ANALOG DEVICES LT8625SP-1 Synchronous Step Down Silent Switcher User Manual

ANALOG DEVICES LT8625SP-1 Synchronous Step-Down Silent Switcher

Product Specifications:

• Model : LT8625SP-1
• Input Voltage Range: 2.7V to 18V
• Output Voltage: Default 1V
• Switching Frequency: Programmable from 300kHz to 4MHz
• Maximum Output Current: 8A
• Efficiency: Up to 77.2%

Product Usage Instructions

Setting the Switching Frequency:
The LT8625SP-1 switching frequency can be programmed via an oscillator resistor or external clock over a range of 300kHz to 4MHz. The default frequency on demo circuit 3220A is 2MHz.

Operating Modes:
By default, the SYNC pin is grounded for low ripple pulse skip mode operation. To synchronize to an external clock, move JP1 toSYNC and connect the external clock to the SYNC terminal. Forced continuous mode (FCM) can be selected by adjusting JP1 shunt.

EMI Performance:
The demo board includes an EMI filter for improved performance. Refer to Figure 3 for Radiated EMI Performance results.

Noise Reduction:
The regulator features ultralow noise over a wide frequency range. See Figure 4 for Noise Spectral Density information.

Quick Start Procedure:

1. Refer to Figure 5 for equipment setup.
2. Avoid long ground leads when measuring voltage ripple.
3. Measure output voltage ripple across the output capacitor directly.
4. Input voltage ripple and remote output voltage ripple can be measured through SMA connectors.
5. Output voltage ripple at capacitor C22 can be measured through the VO_SENSE SMA connector (refer to Figure 6).

DESCRIPTION

Demonstration circuit 3220A is an 18V, 8A synchronous step-down Silent Switcher® 3 with ultralow noise, high efficiency and power density featuring the LT®8625SP-1. The input voltage range of DC3220A is 2.7V to 18V. The default demo board setting is 1V at 8A maximum DC output current. The LT8625SP-1 is a compact, ultralow noise, ultralow emission, high efficiency and high speed synchronous monolithic step-down switching regulator. The uniquely designed combination of the ultralow noise reference and the third- generation Silent Switcher architecture enables the LT8625SP-1 to achieve both high efficiency and excellent wideband noise performance. A minimum on-time of 15ns allows high VIN to low VOUT conversion at high frequencies. The LT8625SP-1 switching frequency can be programmed either via oscillator resistor or external clock over a 300kHz to 4MHz range. The default frequency of demo circuit 3220A is 2MHz. The SYNC pin on the demo board is grounded by default for low ripple pulse skip mode operation. To synchronize to an external clock, move JP1 to SYNC and apply the external clock to the SYNC terminal. Forced continuous mode (FCM) can be selected by moving JP1 shunt. Figure 1 shows the efficiency of the circuit at 5V input and 12V input in forced continuous mode operation (input from VIN terminal). Figure 2 shows the LT8625SP-1 temperature rising on DC3220A demo board under 6A and 8A load conditions. The demo board has an EMI filter installed. The EMI performance of the board is shown on Figure 3. The red line in Radiated EMI Performance is the CISPR32 Class B limit. In addition to the excellent EMI performance, the regulator also features ultralow noise over a wide frequency range, as is shown in Figure 4. The LT8625SP-1 data sheet gives a complete description of the part including operation and application informa-tion. The data sheet must be read in conjunction with this demo manual for demo circuit 3220A. The LT8625SP-1 is assembled in a 4mm × 4mm LQFN package with exposed pads and exposed die for low thermal resistance. The layout recommendations for low EMI operation and maximum thermal performance are available in the datasheet section Low EMI PCB Layout and Thermal Considerations. Design files for this circuit board are available.

PERFORMANCE SUMMARY

QUICK START PROCEDURE

Demonstration circuit 3220A is easy to set up to evaluate the performance of LT8625SP-1. Please refer to Figure 5 for proper equipment setup and follow the test procedures 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 capacitor. For input voltage ripple and the remote output voltage ripple, they can also be measured through the SMA connectors via VIN_SENSE and VO_SENSE. Figure 6 shows the output voltage ripple measured at the output capacitor C22 through the VO_SENSE SMA connector.

1. Place JP1 on FCM position.
2. With power off, connect the input power supply to VIN (J1) and GND (J2).
3. With power off, connect the load from VOUT (J5) to GND (J6).
4. Connect the DMM between the input test points: VIN_SENSE (E1) and SENSE_GND (E2) to monitor the input voltage. Connect DMM between VO_SENSE (E4) and SENSE_GND (E7) to monitor the output voltage
5. Turn on the power supply at the input.
6. Check for the proper output voltage (VOUT = 1V).
7. Once the input and output voltages are properly established, adjust the load current within the operating range of 0A to 8A max. Observe the output voltage regulation, output voltage ripples, switching node waveform, load transient response and other parameters.
8. An external clock can be added to the SYNC terminal when the SYNC function is used (JP1 on the SYNC posi-tion). The RT resistor (R4) should be chosen to set the LT8625SP-1 switching frequency at least 20% below the lowest SYNC frequency.

TYPICAL PERFORMANCE CHARACTERISTICS

PARTS LIST

ITEM| QTY| REFERENCE| PART DESCRIPTION| MANUFACTURER/PART NUMBER
---|---|---|---|---

Required Circuit Components

NMC0603X5R106M25TRPF SAMSUNG, CL10A106MA8NRNC TDK, C1608X5R1E106M080AC
3| 2| C3, C6| CAP., 22µF, X7R, 25V, 10%, 1210| AVX, 12103C226KAT2A KEMET, C1210C226K3RACTU

MURATA, GRM32ER71E226KE15L SAMSUNG, CL32B226KAJNNNE

4| 1| C4| CAP., 100µF, ALUM ELECT, 25V, 20%, 6.3mm × 7.7mm, CE-BS SERIES| SUN ELECTRONIC INDUSTRIES CORP, 25CE100BS
5| 1| C8| CAP., 6800pF, X7R, 25V, 10%, 0603| YAGEO, CC0603KRX7R8BB682 AVX, 06033C682KAT2A

MURATA, GRM188R71E682KA01D WURTH ELEKTRONIK, 885012206064

6| 1| C10| CAP., 0.1µF, X7R, 25V, 10%, 0603, AEC-Q200| MURATA, GCM188R71E104KA57D TDK, CGA3E2X7R1E104K080AA
7| 0| C11, C12, C13| CAP., OPTION, 0603|
8| 1| C14| CAP., 2.2µF, X7R, 25V, 10%, 0805, AEC-Q200| TAIYO YUDEN, TMK212B7225KGHT
9| 3| C15, C20, C29| CAP., 22µF, X5R, 10V, 20%, 0603| AVX, 0603ZD226MAT2A

MURATA, GRM188R61A226ME15D SAMSUNG, CL10A226MP8NUNE

10| 2| C16, C21| CAP., 2.2µF, X7R, 10V, 10%, 0603| MURATA, GRM188R71A225KE15D TDK, C1608X7R1A225K080AC AVX, 0603ZC225KAT2A

YAGEO, CC0603KRX7R6BB225

11| 3| C18, C19, C22| CAP., 100µF, X5R, 10V, 20%, 1206| TDK, C3216X5R1A107M160AC
12| 2| C23, C24| CAP., 27µF, FEED THRU, 6.3V, 20%, 1206, 3-TERM, 5mΩ DCR, 6A| MURATA, NFM31PC276B0J3L
13| 1| C30| CAP., 470pF, C0G, 25V, 10%, 0603| AVX, 06033A471KAT2A KEMET, C0603C471K3GACTU
14| 9| E1, E2, E3, E4, E5, E6, E7, E8, E9| TEST POINT, 0805, 2mm × 1.25mm × 1.45mm, PROBE PAD, FOIL, VERT, SMT, NATURAL| TE CONNECTIVITY, 1625854-2 TE CONNECTIVITY, RCT-0C
15| 1| FB1| IND., 60Ω AT 100MHz, PWR, FERRITE BEAD, 25%, 5100mA, 15mΩ, 0603| WURTH ELEKTRONIK, 74279228600
16| 4| J1, J2, J5, J6| CONN., BANANA JACK, FEMALE, THT, NON-INSULATED, SWAGE, 0.218″| KEYSTONE, 575-4
17| 2| J3, J4| CONN., RF/COAX, SMA JACK, FEMALE, 1PORT, VERT, ST, SMT, 50Ω, Au| MOLEX, 0732511350

MOLEX, 73251-1350

MOLEX, 732511350

18| 2| JP1, JP2| CONN., HDR, MALE, 2×3, 2mm, VERT, ST, THT| WURTH ELEKTRONIK, 62000621121
19| 1| L1| IND., 0.3µH, PWR, SHIELDED, 20%, 18.9A, 3.1mΩ, 4.3mm

× 4.3mm, XEL4030, AEC-Q200

| COILCRAFT, XEL4030-301MEB COILCRAFT, XEL4030-301MEC
20| 1| L2| IND., 1µH, PWR, SHIELDED, 20%, 4A, 52.5mΩ, 1616AB, IHLP-01 SERIES| VISHAY, IHLP1616ABER1R0M01
21| 0| L3| IND., 0.47µH, PWR, SHIELDED, 20%, 15.6A, 4.6mΩ, 4.3mm

× 4.3mm, XEL4030, AEC-Q200

| COILCRAFT, XEL4030-471MEB COILCRAFT, XEL4030-471MEC
22| 1| LB1| LABEL SPEC, DEMO BOARD SERIAL NUMBER| BRADY, THT-96-717-10
23| 4| MP1, MP2, MP3, MP4| STANDOFF, NYLON, SNAP-ON, 0.375″| KEYSTONE, 8832
ITEM| QTY| REFERENCE| PART DESCRIPTION| MANUFACTURER/PART NUMBER
---|---|---|---|---
24| 1| PCB1| PCB, DC3220A| ADI APPROVED SUPPLIER, 600-DC3220A
25| 1| R1| RES., 680Ω, 1%, 1/10W, 0603, AEC-Q200| PANASONIC, ERJ3EKF6800V VISHAY, CRCW0603680RFKEA
26| 1| R2| RES., 1Ω, 1%, 1/10W, 0603, AEC-Q200| NIC, NRC06F1R00TRF VISHAY, CRCW06031R00FKEA
27| 2| R3, R12| RES., 100k, 1%, 1/10W, 0603, AEC-Q200| VISHAY, CRCW0603100KFKEA NIC, NRC06F1003TRF PANASONIC, ERJ3EKF1003V VISHAY, RCA0603100KFKEAHP
28| 1| R4| RES., 47.5k, 1%, 1/10W, 0603| VISHAY, CRCW060347K5FKEA YAGEO, RC0603FR-0747K5L
29| 0| R5, R15, R16| RES., OPTION, 0603|
30| 1| R6| RES., 10k, 1%, 1/10W, 0603, AEC-Q200| VISHAY, CRCW060310K0FKEA KOA SPEER, RK73H1JTTD1002F PANASONIC, ERJ3EKF1002V
31| 2| R7, R14| RES., 0Ω, 1/10W, 0603, AEC-Q200| VISHAY, CRCW06030000Z0EA VISHAY, CRCW06030000Z0EB NIC, NRC06ZOTRF
32| 1| R8| RES., 0Ω, 1/4W, 1206, AEC-Q200| VISHAY, CRCW12060000Z0EA PANASONIC, ERJ8GEY0R00V NIC, NRC12ZOTRF
33| 2| R10, R11| RES., 49.9k, 1%, 1/10W, 0603| NIC, NRC06F4992TRF VISHAY, CRCW060349K9FKEA YAGEO, RC0603FR-0749K9L
34| 1| STNCL1| TOOL, STENCIL, DC3220A| ADI APPROVED SUPPLIER, 830-DC3220A
35| 1| U1| IC, STEP-DOWN SILENT SWITCHER 3, LQFN-24| ANALOG DEVICES, LT8625SP-1#PBF ANALOG DEVICES, LT8625SP-1#TRPBF
36| 2| XJP1, XJP2| CONN., SHUNT, FEMALE, 2-POS, 2mm| WURTH ELEKTRONIK, 60800213421

SCHEMATIC DIAGRAM

REVISION HISTORY

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 are subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.

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.

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FAQ

Q: How do I change the switching frequency on the demo board?
A: The switching frequency can be adjusted by either changing the oscillator resistor or using an external clock input.

Q: What is the default output voltage of the LT8625SP-1?
A: The default output voltage is 1V.

Q: How can I measure the output voltage ripple?
A: To measure output voltage ripple, touch the oscilloscope probe directly across the output capacitor.

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