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lp3963/lp3966 3a fast ultra low dropout linear regulators general description the lp3963/lp3966 series of fast ultra low-dropout linear regulators operate from a +2.5v to +7.0v input supply. wide range of preset output voltage options are available. these ultra low dropout linear regulators respond very quickly to step changes in load which makes them suitable for low voltage microprocessor applications. the lp3963/lp3966 are developed on a cmos process which allows low quies- cent current operation independent of output load current. this cmos process also allows the lp3963/lp3966 to op- erate under extremely low dropout conditions. dropout voltage: ultra low dropout voltage; typically 80mv at 300ma load current and 800mv at 3a load current. ground pin current: typically 6ma at 3a load current. shutdown mode: typically 15a quiescent current when the shutdown pin is pulled low. error flag: error flag goes low when the output voltage drops 10% below nominal value (for lp3963). sense: sense pin improves regulation at remote loads. (for lp3966) precision output voltage: multiple output voltage options are available ranging from 1.2v to 5.0v and adjustable (lp3966), with a guaranteed accuracy of 1.5% at room temperature, and 3.0% over all conditions (varying line, load, and temperature). features n ultra low dropout voltage n low ground pin current n load regulation of 0.06% n 15a quiescent current in shutdown mode n guaranteed output current of 3a dc n available in to-263 and to-220 packages n output voltage accuracy 1.5% n error flag indicates output status (lp3963) n sense option improves load regulation (lp3966) n minimum output capacitor requirements n overtemperature/overcurrent protection n ?40c to +125c junction temperature range applications n microprocessor power supplies n gtl, gtl+, btl, and sstl bus terminators n power supplies for dsps n scsi terminator n post regulators n high efficiency linear regulators n battery chargers n other battery powered applications typical application circuits 10126701 *sd and error pins must be pulled high through a 10k w pull-up resistor. connect the error pin to ground if this function is not used. see applications section for more information. ** see application hints november 2001 lp3963/lp3966 3a fast ultra low dropout linear regulators ? 2001 national semiconductor corporation ds101267 www.national.com
typical application circuits (continued) 10126734 *sd and error pins must be pulled high through a 10k w pull-up resistor. connect the error pin to ground if this function is not used. see applications section for more information. ** see application hints block diagram lp3963 10126703 lp3963/lp3966 www.national.com 2
block diagram lp3966 10126729 block diagram lp3966-adj 10126735 connection diagrams 10126705 top view to220-5 package bent, staggered leads 10126706 top view to263-5 package lp3963/lp3966 www.national.com 3
pin description for to220-5 and to263-5 packages pin # lp3963 lp3966 name function name function 1sd shutdown sd shutdown 2v in input supply v in input supply 3 gnd ground gnd ground 4v out output voltage v out output voltage 5 error error flag sense/adj remote sense pin/output adjust pin ordering information 10126731 package type designator is 't' for to220 package, and 's' for to263 package. table 1. package marking and ordering information output voltage order number description (current, option) package type package marking supplied as: 5.0 lp3963es-5.0 3a, error flag to263-5 lp3963es-5.0 rail 5.0 lp3963esx-5.0 3a, error flag to263-5 lp3963esx-5.0 tape and reel 3.3 lp3963es-3.3 3a, error flag to263-5 lp3963es-3.3 rail 3.3 lp3963esx-3.3 3a, error flag to263-5 lp3963es-3.3 tape and reel 2.5 lp3963es-2.5 3a, error flag to263-5 lp3963es-2.5 rail 2.5 lp3963esx-2.5 3a, error flag to263-5 lp3963es-2.5 tape and reel 1.8 lp3963es-1.8 3a, error flag to263-5 lp3963es-1.8 rail 1.8 lp3963esx-1.8 3a, error flag to263-5 lp3963es-1.8 tape and reel 5.0 lp3966es-5.0 3a, sense to263-5 lp3966es-5.0 rail 5.0 lp3966esx-5.0 3a, sense to263-5 lp3966esx-5.0 tape and reel 3.3 lp3966es-3.3 3a, sense to263-5 lp3966es-3.3 rail 3.3 lp3966esx-3.3 3a, sense to263-5 lp3966es-3.3 tape and reel 2.5 lp3966es-2.5 3a, sense to263-5 lp3966es-2.5 rail 2.5 lp3966esx-2.5 3a, sense to263-5 lp3966es-2.5 tape and reel 1.8 lp3966es-1.8 3a, sense to263-5 lp3966es-1.8 rail 1.8 lp3966esx-1.8 3a, sense to263-5 lp3966es-1.8 tape and reel adj lp3966es-adj 3a, adj to263-5 lp3966es-adj rail adj LP3966ESX-ADJ 3a, adj to263-5 lp3966es-adj tape and reel 5.0 lp3963et-5.0 3a, error flag to220-5 lp3963et-5.0 rail 3.3 lp3963et-3.3 3a, error flag to220-5 lp3963et-3.3 rail 2.5 lp3963et-2.5 3a, error flag to220-5 lp3963et-2.5 rail 1.8 lp3963et-1.8 3a, error flag to220-5 lp3963et-1.8 rail lp3963/lp3966 www.national.com 4
ordering information (continued) table 1. package marking and ordering information (continued) output voltage order number description (current, option) package type package marking supplied as: 5.0 lp3966et-5.0 3a, sense to220-5 lp3966et-5.0 rail 3.3 lp3966et-3.3 3a, sense to220-5 lp3966et-3.3 rail 2.5 lp3966et-2.5 3a, sense to220-5 lp3966et-2.5 rail 1.8 lp3966et-1.8 3a, sense to220-5 lp3966et-1.8 rail adj lp3966et-adj 3a, adj to220-5 lp3966et-adj rail lp3963/lp3966 www.national.com 5
absolute maximum ratings (note 1) if military/aerospace specified devices are required, please contact the national semiconductor sales office/ distributors for availability and specifications. storage temperature range ?65c to +150c lead temperature (soldering, 5 sec.) 260c esd rating (note 3) 2 kv power dissipation (note 2) internally limited input supply voltage (survival) ?0.3v to +7.5v shutdown input voltage (survival) ?0.3v to v in +0.3v output voltage (survival), (note 6), (note 7) ?0.3v to +7.5v i out (survival) short circuit protected maximum voltage for error pin v in +0.3v maximum voltage for sense pin v out +0.3v operating ratings input supply voltage (operating), (note 12) 2.5v to 7.0v shutdown input voltage (operating) ?0.3v to v in +0.3v maximum operating current (dc) 3a operating junction temp. range ?40c to +125c electrical characteristics lp3963/lp3966 limits in standard typeface are for t j = 25c, and limits in boldface type apply over the full operating temperature range . unless otherwise specified: v in =v o(nom) + 1.5v, i l = 10 ma, c out =33f, v sd =v in -0.3v. symbol parameter conditions typ (note 4) lp3963/6 (note 5) units min max v o output voltage tolerance (note 8) v out +1.5v < v in < 7.0v 10 ma < i l < 3a 0 -1.5 -3.0 +1.5 +3.0 % v adj adjust pin voltage (adj version) 10 ma i l 3a v out +1.5v v in 7.0v 1.216 1.198 1.180 1.234 1.253 v d v ol output voltage line regulation (note 8) v out +1.5v < v in < 7.0v 0.02 0.06 % d v o / d i out output voltage load regulation (note 8) 10 ma < i l < 3a 0.06 0.01 % v in -v out dropout voltage (note 10) i l = 300 ma 80 100 120 mv i l = 3a 800 1000 1200 i gnd ground pin current in normal operation mode i l = 300 ma 5 9 10 ma i l =3a 6 14 15 i gnd ground pin current in shutdown mode (note 11) v sd 0.2v 15 25 75 a i o(pk) peak output current (note 2) 4.5 4 3.5 a short circuit protection i sc short circuit current 5.5 a over temperature protection tsh(t) shutdown threshold 165 c tsh(h) thermal shutdown hysteresis 10 c lp3963/lp3966 www.national.com 6
electrical characteristics lp3963/lp3966 (continued) limits in standard typeface are for t j = 25c, and limits in boldface type apply over the full operating temperature range . unless otherwise specified: v in =v o(nom) + 1.5v, i l = 10 ma, c out =33f, v sd =v in -0.3v. symbol parameter conditions typ (note 4) lp3963/6 (note 5) units min max shutdown input v sdt shutdown threshold output = high v in v in 0.3 v output = low 0 0.2 t doff turn-off delay i l =3a 20 s t don turn-on delay i l =3a 25 s i sd sd input current v sd =v in 1na error flag v t threshold (note 9) 10 516 % v th threshold hysteresis (note 9) 5 28 % v ef(sat) error flag saturation i sink = 100a 0.02 0.1 v td flag reset delay 1 s i lk error flag pin leakage current 1na i max error flag pin sink current v error = 0.5v 1ma ac parameters psrr ripple rejection v in =v out + 1.5v c out = 100uf v out = 3.3v 60 db v in =v out + 0.3v c out = 100uf v out = 3.3v 40 r n(l/f output noise density f = 120hz 0.8 v e n output noise voltage (rms) bw = 10hz 100khz 150 v (rms) bw = 300hz 300khz 100 note 1: absolute maximum ratings indicate limits beyond which damage to the device may occur. operating ratings indicate conditions for which the device is intended to be functional, but does not guarantee specific performance limits. for guaranteed specifications and test conditions, see electrical c haracteristics. the guaranteed specifications apply only for the test conditions listed. some performance characteristics may degrade when the device is not operated u nder the listed test conditions. note 2: at elevated temperatures, devices must be derated based on package thermal resistance. the devices in to220 package must be derated at q ja = 50c/w (with 0.5in 2 , 1oz. copper area), junction-to-ambient (with no heat sink). the devices in the to263 surface-mount package must be derated at q ja = 60c/w (with 0.5in 2 , 1oz. copper area), junction-to-ambient. see application hints. note 3: the human body model is a 100pf capacitor discharged through a 1.5k w resistor into each pin. note 4: typical numbers are at 25c and represent the most likely parametric norm. note 5: limits are 100% production tested at 25c. limits over the operating temperature range are guaranteed through correlation using statistical qualit y control (sqc) methods. the limits are used to calculate national's average outgoing quality level (aoql). note 6: if used in a dual-supply system where the regulator load is returned to a negative supply, the lp396x output must be diode-clamped to ground. note 7: the output pmos structure contains a diode between the v in and v out terminals. this diode is normally reverse biased. this diode will get forward biased if the voltage at the output terminal is forced to be higher than the voltage at the input terminal. this diode can typically withstand 200ma of dc curren t and 1amp of peak current. note 8: output voltage line regulation is defined as the change in output voltage from the nominal value due to change in the input line voltage. output voltage load regulation is defined as the change in output voltage from the nominal value due to change in load current. the line and load regulation specification c ontains only the typical number. however, the limits for line and load regulation are included in the output voltage tolerance specification. note 9: error flag threshold and hysteresis are specified as percentage of regulated output voltage. see application hints. note 10: dropout voltage is defined as the minimum input to output differential voltage at which the output drops 2% below the nominal value. dropout voltage specification applies only to output voltages of 2.5v and above. for output voltages below 2.5v, the drop-out voltage is nothing but the input to outpu t differential, since the minimum input voltage is 2.5v. note 11: this specification has been tested for ?40c t j 85c since the temperature rise of the device is negligible under shutdown conditions. note 12: the minimum operating value for v in is equal to either [v out(nom) +v dropout ] or 2.5v, whichever is greater. lp3963/lp3966 www.national.com 7
typical performance characteristics unless otherwise specified, v in =v o(nom) + 1.5v, v out = 2.5v, c out = 33f, i out = 10ma, c in = 68f, v sd =v in , and t a = 25c. drop-out voltage vs temperature for different load currents drop-out voltage vs temperature (i l = 100ma, 1a, v out = 2.5v, dropout at 50mv down) 10126709 10126710 ground pin current vs input voltage (v sd =v in ) ground pin current vs input voltage (v sd =100mv) 10126711 10126715 ground current vs temperature (v sd =v in ) ground current vs temperature (v sd =0v) 10126718 10126712 lp3963/lp3966 www.national.com 8
typical performance characteristics unless otherwise specified, v in =v o(nom) + 1.5v, v out = 2.5v, c out = 33f, i out = 10ma, c in = 68f, v sd =v in , and t a = 25c. (continued) ground pin current vs shutdown pin voltage input voltage vs output voltage 10126716 10126717 output noise density, v out = 2.5v output noise density, v out =5v 10126713 10126714 load transient response ripple rejection vs frequency 10126737 10126738 lp3963/lp3966 www.national.com 9
typical performance characteristics unless otherwise specified, v in =v o(nom) + 1.5v, v out = 2.5v, c out = 33f, i out = 10ma, c in = 68f, v sd =v in , and t a = 25c. (continued) d v out vs temperature noise density v in = 3.5v, v out = 2.5v, i l =10ma 10126739 10126740 line transient response line transient response 10126741 10126742 line transient response (i out = 3.0a) line transient response (i out = 3.0a) 10126743 10126744 lp3963/lp3966 www.national.com 10
application hints external capacitors like any low-dropout regulator, external capacitors are re- quired to assure stability. these capacitors must be correctly selected for proper performance. input capacitor: the lp3963/6 requires a low source impedance to maintain regulator stability because the inter- nal bias circuitry is connected directly to v in . the input capacitor must be located less than 1 cm from the lp3963/6 device and connected directly to the input and ground pins using traces which have no other currents flowing through them (see pcb layout section). the minimum allowable input capacitance for a given appli- cation depends on the type of the capacitor and esr (equivalent series resistance). a lower esr capacitor allows the use of less capacitance, while higher esr types (like aluminum electrolytics) require more capacitance. the lowest value of input capacitance that can be used for stable full-load operation is 68 f (assuming it is a ceramic or low-esr tantalum with esr less than 100 m w ). to determine the minimum input capacitance amount and esr value, an approximation which should be used is: c in esr (m w )/c in (f) 1.5 this shows that input capacitors with higher esr values can be used if sufficient total capacitance is provided. capacitor types (aluminum, ceramic, and tantalum) can be mixed in parallel, but the total equivalent input capacitance/esr must be defined as above to assure stable operation. important: the input capacitor must maintain its esr and capacitance in the 'stable range' over the entire temperature range of the application to assure stability (see capacitor characteristics section). output capacitor: an output capacitor is also required for loop stability. it must be located less than 1 cm from the lp3963/6 device and connected directly to the output and ground pins using traces which have no other currents flow- ing through them (see pcb layout section). the minimum value of the output capacitance that can be used for stable full-load operation is 33 f, but it may be increased without limit. the output capacitor's esr is critical because it forms a zero to provide phase lead which is required for loop stability. the esr must fall within the specified range: 0.2 w c out esr 5 w the lower limit of 200 m w means that ceramic capacitors are not suitable for use as lp3963/6 output capacitors (but can be used on the input). some ceramic capacitance can be used on the output if the total equivalent esr is in the stable range: when using a 100 f tantalum as the output capaci- tor, approximately 3 f of ceramic capacitance can be ap- plied before stability becomes marginal. important: the output capacitor must meet the require- ments for minimum amount of capacitance and also have an appropriate esr value over the full temperature range of the application to assure stability (see capacitor characteristics section). selecting a capacitor it is important to note that capacitance tolerance and varia- tion with temperature must be taken into consideration when selecting a capacitor so that the minimum required amount of capacitance is provided over the full operating tempera- ture range. in general, a good tantalum capacitor will show very little capacitance variation with temperature, but a ce- ramic may not be as good (depending on dielectric type). aluminum electrolytics also typically have large temperature variation of capacitance value. equally important to consider is a capacitor's esr change with temperature: this is not an issue with ceramics, as their esr is extremely low. however, it is very important in tan- talum and aluminum electrolytic capacitors. both show in- creasing esr at colder temperatures, but the increase in aluminum electrolytic capacitors is so severe they may not be feasible for some applications (see capacitor character- istics section). capacitor characteristics ceramic: for values of capacitance in the 10 to 100 f range, ceramics are usually larger and more costly than tantalums but give superior ac performance for bypassing high frequency noise because of very low esr (typically less than 10 m w ). however, some dielectric types do not have good capacitance characteristics as a function of voltage and temperature. z5u and y5v dielectric ceramics have capacitance that drops severely with applied voltage. a typical z5u or y5v capacitor can lose 60% of its rated capacitance with half of the rated voltage applied to it. the z5u and y5v also exhibit a severe temperature effect, losing more than 50% of nomi- nal capacitance at high and low limits of the temperature range. x7r and x5r dielectric ceramic capacitors are strongly rec- ommended if ceramics are used, as they typically maintain a capacitance range within 20% of nominal over full operat- ing ratings of temperature and voltage. of course, they are typically larger and more costly than z5u/y5u types for a given voltage and capacitance. tantalum: solid tantalum capacitors are recommended for use on the output because their typical esr is very close to the ideal value required for loop compensation. they also work well as input capacitors if selected to meet the esr requirements previously listed. tantalums also have good temperature stability: a good quality tantalum will typically show a capacitance value that varies less than 10-15% across the full temperature range of 125c to ?40c. esr will vary only about 2x going from the high to low temperature limits. the increasing esr at lower temperatures can cause oscil- lations when marginal quality capacitors are used (if the esr of the capacitor is near the upper limit of the stability range at room temperature). aluminum: this capacitor type offers the most capaci- tance for the money. the disadvantages are that they are larger in physical size, not widely available in surface mount, and have poor ac performance (especially at higher fre- quencies) due to higher esr and esl. compared by size, the esr of an aluminum electrolytic is higher than either tantalum or ceramic, and it also varies greatly with temperature. a typical aluminum electrolytic can exhibit an esr increase of as much as 50x when going from 25c down to ?40c. it should also be noted that many aluminum electrolytics only specify impedance at a frequency of 120 hz, which indicates they have poor high frequency performance. only aluminum electrolytics that have an impedance specified at a higher frequency (between 20 khz and 100 khz) should be used for lp3963/lp3966 www.national.com 11
application hints (continued) the lp396x. derating must be applied to the manufacturer's esr specification, since it is typically only valid at room temperature. any applications using aluminum electrolytics should be thoroughly tested at the lowest ambient operating tempera- ture where esr is maximum. pcb layout good pc layout practices must be used or instability can be induced because of ground loops and voltage drops. the input and output capacitors must be directly connected to the input, output, and ground pins of the lp3963/6 using traces which do not have other currents flowing in them kelvin connect). the best way to do this is to lay out c in and c out near the device with short traces to the v in ,v out , and ground pins. the regulator ground pin should be connected to the exter- nal circuit ground so that the regulator and its capacitors have a 'single point ground'. it should be noted that stability problems have been seen in applications where 'vias' to an internal ground plane were used at the ground points of the lp3963/6 ic and the input and output capacitors. this was caused by varying ground potentials at these nodes resulting from current flowing through the ground plane. using a single point ground tech- nique for the regulator and it's capacitors fixed the problem. since high current flows through the traces going into v in and coming from v out , kelvin connect the capacitor leads to these pins so there is no voltage drop in series with the input and output capacitors. rfi/emi susceptibility rfi (radio frequency interference) and emi (electromagnetic interference) can degrade any integrated circuit's perfor- mance because of the small dimensions of the geometries inside the device. in applications where circuit sources are present which generate signals with significant high fre- quency energy content ( > 1 mhz), care must be taken to ensure that this does not affect the ic regulator. if rfi/emi noise is present on the input side of the lp396x regulator (such as applications where the input source comes from the output of a switching regulator), good ce- ramic bypass capacitors must be used at the input pin of the lp396x. if a load is connected to the lp396x output which switches at high speed (such as a clock), the high-frequency current pulses required by the load must be supplied by the capaci- tors on the lp396x output. since the bandwidth of the regulator loop is less than 100 khz, the control circuitry cannot respond to load changes above that frequency. the means the effective output impedance of the lp396x at frequencies above 100 khz is determined only by the output capacitor(s). in applications where the load is switching at high speed, the output of the lp396x may need rf isolation from the load. it is recommended that some inductance be placed between the lp396x output capacitor and the load, and good rf bypass capacitors be placed directly across the load. pcb layout is also critical in high noise environments, since rfi/emi is easily radiated directly into pc traces. noisy circuitry should be isolated from 'clean' circuits where pos- sible, and grounded through a separate path. at mhz fre- quencies, ground planes begin to look inductive and rfi/emi can cause ground bounce across the ground plane. in multi-layer pcb applications, care should be taken in layout so that noisy power and ground planes do not radiate directly into adjacent layers which carry analog power and ground. output adjustment an adjustable output device has output voltage range of 1.215v to 5.1v. to obtain a desired output voltage, the following equation can be used with r1 always a 10k w resistor. for output stability, c f must be between 68pf and 100pf. output noise noise is specified in two ways- spot noise or output noise density is the rms sum of all noise sources, measured at the regulator output, at a spe- cific frequency (measured with a 1hz bandwidth). this type of noise is usually plotted on a curve as a function of fre- quency. total output noise or broad-band noise is the rms sum of spot noise over a specified bandwidth, usually several decades of frequencies. attention should be paid to the units of measurement. spot noise is measured in units v/ ? hz or nv/ ? hz and total output noise is measured in v(rms). the primary source of noise in low-dropout regulators is the internal reference. in cmos regulators, noise has a low frequency component and a high frequency component, which depend strongly on the silicon area and quiescent current. noise can be reduced in two ways: by increasing the transistor area or by increasing the current drawn by the internal reference. increasing the area will decrease the chance of fitting the die into a smaller package. increasing the current drawn by the internal reference increases the total supply current (ground pin current). using an optimized trade-off of ground pin current and die size, lp3963/lp3966 achieves low noise performance and low quiescent current operation. the total output noise specification for lp3963/lp3966 is presented in the electrical characteristics table. the output noise density at different frequencies is represented by a curve under typical performance characteristics. short-circuit protection the lp3963 and lp3966 is short circuit protected and in the event of a peak over-current condition, the short-circuit con- trol loop will rapidly drive the output pmos pass element off. once the power pass element shuts down, the control loop will rapidly cycle the output on and off until the average power dissipation causes the thermal shutdown circuit to respond to servo the on/off cycling to a lower frequency. please refer to the section on thermal information for power dissipation calculations. error flag operation the lp3963/lp3966 produces a logic low signal at the error flag pin when the output drops out of regulation due to low input voltage, current limiting, or thermal limiting. this flag lp3963/lp3966 www.national.com 12
application hints (continued) has a built in hysteresis. the timing diagram in figure 1 shows the relationship between the error flag and the output voltage. in this example, the input voltage is changed to demonstrate the functionality of the error flag. the internal error flag comparator has an open drain output stage. hence, the error pin should be pulled high through a pull up resistor. although the error flag pin can sink current of 1ma, this current is energy drain from the input supply. hence, the value of the pull up resistor should be in the range of 10k w to 1m w . the error pin must be connected to ground if this function is not used. it should also be noted that when the shutdown pin is pulled low, the error pin is forced to be invalid for reasons of saving power in shutdown mode. sense pin in applications where the regulator output is not very close to the load, lp3966 can provide better remote load regulation using the sense pin. figure 2 depicts the advantage of the sense option. lp3963 regulates the voltage at the output pin. hence, the voltage at the remote load will be the regu- lator output voltage minus the drop across the trace resis- tance. for example, in the case of a 3.3v output, if the trace resistance is 100m w , the voltage at the remote load will be 3v with 3a of load current, i load . the lp3966 regulates the voltage at the sense pin. connecting the sense pin to the remote load will provide regulation at the remote load, as shown in figure 2 . if the sense option pin is not required, the sense pin must be connected to the v out pin. 10126707 figure 1. error flag operation lp3963/lp3966 www.national.com 13
application hints (continued) shutdown operation a cmos logic level signal at the shutdown ( sd) pin will turn-off the regulator. pin sd must be actively terminated through a 10k w pull-up resistor for a proper operation. if this pin is driven from a source that actively pulls high and low (such as a cmos rail to rail comparator), the pull-up resistor is not required. this pin must be tied to vin if not used. dropout voltage the dropout voltage of a regulator is defined as the minimum input-to-output differential required to stay within 2% of the nominal output voltage. the lp3963/lp3966 use an internal mosfet with an rds(on) of 240m w (typically). for cmos ldos, the dropout voltage is the product of the load current and the rds(on) of the internal mosfet. reverse current path the internal mosfet in lp3963 and lp3966 has an inher- ent parasitic diode. during normal operation, the input volt- age is higher than the output voltage and the parasitic diode is reverse biased. however, if the output is pulled above the input in an application, then current flows from the output to the input as the parasitic diode gets forward biased. the output can be pulled above the input as long as the current in the parasitic diode is limited to 200ma continuous and 1a peak. power dissipation/heatsinking lp3963 and lp3966 can deliver a continuous current of 3a over the full operating temperature range. a heatsink may be required depending on the maximum power dissipation and maximum ambient temperature of the application. under all possible conditions, the junction temperature must be within the range specified under operating conditions. the total power dissipation of the device is given by: p d =(v in ?v out )i out +(v in )i gnd where i gnd is the operating ground current of the device (specified under electrical characteristics). the maximum allowable temperature rise (t rmax ) depends on the maximum ambient temperature (t amax ) of the appli- cation, and the maximum allowable junction temperature (t jmax ): t rmax =t jmax ?t amax the maximum allowable value for junction to ambient ther- mal resistance, q ja , can be calculated using the formula: q ja =t rmax /p d lp3963 and lp3966 are available in to-220 and to-263 packages. the thermal resistance depends on amount of copper area or heat sink, and on air flow. if the maximum allowable value of q ja calculated above is 3 60 c/w for to-220 package and 3 60 c/w for to-263 package no heatsink is needed since the package can dissipate enough heat to satisfy these requirements. if the value for allowable q ja falls below these limits, a heat sink is required. heatsinking to-220 package the thermal resistance of a to220 package can be reduced by attaching it to a heat sink or a copper plane on a pc board. if a copper plane is to be used, the values of q ja will be same as shown in next section for to263 package. the heatsink to be used in the application should have a heatsink to ambient thermal resistance, q ha q ja ? q ch ? q jc . in this equation, q ch is the thermal resistance from the case to the surface of the heat sink and q jc is the thermal resis- tance from the junction to the surface of the case. q jc is about 3c/w for a to220 package. the value for q ch de- pends on method of attachment, insulator, etc. q ch varies between 1.5c/w to 2.5c/w. if the exact value is unknown, 2c/w can be assumed. heatsinking to-263 package the to-263 package uses the copper plane on the pcb as a heatsink. the tab of these packages are soldered to the copper plane for heat sinking. figure 3 shows a curve for the 10126708 figure 2. improving remote load regulation using lp3966 lp3963/lp3966 www.national.com 14
application hints (continued) q ja of to-263 package for different copper area sizes, using a typical pcb with 1 ounce copper and no solder mask over the copper area for heat sinking. as shown in the figure, increasing the copper area beyond 1 square inch produces very little improvement. the minimum value for q ja for the to-263 package mounted to a pcb is 32c/w. figure 4 shows the maximum allowable power dissipation for to-263 packages for different ambient temperatures, assuming q ja is 35c/w and the maximum junction tempera- ture is 125c. 10126732 figure 3. q ja vs copper (1 ounce) area for to-263 package 10126733 figure 4. maximum power dissipation vs ambient temperature for to-263 package lp3963/lp3966 www.national.com 15
physical dimensions inches (millimeters) unless otherwise noted to220 5-lead, molded, stagger bend package (to220-5) ns package number t05d for order numbers, refer to the aordering informationo section of this document. lp3963/lp3966 www.national.com 16
physical dimensions inches (millimeters) unless otherwise noted (continued) to263 5-lead, molded, surface mount package (to263-5) ns package number ts5b for order numbers, refer to the aordering informationo section of this document. life support policy national's products are not authorized for use as critical components in life support devices or systems without the express written approval of the president and general counsel of national semiconductor corporation. as used herein: 1. life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 2. a critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. national semiconductor corporation americas email: support@nsc.com national semiconductor europe fax: +49 (0) 180-530 85 86 email: europe.support@nsc.com deutsch tel: +49 (0) 69 9508 6208 english tel: +44 (0) 870 24 0 2171 fran?ais tel: +33 (0) 1 41 91 8790 national semiconductor asia pacific customer response group tel: 65-2544466 fax: 65-2504466 email: ap.support@nsc.com national semiconductor japan ltd. tel: 81-3-5639-7560 fax: 81-3-5639-7507 www.national.com lp3963/lp3966 3a fast ultra low dropout linear regulators national does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and national reserves the righ t at any time without notice to change said circuitry and specifications.

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