ANALOG DEVICES LT8625S Silent Switcher Instructions

ANALOG DEVICES LT8625S Silent Switcher

Product Information

Specifications

• 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 74.7%

Product Usage Instructions

To set up the LT8625S demo board, follow these steps:

• Program the switching frequency using an oscillator resistor or external clock in the range of 300kHz to 4MHz.
• Ground the SYNC pin for low ripple pulse skip mode operation.
• To synchronize to an external clock, move JP1 to SYNC and apply the clock signal.
• Select forced continuous mode (FCM) by moving the JP1 shunt.
• To include the EMI filter, apply input voltage at the VIN_EMI terminal.
• The efficiency of the circuit at different input voltages and loads is shown in Figures 1 and 2.
• The demo board features ultralow noise over a wide frequency range as shown in Figure 4.
• To set up demonstration circuit 3219A, follow these steps:
• Refer to Figure 5 for proper equipment setup.
• Measure output voltage ripple directly across the output capacitor for accurate results.
• Input voltage ripple and remote output voltage ripple can be measured through SMA connectors via VIN_SENSE and VO_SENSE.

FAQ

• Q: How do I change the switching frequency of LT8625S?
• A: The switching frequency can be programmed using an oscillator resistor or an external clock within the specified range of 300kHz to 4MHz.
• Q: What is the default output voltage of the demo circuit?
• A: The default output voltage is set to 1V.

DESCRIPTION

Demonstration circuit 3219A is an 18V, 8A synchronous step-down Silent Switcher® 3 with ultralow noise, high efficiency, and power density featuring the LT®8625S. The input voltage range of DC3219A is 2.7V to 18V. The default demo board setting is 1V at 8A maximum DC output current. The LT8625S 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 LT8625S to achieve both high efficiency and excellent wideband noise performance. Minimum on-time
of 15ns allows high VIN to low VOUT conversion at high frequencies.
The LT8625S switching frequency can be programmed either via an oscillator resistor or external clock over a 300kHz to 4MHz range. The default frequency of demo circuit 3219A 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 the JP1 shunt. Figure 1 shows the efficiency of the circuit at 5V input and 12V input in force continuous mode operation (input from VIN terminal). Figure 2 shows the LT8625S temperature rising on the DC3219A demo board under 6A and 8A load conditions.
The demo board has an EMI filter installed. This EMI filter can be included by applying the input voltage at the VIN_ EMI terminal. The EMI performance of the board is shown in 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 LT8625S 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 3219A. The LT8625S is assembled in a 4mm × 3mm LQFN package. 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

Specifications are at TA = 25°C

QUICK START PROCEDURE

Demonstration circuit 3219A is easy to set up to evaluate the performance of LT8625S. 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, 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 C20 through the VO_SENSE SMA connector.

1. Place JP1 on FCM position.

2. With power off, connect the input power supply to VIN_EMI (E1) and GND (E2). If the input EMI filter is not desired, connect the input power supply between the VIN (E17) and GND (E18) turrets.

3. With power off, connect the load from VOUT (E19) to GND (E20).

4. Connect the DMM between the input test points: VIN_SENSE (E3) and SENSE_GND (E4) to monitor the input voltage. Connect DMM between VO_SENSE (E10) and SENSE_GND (E11) to monitor the output voltage

5. Turn on the power supply at the input.
   NOTE: Make sure that the input voltage does not exceed 18V.

6. Check for the proper output voltage (VOUT = 1V) NOTE: If there is no output, temporarily disconnect the load to make sure that the load is not set too high.

7. Once the input and output voltages are properly established, adjust the load current within the operating range of 0A to 8A max per channel. 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 LT8625S 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

ELECTRONIC INDUSTRIES CORP, 25CE100BS
5| 1| C5| CAP., 4.7µF, X7S, 50V, 10%, 0805| MURATA, GRM21BC71H475KE11K
6| 0| C7, C9, C13, C16| CAP., OPTION, 0603|
7| 1| C8| CAP., 0.01µF, X7R, 50V, 10%, 0603| AVX, 06035C103KAT2A
8| 1| C10| CAP., 0.1µF, X7R, 25V, 10%, 0603| AVX, 06033C104KAT2A
9| 1| C11| CAP., 82pF, X7R, 50V, 10%, 0603| KEMET, C0603C820K5RAC7867
10| 1| C12| CAP., 1µF, X7R, 10V, 10%, 0603| AVX, 0603ZC105KAT2A
11| 1| C14| CAP., 2.2µF, X7R, 6.3V, 10%, 0805| YAGEO, CC0805KKX7R5BB225
12| 1| C15| CAP., 22µF, X7R, 4V, 10%, 1206, AEC-Q200| TAIYO YUDEN, AMK316AB7226KLHT
13| 2| C18, C19| CAP., 2.2µF, X7S, 4V, 10%, 0603| TDK, CGB3B1X7S0G225K055AC
14| 1| C20| CAP., 100µF, X5R, 4V, 20%, 1206| TAIYO YUDEN, AMK316BJ107ML-T
15| 0| C22| CAP., 100µF, X5R, 4V, 20%, 1206| TAIYO YUDEN, AMK316BJ107ML-T
16| 1| C21| CAP., 10µF, X7S, 6.3V, 20%, 0603| TDK, C1608X7S0J106M080AC
17| 2| C23, C24| CAP., 4.7µF, FEEDTHRU, 10V, 20%, 0805, 3-TERM, SMD, EMI FILTER, 6A| MURATA, NFM21PC475B1A3D
18| 1| C26| CAP., 470pF, X7R, 10V, 10%, 0603| WURTH ELEKTRONIK, 885012206006
19| 11| E1-E6, E8-E12| TEST POINT, 0805, 2mm × 1.25mm × 1.45mm, PROBE PAD, FOIL, VERT, SMT, NATURAL| TE CONNECTIVITY, 1625854-2
20| 4| E17-E20| TEST POINT, SILVER PLATE, PHOSPHOR BRONZE, 3.81mm × 2.03mm, 2.29mm H, SMT| KEYSTONE, 5019
21| 1| FB1| IND., 60Ω AT 100MHz, PWR, FERRITE BEAD, 25%, 5100mA, 15mΩ, 0603| WURTH ELEKTRONIK, 74279228600
22| 2| J5, J6| CONN., RF/COAX, SMA JACK, FEMALE, 1PORT, VERT, ST, SMT, 50Ω, Au| MOLEX, 0732511350
23| 2| JP1, JP2| CONN., HDR, MALE, 2×3, 2mm, VERT, ST, THT| WURTH ELEKTRONIK, 62000621121
24| 1| L2| IND., 1µH, PWR, SHIELDED, 20%, 4A, 52.5mΩ, 1616AB,

IHLP-01 Series

| VISHAY, IHLP1616ABER1R0M01
25| 1| L4| IND., 0.3µH, PWR, SHIELDED, 20%, 18.9A, 3.1mΩ, 4.3mm × 4.3mm, XEL4030, AEC-Q200| COILCRAFT, XEL4030-301MEB
26| 4| MP1-MP4| STANDOFF, NYLON, SNAP-ON, 0.375″| KEYSTONE, 8832
27| 1| R1| RES., 499Ω, 1%, 1/10W, 0603, AEC-Q200| VISHAY, CRCW0603499RFKEA
28| 1| R2| RES., 1Ω, 1%, 1/10W, 0603, AEC-Q200| VISHAY, CRCW06031R00FKEA
29| 2| R3, R12| RES., 100k, 1%, 1/10W, 0603, AEC-Q200| VISHAY, CRCW0603100KFKEA
---|---|---|---|---
30| 1| R4| RES., 47.5k, 1%, 1/10W, 0603| VISHAY, CRCW060347K5FKEA
31| 0| R5, R15-R17| RES., OPTION, 0603|
32| 1| R6| RES., 10k, 1%, 1/10W, 0603, AEC-Q200| VISHAY, CRCW060310K0FKEA
33| 1| R8| RES., 0Ω, 3/4W, 1206, PULSE PROOF, HIGH PWR, AEC-Q200| VISHAY, CRCW12060000Z0EAHP
34| 2| R10, R11| RES., 49.9k, 1%, 1/10W, 0603| VISHAY, CRCW060349K9FKEA
35| 1| R14| RES., 10Ω, 1%, 1/10W, 0603| VISHAY, CRCW060310R0FKEA
36| 1| R18| RES., 0Ω, 1/10W, 0603, AEC-Q200| VISHAY, CRCW06030000Z0EA
37| 1| U1| IC, SYN. STEP-DOWN Silent Switcher, LQFN-20| ANALOG DEVICES, LT8625SIV#PBF
38| 2| XJP1, XJP2| CONN., SHUNT, FEMALE, 2-POS, 2mm| WURTH ELEKTRONIK, 60800213421

SCHEMATIC DIAGRAM

NOTES: UNLESS OTHERWISE SPECIFIED

• ALL RESISTORS ARE 0603.
• ALL CAPACITORS ARE 0603.

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 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.

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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References

• Mixed-signal and digital signal processing ICs | Analog Devices

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