ANALOG DEVICES EVAL-LT8342-AZ Evaluation Board User Guide

: July 31, 2024
: Analog Devices

Table of Contents

ANALOG DEVICES EVAL-LT8342-AZ Evaluation Board
General Description
Features and Benefits
Quick Start
Documents / Resources

ANALOG DEVICES EVAL-LT8342-AZ Evaluation Board

General Description

The EVAL-LT8342-AZ evaluation board provides a proven design to evaluate the LT8342, a 40V, 9A, Low IQ Synchronous Step-Up Silent Switcher™ with Input Disconnect and PassThru™. The application circuit is configured to demonstrate optimum performance and component size. Using the board layout example, optimized for Electromagnetic Interference (EMI), and thermal performance, will help ensure the designer sees similar performance in their system. The evaluation board is configured to run at 2MHz with a 24V output voltage from an input voltage range of 6V to 20V and deliver up to 3A load current when VIN is 12V. The evaluation board features an adjustable input undervoltage- lockout, external clock synchronization, thermal shutdown, selectable mode of operation, input disconnect, and PassThru. The LT8342 converter data sheet provides a complete description of the part that should be read in conjunction with this user guide before operating the evaluation board.

Features and Benefits

Input Voltage Range: 6V to 20V
24V Output Voltage
Up to 3A Load Current at 12V Input
2MHz Switching Frequency
High 95.1% Efficiency (VIN = 12V, IOUT = 2.5A)
Enable/UVLO Input, Resistor-Programmable UVLO Threshold
Selectable Mode of operation (See Table 1 for more details)
Output Short Protection/Inrush Current Reduction
Input Disconnect
PassThru Operation
External Frequency Synchronization
External Compensation
Overtemperature Protection
Proven Printed Circuit Board (PCB) Layout
Fully Assembled and Tested

Quick Start

Required Equipment

One 20V, 12A DC Power Supply
Digital Multimeters (DMM)
Load Resistors Capable of Sinking up to 3A at 24V Output.

Procedure
The evaluation board is fully assembled and tested. Use the following steps below to verify the board operation.
Caution : Do not turn on power supply until all connections are completed.

Disable the power supply and set the input-power supply at a voltage between 6V to 20V.
Connect the positive terminal of the power supply to the VIN_EMI PCB pad and the negative terminal to the nearest GND PCB pad.
Connect the positive terminal of the load to the VOUT PCB pad and the negative terminal to the nearest GND PCB pad.
Caution : Do not enable the Load until power supply is turned on.
Connect the DMM across the VOUT PCB pad and the nearest GND PCB pad.
Verify that the shunt is installed across pins on jumper JP1 to program the desired mode. See Table 1 for more details.
Verify that the shunt is installed properly across pins 1–2 on jumper JP2.
Verify that the shunt is installed properly across pins 1–2 on jumper JP3.
Turn on the input-power supply.
Enable the load.
Verify that the DMM displays the expected terminal voltage with respect to GND.

EVAL-LT8342-AZ Configuration

Typical Performance Characteristics
TA = 25°C, all measurements are in reference to EVAL-LT8342-AZ Schematic. Source connected between VIN_EMI and GND and Load connected between VOUT and GND, unless otherwise noted.

Detailed Description
The EVAL-LT8342-AZ evaluation board is designed to demonstrate the salient features of LT8342, a 40V, 9A, Low IQ Synchronous Step-Up Silent Switcher with Input Disconnect and PassThru. The evaluation board is preset for 24V output from 6V to 20V input and can deliver load current up to 1.5A at 6V input voltage and up to 3A at 12V input voltage with 2MHz switching frequency.

Enable/Undervoltage (EN/UVLO) Programming
The evaluation board offers an adjustable input turn-on/-off thresholds. UVLO is programmed using resistors R3 and R4. The VIN rising threshold for enabling the converter is set to 5.44V (typ), and the VIN falling threshold to disable the converter is set to 5.11V (typ). Refer to the Programming VIN Turn-On and Turn-Off Thresholds with the EN/UVLO Pin section in the LT8342 data sheet for more details.

MODE Selection and External Clock Synchronization

The LT8342 supports five different modes of operation: Pulse Skip Mode, Pulse Skip Mode with Spread Spectrum Modulation (SSFM), Burst Mode, Burst Mode with SSFM, and Pulse Skip Mode with External Clock Synchronization. See Table 1 for Jumper JP1 settings. The converter’s internal oscillators can be synchronized to an external clock signal on the MODE/SYNC pin. By providing a digital clock signal to the SYNC/MODE pin, the IC operates with SYNC clock frequency and automatically enters Pulse Skip operation at light load. If this feature is used, an RT resistor should be chosen to program the switching frequency close to the external clock frequency. Refer to the Programming Switching Frequency and Synchronization section in the LT8342 data sheet for more details.

Table 1. Mode Jumper Description (JP1)

SHUNT POSITION	MODE/SYNC PIN	OPERATING MODE
1–2*	Float	Pulse Skip Mode of Operation
3–4	Connected to INTVCC	Pulse Skip + SSFM Mode of Operation
5–6	Connected to GND	Burst Mode of Operation
7–8	Connected to 100kΩ to GND	Burst + SSFM Mode of Operation
9–10	Connected to External Clock	Synchronized to External Clock

Programming Switching Frequency
The switching frequency of the EVAL-LT8342-AZ can be programmed from 300kHz to 3MHz by using a resistor connected from the RT pin to GND. Resistor R6 programs the desired switching frequency. To optimize performance and component size in the evaluation board, a 2MHz switching frequency has been chosen. Refer to the Programming Switching Frequency and Synchronization section of the LT8342 data sheet to choose different values of resistors for programming the required switching frequency.

Programming the Output Voltage
The LT8342 supports an adjustable output voltage of up to 36V. The output voltage can be programmed using internal feedback or external feedback. EVAL- LT8342-AZ evaluation board is configured to 24V output using internal feedback, Shunt connected between position 1-2 in JP2, and Shunt connected between position 1-2 in JP3. Refer to the Programming the Output Voltage section in the LT8342 data sheet for more details.

Input Capacitor Selection
The input capacitors, C5 and C23, serve to reduce current peaks drawn from the input power supply and reduce the switching frequency ripple at the input. Refer to the Input Capacitor Selection section in the LT8342 data sheet to choose input capacitance. The input capacitors C5 is chosen as 10μF/50V/X7R/1210 and C23 is chosen as 1μF/50V/X5R/0402.

Output Capacitor Selection
The output capacitors C3 and C4 are chosen as 10μF/50V/X7R/1210. Refer to the Output capacitor selection section in the LT8342 data sheet for more details.

Hot Plug-In and Long input cables
The EVAL-LT8342-AZ evaluation board provides optional electrolytic capacitor C7 (33μF/50V) to dampen input voltage peaks and oscillations arising during hot-plug-in and/or due to long input cables. This capacitor limits the peak voltage at the input of the DC-DC converter when the evaluation board is powered directly from a precharged capacitive source or an industrial backplane PCB. Long input cables between an input-power source and the evaluation board circuit can cause input-voltage oscillations due to the inductance of the cables. The equivalent series resistance (ESR) of the electrolytic capacitor helps damp out the oscillations caused by long input cables.

Electromagnetic Interference (EMI)
Compliance with conducted emissions (CE) standards requires an EMI filter at the input of a switching power converter. The EMI filter attenuates high- frequency currents drawn by the switching power converter, and limits the noise injected back into the input power source. The use of EMI filter components as shown in the evaluation board schematic results in lower conducted emissions, below CISPR25 Class 5 limits. The PCB layout is also designed to limit radiated emissions from switching nodes of the power converter, resulting in radiated emissions below CISPR25 Class 5 limits. Further, capacitors placed near the input of the board help in attenuate high- frequency noise. EMI filters may not be necessary for all applications. For a lower parts count and BOM cost EMI filters can be removed.

Input Disconnect, Inrush Current reduction and Output short-circuit Protection
EVAL-LT8342-AZ evaluation board is configured to demonstrate Input Disconnect, Inrush current reduction, and short circuit protection using N-Channel MOSFET Q1, Sense resistor R7, and diode D1 to clamp negative voltage across the Gate of Q1. R7 is selected as 3mΩ to limit the current to 15A (Typ). Q1 is selected as NVTFS5C453NL (40V, 3.1mΩ). Refer to the Output Short-Circuit Protection section in the LT8342 data sheet for more details.

PreBoost
The evaluation board offers a programmable PreBoost feature. See PreBoost Jumper Description (JP4) for jumper setting JP4. Refer to the PREBOOST pin description section in the LT8342 data sheet for more details.

Table 2. PreBoost Jumper Description (JP4)

SHUNT POSITION	PREBOOST PIN	PG PIN STATUS
1–2*	Connected to GND	PG pin pulled high when VOUT within ±10% of the target

voltage
2–3| Connected to INTVCC| PG pin pulled high when VOUT higher than -10% of the target voltage

Ordering Information

PART	TYPE
EVAL-LT8342-AZ	Evaluation Board

Component Suppliers

SUPPLIER	WEBSITE
Murata Americas	www.murata.com
Coilcraft	www.coilcraft.com
Vishay	www.vishay.com
Panasonic Corp.	www.panasonic.com
Yageo	www.yageo.com
TDK	www.tdk.com
Würth Electronik	www.we-online.com
Nexperia	www.nexperia.com
Onsemi	www.onsemi.com
Thin Film Technology	www.thin-film.com
Laird	www.laird.com

Note : When contacting these component suppliers, indicate that the LT8342 is being used.

EVAL-LT8342-AZ Bill of Materials

REQUIRED EVALUATION KIT COMPONENTS

1

| ****

6

| C1, C2, C10, C12, C14, C15| ****

CAP., X7R, 0.1µF, 50V, 10%, 0402

| ****

MURATA, GRM155R71H104KE14J

---|---|---|---|---
2| 2| C11, C16| CAP., X7R, 220pF, 50V, 10%, 0402| WÜRTH ELEKTRONIK, 885012205057
3| 4| C3, C4, C5, C13| CAP., X7R, 10µF, 50V, 10%, 1210| MURATA, GRM32ER71H106KA12L
4| 1| C21| CAP., X7R, 3300pF, 50V, 10%, 0603| TDK, CGA3E2X7R1H332K080AA
5| 1| C23| CAP., X5R, 1µF, 50V, 10%, 0402| MURATA, GRM155R61H105KE05
6| 1| C6| CAP., X7R, 0.1µF, 50V, 10%, 0603| WÜRTH ELEKTRONIK, 885012206095
7| 1| C7| CAP., ALUM, 33µF, 50V, 20%| PANASONIC, EEH-ZC1H330XP
8| 1| C8| CAP., X7R, 0.1µF, 25V, 10%, 0402| MURATA, GRM155R71E104KE14D
9| 1| C9| CAP., X7R, 2.2µF, 10V, 10%, 0603| MURATA, GRM188R71A225KE15D
10| 1| D1| LOW LEAKAGE DIODE, 85V, 0.2A, SOD523| NEXPERIA, BAS716

11

| ****

1

| ****

FB1

| FERRITE BEAD, 700Ω @100MHz, 0.010Ω, 8A, 2220| ****

LAIRD, HR2220V701R-10

12

| ****

1

| ****

FB2

| FERRITE BEAD, 880Ω @100MHz, 0.035Ω, 4A, 1812| ****

WÜRTH ELEKTRONIK, 74279252

13| 1| L1| IND., 1.8UH, 15.3A, 0.0078Ω| COILCRAFT, XGL5050-182MEC
14| 1| Q1| N-CH MOSFET., 40V, 3.1mΩ, 8-WDFN| ONSEMI, NVTFS5C453NLWFTAG

15

| ****

6

| R1, R2, R5, R12, R13, R14| ****

RES., CHIP, 100kΩ, 1%, 1/10W, 0603

| ****

YAGEO, RC0603FR-07100KL

16| 1| R11| RES., CHIP, 60.4kΩ, 1%, 1/10W, 0603| VISHAY, CRCW060360K4FKEA
17| 1| R3| RES., CHIP, 1MΩ, 1%, 1/10W, 0603| VISHAY, CRCW06031M00FKEA
18| 1| R4| RES., CHIP, 243kΩ, 1%, 1/10W, 0603| VISHAY, CRCW0603243KFKEA
19| 1| R6| RES., CHIP, 15kΩ, 1%, 1/10W, 0603| VISHAY, CRCW060315K0FKEB

20

| ****

1

| ****

R7

| ****

RES., CHIP, 0.003Ω, 1%, 1W, 1206

| THIN FILM TECHNOLOGY, D1MPC1206DR003FF-T5

21

| ****

1

| ****

U1

| IC, 40V, 9A, LOW IQ SYNCHRONOUS STEP-UP SILENT SWITCHER WITH INPUT DISCONNECT AND PassThru| ****

ANALOG DEVICES, LT8342RV#PBF

HARDWARE FOR EVALUATION KIT ONLY

1

| ****

8

| E2, E3, E4, E5, E6, E7, E10, E11| ****

TESTPOINT, TURRET, 0.094″

| ****

MILL-MAX, 2501-2-00-80-00-00-07-0

---|---|---|---|---
2| 1| E1| TESTPOINT, TURRET, 0.064″| MILL-MAX, 2308-2-00-80-00-00-07-0
3| 1| JP1| CONN-PCB 2MM P DIL| SAMTEC INC., TMM-105-01-F-D
4| 2| JP2, JP3| CONN-PCB 8POS MALE HDR, DUAL ROW| WÜRTH ELEKTRONIK, 62000821121
5| 1| JP4| CONN-PCB 3POS MALE HDR| WÜRTH ELEKTRONIK, 62000311121
6| 3| C17, C18, C19| OPEN| PACKAGE OUTLINE 1210
7| 2| C20, C22| OPEN| PACKAGE OUTLINE 0603
8| 3| R10, R15, R16| OPEN| PACKAGE OUTLINE 0603

EVAL-LT8342-AZ Schematic

EVAL-LT8342-AZ PCB Layout

Revision History

REVISION NUMBER| REVISION DATE| DESCRIPTION| PAGES CHANGED
---|---|---|---
0| 6/24| Initial Release| —

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