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ams4123 3a 20v step-down converter + 1a ldo 3/5/2010 www.advanced-monolithic.com phone (925) 443-0722 1 fax (925) 443-0723 general description the ams4123 combines a 3a step-down converter with a 1a ldo in a single so-8 exposed paddle package. both the ldo and step-down converter are low esr, ceramic capacitor output, stable. the step-down converter is internally compensated with internal soft-start to minimize the number of external components. an enable pin provides built-in externally programmable power-up sequencing. the step-down converter enable threshold is 2.0v and the ldo enable threshold is 2.5v. it also has hiccup current limit and thermal protection. thermal protection shuts down both the step-down converter and ldo when the die temperature exceeds 135c. both regulators are adjustable using a 0.6v reference for low output voltage settings. the ldo has options for fixed output voltages from 0.6v to 5v in 100mv steps. the ldo external input can be powered from the step-down converter output, for improved efficiency, or from any voltage source that is less than or equal to the device supply voltage (vin). with a dropout voltage of less than 350mv at 1a, the ams4123 ldo makes the perfect solution for a low noise 1.8v power source developed from 2.5v step-down converter output. the ams4123 is a complete solution for lcd tv power requirements when combined with the ams4122 (2a dual switching regulator in so-8). features ? step-down converter + ldo in so-8ep ? internally compensated ? up to 95% efficiency ? low esr ceramic output capacitor stable ? soft start ? under-voltage lockout ? dual threshold enable ? 300 khz switching frequency ? hiccup current limit ? over-temperature shutdown ? ultra-low dropout ldo 350mv @ 1a ? up to 3a step-down output current ? up to 1a ldo output current ? excellent light load efficiency applications ? audio power amplifiers ? portable (notebook) computers ? point of regulation for high performance electronics ? consumer electronics ? dvd, blue-ray dvd writers ? lcd tvs and lcd monitors ? distributed power systems ? battery chargers ? pre-regulator for linear regulation typical application l1 10uh c5 220nf r2 10.0k r4 31.6k r3 10.0k d1 b340lb r1 20.0k c3 2.2uf c1 10uf c8 4.7nf c2 22uf c9 100uf r1 and r4 voltage options 3.3v 45.3k 2.5v 31.6k 5.0v 73.2k 1.8v 20.0k 2.5v at 2a 1.8v at 1a enable vin 4.5v to 20v ldoout 8 en 4 vin 3 bst 2 sw 1 fb ldo 6 ldoin 7 fb sw 5 u1 ams4123 2.5v sw out
ams4123 3a 20v step-down converter + 1a ldo 3/5/2010 www.advanced-monolithic.com phone (925) 443-0722 2 fax (925) 443-0723 pin description pin # symbol description 1 sw step-down converter switching node that conn ects the internal power switch to the output inductor. 2 bst the bootstrap capacitor tied to this pin is used as the bias source for the drive to the internal power switch. use a 220nf or greater capacitor from the bst to the sw pin. 3 vin input power. supplies bias to the ic and is also the power input to the step-down converter main power switch. bypass vin with low impedance ceramic with sufficient capacitance to minimize switching frequency ripple as well as high frequency noise. 4 en enable. a voltage greater than 2v at this pin enables the switching regulator. 2.5v enables the ldo section. 5 fb sw step-down converter feedback input. a resist or network of two resistors is used to set-up the output voltage connected between v sw out and gnd. the node between the two resistors is connected to feedback switch pin. 6 fb ldo ldo feedback input. a resistive voltage divider is used to set the output voltage connected between the ldo output and gnd. the node between the two resistors is connected to fb ldo pin. 7 ldo in ldo input. connect to the output of the st ep-down converter. ldo in can also be powered from any power supply as lo ng as it is 2v less than vin. 8 ldo out ldo output pin. 9 gnd (paddle) ground paddle to be connected to pcb ground plane. this is also the ground for internal voltage reference. pin configuration 8l soic so package (s) top view
ams4123 3a 20v step-down converter + 1a ldo 3/5/2010 www.advanced-monolithic.com phone (925) 443-0722 3 fax (925) 443-0723 absolute maximum ratings (1) v in supply voltage??????...???..?.-0.3v to 23v ldo in supply voltage???????..??...-0.3v to 20v ldo out output voltage???????.?.....-0.3v to 20v bst boot strap voltage??????....?. -0.3v to 27v fbldo,fbsw feedback pins???....??-0.3v to +12v en enable voltage?????????..?.-0.3v to +20v storage temperature range?????...-65 ? c to 150 ? c lead temperature???????..???.?.?? 260 ? c junction temperature???...??????..?? 150 ? c recommended operating conditions (2) input voltage?????????????.???..4.5v to 20v ambient operating temperature?? ?????.-40 ? c to 85 ? c thermal information 8l soic ep ja (3) ??????????????.?...45 ? c/w jc ...........................................................10 ? c/w maximum power dissipation??????????...?.??.2w electrical characteristics t a = 25 c and v in =12v (unless otherwise noted). parameter symbol conditions min. typ. max. units v in v in 4.5 12 20 v ldo feedback voltage v fbldo i ldo =0a tbd 0.586 tbd v switcher feedback voltage v fbsw i sw= 0a tbd 0.596 tbd v ldo output voltage tolerance v ldo out v ldo out =0.6v to 5v in 100mv increments -1.5 1 1.5 % step-down converter bias current i qsw v ldoin =v en =5v v fbsw = 1.5v 1.4 1.9 ma ldo+sw bias current i qsw+ldo v ldoin =v en =5v v fbldo =v fbsw = 1.5v 1.3 2.0 ma ldo bias current i qldo v en = 5v; v fbldo = 1.5v 400 a shutdown supply current i vinsd v en =0v 90 na sw npn saturation voltage v sat i sw out =1a 0.66 v converter current limit i limsw v sw out =5v 4.2 a ldo current limit i limldo v ldo in =5v; c o =2.2 f 1.1 a ldo dropout voltage v do v ldoin =v ldoout -0.1v, io=1a 350 mv ldo load regulation v ldo out / v ldo out i ldo = 0 to1a 0.5 % ldo line regulation v ldo out / v ldo out v ldoin = v ldoout +0.5v to 20v, v in =20v 0.1 % oscillator frequency f osc 260 300 340 khz maximum duty cycle d max v fb =0v 95 99 % minimum duty cycle d min v fb =1.5v 0 % converter enable threshold v en sw 2.0 2.1 v enable hysteresis v enhys 100 mv ldo enable threshold v en ldo 2.5 2.55 v enable pull-up current i en v en = 0v 0.7 a under voltage lockout v uvlo v in rising 4.2 v under voltage lockout hysteresis v uvlo hys 200 mv total power dissipation p d note (4) 2.5 w thermal shutdown t sd 145 c
ams4123 3a 20v step-down converter + 1a ldo 3/5/2010 www.advanced-monolithic.com phone (925) 443-0722 4 fax (925) 443-0723 notes: 1. stresses above those listed in absolute maximu m ratings may cause permanent damage to the device. 2. operation outside of the recommended operating conditions is not guaranteed. 3. measured on approximately 1? square of 1 oz. copper. 4. the total power dissipation for so-8 ed p package is recommended to 2.5w rated at 25 ? c ambient temperature. the thermal resistance junction to case is 45 ? c/w. total power dissipation for the switching regulator and the ldo should be taken in consideration when calculating the outp ut current capability of each regulator.
ams4123 3a 20v step-down converter + 1a ldo 3/5/2010 www.advanced-monolithic.com phone (925) 443-0722 5 fax (925) 443-0723 typical characteristics 20 30 40 50 60 70 80 90 100 0.01 0.1 1 10 efficiency (%) output current (a) efficiency v sw out =5v, l=10h, b340lb schottky v in =12v v in =23v 20 30 40 50 60 70 80 90 100 0.01 0.1 1 10 efficiency (%) output current (a) efficiency v sw out =3.3v, l=10h, b340lb schottky v in ? = 12v v in =23v 20 30 40 50 60 70 80 90 100 0.01 0.1 1 10 efficiency (%) output current (a) efficiency v sw out =2.5v, l=10h, b340lb schottky v in =12v v in =23v -1.0 -0.6 -0.2 0.2 0.6 1.0 0.01 0.1 1 10 v sw out regulation (%) output current (a) load regulation v sw out =5v, l=10h v in =12v v in =23v -1.0 -0.6 -0.2 0.2 0.6 1.0 0.01 0.1 1 10 v sw out regulation (%) output current (a) load regulation v sw out =3.3v, l=10h v in =12v v in =23v -1.0 -0.6 -0.2 0.2 0.6 1.0 0.01 0.1 1 10 v sw out regulation (%) output current (a) load regulation v sw out =2.5v, l=10 h v in =12v v in =23v
ams4123 3a 20v step-down converter + 1a ldo 3/5/2010 www.advanced-monolithic.com phone (925) 443-0722 6 fax (925) 443-0723 typical characteristics 0.0 0.8 1.6 2.4 3.2 0 5 10 15 20 25 input current (ma) input voltage (v) no load input current vs. input voltage v sw out = 2.5v, v ldo out = 1.8v 292 296 300 304 308 0 5 10 15 20 25 switching frequency (khz) input voltage (v) switching frequency vs. input voltage v sw out = 2.5v, v ldo out = 1.8v 0 0.5 1 1.5 2 0 0.2 0.4 0.6 0.8 1 v ldo out voltage (v) output current (a) v ldo out load regulation v sw out = v ldo in =2.5v, v ldo out =1.8v v in =20v v in =15v v in =12v -0.50 -0.25 0.00 0.25 0.50 0 5 10 15 20 25 output error (%) input voltage v in (v) output voltage error vs. input voltage v sw out = v ldo in = 2.5v, v ldo out =1.8v v ldo out v sw out i ldo =0.6a i sw =1.6a 0 0.1 0.2 0.3 0.4 0 0.2 0.4 0.6 0.8 1 dropout voltage (v) ldo output current (v) ldo dropout voltage vs. load current v ldo in = v ldo out -0.1v v ldo out programmed for 1.8v v in = 12v 0.57 0.58 0.59 0.60 0.61 -50 -10 30 70 110 150 feedback voltage (v) ambient temperature (oc) feedback voltage temperature variation fb ldo fb sw i ldo =i sw =0 v ldo ? out =1.8v, ? v sw ? out =2.5v
ams4123 3a 20v step-down converter + 1a ldo 3/5/2010 www.advanced-monolithic.com phone (925) 443-0722 7 fax (925) 443-0723 typical characteristics 20 sec/div step-down converter load transient 200ma to 1.2 a , v sw out = 2.5v , v in =12v i sw out 500ma / div v sw out 100mvac / div 40 sec/div step-down converter load transient 200ma to 2a , v sw out = 2.5v , v in =12v i sw out 500ma / div v sw out 100mvac / div 2 sec/div ldo 200ma to 800ma transient response, v ldo in =3.3v, co=2.2f, v ldo out = 1.8v, v in =12v i ldo out 500ma /d iv v ldo out 100mvac /div 20 sec/div ldo transient response no load to 1a, v ldo in =v sw out =2.5v, i ldo out 1a/div v ldo out 100mvac /div v sw out 200mvac/ div i sw out 1a/div v sw out 100mvac /div 2 msec/div step-down converter load transient no load to 2a , v sw out =2.5v , v in =12v 1 sec/div v sw out 20mvac /div il 1a/div v sw 5v/div step-down converter output ripple v sw out =2.5v, i sw out =1.8a, v in =12v
ams4123 3a 20v step-down converter + 1a ldo 3/5/2010 www.advanced-monolithic.com phone (925) 443-0722 8 fax (925) 443-0723 typical characteristics 220 240 260 280 300 -45 -10 25 60 95 130 switching frequency (khz) ambient temperature (oc) switching frequency temperature variation v sw out =2.5v, v in =12v -2.4 -1.6 -0.8 0.0 0.8 -50 -10 30 70 110 150 feedback voltage error (%) ambient temperature (oc) feedback voltage temperature variation fb ldo fb sw i ldo =i sw =0 v ldo ? out =1.8v, ? v sw ? out =2.5v 0 0.3 0.6 0.9 1.2 0 0.71.42.12.83.5 vcesat (v) current (a) step-down converter power switch saturation voltage v in =12v tamb ? = ? 25 ?? c mounted on ? eval. ? board 1 msec/div start-up response v in =20v v sw out 1v /div v ldo out 1v /div v en 5v /div il 2a/div 2 msec/div start-up response enable=v in =12v v ldo out 1v /div v in 10v /div il 2a/div ? 400 sec/div start-up response v in =12v v sw out 1v /div v ldo out 1v /div v en 5v /div il 2a/div
ams4123 3a 20v step-down converter + 1a ldo 3/5/2010 www.advanced-monolithic.com phone (925) 443-0722 9 fax (925) 443-0723 typical characteristic 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 5 9 13 17 21 25 current limit (a) v in input voltage (v) ldo current limit v ldo in = 3.3v, v ldo out =1.8v voltage mode ? load ? v ldo ? out ? = ? 1.68v 0 10 20 30 40 50 0 200 400 600 800 1000 ground current (ma) load current (ma) ldo ground current v ldo in = 3.3v, v ldo out =1.8v
ams4123 3a 20v step-down converter + 1a ldo 3/5/2010 www.advanced-monolithic.com phone (925) 443-0722 10 fax (925) 443-0723 functional block diagram ldo out vin pgnd sw vref fb ldo fb sw paddle en level shift ldo in vref bst shutdown comparators 4 8 6 2 1 7 5 p uvlo 2.0v 2.5v 4.2v / 3.8v internal vcc regulator 300khz oscillator vcc 3.3v pvin 3 isense q q set clr s r eaout eaout 0.6v vref 0.6v switching regulator shutdown bst reg. sw out
ams4123 3a 20v step-down converter + 1a ldo 3/5/2010 www.advanced-monolithic.com phone (925) 443-0722 11 fax (925) 443-0723 device summary the ams4123 is combines a high voltage 3 amp fixed frequency step-down converter combined with a 1 amp low drop out (ldo) linear regulator on a single die. the peak current mode step-down converter has internal compensation and is stable with a wide range of ceramic, tantalum, and electrolytic output capacitors. the step-down converter output voltage is sensed through an external resistive divider that feeds the negative input to an internal transconductance error amplifier. the output of the error amplifier is connected to the input to a peak current mode comparator. the inductor current is sensed as it passes through the power switch, amplified and is also fed to the current mode comparator. the error amplifier regulates the output voltage by controlling the peak inductor current passing through the power switch so that, in steady state, the average inductor current equals the load current. the step-down converter has an input voltage range of 4.5v to 20v with an output voltage as low as 0.6v. the ldo operates from an input voltage ranging from 1v to 20v and a typical dropout voltage of 350mv at 1a. the input to the ldo can be supplied by the output of the step-down converter or some other available power source that must be 2v less than the input voltage (vin). the ldo is also stable for a wide range of ceramic output capacitors ranging from as low as 1f. enable the enable input has two levels so that the step-down converter can be enabled independently of the ldo. the enable threshold for the step-down converter is 2.0v while the enable threshold for the linear regulator output is 2.5v typical. under voltage lockout the under-voltage lockout (u vlo) feature guarantees sufficient input voltage (vin) bias for proper operation of all internal circuitry prior to activation. the input voltage (vin) is internally monitored and the converter and ldo are enabled when the rising level of vin reaches 4.2v. to prevent uvlo chatter 400mv of hysteresis is built in to the uvlo comparator so that the step-down converter and ldo are disabled when vin drops to 3.8v. fault protection short circuit and over-tem perature shutdown disable the converter and ldo in the event of an overload condition. application inductor the step-down converter indu ctor is typically selected to limit the ripple current to 40% of the full load output current. solve for this value at the maximum input voltage where the inductor ripple current is greatest. l= vin-vo vo vinio0.4fs l= 15v-2.5v 2.5v 15v2a0.4300khz =9.4h for most applications the duty cycle of the ams4123 step down converter is less than 50% duty and does not require slope compensation for stability. this provides some flexibility in the selected inductor value. given the above sele cted value, others values slightly greater or less may be examined to determine the effect on efficiency without a detrimental effect on stability. with and inductor value selected, the ripple current can be calculated: ipp= (vo+vfwd)(1-d) lfs using the maximum input voltage values the ripple is: ipp= (2.5v+0.2v) 1-0.23 10 h300khz =0.7a once the appropriate value is determined, the component is selected bas ed on the dc current and the peak (saturation) current. select an inductor that has a dc current rating greater than the full load current of the application. the dc current rating is also reflected in the dc resistance (dcr) specification of the inductor. the inductor dcr should limit the inductor loss to less than 2% of the step- down converter output power. the peak current at full load is equal to the full load dc current plus one half of the ripple current. as mentioned before, the ripple current varies with input
ams4123 3a 20v step-down converter + 1a ldo 3/5/2010 www.advanced-monolithic.com phone (925) 443-0722 12 fax (925) 443-0723 voltage and is a maximum at the maximum input voltage. ipkmax=io+ (vo+vfwd)(1-dmin) 2lfs dmin= vo vinmax the duty cycle can be more accurately estimated by including the drops of the external schottky diode and the internal power switch: dmin= vo+vfwd vinmax-v o +vfwd dmin= 2.5v+0.2v 15v-0.3v+0.2v =0.23 vfwd is the diode freewheeling diode drop and vsw is the collector to emitter drop of the internal power switch. with a good estimate of the duty cycle (d) the inductor peak current can be determined: ipkmax=2a+ (2.5v+0.2v)(1-0.23) 210h300khz =2.35a there are a wide range 2 and 3 amp, shielded and non-shielded inductors availabl e. table 1 lists a few. table 1. inductor selection guide series type dimensions (mm) w l h coilcraft do3316p non- shielded 9.4 13 5.2 do3308 non- shielded 9.4 13 3.0 sumida cdrh6d26 shielded 7 7 2.8 cdh74 non- shielded 7.3 7.3 5.2 coiltronics sd8328 shielded 8.3 9.5 3.0 step-down converter output capacitor the optimum solution for the switching regulator is to use a large bulk capacitor for large load transients in parallel with a smaller, low esr, x5r or x7r ceramic capacitor to minimize the switching frequency ripple. high frequency ripple the following equation determines the required low esr ceramic output capacitance for a given inductor current ripple (ipp). c= ipp fs8dv = 0.7a 300khz820mv =15 f large signal transient for applications with large load transients an additional capacitor may be required to keep the output voltage within the limits required during large load transients. in this case the required capacitance can be examined for the load application and load removal. for full load to no load transient the required capacitance is cbulk= lio 2 vos 2 -vo 2 = 10 h(2a) 2 (2.7v) 2 -(2.5v) 2 =36 f for the application of a load pulse the capacitance required form hold up depends on the time it takes for the power supply loop to build up the inductor current to match the load current. for the ams4123 this can be estimated to be less than 10 sec or about three clock cycles. cbulk= iot dv = 2a10 sec 0.2v =100 f for applications that do not have any significant load transient requirements a ceramic capacitor alone is typically sufficient. boot strap capacitor an external capacitor is required for the high side switch drive. the capacitor is biased during the off time while the switch node is at ground by way of the freewheeling diode. during the on time portion of the switching cycle the switch node is tied to the input voltage by way of the internal power switch. the boot strap capacitor is always referenced to the switch node so the charge stored in the capacitor during the off time is then used to driv e the internal power switch during the on time.
ams4123 3a 20v step-down converter + 1a ldo 3/5/2010 www.advanced-monolithic.com phone (925) 443-0722 13 fax (925) 443-0723 typical bootstrap capacitor values are in the 220nf to 470nf range. insufficient values will not be able to provide sufficient base drive current to the power switch during the on time. values less than 220nf are not recommended. this will result in excessive losses and reduced efficiency. optional snubber to reduce high frequency ringing at the switching node a snubber network is suggested. the values typically selected are 470pf ceramic in series with a 10 ? resistor. the power dissipation of the 10 ? resistor is about 32mw for a 15v input with a 300khz switching frequency. p r1 =c3vin 2 fsw v in is the maximum input voltage and f sw is the switching frequency. the snubber capacitor must be rated to withstand the input voltage. step-down converter input capacitor the low esr ceramic capacitor required at the input to filter out high frequency noise as well as switching frequency ripple. placement of the capacitor is critical for good high frequency noise rejection. see the pcb layout guidelines section for details. switching frequency ripple is also filtered by the ceramic bypass input capacitor. given a desired input voltage ripple (vripple) limit, the required input capacitor can be estimated with: dmax= vo+vfwd vinmin-v o +vfwd c= dmaxio(1-dmax) fsvripple = 2.5v +0.2v 9v-0.3v+0.2v 2a 1- 2.5v 0.2v 9v-0.3v+0.2v 300khz0.2v =7 f . for high voltage input converters the duty cycle is always less than 50% so the maximum ripple is at the minimum input voltage. the ripple will increase as the duty cycle approaches 50% where it is a maximum. step-down converter feedforward capacitor for optimum start-up and improved transient response place a feed-forward capacitor (c6) across the feedback resistor r2. typical values range from 220pf to 10nf. linear regulator output capacitor the linear regulator is stable with a wide range of ceramic capacitors. the ceramic output capacitor can range from 1uf to 100uf with either x5r or x7r temperature coefficient. the actual values selected within the range will depend on the expected load transients and the output voltage tolerance requirements during the load transient. linear regulator input capacitor place a 2.2uf x5r or x7r or equivalent ceramic bypass capacitor at the ldo input. feedback resistor selection the step down converter and ldo both use a 0.6v reference voltage at the positive terminal of the error amplifier. to set the output voltage a programming resistor form the feedback node to ground must first be selected (r2,r3 of figure 4). a 10k ? resistor is a good selection for a programming resistor. a higher value could result in an excessively sensitive feedback node while a lower value will draw more current and degrade the light load efficiency. the equation for selecting the voltage specific resistor is: r4= vout vref -1 r3 = 2.5v 0.6v -1v 10k ? =31.67k ? table 2. feedback resistor values vout (v) r1,r4 (k ? ) (r2,r3=10k ? ) 1.8 20.0 2.5 31.6 3.3 45.3 5.0 73.2
ams4123 3a 20v step-down converter + 1a ldo 3/5/2010 www.advanced-monolithic.com phone (925) 443-0722 14 fax (925) 443-0723 pcb layout the following guidelines should be followed to insure proper layout. 1. vin capacitor. a low esr ceramic bypass capacitor must be placed as close to the ic as possible. 2. schottky diode. during the off portion of the switching cycle the inductor current flows through the schottky diode to the output cap and returns to the inductor through the output capacitor. the trace that connects the output diode to the output capacitor sees a current signal with a very high di/dt. to minimize the associated spiking and ringing, the inductance and resistance of this trace should be minimized by connecting the diode anode to the output capacitor return with a short wide trace. 3. feedback resistors. the feedback resistors should be placed as close as possible the ic. minimize the length of t he trace from the feedback pin to the resistors. this is a high impedance node susceptible to interference from external rf noise sources. 4. inductor. minimize the length of the sw node trace. this minimizes the radiated emi associated with the sw node. 5. ground. the most quiet ground or return potential available is the output capacitor return. the inductor current flows through the output capacitor during both th e on time and off time, hence it never sees a high di/dt. the only di/dt seen by the output capacito r is the inductor ripple current which is much less than the di/dt of an edge to a square wave current pulse. this is the best place to make a solid connection to the ic ground and input capacitor. this node is used as the star ground shown in figure 1. this method of grounding helps to reduce high di/dt traces, and the detrimental effect associated with them, in a step-down converter. th e inductance of these traces should always be minimized by using wide traces, ground planes, and proper component placement. 6. for good thermal performance vias are required to couple the exposed tab of the so-8 package to the pcb ground plane. the via diameter should be 0.3mm to 0.33mm positioned on a 1.2mm grid. figure 1. step down converter layout ion ioff ion+ ioff ion ioff ion+ioff high di/dt pcb inductance ion ioff high di/dt trace reduction ?star ground?
ams4123 3a 20v step-down converter + 1a ldo 3/5/2010 www.advanced-monolithic.com phone (925) 443-0722 15 fax (925) 443-0723 output power and thermal limits the ams4123 junction temperature, step-down converter and ldo current capability depends on the internal dissipation and the junction to case thermal resistance of the so8 ex posed paddle package. this gives the junction temperature rise above the device paddle and pcb temperature. the temperature of the paddle and pcb will be elevated above the ambient temperature due to the total losses of the step down converter and losses of other circuits and or converters mounted to the pcb. tjmax=pd jc+tpcb+tamb the losses associated with the ams4123 overall efficiency are; 1. output diode conduction losses 2. inductor dcr losses 3. ams4123 internal losses a. power switch forward conduction and switching losses b. quiescent current losses the internal losses contribute to the junction temperature rise above the case and pcb temperature. the junction temperature depends on many factors and should always be verified in the final application at the maximum ambient temp erature. this will assure that the device does not enter over-temperature shutdown when fully loaded at the maximum ambient temperature.
ams4123 3a 20v step-down converter + 1a ldo 3/5/2010 www.advanced-monolithic.com phone (925) 443-0722 16 fax (925) 443-0723 figure 2. ams4123 evaluation board top side figure 3. ams4123 evaluation board bottom side figure 4. ams4123 evaluation board schematic table 3. evaluation board bill of materials component value manufacturer manufacturer part number l1 10h 3.9a 9.4mm x 13mm x 5.2mm coilcraft do3316p c9 100f, 16v, x case general purpose tantalum kemet t491x107m016as c2 22f, 10v, x5r, 0805, ceramic taiyo yuden lmk212bj226mg-t tdk c3225x5r1a226m c1 10f, 50v, x5r, 1210, ceramic taiyo yuden umk325bj106km-t c3,c6 2.2f, 10v, x5r, 0805 murata grm216r61a225ke24 c3,c6 option 2.2f, 10v, x5r, 0603 murata grm39x5r225k10h52v c7 470pf 50v, 20%, x7r, 0603 murata grm188r71h471ma01 c5 220nf 25v, 10%, x7r, 0603 murata grm188r71e224ka88 c8 4.7nf 50v, 20%, x7r, 0603 murata grm188r71h472ma01 c4 22f 35v tantalum case e vishay 293d226x9035e2te3 r5 10 ? , 0.1w, 0603 5% vishay/dale CRCW060310R0JNEA l1 10uh c5 220nf r2 10.0k r4 45.3k c4 22uf 35v r3 10.0k c3 2.2uf j5 enable j4 vldoout j3 vin j2 gnd vlx vout j1 vldoin j6 gnd d1 b340lb ldo out 8 en 4 vin 3 bst 2 sw 1 fb ldo 6 ldo in 7 fb sw 5 u1 ams4123_1 r1 31.6k c6 2.2uf c1 10uf 50v j7 gnd c7 470pf c8 4.7nf r5 10 c2 22uf c9 100uf 16v 1 2 jp1 ld o in pu t
ams4123 3a 20v step-down converter + 1a ldo 3/5/2010 www.advanced-monolithic.com phone (925) 443-0722 17 fax (925) 443-0723 r2,r3 10k ? , 0.1w, 0603 1% various crcw060310k0fkea r1,r4 see table 2 various crcw0603xxkxfkea d1 3a, 40v schottky diodes inc. b340lb u1 step-down converter / ldo ams ams4123 ordering information package dimensions inches (millimeters) unless otherwise noted. 8 lead soic pl astic package (s) package type soic edp temp. range ams4123s -25c to 125c
ams4123 3a 20v step-down converter + 1a ldo 3/5/2010 www.advanced-monolithic.com phone (925) 443-0722 18 fax (925) 443-0723

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