View AAT2504_4553276.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

AAT2504 adjustable 3-channel regulator 2504.2007.06.1.0 1 systempower ? general description the AAT2504 is a three-channel regulator consist- ing of a step-down converter with an input voltage range of 2.7v to 5.5v plus two low dropout (ldo) linear regulators. the two ldos have an input volt- age range of 1.8v to 5.5v, making them well-suited for post regulating from the step-down converter. the step-down converter optimizes power efficiency throughout the load range. pulling the mode/sync pin high enables "pwm only" operation, maintaining constant frequency and low output ripple across the operating range. alternatively, the converter may be synchronized to an external clock to the mode/ sync pin. the step-down converter delivers up to 800ma of output current. the switching frequency is 2mhz, minimizing the size of external components. the two ldos (ldoa/ldob) have independent inputs and are capable of delivering up to 300ma each. a power-ok (pok) function provides an open drain output signal when ldoa is within regulation. both ldos feature low quiescent current and a low dropout voltage. the output voltages for both ldos are adjustable to as low as 0.6v. the linear regula- tors have independent enable pins. typical no load quiescent current is a low 80a when the step- down converter and ldos are enabled. the AAT2504 is available in a pb-free 3x4mm qfn34-20 package and is rated over the -40c to +85c temperature range. features ? 800ma buck converter v in range: 2.7v to 5.5v v out range: 0.9v to v in , adjustable high efficiency: 95% 2mhz switching frequency synchronizable to external clock internal soft start ? two 300ma linear regulators v in range: 1.8v to 5.5v low dropout voltage high output accuracy: 1.5% ? low total quiescent current i q (80a) ? independent enable pins ? over-temperature protection ? qfn34-20 package ? -40c to +85c temperature range applications ? cellular phones ? digital cameras ? handheld instruments ? microprocessor/dsp core/io power ? pdas and handheld computers typical application AAT2504 r 2b r 1b r 2a r 1a 2.2 f outa outb pok pok outa outb agnd vldoa vldob lx fb l v out (step-down) pgnd vin vp fbb c out fba r 2 r 1 2.2 f enb en ena v in 100k mode/sync
pin descriptions pin # symbol function 1 fbb feedback input pin for ldob. this pin is used to regulate the output of ldob to the desired value via an external resistor divider. 2 ena enable pin for ldoa. active high. 3 enb enable pin for ldob. active high. 4 mode/sync pwm operation and oscillator synchronization pin. connect to ground for pwm/light load operation and optimized efficiency throughout the load range. connect high for low noise pwm operation under all operating conditions. when connected to an external clock, the internal oscillator is disabled and the step-down converter is synchronized to an external clock applied to this pin (pwm only). 5 fb feedback input pin for the step-down converter. this pin is used to see the output of the converter to regulate to the desired value via an external resistor divider. 6 agnd ground connection pin. 7 pgnd main power ground return pin for the step-down converter. connect to the output and input capacitor return. 8, 9 lx connect inductor to this pin. switching node internally connected to the drain of both high- and low-side mosfets. 10 vp input supply voltage for the converter. must be closely decoupled. 11, 12 n/c not connected. 13 vin bias supply. supply power for the internal circuitry. connect to input power via low pass filter with decoupling to agnd. 14 en enable for the step-down converter. active high. 15 pok power-ok pin with open drain output. it is pulled low when the outa pin is outside the regu- lation window. place a pull-up resistor between pok and outa. 16 fba feedback input pin for ldoa. this pin is used to regulate the output of ldoa to the desired value via an external resistor divider. 17 outa ldoa output pin; should be closely decoupled with a low-esr ceramic capacitor. 18 vldoa input voltage pin for linear regulator a; should be closely decoupled. 19 vldob input voltage pin for linear regulator b; should be closely decoupled. 20 outb ldob output pin; should be closely decoupled with a low-esr ceramic capacitor. ep exposed paddle; connect to ground directly beneath the package. AAT2504 adjustable 3-channel regulator 2 2504.2007.06.1.0
pin configuration qfn34-20 (top view) absolute maximum ratings 1 thermal information symbol description value units p d maximum power dissipation (t a = 25c) 2.0 w ja thermal resistance 2 50 c/w symbol description value units v p , v in , v ldo input voltage and bias power to gnd 6.0 v v lx lx to gnd -0.3 to v p + 0.3 v v fb fb to gnd -0.3 to v p + 0.3 v v en en and en_ldo to gnd -0.3 to 6.0 v t j operating junction temperature range -40 to 150 c t lead maximum soldering temperature (at leads, 10 sec) 300 c AAT2504 adjustable 3-channel regulator 2504.2007.06.1.0 3 1. stresses above those listed in absolute maximum ratings may cause permanent damage to the device. functional operation at co ndi- tions other than the operating conditions specified is not implied. only one absolute maximum rating should be applied at any o ne time. 2. mounted on an fr4 board. 1 3 2 5 4 6 16 14 15 12 13 11 9 10 7 8 18 17 20 19 fbb ena enb mode/sync fb agnd pgnd lx lx vp vin en n/c n/c po k fba outa vldoa vldob outb
electrical characteristics 1 v in = 3.6v; t a = -40c to +85c, unless otherwise noted. typical values are t a = 25c. symbol description conditions min typ max units bias power supply i q quiescent current ena = enb = en = v in ; i load = 0 80 145 a i shdn shutdown current ena = enb = en = gnd 1.0 a v in rising 2.2 v uvlo under-voltage lockout voltage hysteresis 250 mv v in falling 1.7 v ldoa, ldob v ldo input voltage 1.8 5.5 v v out output voltage tolerance i out = 1ma t a = 25c -1.5 1.5 % to 300ma t a = -40c to +85c -2.5 2.5 v fb feedback voltage 0.593 0.6 0.607 v v do dropout voltage 2, 3 i out = 300ma 300 mv v linereg / v in line regulation 4 v in = v out + 1 to 5.0v 0.09 %/v v en(l) enable threshold low 0.6 v v en(h) enable threshold high 1.4 v i out output current v ldo (min) = 2.5 300 ma i sht shutdown current v in = 5v 1.0 a t sd over-temperature shutdown 140 c threshold t hys over-temperature shutdown 15 c hysteresis ldoa v pok power-ok trip threshold v out rising, t a = 25c 80 90 98 % of v out v pokhys power-ok hysteresis 1.0 % of v out v pok(lo) power-ok output voltage low i sink = 1ma 0.4 v i pok power-ok output leakage current v pok <5.5v, v out in regulation 1.0 a AAT2504 adjustable 3-channel regulator 4 2504.2007.06.1.0 1. the AAT2504 is guaranteed to meet performance specifications over the -40c to +85c operating temperature range and is assu red by design, characterization, and correlation with statistical process controls. 2. v do is defined as v in - v out when v out is 98% of nominal. 3. for v out < 1.5v, v do = 1.8 - v out . 4. c in = 10f.
electrical characteristics (continued) 1 v in = 3.6v; t a = -40c to +85c, unless otherwise noted. typical values are t a = 25c. symbol description conditions min typ max units step-down converter v in input voltage 2.7 5.5 v v out output voltage tolerance i out = 0 to 800ma; -3.0 3.0 % v in = 2.7v to 5.5v v out v out programmable range 0.9 v in v v fb feedback threshold voltage 0.891 0.9 0.909 v i shdn shutdown current en = gnd 1.0 a i lx _ leak lx leakage current v in = 5.5, v lx = 0 - v in 1.0 a i fb feedback leakage v fb = 1.0v 0.2 a i lim current limit 1.2 a r ds(on)h high side switch on resistance 280 m r ds(on)l low side switch on resistance 160 m v loadreg / load regulation i load = 10 to 800ma 0.2 % v out v linereg / v in line regulation 0.2 %/v f osc oscillator frequency 1.6 2.0 2.4 mhz t sd over-temperature shutdown 140 c threshold t hys over-temperature shutdown 15 c hysteresis v en(l) enable threshold low 0.6 v v en(h) enable threshold high 1.4 v i en en input leakage v en = 5v, v in = 5v -1.0 1.0 a AAT2504 adjustable 3-channel regulator 2504.2007.06.1.0 5 1. the AAT2504 is guaranteed to meet performance specifications over the -40c to +85c operating temperature range and is assu red by design, characterization, and correlation with statistical process controls.
typical characteristicsCstep-down converter AAT2504 adjustable 3-channel regulator 6 2504.2007.06.1.0 step-down converter output ripple (v in = 3.6v; v out = 1.8v; i out = 800ma) time (200ns/div) inductor current (bottom) (a) output voltage (top) (v) 1.79 1.80 1.81 1.82 0.2 0.4 0.6 0.8 1.0 v out i inductor step-down converter load transient (v in = 3.6v; i out = 300ma to 650ma) time (20s/div) output voltage (top) (v) load and inductor current (bottom) (a) 1.6 1.8 2.0 2.2 0.0 0.3 0.6 0.9 v out i out i l step-down converter load regulation (v out = 2.5v; forced pwm) output current (ma) output voltage error (%) -0.3 -0.2 -0.1 0.0 0.1 0.2 0.1 1 10 100 1000 v in = 3v v in = 3.6v v in = 5.5v v in = 4.2v step-down converter line regulation (v out = 2.5v; forced pwm) input voltage (v) output voltage error (%) -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 2.8 3.1 3.4 3.7 4.0 4.3 4.6 4.9 5.2 5.5 800ma 600ma 100ma 50ma 1ma step-down converter efficiency vs. output current (v out = 1.8v) output current (ma) efficiency (%) 0 10 20 30 40 50 60 70 80 90 100 0.1 1 10 100 1000 v in = 2.7v v in = 3.6v v in = 4.2v v in = 5.5v pwm/light load mode forced pwm mode output voltage error vs. temperature (v in = 3.6v; v out = 2.5v) temperature (c) output error (%) -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 -40 -15 10 35 60 85 800ma 600ma 400ma 100ma
typical characteristicsCstep-down converter AAT2504 adjustable 3-channel regulator 2504.2007.06.1.0 7 step-down converter soft start (v in = 3.6v; v out = 1.8v; i out = 800ma) time (50s/div) inductor current (bottom) (a) enable (top) (v) v out (middle) (v) 0 2 4 6 0.0 0.5 1.0 1.5 en v out i l 0v 1.8v step-down converter turn-off (v in = 3.6v; v out = 1.8v; i out = 800ma) time (100s/div) inductor current (bottom) (a) enable (top) (v) v out (middle) (v) 0 2 4 6 0.0 0.5 1.0 en v out i l 0v 1.8v no load quiescent current vs. input voltage (step-down converter enabled; both ldos disabled) input voltage (v) quiescent current (a) 20 30 40 50 60 70 80 90 100 110 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 85c 25c -40c step-down converter switching frequency vs. temperature (v in = 3.6v; v out = 1.2v) temperature (oc) switching frequency (mhz) 1.75 1.80 1.85 1.90 1.95 2.00 2.05 -40 -15 10 35 60 8 5 800ma 600ma 400ma step-down converter line transient (v out = 1.8v; i out = 800ma; v in = 3.6v-4.2v) time (20s/div) input voltage (top) (v) output voltage (ac coupled) (bottom) (v) 3.5 4.0 4.5 5.0 -0.02 0.00 0.02 no load quiescent current vs. input voltage (step-down converter enabled; both ldos enabled) input voltage (v) quiescent current (a) 0 20 40 60 80 100 120 140 160 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 85c 25c -40c
typical characteristicsCstep-down converter AAT2504 adjustable 3-channel regulator 8 2504.2007.06.1.0 high side switch on resistance vs. input voltage input voltage (v) r ds(on)h (m ) 220 240 260 280 300 320 340 360 380 400 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 120c 100c 85c 25c low side switch on resistance vs. input voltage input voltage (v) r ds(on)l (m ) 50 100 150 200 250 300 350 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 120c 100c 85c 25c
typical characteristicsCldo regulator AAT2504 adjustable 3-channel regulator 2504.2007.06.1.0 9 output voltage vs. input voltage (v out = 3.3v) input voltage (v) output voltage (v) 2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.1 3.3 3.5 3.7 3.9 4.1 300ma 200ma 100ma 50ma 1ma dropout voltage vs. output current (v out = 3.3v) output current (ma) dropout voltage (mv) 0 20 40 60 80 100 120 140 160 0 50 100 150 200 250 300 25c 85c -40c dropout voltage vs. output current (v out = 2.5v) output current (ma) dropout voltage (mv) 0 20 40 60 80 100 120 140 160 180 200 0 50 100 150 200 250 300 25c 85c -40c output voltage vs. input voltage (v out = 2.5v) input voltage (v) output voltage (v) 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.5 2.7 2.9 3.1 3.3 3.5 300ma 250ma 200ma 100ma 50ma ldo output voltage variation vs. temperature (v out = 2.5v) temperature (c) output voltage error (%) -0.30 -0.25 -0.20 -0.15 -0.10 -0.05 0.00 0.05 0.10 -40 -15 10 35 60 85 300ma 200ma 100ma ldo line regulation (v out = 2.5v) input voltage (v) output voltage error (%) -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 300ma 200ma 50ma 100ma 10ma 1ma
typical characteristicsCldo regulator AAT2504 adjustable 3-channel regulator 10 2504.2007.06.1.0 turn-on time (v in = 3.6v; v out = 1.8v; i out = 300ma) time (25s/div) output voltage (bottom) (v) enable (top) (v) 0 2 4 0.0 0.5 1.0 1.5 2.0 turn-off time (v in = 3.6v; v out = 1.8v; i out = 300ma) time (25s/div) output voltage (top) (v) enable (bottom) (v) 0.0 0.5 1.0 1.5 2.0 0 2 4 ldo load regulation (v out = 2.5v) output current (ma) output voltage error (%) -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.1 1 10 100 1000 v in = 5.5v v in = 3.6v v in = 2.7v v in = 4.2v ldo load transient (v out = 1.8v) time (50s/div) output voltage (ac coupled) (top) (mv) output current (bottom) (a) -25 0 25 50 0.0 0.1 0.2 0.3 ldo line transient (v out = 1.8v; i out = 300ma) time (50s/div) output voltage (ac coupled) (top) (mv) input voltage (bottom) (v) -50 0 50 100 3.0 3.5 4.0 4.5 no load quiescent current vs. input voltage (both ldos enabled, step-down converter disabled) input voltage (v) quiescent current (a) 10 15 20 25 30 35 40 45 50 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 85c 25c -40c
AAT2504 adjustable 3-channel regulator 2504.2007.06.1.0 11 functional block diagram functional description the AAT2504 is a high performance power man- agement ic comprised of a step-down converter and two linear regulators. the step-down convert- er operates in both fixed and variable frequency modes for high efficiency performance. the switch- ing frequency is 2mhz, minimizing the size of the inductor. the converter requires only three external power components (c in , c out , and l). each ldo can deliver up to 300ma. each regulator has inde- pendent input voltage and enable pins and oper- ates with ceramic capacitors. switch-mode step-down converter the switching regulator is a monolithic step-down converter operating with input voltage range of 2.7v to 5.5v. power devices are sized for 800ma current capability and achieves over 95% efficiency. the internal oscillator operates at 2mhz, minimizing the cost and size of external components. light load operation maintains high efficiency under light load conditions (typically <50ma) when mode/sync is grounded. the mode/sync pin tied high allows optional "pwm only" operation. this maintains con- stant frequency and low output ripple across all load conditions. alternatively, by connecting an external clock to the AAT2504's mode/sync pin, the inter- nal clock is disabled. the external synchronization must stay between 1mhz and 3mhz. the current through the p-channel mosfet (high side) is sensed for current loop control, as well as short-circuit and overload protection. a fixed slope compensation signal is added to the sensed current to maintain stability for duty cycles greater than 50%. the peak current mode loop appears as a voltage-programmed current source in parallel with the output capacitor. the output of the voltage error amplifier programs the current mode loop for the necessary peak switch current to force a constant output voltage for all load and line conditions. internal loop compen- en vldoa outb mode/sync pok lx logic dh dl pgnd vp agnd outa vldob fbb fba ena enb vin control logic voltage reference voltage reference 90% v ref err. amp. err. amp. err. amp. over-current protection over-current protection fb
AAT2504 adjustable 3-channel regulator 12 2504.2007.06.1.0 sation terminates the transconductance voltage error amplifier output. the internal error amplifier reference is fixed at 0.9v. a logic low on the en pin shuts the converter down and makes it consume less than 1a of current. soft start increases the inductor current limit point in discrete steps when the input voltage or enable input is applied. it limits the current surge seen at the input and eliminates output voltage overshoot. for overload conditions, the peak input current is limited. as load impedance decreases and the out- put voltage falls closer to zero, more power is dis- sipated internally, raising the device temperature. thermal protection completely disables switching when internal dissipation becomes excessive, pro- tecting the device from damage. the junction over-temperature threshold is 140c with 15c of hysteresis. linear regulators the two linear regulators are high performance ldos where each ldo sources 300ma of current. for added flexibility, both regulators have inde- pendent input voltages operating from 1.8v to 5.5v. an external feedback pin for each ldo allows pro- gramming the output voltage from 3.6v to 0.6v. the regulators have thermal protection in case of adverse operating conditions. ldoa features an integrated power-ok compara- tor which indicates when the output is out of regu- lation. the pok is an open drain output and it is held low when the AAT2504 is in shutdown mode. under-voltage lockout internal bias of all circuits is controlled via the vin pin. under-voltage lockout guarantees sufficient v in bias and proper operation of all internal circuits prior to activation. over-temperature protection thermal protection completely disables switching when internal dissipation becomes excessive. the junction over-temperature threshold is 140c with 15c of hysteresis. once an over-temperature or over-current fault condition is removed, the output voltage automatically recovers. applications information step-down converter inductor selection the step-down converter uses peak current mode control with slope compensation to maintain stabil- ity for duty cycles greater than 50%. the output inductor value must be selected so the inductor current down slope meets the internal slope com- pensation requirements. the internal slope com- pensation for the AAT2504 step-down converter is 0.51a/sec. this equates to a slope compensation that is 75% of the inductor current down slope for a 1.5v output and 2.2h inductor. manufacturer's specifications list both the inductor dc current rating, which is a thermal limitation, and the peak current rating, which is determined by the saturation characteristics. the inductor should not show any appreciable saturation under normal load conditions. some inductors may meet the peak and average current ratings yet result in excessive loss- es due to a high dcr. always consider the losses associated with the dcr and its effect on the total converter efficiency when selecting an inductor. the 2.2h cdrh2d14 series sumida inductor has a 94m dcr and a 1.5a dc current rating. at full 800ma load, the inductor dc loss is 60mw which gives a 4.16% loss in efficiency for a 800ma, 1.8v output. input capacitor select a 4.7f to 10f x7r or x5r ceramic capac- itor for the input of the step-down converter. to esti- mate the required input capacitor size, determine the acceptable input ripple level (v pp ) and solve for c in . the calculated value varies with input voltage and is a maximum when v in is double the output voltage. 0.75 ? v o m = = = 0.51 l 0.75 ? 1.5v 2.2 h a sec
AAT2504 adjustable 3-channel regulator 2504.2007.06.1.0 13 always examine the ceramic capacitor dc voltage coefficient characteristics when selecting the prop- er value. for example, the capacitance of a 10f, 6.3v, x5r ceramic capacitor with 5.0v dc applied is actually about 6f. the maximum input capacitor rms current is: the input capacitor rms ripple current varies with the input and output voltage and will always be less than or equal to half of the total dc load current. for v in = 2 x v o : the term appears in both the input voltage ripple and input capacitor rms current equations and is a maximum when v o is twice v in . this is why the input voltage ripple and the input capacitor rms current ripple are a maximum at 50% duty cycle. the input capacitor provides a low impedance loop for the edges of pulsed current drawn by the AAT2504. low esr/esl x7r and x5r ceramic capacitors are ideal for this function. to minimize stray inductance, the capacitor should be placed as closely as possible to the ic. this keeps the high frequency content of the input current localized, minimizing emi and input voltage ripple. a laboratory test set-up typically consists of two long wires running from the bench power supply to the evaluation board input voltage pins. the induc- tance of these wires, along with the low-esr ceramic input capacitor, can create a high q net- work that may affect converter performance. this problem often becomes apparent in the form of excessive ringing in the output voltage during load transients. errors in the loop phase and gain meas- urements can also result. since the inductance of a short pcb trace feeding the input voltage is significantly lower than the power leads from the bench power supply, most applications do not exhibit this problem. in applications where the input power source lead inductance cannot be reduced to a level that does not affect the converter performance, a high esr tantalum or aluminum electrolytic should be placed in parallel with the low esr, esl bypass ceramic. this dampens the high q network and stabilizes the system. table 1: inductor values. configuration output voltage inductor 0.9v adjustable with 1v, 1.2v 1.5h external feedback 1.5v, 1.8v 2.2h 2.5v, 3.3v 3.3h ?? 1 - ?? v o v in v o v in i o rms(max) i 2 = ?? 1 - = d (1 - d) = 0.5 2 = ?? v o v in v o v in 1 2 ?? i rms = i o 1 - ?? v o v in v o v in c in(min) = 1 ?? - esr 4 f s ?? v pp i o ?? 1 - = for v in = 2 v o ?? v o v in v o v in 1 4 ?? 1 - ?? v o v in c in = v o v in ?? - esr f s ?? v pp i o
AAT2504 adjustable 3-channel regulator 14 2504.2007.06.1.0 output capacitor the output capacitor limits the output ripple and provides holdup during large load transitions. a 4.7f to 10f x5r or x7r ceramic capacitor typi- cally provides sufficient bulk capacitance to stabi- lize the output during large load transitions and has the esr and esl characteristics necessary for low output ripple. the output voltage droop due to a load transient is dominated by the capacitance of the ceramic out- put capacitor. during a step increase in load cur- rent, the ceramic output capacitor alone supplies the load current until the loop responds. within two or three switching cycles, the loop responds and the inductor current increases to match the load current demand. the relationship of the output volt- age droop during the three switching cycles to the output capacitance can be estimated by: once the average inductor current increases to the dc load level, the output voltage recovers. the above equation establishes a limit on the minimum value for the output capacitor with respect to load transients. the internal voltage loop compensation also limits the minimum output capacitor value to 4.7f. this is due to its effect on the loop crossover frequency (bandwidth), phase margin, and gain margin. increased output capacitance will reduce the crossover frequency with greater phase margin. adjustable output resistor selection the output voltage on the step-down converter is programmed with external resistors r2 and r6. to limit the bias current required for the external feed- back resistor string while maintaining good noise immunity, the minimum suggested value for r6 is 59k . although a larger value will further reduce quiescent current, it will also increase the imped- ance of the feedback node, making it more sensitive to external noise and interference. table 2 summa- rizes the resistor values for various output voltages with r6 set to either 59k for good noise immunity or 221k for reduced no load input current. with enhanced transient response for extreme pulsed load application, an external feed-forward capacitor (c1 in fig.3) can be added. table 2: step-down converter resistor values for various output voltages. thermal calculations there are three types of losses associated with the AAT2504 step-down converter: switching losses, conduction losses, and quiescent current losses. conduction losses are associated with the r ds(on) characteristics of the power output switching devices. switching losses are dominated by the gate charge of the power output switching devices. at full load, assuming continuous conduction mode (ccm), a simplified form of the ldo losses is given by: r6 = 59k r6 = 221k v out (v) r2 (k ) r2 (k ) 0.9* 0 0 1.0 6.65 24.3 1.1 13.3 48.7 1.2 19.6 73.2 1.3 26.1 97.6 1.4 32.4 124 1.5 39.2 147 1.8 59.0 221 1.85 61.9 232 2.0 71.5 274 2.5 105 392 2.8 124 464 3.0 137 511 3.3 158 590 * for the 0.9v output, r6 is open. p total i o 2 (r dson(hs) v o + r dson(ls) [v in - v o ]) v in = + (t sw f i o + i q ) v in c out = 3 i load v droop f s
AAT2504 adjustable 3-channel regulator 2504.2007.06.1.0 15 i q is the step-down converter quiescent current. the term t sw is used to estimate the full load step- down converter switching losses. for the condition where the step-down converter is in dropout at 100% duty cycle, the total device dis- sipation reduces to: since r ds(on) , quiescent current, and switching losses all vary with input voltage, the total losses should be investigated over the complete input voltage range. given the total losses, the maximum junction tem- perature can be derived from the ja for the qfn34-20 package which is 50c/w. ldo linear regulator input capacitor a 1f or larger capacitor is typically recommended for c in in most applications. a c in capacitor is not required for basic ldo regulator operation; howev- er, if the AAT2504 is physically located more than three centimeters from an input power source, a c in capacitor will be needed for stable operation. c in should be located as closely to the device vldo pins as practically possible. c in values greater than 1f will offer superior input line tran- sient response and will assist in maximizing the highest possible power supply ripple rejection. ceramic, tantalum, or aluminum electrolytic capac- itors may be selected for c in . there is no specific capacitor esr requirement for c in ; however, ceramic capacitors are recommended for c in due to their inherent capability over tantalum capacitors to withstand input current surges from low imped- ance sources such as batteries in portable devices. output capacitor for proper load voltage regulation and operational stability, a capacitor is required between pins outa, outb, and gnd. the c out capacitor connection to the ldo regulator ground pin should be made as direct as practically possible for maximum device performance. the AAT2504 has been specifically designed to function with very low esr ceramic capacitors. for best performance, ceramic capaci- tors are recommended. typical output capacitor values for maximum out- put current conditions range from 1f to 10f. applications utilizing the exceptionally low output noise and optimum power supply ripple rejection characteristics of the AAT2504 should use 2.2f or greater for c out . if desired, c out may be increased without limit. in low output current applications where output load is less than 10ma, the minimum value for c out can be as low as 0.47f. capacitor characteristics ceramic composition capacitors are highly recom- mended over all other types of capacitors for use with the AAT2504. ceramic capacitors offer many advantages over their tantalum and aluminum elec- trolytic counterparts. a ceramic capacitor typically has very low esr, is lower cost, has a smaller pcb footprint, and is non-polarized. line and load tran- sient response of the ldo regulator is improved by using low esr ceramic capacitors. since ceramic capacitors are non-polarized, they are not prone to incorrect connection damage. equivalent series resistance esr is a very important characteristic to consider when selecting a capacitor. esr is the internal series resistance associated with a capacitor that includes lead resistance, internal connections, size and area, material composition, and ambient tem- perature. typically, capacitor esr is measured in milliohms for ceramic capacitors and can range to more than several ohms for tantalum or aluminum electrolytic capacitors. ceramic capacitor materials ceramic capacitors less than 0.1f are typically made from npo or c0g materials. npo and c0g materials generally have tight tolerance and are very stable over temperature. larger capacitor values are usually composed of x7r, x5r, z5u, or y5v dielec- tric materials. npo and c0g material types are not recommended for use with ldo regulators since the t j(max) = p total ja + t amb p total = i o 2 r dson(hs) + i q v in
AAT2504 adjustable 3-channel regulator 16 2504.2007.06.1.0 capacitor tolerance can vary more than 50% over the operating temperature range of the device. a 2.2f y5v capacitor could be reduced to 1f over temperature; this could cause problems for circuit operation. x7r and x5r dielectrics are much more desirable. the temperature tolerance of x7r dielec- tric is better than 15%. capacitor area is another contributor to esr. capacitors which are physically large in size will have a lower esr when compared to a smaller sized capacitor of an equivalent materi- al and capacitance value. these larger devices can improve circuit transient response when compared to an equal value capacitor in a smaller package size. consult capacitor vendor datasheets carefully when selecting capacitors for ldo regulators. adjustable output resistor selection the output voltage on the linear regulator is pro- grammed with external resistors: r4 and r7 for ldoa and r5 and r8 for ldob. table 3 summa- rizes the resistor values for various output volt- ages with r4 and r5 set to either 59k for good noise immunity or 221k for reduced no load input current. table 3: ldo linear regulators resistor values for various output voltages. pok output ldoa of the AAT2504 features an integrated power ok comparator which can be used as an error flag. the pok open drain output goes low when output voltage is 10% (typ) below its nominal regulation voltage. additionally, any time ldoa is in shutdown, the pok output is pulled low. connect a pull-up resistor from pok to outa. enable function the AAT2504 features an ldo regulator enable/dis- able function. each ldo has its own dedicated enable pin. these pins (ena, enb) are active high and are compatible with cmos logic. to assure the ldo regulators will switch on, ena/b must be greater than 1.4v. the ldo regulators will shut down when the voltage on the ena/b pins falls below 0.6v. in shutdown, the ldo regulators will consume less than 1.0a of current. if the enable function is not needed in a specific application, it may be tied to v in to keep the ldo regulator in a continuously on state. thermal protection each of the two ldos of the AAT2504 has an inter- nal thermal protection circuit which will turn on when the device die temperature exceeds 140c. the ldo regulator outputs will remain in a shutdown state until the internal die temperature falls back below the 125c trip point. no-load stability the ldos in the AAT2504 are designed to main- tain output voltage regulation and stability under operational no-load conditions. this is an important characteristic for applications where the output cur- rent may drop to zero. ldo r7, r8 = 59k r7, r8 = 221k v out (v) r4, r5 (k ) r4, r5 (k ) 0.6* 0 0 0.8 19.6 75 0.9 29.4 113 1.0 39.2 150 1.1 49.9 187 1.2 59.0 221 1.3 68.1 261 1.4 78.7 301 1.5 88.7 332 1.8 118 442 1.85 124 464 2.0 137 523 2.5 187 715 3.3 267 1000 * for the 0.6v output, r7 and r8 are open.
AAT2504 adjustable 3-channel regulator 2504.2007.06.1.0 17 reverse output-to-input voltage conditions and protection under normal operating conditions, a parasitic diode exists between the output and input of the ldo reg- ulator. the input voltage should always remain greater than the output load voltage maintaining a reverse bias on the internal parasitic diode. conditions where v out might exceed v in should be avoided since this would forward bias the internal parasitic diode and allow excessive current flow into the v out pin, possibly damaging the ldo regulator. in applications where there is a possibility of v out exceeding v in for brief amounts of time during nor- mal operation, the use of a larger value c in capaci- tor is highly recommended. a larger value of c in with respect to c out will effect a slower c in decay rate during shutdown, thus preventing v out from exceeding v in . in applications where there is a greater danger of v out exceeding v in for extended periods of time, it is recommended to place a schottky diode across v in to v out (connecting the cathode to v in and anode to v out ). the schottky diode forward voltage should be less than 0.45v. thermal considerations and high output current applications the ldos of the AAT2504 are designed to deliver continuous output load currents of 300ma each under normal operation. this is desirable for circuit applications where there might be a brief high in- rush current during a power-on event. the limiting characteristic for the maximum output load current safe operating area is essentially package power dissipation and the internal preset thermal limit of the device. in order to obtain high operating currents, careful device layout and circuit operating conditions need to be taken into account. the following discussions will assume the ldo regulator is mounted on a printed circuit board uti- lizing the minimum recommended footprint as stat- ed in the layout considerations section of this doc- ument. at any given ambient temperature (t a ), the maximum package power dissipation can be deter- mined by the following equation: constants for the AAT2504 are t j(max) (the maxi- mum junction temperature for the device, which is 125c) and ja = 50c/w (the package thermal resistance). typically, maximum conditions are cal- culated at the maximum operating temperature of t a = 85c and under normal ambient conditions where t a = 25c. given t a = 85c, the maximum package power dissipation is 800mw. at t a = 25c, the max- imum package power dissipation is 2w. the maximum continuous output current for the AAT2504 is a function of the package power dissi- pation and the input-to-output voltage drop across the ldo regulator. to determine the maximum out- put current for a given output voltage, refer to the following equation. this calculation accounts for the total power dissipation of the ldo regulator, including that caused by ground current. p d(max) = t j(max) - t a ja p d(max) = [(v in - v outa )i outa + (v in i gnd )] + [(v in - v outb )i outb + (v in i gnd )]
AAT2504 adjustable 3-channel regulator 18 2504.2007.06.1.0 layout the suggested pcb layout for the AAT2504 is shown in figures 1 and 2. the following guidelines should be used to help ensure a proper layout. 1. the input capacitors (c4, c7, c8, and c9) should connect as closely as possible to vin, vldoa, vldob, vp, and pgnd. 2. the output capacitor (c5, and c6) of the ldos connect as closely as possible to out. c2 and l1 should be connected as closely as possible. the connection of l1 to the lx pin should be as short as possible. do not make the node small by using a narrow trace. the trace should be kept wide, direct, and short. 3. the feedback trace should be separate from any power trace and connect as closely as pos- sible to the load point. sensing along a high- current load trace will degrade dc load regula- tion. feedback resistors should be placed as closely as possible to vout to minimize the length of the high impedance feedback trace. if possible, they should also be placed away from the lx (switching node) and inductor to improve noise immunity. 4. the resistance of the trace from the load return to the pgnd should be kept to a minimum. this will help to minimize any error in dc regulation due to differences in the potential of the inter- nal signal ground and the power ground. 5. ensure all ground pins are tied to the ground plane. no pins should be left floating. for maxi- mum power dissipation, it is recommended that the exposed pad (ep) must be soldered to a good conductive pcb ground plane layer to fur- ther increase local heat dissipation. figure 1: AAT2504 evaluation board figure 2: AAT2504 evaluation board top side layout. bottom side layout.
AAT2504 adjustable 3-channel regulator 2504.2007.06.1.0 19 figure 3: AAT2504 evaluation board schematic. table 4: surface mount capacitors. table 5: suggested inductors and suppliers. inductance saturated rated dcr size (mm) manufacturer part number (h) current (ma) (m ) lxwxh type sumida cdrh2d14-1r5 1.5 1800 63 3.2x3.2x1.55 shielded sumida cdrh2d14-2r2 2.2 1500 94 3.2x3.2x1.55 shielded sumida cdrh2d14-3r3 3.3 1200 125 3.2x3.2x1.55 shielded coiltronics sd3812-1r5 1.5 1580 78 4.0x4.0x1.2 shielded coiltronics sd3812-2r2 2.2 1320 111 4.0x4.0x1.2 shielded coiltronics sd3812-3r3 3.3 1100 159 4.0x4.0x1.2 shielded taiyo yuden nr3010-1r5 1.5 1200 80 3.0x3.0x1.0 shielded taiyo yuden nr3010-2r2 2.2 1100 95 3.0x3.0x1.0 shielded taiyo yuden nr3010-3r3 3.3 870 140 3.0x3.0x1.0 shielded manufacturer part number value (f) voltage rating temp. co. case size murata grm219r60j106ke19 10 6.3 x5r 0805 murata grm188r60j475ke19 4.7 6.3 x5r 0603 murata grm188r61a225ke34 2.2 10 x5r 0603 murata grm188r61a105ka61 1.0 10 x5r 0603 murata grm185r60j105ke26 1.0 6.3 x5r 0603 cdrh2d14 l1 10f c2 10f c7 vout_buck gnd gnd vin 1 2 3 en lx pok r2 59.0k r6 v out_ldo (v) r4, r5 (k ) 0.8 19.6 0.9 29.4 1.0 39.2 1.1 49.9 1.2 59.0 1.3 68.1 1.4 78.7 1.5 88.7 1.8 118 1.85 124 2.0 137 2.5 187 3.3 267 2.2f c6 2.2f c5 1 2 3 enb vp lx fb outa gnd ena en 100 r1 0.1f c4 vin outa 1 2 3 vina gnd .01f c3 r4 59.0k r8 r5 100k r3 59.0k r7 outb enb sync 1 2 3 ena outb buckout fba fbb pok mode/sync 1 2 3 vinb vldob vldoa c5, c6 2.2uf, 10v, x5r, 0603 grm188r61a225ke34 c8, c9 1uf, 6.3v, x5r, 0603 grm185r60j105ke26 c2, c7 10uf, 6.3v, x5r, 0805 grm219r60j106ke19 1f c9 1f c8 (open) r12 100k r10 fb 5 vin 13 vldoa vldob 18 19 agnd 6 pgnd 7 fbb 1 outb 20 vp 10 en 14 ena 2 enb 3 fba 16 pok 15 outa 17 lx 8 lx 9 mode/sync 4 ep AAT2504 u1 v out_buck (v) r2 (k ) l1 (h) 0.9 0 1.5 1.0 6.65 1.5 1.1 13.3 1.5 1.2 19.6 1.5 1.3 26.1 1.5 1.4 32.4 1.5 1.5 39.2 2.2 1.8 59 2.2 1.85 61.9 2.2 2.0 71.5 2.2 2.5 105 3.3 2.8 124 3.3 3.0 137 3.3 3.3 158 3.3 l1 sumida cdrh2d14 or coltronics sd3812 100pf c1 u1 AAT2504 qfn34-20
AAT2504 adjustable 3-channel regulator 20 2504.2007.06.1.0 ordering information voltage package channel 1 channel 2 channel 3 marking 1 part number (tape and reel) 2 qfn34-20 0.9v 0.6v 0.6v xwxyy AAT2504izl-baa-t1 legend voltage code adjustable a (0.6v) 0.9 b 1.2 e 1.5 g 1.8 i 1.9 y 2.5 n 2.6 o 2.7 p 2.8 q 2.85 r 2.9 s 3.0 t 3.3 w 4.2 c 1. xyy = assembly and date code. 2. sample stock is generally held on part numbers listed in bold . all analogictech products are offered in pb-free packaging. the term pb-free means semiconductor products that are in compliance with current rohs standards, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. for more information, please visit our website at http://www.analogictech.com/pbfree.
AAT2504 adjustable 3-channel regulator 2504.2007.06.1.0 21 package information qfn34-20 all dimensions in millimeters. 1. the leadless package family, which includes qfn, tqfn, dfn, tdfn and stdfn, has exposed copper (unplated) at the end of the lead terminals due to the manufacturing process. a solder fillet at the exposed copper edge cannot be guaranteed and is not re quired to ensure a proper bottom solder connection. 4.00 top view bottom view side view detail "b" detail "a" option a: c0.30 (4x) max chamfered corner option b: r0.30 (4x) max round corner pin 1 indicator (optional) detail "a" index area (d/2 x e/2) detail "b"
AAT2504 adjustable 3-channel regulator 22 2504.2007.06.1.0 advanced analogic technologies, inc. 830 e. arques avenue, sunnyvale, ca 94085 phone (408) 737-4600 fax (408) 737-4611 ? advanced analogic technologies, inc. analogictech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an analogictech pr oduct. no circuit patent licenses, copyrights, mask work rights, or other intellectual property rights are implied. analogictech reserves the right to make changes to their products or specifications or to discontinue any product or service with- out notice. except as provided in analogictechs terms and conditions of sale, analogictech assumes no liability whatsoever, an d analogictech disclaims any express or implied war- ranty relating to the sale and/or use of analogictech products including liability or warranties relating to fitness for a part icular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. in order to minimize risks associated with the customers applications, adequa te design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. testing and other quality control techniques are utilized to the extent an alogictech deems necessary to support this warranty. specific testing of all parameters of each device is not necessarily performed. analogictech and the analogictech logo are trad emarks of advanced analogic technologies incorporated. all other brand and product names appearing in this document are registered trademarks or trademarks of their respective holder s.

▲Up To Search▲

Price & Availability of AAT2504

	To Download AAT2504 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .