LT8624S Synchronous Step-Down Silent Switcher

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Product Information

Specifications:

• Product Name: LT8624S 18V, 4A Synchronous Step-Down Silent
  Switcher with Ultra-Low Noise Reference

• Input Voltage Range: 2.7V – 18V

• Output Voltage Default: 0.992V – 1.008V

• Switching Frequency: 1.93MHz – 2.07MHz

• Maximum Output Current: 4A

• Efficiency: 85% – 90%

Product Usage Instructions:

General Description:

The LT8624S is a synchronous step-down silent switcher with
ultra-low noise reference. It features excellent EMI performance
and ultra-low noise over a wide frequency range.

Setup:

1. Connect the input voltage to the VIN_EMI terminal to activate
   the EMI filter.

2. Refer to the data sheet for detailed operation and application
   information.

3. Follow the layout recommendations for low EMI operation and
   maximum thermal performance provided in the data sheet.

Quick Start Procedure:

1. Set up the demonstration circuit EVAL-LT8624S-AZ as shown in
   Figure 5.

2. When measuring voltage ripple, avoid long ground leads on
   oscilloscope probes.

3. Measure output voltage ripple by touching the probe tip
   directly across the output capacitor.

4. For input voltage ripple and remote output voltage ripple,
   measure through the SMA connectors VIN_SENSE and VO_SENSE.

FAQ:

Q: How can I improve EMI performance?

A: To improve EMI performance, make sure to follow the layout
recommendations provided in the data sheet for low EMI
operation.

Q: What is the maximum output current supported?

A: The LT8624S supports a maximum output current of 4A.

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EVAL-LT8624S-AZ User Guide

LT8624S 18V, 4A Synchronous Step-Down Silent Switcher
with Ultra-Low Noise Reference

General Description
The demonstration circuit EVAL-LT8624S-AZ is a 18V, 4A synchronous step-down Silent Switcher 3 with ultra-low noise, high efficiency, and power density featuring the LT8624S. The input voltage range of EVAL-LT8624S-AZ is 2.7V to 18V. The default demo board setting is 1.0V at 4A maximum DC output current. The LT8624S is a compact, ultra-low noise, ultra-low emission, high efficiency, and high speed synchronous monolithic stepdown switching regulator. The uniquely designed combination of the ultra-low noise reference and thirdgeneration Silent Switcher architecture enables the LT8624S to achieve both high efficiency and excellent wideband noise performance. Minimum on-time of 12ns allows high VIN to low VOUT conversion at high frequency.
Program the LT8624S switching frequency either through the oscillator resistor or external clock over a 300kHz to 6MHz range. The default frequency of demo circuit EVALLT8624S-AZ 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. Select the forced continuous mode (FCM) respectively by moving the JP1 shunt. Figure 1 shows the efficiency of the circuit at 5V input and 12V input in the force continuous mode operation (input from VIN terminal). Figure 2 shows the LT8624S temperature rising on the EVAL-LT8624S-AZ demo board under 3A and 4A 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. Figure 3 shows the EMI performance of the board. The red line in Radiated EMI Performance is the CISPR32 Class B limit. In addition to the excellent EMI performance, the regulator also features ultra-low noise over a wide frequency range, as shown in Figure 4.
The LT8624S data sheet gives a complete description of the part, including operation and application information. Read the data sheet in conjunction with this demo manual for demo circuit EVAL-LT8624S-AZ. The LT8624S is assembled in a 4mm x 3mm LQFN package with exposed ground 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.

© 2024 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners.

EVAL-LT8624S-AZ User Guide

LT8624S 18V, 4A Synchronous Step-Down Silent Switcher
with Ultra-Low Noise Reference

Performance Summary Specifications are at TA = 25°C

PARAMETER Input Voltage Range VIN
Output Voltage Default Switching Frequency
Maximum Output Current
Efficiency

CONDITIONS
Derating is Necessary for Certain VIN and Thermal Conditions VIN = 12V fSW = 2MHz
VOUT = 1.0V at IOUT = 4A

MIN 2.7 0.992 1.93
4

TYP 1.0 2.0
78

MAX 18
1.008 2.07

UNITS V V
MHz

%

90
85 EFFICIENCY
80

2.4

SVIN = 3.3V

VOUT = 1V

fSW = 2MHz
JP1 = FCM

2.0

1.6

POWER LOSS (W)

EFFICIENCY (%)

75

1.2

70

0.8

65

0.4

POWER LOSS

VIN = 12V VIN = 5V

60

0

0

1

2

3

4

5

LOAD CURRENT (A)

001

Figure 1. LT8624S Demo Circuit EVAL-LT8624S-AZ Efficiency vs. Load Current (Input from VIN Terminal)

30

SVIN = VIN

VOUT = 1V

25

fSW = 2MHz

CASE TEMPERATURE RISING (°C)

20

15

10

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5

IOUT = 4A

IOUT = 3A

0

3

6

9

12

15

18

INPUT VOLTAGE (V)

Figure 2. Temperature Rising vs. VIN

002

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EVAL-LT8624S-AZ User Guide

LT8624S 18V, 4A Synchronous Step-Down Silent Switcher
with Ultra-Low Noise Reference

70 STANDARD DEMO BOARD
60 WITH EMI FILTER
50

CLASS B LIMIT

AMPLITUDE (dBµV/m)

40

30

20

10

0 ­10
0

HORIZONTAL OPERATING VERTICAL OPERATING
100 200 300 400 500 600 700 800 900 1000

FREQUENCY (MHz)

12V INPUT TO 1V OUTPUT AT 4A, fSW = 2MHz

Figure 3. LT8624S Demo Circuit EVAL-LT8624S-AZ EMI Performance (12V Input to 1.0V Output at 4.A, fSW = 2MHz)

1000 100

ILOAD = 0A (VO,RMS = 5.2µVRMS) ILOAD = 2A (VO,RMS = 5.7µVRMS) ILOAD = 4A (VO,RMS = 4.8µVRMS)
(VO,RMS = INTEGRATED NOISE FROM 10Hz TO 100kHz)

129 104

OUTPUT NOISE (nV/Hz)

10

fSW = 2MHz, VOUT = 1V

TYPICAL APPLICATION CIRCUIT

1

10

100

1k

10k

100k

1M

FREQUENCY (Hz)

Figure 4. LT8624S Data Sheet Typical Application Circuit Noise Spectral Density (12V Input to 1.0V Output, fSW = 2MHz)

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Analog Devices | 3

EVAL-LT8624S-AZ User Guide

LT8624S 18V, 4A Synchronous Step-Down Silent Switcher
with Ultra-Low Noise Reference

Quick Start Procedure
The demonstration circuit EVAL-LT8624S-AZ is easy to set up to evaluate the performance of LT8624S. See Figure 5 for proper equipment setup and follow these test procedures.
NOTE: When measuring the input or output voltage ripple, be careful 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 remote output voltage ripple, measure them through the SMA connectors through 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 the FCM position.
2. With power off, connect the input power supply to VIN (E1) and GND (E2).
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.
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 4A maximum per channel. Observe the output voltage regulation, output voltage ripples, switching node waveform, load transient response, and other parameters.
8. Add an external clock to the SYNC terminal when using the SYNC function (JP1 on the SYNC position). Choose the RT resistor (R4) to set the LT8624S switching frequency at least 20% below the lowest SYNC frequency.

005

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Figure 5. Proper Measurement Equipment Setup

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EVAL-LT8624S-AZ User Guide
Typical Performance Characteristics

LT8624S 18V, 4A Synchronous Step-Down Silent Switcher
with Ultra-Low Noise Reference

VOUT AC COUPLED (1mV/DIV)
006 008
TEMPERATURE (°C)
007

500ns/DIV
Figure 6. LT8624S Demo Circuit EVAL-LT8624S-AZ Output Voltage Ripple Measured Through J6
(12V Input, Remote Sense enabled, IOUT = 4A, 200MHz BW)
58.3 56 54 52 50 48 46 44 42 40 38 36 34 32 30 28.9
Figure 7. Thermal Performance at VIN = 12V, SVIN = VIN, fSW = 2MHz, VOUT = 1.0V, ILOAD = 4A, TA = 25°C

LOAD STEP 1A/DIV

VOUT AC COUPLED
50mV/DIV

50µs/DIV

Figure 8. Transient Response with Load Steps 0A to 2A to 0A at dI/dt = 2A/µs. VOUT measured at C21.

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Analog Devices | 5

EVAL-LT8624S-AZ User Guide

LT8624S 18V, 4A Synchronous Step-Down Silent Switcher
with Ultra-Low Noise Reference

LT8624S EV Kit Bill of Materials

ITEM QTY

REFERENCE

1

1

C1

2

0

C3, C6

3

1

C4

4

1

C5

5

1

C8

6

1

C10

7

1

C11

8

0

C12, C13

9

2

C14, C18

10

1

C15

11

2

C19, C20

12

1

C21

13

4

E1, E2, E19, E20

14

11 E3-E6, E8-E12

15

2

16

2

17

2

18

1

19

1

20

1

21

4

22

1

FB1, R18 J5, J6 JP1, JP2 L2 L4 LB1 MP1-MP4 PCB1

PART DESCRIPTION REQUIRED CIRCUIT COMPONENTS CAP.,0.22µF, X7R, 25V, 10%, 0402 CAP., OPTION, 1210 CAP.,100µF,ALUM ELECT, 25V, 20%, 6.3mm x 7.7mm, CE-BS Series CAP., 4.7µF, X5R, 25V, 10%, 0603 CAP., 0.01µF, X7R, 50V, 10%, 0603 CAP., 0.1µF, X7R, 25V, 10%, 0603 CAP., 82pF, X7R, 50V, 10%, 0603 CAP., OPTION, 0603 CAP., 2.2µF, X7R, 6.3V, 10%, 0603, AECQ200 CAP., 22µF, X7R, 4V, 20%, 0603 CAP., 47µF, X5R, 4V, 20%, 0603 CAP., 10µF, X7S, 4V, 20%, 0603 TEST POINT, SILVER PLATE, PHOSPHOR BRONZE, 3.81mm x 2.03mm, 2.29mm H, SMT TEST POINT, 0805, 2mm x 1.25mm x 1.45mm, PROBE PAD, FOIL, VERT, SMT, NATURAL RES.,0, 1/10W, 0603, AEC-Q200 CONN., RF/COAX, SMA JACK, FEMALE, 1 PORT, VERT, ST, SMT, 50, Au CONN., HDR, MALE, 2mm x 3,2mm, VERT, ST, THT IND.,1µH, PWR, SHIELDED, 20%, 4A, 52.5m,1616AB, IHLP-01 Series IND.,0.3µH, PWR,20%, 21.2A, 3.4m, SMD, AEC-Q200, SHIELDED LABEL SPEC, DEMO BOARD SERIAL NUMBER STANDOFF, NYLON, SNAPON, 0.375″ PCB, EVAL-LT8624S-AZ

23

1

R1

RES., 499, 1%, 1/10W, 0603, AEC-Q200

MANUFACTURER/PART NUMBER
TDK, CGA2B3X7R1E224K050BB
SUN ELECTRONIC INDUSTRIES CORP, 25CE100BS MURATA, GRM188R61E475KE15D
AVX, 06035C103KAT2A AVX, 06033C104KAT2A
MURATA, GCM188R70J225KE22J
YAGEO, CC0805KKX7R5BB225 MURATA, GRM188R60G476ME15D TDK, C1608X7S0G106M080AB TE CONNECTIVITY, 1625854-2
WURTH ELEKTRONIK, 885012206006
VISHAY, CRCW06030000Z0EA MOLEX, 0732511350
WURTH ELEKTRONIK, 62000621121
VISHAY, IHLP1616ABER1R0M01
COILCRAFT, XGL4030-301MEC
BRADY, THT-96-717-10
KEYSTONE, 8832
ADI APPROVED SUPPLIER, 600EVAL-LT8624S-AZ VISHAY, CRCW0603499RFKEA

24

1

R2

25

2

R3, R12

RES.,1, 1%, 1/10W, 0603, AEC-Q200 RES.,100k, 1%, 1/10W, 0603, AEC-Q200

NIC, NRC06F1R00TRF VISHAY, CRCW0603100KFKEA

26

1

R4

RES.,47.5k, 1%, 1/10W, 0603

VISHAY, CRCW060347K5FKEA

27

0

R5, R15, R16, R17

28

1

R6

RES., OPTION, 0603 RES., 10k, 1%, 1/10W, 0603, AEC-Q200

VISHAY, CRCW060310K0FKEA

29

1

R8

30

2

R10, R11

RES., 0, 3/4W, 1206, PULSE PROOF, HIGH PWR, AEC-Q200 RES., 49.9k, 1%,1 /10W, 0603

VISHAY, CRCW12060000Z0EAHP VISHAY, CRCW060349K9FKEA

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Analog Devices | 6

EVAL-LT8624S-AZ User Guide

LT8624S 18V, 4A Synchronous Step-Down Silent Switcher
with Ultra-Low Noise Reference

31

1

R14

32

1

U1

33

2

XJP1, XJP2

RES.,10, 1%, 1/10W, 0603 IC, SYNC. STEP-DOWN SILENT SWITCHER,LQFN-20 CONN., SHUNT, FEMALE, 2-POS,2mm

VISHAY, CRCW06030000Z0EA ANALOG DEVICES, LT8624SAV#PBF
WURTH ELEKTRONIK, 60800213421

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Analog Devices | 7

EVAL-LT8624S-AZ User Guide
LT8624S EV Kit Schematic

LT8624S 18V, 4A Synchronous Step-Down Silent Switcher
with Ultra-Low Noise Reference

www.analog.com

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EVAL-LT8624S-AZ User Guide

Revision History

REVISION NUMBER
A

REVISION DATE 05/24 Initial release for open market

LT8624S 18V, 4A Synchronous
Step-Down Silent Switcher with Ultra-Low Noise Reference

DESCRIPTION

PAGES CHANGED
—

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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. Trademarks and registered trademarks are the property of their respective owners.
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