ANALOG DEVICES LT8624S-AZ-IBB Synchronous Step-Down Silent Switcher User Guide

: June 13, 2024
: Analog Devices

Table of Contents

ANALOG DEVICES LT8624S-AZ-IBB Synchronous Step-Down Silent Switcher
Product Information
Product Usage Instructions
FAQ
General Description
CONTACT
References
Read User Manual Online (PDF format)
Download This Manual (PDF format)

ANALOG DEVICES LT8624S-AZ-IBB Synchronous Step-Down Silent Switcher

Product Information

Specifications

Product Name: EVAL-LT8624S-AZ-IBB
Model: LT8624S
Input Voltage Range: 2.7V to 18V
Output Voltage: -5V
Default Switching Frequency: 2MHz
Maximum Output Current: 4A
Efficiency: 85%

Product Usage Instructions

General Description

The LT8624S is an 18V, 4A Synchronous Step-Down Silent Switcher with Ultra-Low Noise Reference used as an IBB Converter. It features FCM operation and excellent EMI performance.

Quick Start Procedure

Place JP1 on the FCM position.
Connect the input power supply to VIN (E1) and GND (E2).
Connect the load’s – input to the board’s -VOUT (E4) and the load’s + input to the board’s GND (E5).
Monitor input voltage using VIN SENSE (E10) and output voltage using -VOUT SENSE (E6) with digital multimeters.

FAQ

Q: What is the input voltage range for the LT8624S?
A: The input voltage range for the LT8624S is 2.7V to 18V.
Q: What is the maximum output current supported by the LT8624S?
A: The LT8624S supports a maximum output current of 4A.

General Description

The EVAL-LT8624S-AZ-IBB demonstration board is the inverting buck-boost topology version of the LT8624S, an 18V, 4A synchronous Silent Switcher®3 step-down regulator with ultra-low noise, high efficiency, and power density.
The input voltage range of the EVAL-LT8624S-AZ-IBB is 2.7V to (18V – |VOUT|). The default demo board setting is -5V for a 2A maximum DC output current with a 5V input, or a 4A maximum DC output current with a 12V input. The LT8624S is a compact, ultra-low noise, ultra-low emission, high efficiency, and high-speed synchronous monolithic step-down switching regulator used as an inverting buck-boost converter. The uniquely designed combination of the ultra-low noise reference and third-generation Silent Switcher architecture enables the LT8624S to achieve both high efficiency and excellent wideband noise performance. A minimum on-time of 12ns allows high VIN to low VOUT conversion at high frequency.
The LT8624S switching frequency can be programmed either through an external resistor RT, or an external clock over a 300kHz to 6MHz range. The default frequency of the EVAL-LT8624S-AZ-IBB demo board is 2MHz. The SYNC pin on the demo board is connected to -VOUT for 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) by moving the JP1 shunt respectively. Figure 1 shows the efficiency of the circuit at 5V input and 12V input in the FCM operation (input from VIN terminal). Figure 2 shows the LT8624S temperature rising on the EVAL-LT8624S-AZ-IBB demo board under 1A, 2A, and 3A load conditions, for the full input voltage range. The case temperature rise was measured with the following reference points: The peak IC case temperature and a point on the board, marked with a red ‘X’ as shown in the thermal picture in Figure 7.
The demo board has an electromagnetic interference (EMI) filter installed by default between VIN terminal and the IC. 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 ultra-low noise over a wide frequency range, as is shown in Figure 4.
The LT8622S/LT8624S data sheet gives a complete description of the LT8624S part, including operation and application information. Read the data sheet in conjunction with this demo manual for the LT8624S-AZ-IBB demo board. 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
LT8622S/LT8624S data sheet section ‘PCB Layout Recommendations.’
Design files for this circuit board are available in the Design Center at www.analog.com.

Performance Summary (TA = 25°C)

PARAMETER	CONDITIONS	MIN	TYP	MAX	UNITS
Input Voltage Range VIN Output Voltage		2.7		18 –	VOUT
	-4.96	-5	-5.04	V
Default Switching Frequency		2	MHz
Maximum Output Current	Derating Necessary for Certain VIN,

VOUT, and Thermal Conditions

| 2

(VIN = 5V)

| | 4

(VIN = 12V)

| A

Efficiency

| VIN = 5V FSW = 2MHz

VOUT = -5V at IOUT = 2A

| ****

85

| ****

%

Typical Performance Characteristics
(Standard Demo Board at FSW = 2MHz, MODE = FCM, TA = +25°C, unless otherwise noted.)

Quick Start Procedure
The EVAL-LT8624S-AZ-IBB demo board is easy to set up to evaluate the performance of LT8624S operating as an inverting buck-boost converter. See Figure 8 for a proper test setup and follow this test procedure.
NOTE: When measuring the input or output voltage ripple, be careful to avoid a long ground lead on the oscilloscope probe. For the input and output voltage ripple, measure them through the U.FL connectors—“VIN” (J2), and “-VOUT” (J3), respectively. Figure 5 shows the output voltage ripple measured at the output capacitor C9 through the “-VOUT” U.FL connector.

Place JP1 on the FCM position.
With power off, connect the input power supply to VIN (E1) and GND (E2).
With power off, connect the load’s “-“ input to the board’s -VOUT (E4), and connect the load’s “+” input to the board’s GND (E5).
Connect the digital multimeter (DMM) between the input test points: “VIN SENSE” (E10) and “GND SENSE” (E12) to monitor the input voltage. Connect another DMM between “-VOUT SENSE” (E6) and “GND SENSE” (E8) to monitor the output voltage.
Set the power supply voltage to 5V and enable it.
Check for the proper output voltage (VOUT = -5V).
Once the input and output voltages are properly established, adjust the load current within the operating range of 0A to 2A maximum. Observe the output voltage regulation, output voltage ripples, switching node waveform, load transient response, and other parameters.
Add an external clock to the SYNC terminal when using the SYNC function (JP1 on the SYNC position). Choose the RT resistor (R23) to set the LT8624S switching frequency at least 20% below the lowest SYNC frequency.

Bill of Materials

ITEM| QTY| DESIGNATOR| DESCRIPTION| MANUFACTURER PART NUMBER
---|---|---|---|---
REQUIRED CIRCUIT COMPONENTS
1| 2| C1,C2| CAP.,10uF,X5R,25V,20%,0603| MURATA,

GRM188R61E106MA73D

2| 2| C3, C13| CAP TANT POLY 100UF 20V 2917| KYOCERA AVX,

TCJY107M020R0055

3| 5| C6, C8, C9, C33, C34| CAP.,2.2uF,X5R,25V,10%,0402| MURATA,

GRM155R61E225KE11D

4| 10| C11, C12, C14-C18, C26-

C28

| CAP.,22uF,X5R,25V,20%,0805| MURATA,

GRM21BR61E226ME44L

5| 2| C20, C23| CAP.,1uF,X7R,16V,20%,0603| AVX, 0603YC105MAT2A
6| 1| C21| CAP.,56pF,C0G,50V,5%,0603| AVX, 06035A560JAT2A
7| 1| C22| CAP.,6800pF,X7R,50V,20%,0603| AVX, 06035C682MAT2A
8| 1| C30| CAP.,1uF,X7R,25V,10%,0603,AEC-Q200| MURATA,

GCM188R71E105KA64D

9| 2| C31, C32| CAP.,22uF,X7R,25V,10%,1210| AVX, 12103C226KAT2A
10| 1| L1| IND.,1.5uH,PWR,SHIELDED,20%,11.1A,14.3 mOHMS,4.3mmX4.3mm,AEC-Q200| COILCRAFT, XGL4020- 152MEC
11| 1| L3| IND.,60 OHMS@100MHz,PWR,FERRITE BEAD,25%,5100mA,15mOHMS,0603| WURTH ELEKTRONIK, 74279228600
12| 1| L4| IND.,1uH,PWR,SHIELDED,20%,4A,52.5mOH MS,1616AB,IHLP-01 Series| VISHAY, IHLP1616ABER1R0M01
13| 2| Q1, Q2| TRANS PNP 40V 0.6A SOT23| CENTRAL SEMI., CMPT4403 TR PBFREE
14| 3| R1-R3| RES.,1M OHM,1%,1/10W,0603| VISHAY, CRCW06031M00FKEA
15| 0| R4, R9, R12, R19, R24, R26| RES., OPTION, 0603|
16| 1| R5| RES.,10 OHMS,1%,1/16W,0402,AEC-Q200| NIC, NRC04F10R0TRF
17| 2| R6, R25| RES.,50 OHMS,0.1%,1/20W,0402,HIGH FREQ.| VISHAY, FC0402E50R0BST1
18| 2| R7, R22| RES.,0 OHM,1/10W,0603,AEC-Q200| VISHAY, CRCW06030000Z0EA
19| 1| R8| RES.,10 OHMS,1%,1/10W,0603| VISHAY, CRCW060310R0FKEA
20| 3| R10, R13, R15| RES.,10k OHMS,1%,1/10W,0603| VISHAY, CRCW060310K0FKEC
21| 1| R11| RES.,0.001 OHM,5%,1.5W,1206,LONG-SIDE TERM,METAL,SENSE,AEC-Q200| SUSUMU, KRL3216D-M- R001-J-T5
22| 1| R14| RES.,453k OHMS,1%,1/10W,0603,AEC-Q200| VISHAY, CRCW0603453KFKEA
23| 1| R16| RES.,100k OHMS,1%,1/10W,0603,AEC-Q200| PANASONIC, ERJ3EKF1003V
24| 2| R18, R20| RES.,49.9k OHMS,0.1%,1/10W,0603,AEC-

Q200

| VISHAY,

TNPU060349K9BZEN00

25| 1| R21| RES.,1.21k OHMS,1%,1/10W,0603| PANASONIC, ERJ3EKF1211V
26| 1| R23| RES.,47.5k OHMS,1%,1/10W,0603| VISHAY, CRCW060347K5FKEA
27| 1| U1| IC,SYN STEP-DOWN SILENT SWITCHER,LQFN-20,PRELIM.| ANALOG DEVICES, LT8624SAV#PBF
OPTIONAL CIRCUIT COMPONENTS

1| 0| C4, C5, C24, C25| CAP., OPTION, 0805|
2| 0| C7| CAP., OPTION, 0603|
3| 0| C35, C36| CAP., OPTION, 0402|
4| 0| L2| IND., OPTION, 0603|
HARDWARE – FOR EVALUTATION CIRCUIT ONLY
1| 4| E1, E2, E4, E5| CONN.,BANANA JACK,FEMALE,THT,NON- INSULATED,SWAGE,0.218″| KEYSTONE, 575-4
2| 9| E3, E6-E13| TEST POINT,TURRET,0.064″ MTG. HOLE,PCB 0.062″ THK| MILL-MAX, 2308-2-00-80-00-

00-07-0

3| 2| J1, J2| CONN.,UMC,RCPT,STR,50 OHM SMD| SAMTEC, RSP-122811-01
4| 1| JP1| CONN.,HDR,MALE,2×3,2mm,VERT,ST,THT| WURTH ELEKTRONIK, 62000621121
5| 4| MH1-MH4| STANDOFF, NYLON, SNAP-ON,0.375″| KEYSTONE, 8832
6| 2| MP1, MP2| CBL ASSY U.FL-SMA JACK-PLUG 3″| PULSE ELECTRONICS,

W9003M

7| 1| XJP1| CONN.,SHUNT,FEMALE,2 POS,2.54mm| SAMTEC, SNT-100-BK-G

LT8624S-IBB EV Kit Schematic

Revision History

Revision Number| Revision Date| Nature of Change| Page Number
---|---|---|---
A| 4/24| Initial Release for open market| —

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