ANALOG DEVICES LT8350S Evaluation Board User Guide

ANALOG DEVICES LT8350S Evaluation Board

Product Information

Specifications

• Product Name: EVAL-LT8350S-AZ
• Model: LT8350S
• Input Voltage Range: 3V to 40V
• Output Voltage Range: 18V
• Maximum Output Current: 6A
• Switching Frequency: 200kHz to 2MHz
• Features: Synchronous Buck-Boost, Adjustable switching frequency, Internal MOSFETs, EMI filters

Product Usage Instructions

1. Connection and Setup
   Ensure the input voltage is within the range of 3V to 40V. Connect the necessary input and output components following the recommended layout.

2. Adjusting Output Current
   To regulate output current, adjust ISP and ISN settings. For constant voltage regulation, limit the maximum load current. For LED driver or battery charger applications, ensure constant current regulation by adjusting the CTRL pin voltage.

3. Monitoring and Improving Load Response
   Monitor output current through the ISMON pin. Use ISMON to enhance load transient response by injecting load current to VC.

4. EMI Filtering and Layout
   Utilize the inductor and ferrite bead EMI filters on the input and output. Follow the recommended layout and use a four-layer PCB with proper board thickness for low EMI applications.

5. Thermal Performance
   Ensure proper board layout for maximum thermal performance, especially due to the thermally enhanced exposed ground pads in the laminate package.

FAQ (Frequently Asked Questions)

• Q: What is the recommended input voltage range for LT8350S?
  A: The operating input voltage range for LT8350S is 3V to 40V.

• Q: How can I adjust the output current of LT8350S?
  A: Output current can be regulated using ISP, ISN, and by adjusting the CTRL pin voltage.

• Q: How can I improve load transient response?
  A: Monitor output current through ISMON and inject load current to VC to enhance load transient response.

Evaluation Board User Guide
EVAL-LT8350S-AZ
LT8350S 40VIN, 18VOUT, 6A Synchronous Buck-Boost Silent Switcher 2

General Description

• The EVAL-LT8350S-AZ Evaluation board is a 40V synchronous buck-boost converter featuring the LT®8350S. It drives up to 2.5A load at 12V output when VIN is between 9V and 40V and will run down to 3VIN with reduced output current. EVAL-LT8350S-AZ runs at 350kHz switching frequency with spread spectrum frequency modulation (SSFM) disabled. When enabled, SSFM spreads the switching frequency of the LT8350S from fSW to fSW + 25% for a reduced electromagnetic interference (EMI) emission.
• The LT8350S has an operating input voltage range of 3V to 40V. It has internal, synchronous 42V MOSFETs on the buck side and 20V MOSFETs on the boost side for high efficiency and small size. It has an adjustable switching frequency between 200kHz and 2MHz. The LT8350S can be synchronized to an external source, programmed with SSFM enabled for low EMI, or set to normal operation.
• The LT8350S’ integrated LOADTG high-side PMOS driver assists with disconnecting load when a fault is triggered. LOADTG turns off the PMOS when FB<0.25V or FB>1.1V, or
• ISP–ISN > 0.75V. LOADEN can be used directly to turn off LOADTG and all power switches.
• The LT8350S can regulate output current using ISP and ISN. Maximum load current can be limited when LT8350S is used for a constant voltage regulator. It can also be used for an LED driver or a battery charger where constant current regulation is required. Output current can be adjusted by placing a controllable DC voltage on the CTRL pin.
• The output current can be monitored through the ISMON output pin. ISMON can be used to improve load transient response by injecting load current to VC. The load current  injection is described in the following sections.
• An Undervoltage lockout can be adjusted on EVAL-LT8350S-AZ with a few simple resistor choices.
• Small ceramic input and output capacitors are used to save space and cost. Although LT8350S has in-built high-frequency capacitors(100nF) on the input and output, the board is designed with tiny, high-frequency capacitors placed near the VIN and VOUT pins for added flexibility.
• There is an inductor EMI filter and a small ferrite bead EMI filter on the input and output of EVAL-LT8350S-AZ. These filters, combined with proper board layout and SSFM, are effective in reducing EMI to pass CISPR25 class 5 conducted EMI. Follow the recommended layout and four-layer printed circuit board (PCB) thickness of EVAL-LT8350S-AZ for low EMI applications.
• The LT8350S data sheet provides a complete description of the part, operation, and applications information. The data sheet must be read in conjunction with this demo manual for EVAL-LT8350S-AZ. The LT8350S is assembled in a 32-lead laminate package with QFN footprint (LQFN) with thermally enhanced exposed ground pads. Proper board layout is essential for maximum thermal performance.
• Design files for this circuit board are available at Product Evaluation Boards and Kits | Design Center | Analog Devices.

Features and Benefits

• 3V–40V Operating Input Voltage
• Reduced EMI emissions for CISPR 25 Class 5
• Spread Spectrum Frequency Modulation
• Input and Output EMI filter
• In-built Input and Output high-frequency capacitors
• Adjustable UVLO, VOUT, fSW, Output Current and Limit
• Voltage-Monitoring (PGOOD) and Current-Monitoring (ISMON)
• Configurable SYNC pin for Forced Continuous Mode (FCM), Discontinuous Conduction Mode (DCM), SSFM, and external Frequency Synchronization
• Feed Forward Function for improved transient response

Ordering Information appears at end of data sheet

EVAL-LT8350S-AZ Board Photo

Figure 1. EVAL-LT8350S-AZ Board Photo Front View

Table 1. Performance Summary (Specifications are at TA = 25°C)

PARAMETER| CONDITIONS/NOTES| MIN| TYP| MAX| UNITS
---|---|---|---|---|---
Input Voltage VIN Range| Operating, R7 = 402kΩ, R12 = OPEN| 3| | 40| V
Full Load (2.5A) Input Voltage Range| Component Temperature < 85°C at Room Temperature with No Airflow| 7| | 40| V
Output Voltage (VOUT)| R22 = 100kΩ, R3 = 10.0kΩ| 12.0| V
Output Voltage Ripple| VIN = 12V, VOUT = 12V, IOUT = 2.5A| 50| mV
Maximum Output Current| 7.0V < VIN < 40V, VOUT = 12V, fSW = 350kHz| 2.5| A
| 7.0V < VIN < 40V, VOUT = 12V, fSW = 2MHz| 2.0| A
Switching Frequency (fSW)| R4 = 143kΩ, SSFM = OFF| 350| kHz
| R4 = 143kΩ, SSFM = ON| 350-400| kHz
| R4 = 14.3kΩ, SSFM = OFF| 2000| kHz
| R4 = 14.3kΩ, SSFM = ON| 2000-2520| kHz
Typical Efficiency without EMI filters| VIN = 12V, VOUT = 12V, IOUT = 2.5A| 95| %
Typical Efficiency with EMI filters| VIN = 12V, VOUT = 12V, IOUT = 2.5A| 94| %
Peak Switch Current Limit| | 6| 7| 8| A
VOUT Overvoltage Threshold| R22 = 110kΩ, R3 = 10.0kΩ| 13.2| V
VIN Undervoltage Lockout (UVLO) Falling| R7 = 402kΩ, R12 = 84.5kΩ, IOUT = 2.5A| ****

7.2

| ****

V

VIN Enable Turn-On (EN) Rising| R7 = 402kΩ, R12 = 84.5kΩ, IOUT = 2.5A| 8.0| V

Quick Start Required Equipment

• EVAL-LT8350S-AZ
• Power Supply
• Voltmeters
• Ammeters
• Electronic Load

Procedure
EVAL-LT8350S-AZ Evaluation board is easy to set up to evaluate the performance of the LT8350S. See Figure 3 for proper measurement equipment setup and follow the procedure below. Ensure that the voltage applied to VIN does not exceed 40V, which is the voltage rating for input side MOSFETs.

1. With power off, connect a load capable of 12V 2.5A operation between OUT and GND terminal on the PCB, as shown in Figure 3.
2. Connect the EN/UVLO terminal to GND with a clip-on lead. Connect the power supply (with power off) and meters, as shown in Figure 3.
3. Set JP1 at NO SSFM to disable SSFM and at SSFM to enable SSFM.
4. Set JP2 at RC for typical loop compensation, at RC+FF for load current injection scheme which improves load transient response.
5. After all the connections are established, turn on the input power and verify that the input voltage is between 7V and 40V.
6. Remove the clip-on lead from EN/UVLO. Verify that the output voltage is 12V.

NOTE: If the output voltage is low, temporarily disconnect the load to ensure that it is not set too high. Once the proper output voltage is established, adjust the input voltage and load within the operating ranges and observe the output voltage regulation, ripple voltage, efficiency, and other parameters.

Hardware Set-Up

Test Results fSW = 350kHz

• Figure 4. EVAL-LT8350S-AZ Efficiency vs Input Voltage for 2.5A Load with SSFM
• Figure 5. EVAL-LT8350S-AZ Output Voltage Ripple at 12V Input Voltage and 2.5A Load

• Figure 6. EVAL-LT8350S-AZ Transient Response with JP2 = RC (12VIN and 12VOUT 2.5A to 1.25A)

• Figure 7. EVAL-LT8350S-AZ Transient Response with JP2 = RC (12VIN and 12VOUT 2.5A to 0A)

• Figure 10. EVAL-LT8350S-AZ Efficiency vs Input Voltage for 2A Load with SSFM

• Figure 11. EVAL-LT8350S-AZ Output Voltage Ripple at 12V Input Voltage and 2A Load
  

• Figure 12. EVAL-LT8350S-AZ Transient Response with JP2 = RC (12VIN and 12VOUT 2A to 1A)

• Figure 13. EVAL-LT8350S-AZ Transient Response with JP2 = RC (12VIN and 12VOUT 2A to 0A)

• Figure 14. EVAL-LT8350S-AZ Thermals 12VIN to 12VOUT 2A with SSFM ON

• Figure 15. EVAL-LT8350S-AZ Thermals, Worst Case (4-Switch Operation) 9.5VIN to 12VOUT 2A with SSFM ON

Load Current Injection for Faster Load Transient Response

• Load transient response can be improved with JP2 = RC + FF, called load current injection. The idea is to inject or feedforward load current to VC using ISMON and a voltage divider (VR1 and R17). With JP2 = RC + FF, the RC compensation, R5 and C6, is connected to ISMON through the voltage divider instead of GND. When the load current rises stepwise, ISMON rises immediately, and thus, VC is boosted faster compared to when the load current injection is not used (JP2 = RC). To determine the proper amount of load current injection, use the following Equation.
• Figure 16. EVAL-LT8350S-AZ Transient Response with JP2 = RC + FF (12VIN, 12VOUT, 2.5A to 1.25A)
• Figure 17. EVAL-LT8350S-AZ Transient Response with JP2 = RC + FF (12VIN, 12VOUT, 2.5A to 0A)
• Figure 18. EVAL-LT8350S-AZ Transient Response with JP2 = RC + FF (12VIN, 12VOUT, 2A to 1A)
• Figure 19. EVAL-LT8350S-AZ Transient Response with JP2 = RC + FF (12VIN, 12VOUT, 2A to 0A)

Electromagnetic Interference Result

fSW = 350kHz

Figure 20. EVAL-LT8350S-AZ CISPR25 Voltage Conducted EMI Performance with 12VIN to 12VOUT at 2.5A, JP1 = DCM + SSFM

Figure 21. EVAL-LT8350S-AZ CISPR25 Radiated EMI Performance with 12VIN to 12VOUT at 2.5A, JP1 = DCM + SSFM

Figure 22. EVAL-LT8350S-AZ CISPR25 Voltage Conducted EMI Performance with 12VIN to 12VOUT at 2A, JP1 = DCM + SSFM

Figure 23. EVAL-LT8350S-AZ CISPR25 Radiated EMI Performance with 12VIN to 12VOUT at 2.5A, JP1 = DCM + SSFM

Ordering Information

Evaluation Board Bill of Materials

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

DEFAULT ELECTRICAL COMPONENTS

2| C4, C17| CAP., 0.1µF, X7R, 50V, 10%, 0402, AEC-Q200| MURATA, GCM155R71H104KE02D
---|---|---|---
1| C3| CAP., 4.7µF, X5R, 10V, 20%, 0402, AEC-Q200| MURATA, GRT155R61A475ME13D
1| C5| CAP., 0.47µF, X7S, 10V, 10%, 0402, AEC-Q200| MURATA, GCM155C71A474KE36D
1| JP1| CONN., HDR, MALE, 2×4, 2mm, VERT, ST, THT| WURTH ELECTRONIK, 62000821121
1| JP2| CONN., HDR, MALE, 1×3, 2mm, VERT, ST, THT| WURTH ELEKTRONIK, 62000311121
1| R12| RES., 84.5kΩ, 1/16W, 0402, AEC-Q200| VISHAY, CRCW040284K5FKED
2| R13, R14| RES., 100kΩ, 1/16W, 0402, AEC-Q200| VISHAY, CRCW0402100KJNED
1| R22| RES., 110k, 0.5%, 1/16W, 0402, AEC-Q200| PANASONIC, ERJ-2RKD1103X
1| R3| RES., 10k, 1%, 1/10W, 0402, AEC-Q200| PANASONIC, ERJ-2RKF1002X
1| R7| RES., 402k, 1%, 1/10W, 0402, AEC-Q200| PANASONIC, ERJ-2RKF4023X

11

| TP1, TP4–TP7, TP9, TP12-TP14, TP16, TP17| ****

TEST POINT, TURRET, 0.064″ MTG. HOLE, PCB 0.062″ THK

| ****

MILL-MAX, 2308-2-00-80-00-00-07-0

4

| TP2, TP3, TP10, TP11| TEST POINT, BANANA JACK, 0.312” MTG. HOLE, PCB 0.203” THT| KEYSTONE ELECTRONICS, 575-4

1

| TP15| TEST POINT, TURRET, 0.094″ MTG. HOLE, PCB 0.062″ THK| MILL-MAX, 2501-2-00-80-00-00-07-0

1

| U1| IC, BUCK-BOOST VOLTAGE REGULATOR, LQFN-32| ANALOG DEVICES, LT8350SAV#WPBF
1| CONNECTOR| CONN., SHUNT, FEMALE, 2-POS, 2mm| WURTH ELEKTRONIK, 60800213421

1

| STAND-OFF| STANDOFF, SELF-RETAINING SPACER, 12.7MM LENGTH| WURTH ELEKTRONIK, 702935000

350kHz APPLICATION COMPONENTS (DEFAULT)

1

| ****

L1

| IND., 6.8µH, PWR, SHIELDED, 20%, 9A, 20.80mΩ,

6.56mm x 6.36mm, AEC-Q200, XAL6060

| ****

COILCRAFT INC., XAL6060-682MEC

---|---|---|---
1| R4| RES., 143k, 1%, 1/16W, 0402, AEC-Q200| VISHAY, CRCW0402143KFKED
1| R5| RES., 12k, 1%, 1/10W, 0402, AEC-Q200| PANASONIC, ERJ2RKF1202X
1| C6| CAP., 4700pF, X7R, 50V, 10%, 0402, AEC-Q200| MURATA, GCM155R71H472KA37D
4| C10, C11, C22, C23| CAP., 10µF, X7S, 50V, 10%, 1210, AEC-Q200| MURATA, GCJ32EC71H106KA01
4| C7, C13, C16, C19| CAP., 22µF, X7R, 16V, 20%, 1210, AEC-Q200| TDK, CGA6P1X7R1C226K
2MHz| APPLICATION COMPON| ENTS|
---|---|---|---

1

| ****

L1

| IND., 2.2μH, PWR, SHIELDED, 20%, 12.1A, 4.8mΩ,

6.56mm x 6.36mm, AEC-Q200, XAL6060

| ****

COILCRAFT INC., XGL6060-222MEC

1| R4| RES., 14.3k, 0.5%, 1/16W, 0402, AEC-Q200|
1| R20| RES., 0, 1/16W, 0402, AEC-Q200|
1| R5| RES., 30k, 1%, 1/16W, 0402, AEC-Q200|
1| C6| CAP., 680pF, X7R, 16V, 10%, 0402, AEC-Q200|
1| C25| CAP., 10pF, X7R, 25V, 10%, 0402, AEC-Q200|

4

| C7, C10, C11, C22, C23| ****

CAP., 10µF, X7S, 50V, 10%, 1210, AEC-Q200

| ****

MURATA, GCJ32EC71H106KA01

OPTIONAL LOW EMI COMPONENTS

1| L2| IND., 2.2µH, PWR, SHIELDED, 20%, 9.7A, 14.5mΩ,

5.48mm x 5.28mm, XAL5030, AEC-Q200

| COILCRAFT INC., XAL5030-222MEC
---|---|---|---
1| C12| CAP., 10µF, X7S, 50V, 10%, 1210, AEC-Q200| MURATA, GCJ32EC71H106KA01
1| C29| CAP., 4.7µF, X7R, 16V, 10%, 0805, AEC-Q200| MURATA, GCJ21BR71C475KA01L
1| FB3| IND., 220Ω AT 100MHz, FERRITE BEAD, 25%, 3A, 40mΩ, 0805, AEC-Q200| TDK, MPZ2012S221ATD25
4| C1, C2, C20, C21| CAP., OPTION, 1210|
2| C14, C28| CAP., OPTION, 0805|
2| FB1, FB2| IND., 220Ω AT 100MHz, FERRITE BEAD, 25%, 3A, 40mΩ, 0805, AEC-Q200| TDK, MPZ2012S221ATD25
4| C26, C27, C32, C33| CAP., OPTION, 0402|

OPTIONAL ELECTRICAL COMPONENTS

1| R1| RES., 0.010Ω, 1%, 1W, 0805 LONG-SIDE, AEC-Q200, CURRENT SENSE| SUSUMU CO, LTD., KRL2012E-M- R010-F-T5
---|---|---|---
2| R2, R10| RES., 0Ω, 1/16W, 0402, AEC-Q200| VISHAY, CRCW04020000Z0EDHP
1| R17| RES., 3.01k, 1%, 1/10W, 0402, AEC-Q200| PANASONIC, ERJ-2RKF3011X
1| VR1| RES., 20k, 20%, 1/8W, SMD 3mm SQ, 1-TURN, TOP ADJ., TRIMPOT| BOURNS, 3313J-1-203E
8| R8, R9, R11, R15, R16, R18, R19| RES., OPTION, 0402|
1| M1| XSTR., OPTION, MOSFET, P-CH, SOT-23|
3| C15, C18, C25| CAP., OPTION, 0402|
1| C24| CAP., OPTION, ALUM POLY, SMD, 8.0mm × 10.0mm|
1| C30| CAP., OPTION, ALUM POLY, SMD, 5.0mm × 5.8mm, AEC-Q200|

Evaluation Board Schematic

Evaluation Board PCB Layout

Revision History

REVISION NUMBER| REVISION DATE| DESCRIPTION| PAGES CHANGED
---|---|---|---
0| 04/24| Initial release| —

Notes
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 LICENCE, EITHER EXPRESSED OR IMPLIED, IS GRANTED UNDER ANY ADI PATENT RIGHT, COPYRIGHT, MASK WORK RIGHT, OR ANY OTHER ADI INTELLECTUAL PROPERTY RIGHT RELATING TO ANY COMBINATION, MACHINE, OR PROCESS WHICH ADI PRODUCTS ALL INFORMATION CONTAINED HEREIN IS PROVIDED “AS IS” WITHOUT REPRESENTATION OR WARRANTY. NO RESPONSIBILITY IS OR SERVICES ARE USED. TRADEMARKS AND REGISTERED TRADEMARKS ARE THE PROPERTY OF THEIR RESPECTIVE OWNERS.
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References

• Mixed-signal and digital signal processing ICs | Analog Devices
• Document Feedback Form | Analog Devices
• Product Evaluation Boards and Kits | Analog Devices
• Mixed-signal and digital signal processing ICs | Analog Devices

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