flow (forced or natural convection) can help reduce the junction temperatures. 20 submit documentation feedback copyright ? 2010 ? 2013, texas instruments incorporated product folder links: lm34919b lm34919b-q1 fb sw l1 r1 lm34919b r2 r3 c2 v out
lm34919b lm34919b-q1 www.ti.com snvs623b ? may 2010 ? revised july 2013 revision history changes from revision a (february 2013) to revision b page ? changed layout of national data sheet to ti format .......................................................................................................... 20 copyright ? 2010 ? 2013, texas instruments incorporated submit documentation feedback 21 product folder links: lm34919b lm34919b-q1
package option addendum www.ti.com 1-jul-2013 addendum-page 1 packaging information orderable device status (1) package type package drawing pins package qty eco plan (2) lead/ball finish msl peak temp (3) op temp (c) device marking (4/5) samples lm34919bqtl/nopb active dsbga ypa 10 250 green (rohs & no sb/br) snagcu level-1-260c-unlim -40 to 125 szrb lm34919bqtlx/nopb active dsbga ypa 10 3000 green (rohs & no sb/br) snagcu level-1-260c-unlim -40 to 125 szrb lm34919btl/nopb active dsbga ypa 10 250 green (rohs & no sb/br) snagcu level-1-260c-unlim -40 to 125 szcb lm34919btlx/nopb active dsbga ypa 10 3000 green (rohs & no sb/br) snagcu level-1-260c-unlim -40 to 125 szcb (1) the marketing status values are defined as follows: active: product device recommended for new designs. lifebuy: ti has announced that the device will be discontinued, and a lifetime-buy period is in effect. nrnd: not recommended for new designs. device is in production to support existing customers, but ti does not recommend using this part in a new design. preview: device has been announced but is not in production. samples may or may not be available. obsolete: ti has discontinued the production of the device. (2) eco plan - the planned eco-friendly classification: pb-free (rohs), pb-free (rohs exempt), or green (rohs & no sb/br) - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. tbd: the pb-free/green conversion plan has not been defined. pb-free (rohs): ti's terms "lead-free" or "pb-free" mean semiconductor products that are compatible with the current rohs requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. where designed to be soldered at high temperatures, ti pb-free products are suitable for use in specified lead-free processes. pb-free (rohs exempt): this component has a rohs exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between the die and leadframe. the component is otherwise considered pb-free (rohs compatible) as defined above. green (rohs & no sb/br): ti defines "green" to mean pb-free (rohs compatible), and free of bromine (br) and antimony (sb) based flame retardants (br or sb do not exceed 0.1% by weight in homogeneous material) (3) msl, peak temp. -- the moisture sensitivity level rating according to the jedec industry standard classifications, and peak solder temperature. (4) there may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device. (5) multiple device markings will be inside parentheses. only one device marking contained in parentheses and separated by a "~" will appear on a device. if a line is indented then it is a continuation of the previous line and the two combined represent the entire device marking for that device. important information and disclaimer: the information provided on this page represents ti's knowledge and belief as of the date that it is provided. ti bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the accuracy of such information. efforts are underway to better integrate information from third parties. ti has taken and
package option addendum www.ti.com 1-jul-2013 addendum-page 2 continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals. ti and ti suppliers consider certain information to be proprietary, and thus cas numbers and other limited information may not be available for release. in no event shall ti's liability arising out of such information exceed the total purchase price of the ti part(s) at issue in this document sold by ti to customer on an annual basis. other qualified versions of lm34919b, lm34919b-q1 : ? catalog: lm34919b ? automotive: lm34919b-q1 note: qualified version definitions: ? catalog - ti's standard catalog product ? automotive - q100 devices qualified for high-reliability automotive applications targeting zero defects
tape and reel information *all dimensions are nominal device package type package drawing pins spq reel diameter (mm) reel width w1 (mm) a0 (mm) b0 (mm) k0 (mm) p1 (mm) w (mm) pin1 quadrant lm34919bqtl/nopb dsbga ypa 10 250 178.0 8.4 1.89 2.2 0.69 4.0 8.0 q1 lm34919bqtlx/nopb dsbga ypa 10 3000 178.0 8.4 1.89 2.2 0.69 4.0 8.0 q1 lm34919btl/nopb dsbga ypa 10 250 178.0 8.4 1.89 2.2 0.69 4.0 8.0 q1 lm34919btlx/nopb dsbga ypa 10 3000 178.0 8.4 1.89 2.2 0.69 4.0 8.0 q1 package materials information www.ti.com 1-jul-2013 pack materials-page 1
*all dimensions are nominal device package type package drawing pins spq length (mm) width (mm) height (mm) lm34919bqtl/nopb dsbga ypa 10 250 210.0 185.0 35.0 lm34919bqtlx/nopb dsbga ypa 10 3000 210.0 185.0 35.0 lm34919btl/nopb dsbga ypa 10 250 210.0 185.0 35.0 lm34919btlx/nopb dsbga ypa 10 3000 210.0 185.0 35.0 package materials information www.ti.com 1-jul-2013 pack materials-page 2
mechanical data ypa0010 www.ti.com tlp10xxx (rev d) a . all linear dimensions are in millimeters. dimensioning and tolerancing per asme y14.5m-1994. b. this drawing is subject to change without notice. 4215069/a 12/12 notes: 0.600 0.075 e dd: max = e: max = 2.012 mm, min = 1.779 mm, min = 1.951 mm1.718 mm
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