LT8646S LINER

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DESCRIPTION

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 LT8646S 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 VOUT conversion at high frequency. The LT8646S 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

Figure 4. LT8646S Demo Circuit DC2660A EMI Performance

  1. Place JP1 on BURST position.
  2. With power off, connect the input power supply to

connect the input power supply to VIN and GND.

  1. With power off, connect the load from VOUT to GND.
  2. Turn on the power at the input.
  3. Check for the proper output voltage (VOUT = 5V).
  4. Once the proper output voltage is established, adjust
  5. An external clock can be added to the SYNC terminal

Figure 5. Proper Measurement Equipment Setup

ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER Required Circuit Components 1 2 C2, C12 CAP ., X7R, 0.47µF, 100V, 10%, 0805 MURATA, GRM21BR72A474KA73L 2 1 C5 CAP ., C0G, 330pF, 50V, 5%, 0603 MURATA, GRM1885C1H331JA01D 3 1 C6 CAP ., X5R, 100µF, 10V, 20%, 1210 MURATA, GRM32ER61A107ME20L 4 1 C8 CAP ., X7R, 0.1µF, 25V, 10%, 0603 MURATA, GRM188R71E104KA01D 5 1 C9 CAP ., X5R, 10µF, 25V, 20%, 0603 MURATA, GRM188R61E106MA73D 6 1 C16 CAP ., C0G, 4.7pF, 50V, ±0.25pF, 0603 MURATA, GRM1885C1H4R7CA01D 7 1 C17 CAP ., X7S, 4.7µF, 100V, 10%, 1210 MURATA, GRJ32DC72A475KE11L 8 1 C20 CAP ., X5R, 1µF, 16V, 10%, 0603 MURATA, GRM188R61C105KA12D 9 1 L1 INDUCTOR, 1.0µH, XEL6030 COILCRAFT , XEL6030-102MEC 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, CRCW060317K8FKEA 12 1 R3 RES., CHIP , 243k, 1/10W, 1%, 0603 VISHAY, CRCW0603243KFKEA 13 1 R4 RES., CHIP , 7.5k, 1/10W, 1%, 0603 VISHAY, CRCW06037K50FKEA 14 1 R7 RES., CHIP , 1M, 1/10W, 1%, 0603 VISHAY, CRCW06031M00FKEA 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 22µF, 100V, 20% SUNCON, 100CE22BS 2 2 C3,C10 CAP ., X7R, 2.2µF, 100V, 10%, 1210 MURATA, GRM32ER72A225KA35L 3 1 C4 CAP ., X7R, 0.1µF, 100V, 10%, 0603 MURATA, GRM188R72A104KA35D 4 1 C14 CAP ., X5R, 0.1µF, 100V, 10%, 0402 MURATA, GRM155R62A104KE14D 5 0 C15, C18 (OPT) CAP ., 0603 6 0 C19 (OPT) CAP ., 1210 7 1 FB1 FERRITE BEAD, 0.006Ω 8A, 1812 WURTH ELEKTRONIK, 74279226101 8 0 R6 (OPT) RES., OPTION, 0603 9 1 R8 RES., CHIP , 0Ω, 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 2×4, 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

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 17.8K GND FB1 74279226101 E11 EN 0.47uF 100V 0805 GND OPT C17 4.7uF 100V 1210 C14 0.1uF 0402 100V JP1 1 2 SYNC PG 330pF C12 0.47uF 100V 0805 J15.6V - 65V 100uF 10V 1210 + C1 22uF 100V 243K 2.2uF 1210 100V VOUT 5V / 8A TR/SS VIN GND C16 4.7pF C18 OPT C20 1uF 16V 1.0uH XEL6030-102 10uF 25V 0.1uF C15 OPT E10 VEMI C10 2.2uF 1210 100V CLKOUT 100K E12 E14 VC 0.1uF 100V LT8646S VIN4 EN SYNC28 VCC2 RT FB 32 PG 31 BIAS 1 BST 11 GND18 GND210 TR/SS29 GND19 GND217 VIN5 VIN6 VIN21 VIN22 VIN23 GND218 GND219 VC30 CLKOUT 27 SW 12 SW 13 SW 14 SW 15 SW 16 NC NC NC NC GND GND GND GND GND GND GND GND C19 OPT 1210 E15 BIAS E13 7.50K 100K VIN

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