ANALOG DEVICES LT8640SA Synchronous Step-Down Silent Switcher 2
Product Information
Specifications
- Product Name: EVAL-LT8640SA-AZ
- Model: LT8640SA
- Input Supply Range: 5.8V – 42V
- Output Voltage: 4.85V – 5.15V
- Maximum Output Current: 6A
- Switching Frequency: 1.85MHz – 2.15MHz
- Efficiency: 94.3%
Product Usage Instructions
- Place JP1 on the BURST position.
- With the power off, connect the input power supply to VIN and GND.
- With the power off, connect the load from VOUT to GND.
- Turn on the power supply at the input. (Make sure input voltage does not exceed 42V)
- Check for the proper output voltage (VOUT = 5V).
- If there is no output, temporarily disconnect the load to ensure it is within operating ranges.
- Adjust the load within the operating ranges and observe the output.
General Description
- The demonstration circuit EVAL-LT8640SA-AZ is a 42V, 6A micropower synchronous step-down second generation Silent Switcher® with spread spectrum frequency modulation featuring the LT8640SA.
- The demo board is designed for 5V output from a 5.8V to 42V input.
- The wide input range allows a variety of input sources, such as automotive batteries and industrial supplies.
- The LT8640SA is a compact, ultra-low emission, high efficiency, and high speed synchronous 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.
- A selectable spread spectrum mode can further improve EMI/EMC performance.
- Ultra-low quiescent current in Burst Mode® operation achieves high efficiency at very light loads.
- Fast minimum on-time of 30ns enables high VIN to low VOUT conversion at high frequency.
- Program the LT8640SA switching frequency either through the oscillator resistor or external clock over a 200kHz to 3MHz range.
- The default frequency of demo circuit EVAL-LT8640SA-AZ 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.
- Select the spread spectrum mode and forced continuous mode (FCM) respectively by moving JP1 shunt. Figure 3 shows the efficiency of the circuit at 12V input and 24V input in Burst Mode Operation. Figure 4 shows the LT8640SA temperature rising on the EVAL-LT8640SA-AZ demo board under different load conditions.
- The rated maximum load current is 6A, while derating is necessary for certain input voltage and thermal conditions.
The demo board doesn’t have an EMI filter installed, but it leaves footprints for the filter components. Figure 5 shows the EMI performance of the board (without EMI filter). - The red line in Radiated EMI Performance is the CISPR32 Class B limit. The figure shows that the circuit passes the test with a wide margin. An inductor and input capacitors can be added in the EMI filter footprint to further reduce the EMI emission.
- The LT8640SA data sheet gives a complete description of the part, operation and application information.
- Read the data sheet in conjunction with this demo manual for EVAL-LT8640SA-AZ.
- The LT8640SA is assembled in a 4mm x 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 and Peak Output Current’.
Performance Summary
Performance Summary Specifications are at TA = 25°C
| PARAMETER | SYMBOL | CONDITIONS | MIN | TYP | MAX | UNIT |
| Input Supply Range | VIN | 5.8 | 42 | V | ||
| Output Voltage | VOUT | 4.85 | 5 | 5.15 | V | |
| Maximum Output Current | IOUT | 6 | A | |||
| Switching Frequency | fSW | Derating is Necessary for Certain VIN and Thermal Conditions | 1.85 | 2 | 2.15 | MHz |
| Efficiency | EFF | VIN = 12V, IOUT = 3A | 94.3 | % | ||
Quick Start Procedure
The demonstration circuit EVAL-LT8640SA-AZ is easy to set up to evaluate the performance of LT8640SA. See Figure 1 for proper measurement equipment setup, and follow the procedures below:
NOTE: When measuring the input or output voltage ripple, be careful to avoid a long ground lead on the oscilloscope probe. See Figure 2 for the proper scope technique.
- Place JP1 on the BURST position.
- With the power off, connect the input power supply to VIN and GND.
- With the power off, connect the load from VOUT to GND.
- Turn on the power supply at the input.
NOTE: Make sure that the input voltage does not exceed 42V. - Check for the proper output voltage (VOUT = 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. - 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.
- Add an external clock to the SYNC terminal when using the SYNC function (JP1 on the SYNC position). Choose R2 to set the LT8640SA switching frequency equal to or below the lowest SYNC frequency. JP1 can also set LT8640SA in spread spectrum mode (JP1 on the SPREAD-SPECTRUM position) or forced continuous mode (JP1 on the FCM position).
Typical Performance Characteristics
EVAL-LT8640SA-AZ Kit Schematic
EVAL-LT8640SA-AZ Kit Bill of Materials
| ITEM | QTY | REFERENCE | PART DESCRIPTION | MANUFACTURER/PART NUMBER |
| REQUIRED CIRCUIT COMPONENTS | ||||
| 1 | 1 | C1 | CAP., ALUM ELECT 22μF, 63V, 20%, 6.3mm x 7.7mm,
AEC-Q200, 1.2Ω, 120MA, 2000H |
EEEFN1J220XP |
| 2 | 1 | C12 | CAP., CER 0.1μF, 50V, 10%, X7R 0402m, AEC-Q200, LOW ESR | CGA2B3X7R1H104K050BB |
| 3 | 2 | C17, C18 | CAP., CER 1μF, 10V, 10%, X7S 0402 | C1005X7S1A105K050BC |
| 4 | 1 | C2 | CAP., CER 10μF, 50V, 10%, X7R 1210, AEC-Q200 | 12105C106K4T2A |
| 5 | 2 | C3, C4 | CAP., CER 1μF, 50V, 10%, X5R 0603, AEC-Q200 | GRT188R61H105KE13D |
| 6 | 1 | C5 | CAP., CER 0.1μF, 16V, 10%, X7R 0603 | C0603C104K4RAC |
| 7 | 1 | C6 | CAP., CER 10pF, 50V, 5%, C0G 0603 | C0603H100J5GAC7867 |
| 8 | 1 | C7 | CAP., CER 100μF, 10V, 20%, X5R 1210 | GRM32ER61A107ME20L |
| 9 | 1 | C8 | CAP., CER 1μF, 10V, 10%, X7R 0603 | C0603C105K8RACTU |
| 10 | 1 | C9 | CAP., CER 10μF, 10V, 10%, X5R 0603, LOW ESR | C1608X5R1A106K080AC |
| 11 | 1 | L1 | IND POWER SHIELDED WIREWOUND 1.5μH, 20%, 1MHZ, 14A, 0.01052Ω, DCR HIGH CURRENT, AEC-Q200 | XEL6030-152MEB |
| 12 | 1 | Q1 | TRAN N-CH MOSFET, 40V, 14A | SUD50N04-8M8P-4GE3 |
| 13 | 2 | R1, R4 | RES., SMD 100KΩ, 1%, 1/10W, 0603, AEC-Q200 | CRCW0603100KFKEA |
| 14 | 1 | R10 | RES., SMD 49.9Ω, 1%, 1/10W, 0603, AEC-Q200 | ERJ-3EKF49R9V |
| 15 | 1 | R2 | RES., SMD 17.8KΩ, 1%, 1/10W, 0603, AEC-Q200 | CRCW060317K8FKEA |
| 16 | 1 | R3 | RES., SMD 243KΩ, 1%, 1/10W, 0603, AEC-Q200 | CRCW0603243KFKEA |
| 17 | 1 | R5 | RES., SMD 50Ω, 1%, 1/10W, 0603, AEC-Q200 | CRCW060350R0FKEA |
| 18 | 1 | R6 | RES., SMD 1MΩ, 1%, 1/10W, 0603, AEC-Q200 | CRCW06031M00FKEA |
| 19 | 1 | R7 | RES., SMD 0Ω, JUMPER, 1/10W 0603, AEC-Q200 | ERJ-3GEY0R00V |
| 20 | 1 | R9 | RES., SMD 0.1Ω, 1%, 3W, 1225 WIDE, AEC-Q200 | KRL6432E-C-R100-F-T1 |
| 21 | 1 | U1 | IC-ADI LT8640SA | LT8640SAAV#TRPBF |
| ADDITIONAL EVALUATION BOARD CIRCUIT COMPONENTS | ||||
| 22 | 2 | C10, C11 | CAP CER, 10μF, 50V, 10%, X7R 1210 | GRM32ER71H106KA12L |
| 23 | 1 | C13 | CAP CER, 0.1μF, 50V, 10%, X7R 0402, AEC-Q200 LOW ESR | CGA2B3X7R1H104K050BB |
| 24 | 3 | C14, C15, C16 | TBD0603 | |
| 25 | 1 | FB1 | IND FERRITE BEAD MULTI LAYER 100Ω AT 100MHZ, 25%, 8A, 0.006Ω, 1812, AEC-Q200 | 74279226101 |
| 26 | 1 | R8 | TBD0603 | |
| HARDWARE: FOR EVALUATION BOARD ONLY | ||||
| 27 | 1 | SHUNT FEMALE 2POS 2mm | 60800213421 | |
| 28 | 4 | STANDOFF, SELF-RETAINING SPACER, 12.7mm LENGTH | 702935000 | |
|
29 |
12 |
TP1, TP2, TP3, TP4, TP5, TP6, TP7, TP8, TP9, TP10,TP11,TP12 |
CONN-PCB SOLDER TERMINAL TEST POINT TURRET 0.094″ MTG, HOLE PCB 0.062 INCH THK |
2501-2-00-80-00-00-07-0 |
| 30 | 4 | J1, J2, J3, J4 | CONN-PCB, BANANA JACK, FEMALE, NON-INSULATED, THT, SWAGE, 0.218 INCHES LENGTH | 575-4 |
| 31 | 2 | J5, J6 | CONN-PCB BNC JACK ST 50Ω | 112404 |
| 32 | 1 | JP1 | CONN-PCB 8POS MALE HDR UNSHROUDED DUAL ROW ST, 2mm PITCH, 2.80mm SOLDER TAIL | 62000821121 |
EVAL-LT8640SA-AZ Kit PCB Layout
Revision History
| REVISION NUMBER | REVISION DATE | DESCRIPTION | PAGES CHANGED |
| 0 | 09/24 | Initial release | — |
Notes
ALL INFORMATION CONTAINED HEREIN IS PROVIDED “AS IS” WITHOUT REPRESENTATION OR WARRANTY. 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 ARE SUBJECT TO CHANGE WITHOUT NOTICE. NO LICENSE, EITHER EXPRESSED OR IMPLIED, IS GRANTED UNDER ANY ADI PATENT RIGHT, COPYRIGHT, MASK WORK RIGHT, OR ANY OTHER ADI INTELLECTUAL PROPERTY RIGHT RELATING TO ANY COMBINATION, MACHINE, OR PROCESS IN WHICH ADI PRODUCTS OR SERVICES ARE USED. TRADEMARKS AND REGISTERED TRADEMARKS ARE THE PROPERTY OF THEIR RESPECTIVE OWNERS. ALL ANALOG DEVICES PRODUCTS CONTAINED HEREIN ARE SUBJECT TO RELEASE AND AVAILABILITY.
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FAQ
Q: What is the default switching frequency of the demo circuit?
A: The default switching frequency of demo circuit EVAL-LT8640SA-AZ is 2MHz.
Q: How can I synchronize to an external clock?
A: Move JP1 to SYNC and apply the external clock to the SYNC terminal to synchronize to an external clock.
Q: What is the maximum load current of LT8640SA?
A: The rated maximum load current is 6A, but derating is necessary for certain input voltage and thermal conditions.
Q: Does the demo board have an EMI filter installed?
A: The demo board doesn't have an EMI filter installed, but it leaves footprints for the filter components.
Documents / Resources
 |
ANALOG DEVICES LT8640SA Synchronous Step-Down Silent Switcher 2 [pdf] User Guide EVAL-LT8640SA-AZ, LT8640SA Synchronous Step-Down Silent Switcher 2, LT8640SA, Synchronous Step-Down Silent Switcher 2, Step-Down Silent Switcher 2, Silent Switcher 2, Switcher 2 |