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IRDC3840 02/02/2009 1 user guide for ir3840 evaluation board description the ir3840 is a synchronous buck converter, providing a compact, high performance and flexible solution in a small 5mmx6mm power qfn package. key features offered by the ir3840 include programmable soft-start ramp, precision 0.7v reference voltage, power good , thermal protection, programmable switching frequency, sequence input, enable input, input under-voltage lockout for proper start- up, and pre-bias start-up. an output over-current protection function is implemented by sensing the voltage developed across the on-resistance of the synchronous rectifier mosfet for optimum cost and performance. this user guide contains the schematic and bill of materials for the ir3840 evaluation board. the guide describes operation and use of the evaluation board itself. detailed application information for ir3840 is available in the ir3840 data sheet. board features ? v in = +12v (13.2v max) ? v cc =+5v (5.5v max) ? v out = +1.8v @ 0- 12a ? f s =600khz ? l= 0.6uh ? c in = 4x10uf (ceramic 1206) + 330uf (electrolytic) ? c out = 6x22uf (ceramic 0805) sup ir buck tm
IRDC3840 02/02/2009 2 a well regulated +12v input supply should be connected to vin+ and vin-. a maximum 12a load should be connected to vout+ and vout-. the connection diagram is shown in fig. 1 and inputs and outputs of the board are listed in table i. ir3840 has two input supplies, one for biasing (vcc) and the other as input voltage (vin). separate supplies should be applied to these inputs. vcc input should be a well regulated 4.5v-5.5v supply and it would be connected to vcc+ and vcc-. if single 12v application is required connect r7 (zero ohm resistor) which enables the on board bias regulator (see schematic). in this case there is no need of external vcc supply. the output can track a sequencing input at the start-up. for sequencing application, r16 should be removed and the external sequencing source should be applied between seq. and agnd. the value of r14 and r28 can be selected to provide the desired ratio between the output voltage and the tracking input. for proper operation of ir3840, the voltage at seq. pin should not exceed vcc. connections and operating instructions layout the pcb is a 4-layer board. all of layers are 2 oz. copper. the ir3840 supirbuck and all of the passive components are mounted on the top side of the board. power supply decoupling capacitors, the bootstrap capacitor and feedback components are located close to ir3840. the feedback resistors are connected to the output voltage at the point of regulation and are located close to the supirbuck. to improve efficiency, the circuit board is designed to minimize the length of the on-board power ground current path. table i. connections sequence input seq. v out (+1.8v) vout+ ground for vcc input vcc- vcc input vcc+ enable enable power good signal p_good ground of v out vout- ground of v in vin- v in (+12v) vin+ signal name connection
IRDC3840 02/02/2009 3 connection diagram fig. 1: connection diagram of ir384x evaluation boards vin pgood vo gnd gnd enable ss seq agnd vcc gnd
IRDC3840 02/02/2009 4 fig. 2: board layout, top overlay fig. 3: board layout, bottom overlay (rear view)
IRDC3840 02/02/2009 5 fig. 4: board layout, mid-layer i. fig. 5: board layout, mid-layer ii. single point connection between agnd and pgnd. agnd plane pgnd plane
IRDC3840 02/02/2009 6 fig. 6: schematic of the ir3840 evaluation board single point of connection between power ground and signal ( ?analog? ) ground vout- 1 c32 0.1uf seq. 1 c21 n/s c22 n/s vin c14 0.1uf vcc- 1 c10 0.1uf pgnd 1 l1 600nh r28 n/s c24 0.1uf c26 10000pf c13 0.1uf r19 750 r14 n/s ss 1 vout vcc+ 1 c2 10uf r9 23.7k c5 10uf r1 1.87k c3 10uf r16 0 r3 2.49k vin vcc r4 130 d1 mm3z5v6b 2 1 optional +5v supply for vcc r2 3.92k r5 3.30k q1 mmbt3904-tp c15 22uf c4 10uf r6 20 c34 10uf c16 22uf c25 n/s c17 22uf r12 3.32k c18 22uf c19 22uf c20 22uf vcc u1 ir3840 en 14 boot 13 agnd1 15 rt 5 sw 11 vcc 9 comp 3 ocset 7 pgnd 10 ss 6 seq 1 fb 2 agnd 4 pgood 8 vin 12 a 1 seq b 1 r18 4.99k + c1 330uf r* 0 c27 n/s vcc c8 2200pf c7 0.1uf vcc r7 n/s + c36 n/s + c35 n/s agnd 1 c28 n/s vin+ 1 c29 n/s vin- 1 c30 n/s vout+ 1 vout- 1 r17 10k pgood 1 c11 220pf c6 n/s enable 1 vin+ 1 vin- 1 vout+ 1
IRDC3840 02/02/2009 7 bill of materials item quantity part reference value description manufacturer part number 1 1 c1 330uf smd elecrolytic, fsize, 25v, 20% panasonic eev-fk1e331p 2 1 c34 10uf 0805, 10v, x5r, 20% panasonic - ecg ecj-gvb1a106m 3 4 c3 c4 c5 c2 10uf 1206, 16v, x5r, 20% panasonic - ecg ecj-3yb1c106m 4 6 c7 c10 c13 c14 c24 c32 0.1uf 0603, 25v, x7r, 10% panasonic - ecg ecj-1vb1e104k 5 1 c8 2200pf 0603, 50v, np0, 5% murata grm1885c1h222ja01d 6 1 c11 220pf 0603, 50v, np0, 5% panasonic- ecg ecj-1vc1h221j 76 c15 c16 c17 c18 c19 c20 22uf 0805, 6.3v, x5r, 20% panasonic- ecg ecj-2fb0j226m 8 1 c26 10000pf 0603, 50v, x7r, 10% panasonic - ecg ecj-1vb1h103k 9 1 d1 mm3z5v6b mm3z5v6b,zener, 5.6v fairchild mm3z5v6b 10 1 l1 0.6uh 11.5x10x4mm, 20%, 1.7mohm delta mpl104-0r6ir 11 1 q1 mmbt3904/sot npn, 40v, 200ma, sot-23 fairchild mmbt3904/sot 12 1 r5 3.3k thick film, 0603,1/10w,1% rohm mcr03ezpfx3301 13 1 r18 4.99k thick film, 0603,1/10w,1% rohm mcr03ezpfx4991 14 1 r4 130 thick film, 0603,1/10w,1% panasonic - ecg erj-3ekf1300v 15 1 r6 20 thick film, 0603,1/10 w,1% vishey/dale crcw060320r0fkea 16 1 r9 23.7k thick film, 0603,1/10w,1% rohm mcr03ezpfx2372 17 1 r16 0 thick film, 0603,1/10 w,5% vishay/dale crcw06030000z0ea 18 1 r12 3.32k thick film, 0603,1/10 w,1% rohm mcr03ezpfx3321 19 1 r17 10.0k thick film, 0603,1/10w,1% rohm mcr03ezpfx1002 20 1 r19 750 thick film, 0603,1/10w,1% rohm mcr03ezpfx7500 21 1 r1 1.87k thick film, 0603,1/10w,1% rohm mcr03ezpfx1871 22 1 r2 3.92k thick film, 0603,1/10w,1% rohm mcr03ezpfx3921 23 1 r3 2.49k thick film, 0603,1/10w,1% rohm mcr03ezpfx2491 24 1 u1 ir3840 pqfn, 6mmx5mm, 12a supirbuck international rectifier ir3840mpbf
IRDC3840 02/02/2009 8 typical operating waveforms vin=12.0v, vcc=5v, vo=1.8v, io=0-12a, room temperature, no air flow fig. 10: output voltage ripple, 12a load ch 1 : v out fig. 12: short (hiccup) recovery ch 1 :v out , ch 3 :v ss fig. 8: start up at 12a load, ch 1 :v o , ch 2 :v in , ch 3 :v ss , ch 4 :v pgood fig. 7: start up at 12a load ch 1 :v o , ch 2 :v in , ch 3 :v ss , ch 4 :enable fig. 9: start up with 1.62v pre bias, 0a load, ch 1 :v o , ch 3 :v ss fig. 11: inductor node at 12a load ch 3 :lx
IRDC3840 02/02/2009 9 typical operating waveforms vin=12v, vcc=5v, vo=1.8v, io=0-12a, room temperature, no air flow fig. 13: transient response, 6a to 12a step 2.5a/ s ch 1 :v out , ch 4 :i out
IRDC3840 02/02/2009 10 typical operating waveforms vin=12v, vcc=5v, vo=1.8v, io=12a, room temperature, no air flow fig. 14: bode plot at 12a load shows a bandwidth of 109khz and phase margin of 51 degrees
IRDC3840 02/02/2009 11 fig.16: power loss versus load current fig.15: efficiency versus load current typical operating waveforms vin=12v, vo=1.8v, io=0- 12a, room temperature, no air flow 88.0 88.5 89.0 89.5 90.0 90.5 91.0 91.5 92.0 92.5 10 20 30 40 50 60 70 80 90 100 load percentage (%) efficiency (%) 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 10 20 30 40 50 60 70 80 90 100 load percentage(%) power loss (w)
IRDC3840 02/02/2009 12 thermal images vin=12v, vo=1.8v, io=12a, room temperature, no air flow fig. 17: thermal image at 12a load test points 1 and 2 are ir3840 and inductor, respectively.
IRDC3840 02/02/2009 13 simultaneous tracking at power up and power down vin=12v, vo=1.8v, io=12a, room temperature, no air flow fig. 18: simultaneous tracking a 3.3v input at power-up and shut-down ch2: seq ch3:vo ch4: ss (1.8v) in order to run the ir3840 in the simultaneous tracking mode, followin g steps should be taken: - remove r16 from the board. - set the value of r14 and r28 as r2 (3.92k) and r3 (2.49k), respectively. - connect the controlling input across seq and agnd test points on the board. this voltage should be at least 1.15 time greater than vo. for the following te st results a 0-3.3v source is applied to seq pin. - the controlling input should be applied a fter the ss pin is clamped to 3.0v.
IRDC3840 02/02/2009 pcb metal and components placement the lead lands (the 11 ic pins) width should be equal to the nominal part lead width. the minimum lead to lead spacing should be 0.2mm to minimize shorting. lead land length should be equal to the maximum part lead length + 0.3 mm outboard extension. the outboard extension ensures a large and inspectable toe fillet. the pad lands (the 4 big pads other than the 11 ic pins) length and width should be equal to maximum part pad length and width. however, the minimum metal to metal spacing should be no less than 0.17mm for 2 oz. copper; no less than 0.1mm for 1 oz. copper and no less than 0.23mm for 3 oz. copper.
IRDC3840 02/02/2009 solder resist it is recommended that the lead lands are non solder mask defined (nsmd). the solder resist should be pulled away from th e metal lead lands by a minimum of 0.025mm to ensure nsmd pads. the land pad should be solder mask defined (smd ), with a minimum overlap of the solder resist onto the copper of 0.05 mm to accommodate solder resist mis-alignment. ensure that the solder resist in be tween the lead lands and the pad land is 0.15mm due to the high aspect ratio of the solder resist stri p separating the lead lands from the pad land.
IRDC3840 02/02/2009 stencil design ? the stencil apertures for the lead lands should be approximately 80% of the area of the lead lads. reducing the amount of solder deposited will minimize the occurrences of lead shorts. if too much solder is deposited on th e center pad the part will float and the lead lands will be open. ? the maximum length and width of the land p ad stencil aperture s hould be equal to the solder resist opening minus an annular 0. 2mm pull back to decreas e the incidence of shorting the center land to the lead lands when the part is pushed in to the solder paste.
IRDC3840 02/02/2009 ir world headquarters: 233 kansas st., el segundo, californ ia 90245, usa tel: (310) 252-7105 tac fax: (310) 252-7903 this product has been designed and qualified for the consumer market. visit us at www.irf.com for sales contact information data and specifications subject to change without notice. 11/07 bottom view

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