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rt 2872 g sp evaluation board evb_rt2872 g sp - 00 june 2015 http://www.richtek.com rt 2872 step - down converter evaluation board purpose the rt2872 is a high - efficiency current mode synchronous step - down regulator that can deliver up to 3a output current from a wide input voltage range of 4.5v to 36v. this document explains the function a nd use of the rt2872 evaluation board (evb) and provides information to enable operation and modification of the evaluation board and circuit to suit individual requirements. table of contents purp ose ................................ ................................ ................................ ................................ ............................... 1 introduction ................................ ................................ ................................ ................................ .......................... 2 general product description ................................ ................................ ................................ ................................ 2 product features ................................ ................................ ................................ ................................ ................. 2 application ................................ ................................ ................................ ................................ ........................... 2 evaluation board ................................ ................................ ................................ ................................ ................. 3 specification ................................ ................................ ................................ ................................ ........................ 4 schematic ................................ ................................ ................................ ................................ ............................ 4 bom ................................ ................................ ................................ ................................ ................................ .... 5 pcb layout ................................ ................................ ................................ ................................ ......................... 6 step - down converter efficiency test ................................ ................................ ................................ ................. 10 more information ................................ ................................ ................................ ................................ ................ 11 important notice for richtek evaluation board ................................ ................................ ................................ ... 11 y o u r p o w e r p a r t n e r .
rt 2872 g sp evaluation board evb_rt2872 g sp - 00 june 2015 http://www.richtek.com introduction general product description the rt2872 is a high efficiency, current mode synchronous step - down dc/dc converter that can deliver up to 3a output current over a wide input voltage range from 4.5v to 36v. the device int egrates a 1 05 m high side and an 80m low side mosfet to achieve high conversion efficiency up to 95%. the current mode control architecture supports fast transient response and uses a simple compensation circuit. a cycle - by - cycle current limit function provides prote ction against a shorted output and an internal soft - start eliminates input surge current during start - up. the rt2872 provides complete protection functions such as input under voltage lockout, output under voltage protection, over current protection and th ermal shutdown. the rt2872 is available in the thermal enhanced sop - 8 (exposed pad) package. product features ? 4.5v to 36v input voltage range ? 3a output current ? internal n - mosfets ? current mode control ? frequency operation : 300khz to 1mhz ? adjustable output voltage from 0.8v to 30v ? high efficiency up to 95% ? stable with low esr ceramic output capacitors ? cycle - by - cycle current limit ? aec - q100 grade 3 certification application ? point of load regulator in distributed power systems ? digital set top boxes ? broadband co mmunications ? vehicle electronics ? automotive audio, navigation, and information systems ? enterprise datacom platforms point of load (pol) ? industrial grade general purpose point of load y o u r p o w e r p a r t n e r .
rt 2872 g sp evaluation board evb_rt2872 g sp - 00 june 2015 http://www.richtek.com evaluation board please carefully inspect the evb ic and external com ponents, comparing them to the following bill of materials, to ensure that all components are installed and undamaged. if any components are missing or damaged during transportation, please contact the distributor o r send e - mail to evb_service@richtek.com test points the evb is provided with the test points and pin names listed in the table below. test point/pin name signal comment (expected waveforms or voltage levels on test points) vin input voltage input voltage range = 4.5v to 36v vout output voltage default output voltage = 3.3v output voltage range = 0.8v to 30v (see output voltage setting section for changing output voltage level) sw switch node sw waveform en chip enable operation enable sig nal. en is automatically pulled high (by r4) to enable operation. connect en low to disable operation. boot boot strap supply test point floating supply voltage for the high - side n - mosfet switch mode r t test point switch frequency setting point gnd grou nd ground power - up & measurement procedure 1. apply a 12v nominal input power supply (4.5v < v in < 36v) to the vin and gnd terminals. 2. the en voltage is pulled to logic high by r4 (100k to vin) to enable operation. drive en high (>2.0v) to enable operation o r low (<0.4v) to disable operation. 3. verify the output voltage (approximately 3.3v) between vout and gnd. 4. connect an external load up to 3a to the vout and gnd terminals and verify the output voltage and current. y o u r p o w e r p a r t n e r .
rt 2872g sp evaluation board evb_rt2872g sp -00 june 2015 http://www.richtek.com output voltage setting set the output volta ge with the resistive divider (r1, r2) between vout and gnd with the midpoint connected to fb through rcamp. the output is set by the following formula: the installed v out capacitors (c4, c5) are 22 f, 16v x5r ceramic types. do not exceed their operating voltage range and consider their voltage coefficient (capacitance vs. bias voltage) and ensure that the capacitance is sufficient to maintain stability and provide sufficient transient response for y our application. this can be verified by checking the output transient response as described in the rt2872 ic data sheet. specification parameter symbol min typ . max units input voltage range v in 4 .5 3 6 v output voltage v out 3.3 v oscillator frequency f osc 300k 1m hz output current i out 3 a high - side switch current limit range u oc 4.25 5 5.75 a schematic y o u r p o w e r p a r t n e r . out r1 v = 0.8 x (1 + ) r2 gnd u1 sop-8(exposed pad) boot 2 vin 8 sw 1 gnd 4,9 r7 7 en 3 comp 6 fb 5 l1 4.7uh r7 137k tp2 mode r4 100k r5 nf c13 nf rcamp 0 c1 10uf c2 10uf c4 22uf c8 nf c7 2.7nf c3 0.1uf c5 22uf r1 75k r2 24k r3 13k c6 0.1uf tp1 en c11 0.1uf c9 nf d2 nf d1 nf r6 0 gp1 vin gp2 gnd gp3 vout gp4 gnd tp3 sw tp4 boot c12 nf
rt 2872 g sp evaluation board evb_rt2872 g sp - 00 june 2015 http://www.richtek.com bom reference q'ty p/n description package manufacture u1 1 rt 2872 gsp dc/dc converter psop - 8 r ichtek c1, c2 2 c3216x5r1h106k160ab 10f/10%/50v/x5r ceramic capacitor 1206 tdk c4, c5 2 grm32er61c226ke20# 22f/10%/16v/x5r ceramic capacitor 1210 murata c7 1 0603b272k500 2.7nf/10%/50v/x7r ceramic capacitor 0603 walsin c3, c6, c11 3 c1608x7r1h104k080aa 0.1f/10%/50v/x7r ceramic capa citor 0603 tdk c8, c9, c12, c13 0 not installed 0603 l1 1 7447714047 4.7h, 8a, dcr = 12.4m 10.00mm x 10.00mm we r1 1 75k/1%, resistor 0603 r2 1 24k/1%, resistor 0603 r3 1 13k/1%, resistor 0603 r4 1 100k/1%, resistor 0603 r5, d1, d2 0 not installed r6, rcamp 2 0, resistor 0603 r t 1 1 13 k/1%, resistor 0603 tp 4 test pin gp 4 golden pin y o u r p o w e r p a r t n e r .
rt 2872 g sp evaluation board evb_rt2872 g sp - 00 june 2015 http://www.richtek.com pcb layout top view (1 st la yer) bottom view ( 4 th layer) y o u r p o w e r p a r t n e r .
rt 2872 g sp evaluation board evb_rt2872 g sp - 00 june 2015 http://www.richtek.com component placement guide component side (1 st la yer) pcb layout component side (1 st layer) y o u r p o w e r p a r t n e r .
rt 2872 g sp evaluation board evb_rt2872 g sp - 00 june 2015 http://www.richtek.com pcb l ayout inner side (2 n d layer) pcb l ayout inner side (3 rd l ayer) y o u r p o w e r p a r t n e r .
rt 2872 g sp evaluation board evb_rt2872 g sp - 00 june 2015 http://www.richtek.com componen t placement guide bottom side (4 th layer) pcb layout bottom side (4 th layer) y o u r p o w e r p a r t n e r .
rt 2872 g sp evaluation board evb_rt2872 g sp - 00 june 2015 http://www.richtek.com step - down converter efficiency test y o u r p o w e r p a r t n e r .
rt 2872 g sp evaluation board evb_rt2872 g sp - 00 june 2015 http://www.richtek.com more information for more information, please find the related datasheet or application notes from rich t ek website http://www. richtek .com. important notice for richtek evaluation board this document is for reference only, nothing contain ed in this document shall be construed as richteks warranty, express or implied, under contract, tort or statutory, with respect to the presentation herein. in no event shall richtek be liable t o buyer or user for any and all damages including without lim itation to direct, indirect, special, punitive or consequential damages. y o u r p o w e r p a r t n e r .

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