1 description lt8646 s 65v , 8a synchronous step-down silent switcher 2 demonstration circuit 2660a is a 65v, 8a synchronous step-down second generation silent switcher ? with spread spectrum frequency modulation featuring the lt ? 8646s. the demo board is designed for 5v output from a 5.6v to 65v input. the wide input range allows a variety of input sources, such as automotive batter - ies and industrial supplies. the lt8646 s is a compact, ultralow emission, high efficiency, and high speed syn - chronous monolithic step-down switching regulator. the integrated bypass capacitors optimize all the fast current loops and make it easier to minimize emi/emc emissions by reducing layout sensitivity. selectable spread spectrum mode can further improve emi/emc performance. fast minimum on-time of 40ns enables high v in to low v out conversion at high frequency. the lt8646 s switching frequency can be programmed either via oscillator resistor or external clock over a 200khz to 2.2mhz range. the default frequency of demo circuit 2660a is 2mhz. the sync pin on the demo board is grounded (jp1 at burst position) by default for low ripple burst mode operation. to synchronize to an external clock, move jp1 to sync and apply the external clock to the sync terminal. spread spectrum mode and pulse skipping mode can be selected respectively by moving jp1 shunt. figure?1 shows the efficiency of the circuit at 12v input and 24v input in burst mode operation (input from vin terminal to bypass the emi filter). figure? 2 shows the LT8646S temperature rising on dc2660a demo board under different load conditions. the rated all registered trademarks and trademarks are the property of their respective owners. performance summary maximum load current is 8a, while derating is neces - sary for certain input voltage and thermal conditions. low switching frequency can extend the output load capability by reducing the power dissipations. figure?3 shows the temperature rising at 500khz switching frequency. the demo board has an emi filter installed. the emi performance of the board (with emi filter) is shown on figure?4. the red line in radiated emi performance is cisp r25 class 5 peak limit. the figure shows that the circuit passes the test with a wide margin. to achieve emi/ emc performance as shown in figure?4, the input emi filter is required and the input voltage should be applied at vemi terminal. an inductor can be added in the emi filter to further reduce the conducted emission. the emi filter can be bypassed by applying the input voltage at vin terminal. the LT8646S data sheet gives a complete description of the part, operation and application information. the data sheet must be read in conjunction with this demo manual for demo circuit 2660a. the LT8646S is assembled in a 6mm 4mm lqfn package with exposed pads for low thermal resistance. the layout recommendations for low emi operation and maximum thermal performance are available in the data sheet section low emi pcb layout and thermal considerations. design files for this circuit board are available at http://www.linear.com/demo/dc2660a specifications are at t a = 25c symbol parameter conditions min typ max units v in_emi input supply range with emi filter 5.6 65 v v out output voltage 4.85 5 5.15 v i out maximum output current derating is necessary for certain v in and thermal conditions 8 a f sw switching frequency 1.85 2 2.15 mhz eff efficiency v in = 12v , i out = 4a 93.8 % dc2660af demo manual dc2660a
2 description figure?1. LT8646S demo circuit dc2660a efficiency vs load current (input from vin terminal) figure?2. LT8646S demo circuit dc2660 a case temperature rising vs input voltage ( 2mhz) figure?3. LT8646S demo circuit dc2660 a case temperature rising vs input voltage ( 500khz) f 2 v out = 5v f sw = 500khz dc2660af demo manual dc2660a power loss 4 5 6 7 8 60 65 70 75 80 v out = 5v f sw = 2mhz sync/mode = gnd 85 90 95 100 0 0.8 1.6 2.4 3.2 4.0 efficiency 4.8 5.6 6.4 efficiency (%) power loss (w) dc2660a f01 i out = 8a i out = 6a i out = 4a input voltage (v) v in =12v 12 18 24 30 36 42 48 54 60 0 v in =24v 10 20 30 40 50 60 70 80 90 100 load current (a) case temperature rising (c) dc2660a f02 i out = 8a i out = 6a i out = 4a input voltage (v) 12 18 24 30 1 36 42 48 54 60 0 10 20 30 40 2 50 60 70 80 90 100 case temperature rising (c) dc2660a f03 3
3 description figure?4. LT8646S demo circuit dc2660a emi performance (14v input from vemi, with emi filter, i out = 4a) (with emi filter installed) 14v input to 5v output at 4a, f sw = 2mhz (with emi filter installed) 14v input to 5v output at 4a, f sw = 2mhz dc2660a f04a dc2660a f04b dc2660a f04c conducted emi performance radiated emi performance (cispr25 radiated emission t est with class 5 peak limits) ver tical polariza tion peak detector 0 100 200 300 400 500 600 700 800 900 1000 0 3 6 9 12 15 18 21 24 27 30 0 100 amplitude (dbv/m) amplitude (dbv/m) amplitude (dbv) 200 300 400 500 600 700 800 900 1000 horizontal polariza tion peak detector class 5 peak limit spread spectrum mode fixed frequency mode class 5 peak limit spread spectrum mode fixed frequency mode fixed frequency mode spread spectrum mode dc2660af demo manual dc2660a frequency (mhz) 30 35 40 45 50 ?30 ?20 ?10 0 10 frequency (mhz) 20 30 40 50 60 ?5 0 5 10 15 ?5 20 25 30 35 40 45 50 frequency (mhz) 0 5 10 15 20 25
4 quick start procedure demonstration circuit 2660a is easy to set up to evalu - ate the performance of the lt8646 s. refer to figure?5 for proper measurement equipment setup and follow the procedure below: note: when measuring the input or output voltage ripple, care must be taken to avoid a long ground lead on the oscilloscope probe. measure the output voltage ripple by touching the probe tip directly across the output capaci - tor. see figure?6 for the proper scope technique. figure?7 shows the output voltage ripple measured at the output capacitor c9. 1. place jp1 on burst position. 2. with power off, connect the input power supply to vemi and gnd. if the input emi filter is not desired, connect the input power supply to vin and gnd. 3. with power off, connect the load from v out to gnd. 4. turn on the power at the input. note: make sure that the input voltage does not exceed 65v. 5. check for the proper output voltage (v out = 5v). note: if there is no output, temporarily disconnect the load to make sure that the load is not set too high or is shorted. 6. once the proper output voltage is established, adjust the load within the operating ranges and observe the output voltage regulation, ripple voltage, efficiency and other parameters. 7. an external clock can be added to the sync terminal when sync function is used (jp1 on the sync posi - tion). please make sure that r2 should be chose to set the lt8646 s switching frequency equal to or below the lowest sync frequency. jp1 can also set LT8646S in spread spectrum mode (jp1 on the spread-spec - trum position) or pulse skipping mode (jp1 on the pulse-skipping position). _ e m i figure?5. proper measurement equipment setup dc2660af demo manual dc2660a
5 quick start procedure figure?6. measuring output ripple at output capacitor c9 figure?7. LT8646S demo circuit dc2660 a output voltage ripple (12v input, i out = 8a, full bw) dc2660a f07 + ? v out gnd c9 dc2660af demo manual dc2660a 500ns/div v out 5mv/div ac coupled
6 parts list item qty reference part description manufacturer/part number required circuit components 1 2 c2, c12 cap., x7r, 0.47f, 100v, 10%, 0805 murata, gr m21br72a474ka73l 2 1 c5 cap., c0g, 330pf, 50v, 5%, 0603 murata, gr m1885c1h331ja01d 3 1 c6 cap., x5r, 100f, 10v, 20%, 1210 murata, gr m32er61a107me20l 4 1 c8 cap., x7r, 0.1f, 25v, 10%, 0603 murata, gr m188r71e104ka01d 5 1 c9 cap., x5r, 10f, 25v, 20%, 0603 murata, gr m188r61e106ma73d 6 1 c16 cap., c0g, 4.7pf, 50v, 0.25pf, 0603 murata, gr m1885c1h4r7ca01d 7 1 c17 cap., x7s, 4.7f, 100v, 10%, 1210 murata, gr j32dc72a475ke11l 8 1 c20 cap., x5r, 1f, 16v, 10%, 0603 murata, gr m188r61c105ka12d 9 1 l1 inductor, 1.0h, xel6030 coilcraft, xe l6030-102mec 10 2 r1, r5 res., chip, 100k, 1/10w, 1%, 0603 vishay, crcw0603100kfkea 11 1 r2 res., chip, 17.8k, 1/10w, 1%, 0603 vishay, crcw060317 k8fkea 12 1 r3 res., chip, 243k, 1/10w, 1%, 0603 vishay, crcw0603243kfkea 13 1 r4 res., chip, 7.5k, 1/10w, 1%, 0603 vishay, crcw06037 k50fkea 14 1 r7 res., chip, 1m, 1/ 10w, 1%, 0603 vishay, crcw06031 m00fkea 15 1 u1 i.c., 65v, 8a sync buck, 6mm 4mm lqfn linear tech., LT8646Sev#pbf additional demo board circuit components 1 1 c1 cap., alum 22f, 100v, 20% suncon, 100ce22bs 2 2 c3,c10 cap., x7r, 2.2f, 100v, 10%, 1210 murata, gr m32er72a225ka35l 3 1 c4 cap., x7r, 0.1f, 100v, 10%, 0603 murata, gr m188r72a104ka35d 4 1 c14 cap., x5r, 0.1f, 100v, 10%, 0402 murata, gr m155r62a104ke14d 5 0 c15, c18 (opt) cap., 0603 6 0 c19 (opt) cap., 1210 7 1 fb1 ferrite bead, 0.006 8a, 1812 wurth elektronik, 74279226101 8 0 r6 (opt) res., option, 0603 9 1 r8 res., chip, 0, 1/10w, 1%, 0603 vishay, crcw06030000z0ea hardware: for demo board only 1 9 e1, e5-e9, e11, e14-e15 testpoint, turret, .094" mill-max, 2501-2-00-80-00-00-07-0 2 4 e2, e10, e12, e13 testpoint, turret, .061" mill-max, 2308-2-00-80-00-00-07-0 3 1 jp1 24, 2mm double row header wurth elektronik, 62000821121 4 1 xjp1 shunt, 2mm center wurth elektronik, 60800213421 5 4 j1-j4 jack banana keystone, 575-4 6 4 mh1-mh4 stand-off, nylon 0.50" tall wurth elektronik, 702935000 dc2660af demo manual dc2660a
7 information furnished by analog devices is believed to be accurate and reliable. however, no responsibility is assumed by analog devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. specifications subject to change without notice. no license is granted by implication or otherwise under any patent or patent rights of analog devices. schematic diagram all capacitors are 0603. notes: unless otherwise specified 1. all resistors are 0603. 100ce22bs sync burst spread-spectrum pulse-skipping * * see demo manual r2 17.8k e9 gnd fb1 74279226101 e11 en c2 0.47uf 100v 0805 e2 gnd r6 opt c17 4.7uf 100v 1210 c14 0.1uf 0402 100v jp1 1 2 3 5 7 4 6 8 r8 0 e5 sync e8 pg c5 330pf c12 0.47uf 100v 0805 j1 5.6v - 65v c6 100uf 10v 1210 + c1 22uf 100v r3 243k r7 1m c3 2.2uf 1210 100v j3 vout 5v / 8a e7 tr/ss e1 vin j4 gnd c16 4.7pf c18 opt c20 1uf 16v l1 1.0uh xel6030-102 c9 10uf 25v c8 0.1uf c15 opt e10 vemi c10 2.2uf 1210 100v e6 clkout j2 r5 100k e12 e14 vc c4 0.1uf 100v u1 LT8646S vin 4 en 2 5 sync 28 vcc 2 rt 2 6 fb 32 pg 31 bias 1 bst 11 gnd1 8 gnd2 10 tr/ss 29 gnd1 9 gnd2 17 vin 5 vin 6 vin 21 vin 22 vin 23 gnd2 18 gnd2 19 vc 30 clkout 27 sw 12 sw 13 sw 14 sw 15 sw 16 nc 3 nc 7 nc 2 0 nc 2 4 gnd 3 3 gnd 3 4 gnd 3 5 gnd 3 6 gnd 3 7 gnd 3 8 gnd 4 0 gnd 4 1 c19 opt 1210 e15 bias e13 r4 7.50k r1 100k vin dc2660af demo manual dc2660a
8 lt 0218 ? printed in usa ? analog devices, inc. 2018 esd caution esd (electrostatic discharge) sensitive device. charged devices and circuit boards can discharge without detection. although this product features patented or proprietary protection circuitry, damage may occur on devices subjected to high energy esd. therefore, proper esd precautions should be taken to avoid performance degradation or loss of functionality. legal terms and conditions by using the evaluation board discussed herein (together with any tools, components documentation or support materials, the evaluation board), you are agreeing to be bound by the terms and conditions set forth below ( agreement ) unless you have purchased the evaluation board, in which case the analog devices standard terms and conditions of sale shall govern. do not use the evaluation board until you have read and agreed to the agreement. your use of the evaluation board shall signify your acceptance of the agreement. this agreement is made by and between you ( customer) and analog devices, inc. (adi ), with its principal place of business at one technology way, norwood, ma 02062, usa. subject to the terms and conditions of the agreement, adi hereby grants to customer a free, limited, personal, temporary, non-exclusive, non-sublicensable, non-transferable license to use the evaluation board for evaluation purposes only. customer understands and agrees that the evaluation board is provided for the sole and exclusive purpose referenced above, and agrees not to use the evaluation board for any other purpose. furthermore, the license granted is expressly made subject to the following additional limitations: customer shall not (i) rent, lease, display, sell, transfer, assign, sublicense, or distribute the evaluation board; and (ii) permit any third party to access the evaluation board. as used herein, the term third party includes any entity other than adi, customer, their employees, affiliates and in-house consultants. the evaluation board is not sold to customer; all rights not expressly granted herein, including ownership of the evaluation board, are reserved by adi. confidentiality. this agreement and the evaluation board shall all be considered the confidential and proprietary information of adi. customer may not disclose or transfer any portion of the evaluation board to any other party for any reason. upon discontinuation of use of the evaluation board or termination of this agreement, customer agrees to promptly return the evaluation board to adi. additional restrictions. customer may not disassemble, decompile or reverse engineer chips on the evaluation board. customer shall inform adi of any occurred damages or any modifications or alterations it makes to the evaluation board, including but not limited to soldering or any other activity that affects the material content of the evaluation board. modifications to the evaluation b oard must comply with applicable law, including but not limited to the rohs directive. termination. adi may terminate this agreement at any time upon giving written notice to customer. customer agrees to return to adi the evaluation board at that time. limitation of liability. the evaluation board provided hereunder is provided as is and adi makes no warranties or representations of any kind with respect to it. adi specifically disclaims any representations, endorsements, guarantees, or warranties, express or implied, related to the evaluation board including, but not limited to, the implied warranty of merchantability, title, fitness for a particular purpose or noninfringement of intellectual property rights. in no event will adi and its licensors be liable for any incidental, special, indirect, or consequential damages resulting from customer s possession or use of the evaluation board, including but not limited to lost profits, delay costs, labor costs or loss of goodwill. adi s total liability from any and all causes shall be limited to the amount of one hundred us dollars ($100.00). export. customer agrees that it will not directly or indirectly export the evaluation board to another country, and that it will comply with all applicable united states federal laws and regulations relating to exports. governing law. this agreement shall be governed by and construed in accordance with the substantive laws of the commonwealth of massachusetts (excluding conflict of law rules). any legal action regarding this agreement will be heard in the state or federal courts havin g jurisdiction in suffolk county, massachusetts, and customer hereby submits to the personal jurisdiction and venue of such courts. the united nations convention on contracts for the international sale of goods shall not apply to this agreement and is expressly disclaimed. dc2660af demo manual dc2660a
|
