LT3935 36V, 4A同步降压LED驱动器说明书-USB迷|专注于互联网分享

2024年7月17日发(作者：訾敏)

DEMO MANUAL DC2987A

LT3935

36V, 4A Synchronous Buck

LED Driver with Silent Switcher

DESCRIPTION

Demonstration circuit 2987A is a 36V, 4A synchronous

2MHz buck LED driver featuring the LT

3935. This

demonstration circuit powers one or two LEDs at 4A.

DC2987A runs from an input voltage of 8V to 36V as

built and can run down to 3.6V

if UVLO is adjusted. It

runs at 2MHz switching frequency. With Spread Spectrum

Frequency Modulation (SSFM) turned on, it runs from

2MHz to 2.5MHz. An optional low-side NMOS PWM dim-

ming MOSFET can be used for a high PWM dimming ratio.

DC2987A features undervoltage lockout (UVLO) set at 7V

with 0.7V hysteresis for turn-on. This Silent Switcher

demo circuit features low emissions.

The LT3935 has an input voltage range from 3.6V to

36V. It has internal, synchronous 5.8A, 40V switches

for high power, and high efficiency with a single IC. It

has an adjustable switching frequency between 200kHz

and 2MHz. It can be synchronized (SYNC) to an external

source or run with SSFM for low EMI.

The LT3935 can be PWM dimmed for accurate brightness

control. An optional low-side MOSFET can be driven from

the PWM input source for high and accurate dimming

ratio. However, LED

–

can be connected directly to GND

for the least components. In this arrangement, PWM dim-

ming has less range. Analog dimming is accomplished by

driving the CTRL pin with a voltage below 1.5V to lower

the LED sense voltage.

Small ceramic input and output capacitors save space and

cost. The open LED overvoltage protection uses the IC’s

constant-voltage regulation loop to regulate the output

to approximately 9V if the LED string is opened. Then a

fault flag is asserted. The output current can be monitored

through the ISMON output pin.

The UVLO voltage, LED current, output voltage range,

switching frequency, brightness control, and SSFM can all

be adjusted with simple modifications to the demo circuit.

The LT3935 data sheet gives a complete description of

the device, operation and applications information. The

data sheet must be read in conjunction with this demo

manual for DC2987A. The LT3935JV is assembled in

a 28-lead 5mm × 4mm LQFN package with a thermally

enhanced GND.

Design files for this circuit board are available.

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

PERFORMANCE SUMMARY

PARAMETER

Input Voltage V

Range

Undervoltage Lockout (UVLO) Falling

Enable Turn-On (EN) Rising

Safe Input Voltage V

Range

Switching Frequency (f

)

LED Current I

LED

LED Voltage V

LED

Range

Open LED Voltage V

OUT

Efficiency (100% PWM DC)

Specifications are at T

= 25°C

MIN

7.0

7.7

036

2.0

2.0 – 2.5

4.0

2.4

9.0V

91%

8.0V

TYPMAX

UNIT

MHz

CONDITION

Operating I

LED

Operating V

LED

= 7.2V I

LED

= 4A

R5 = 45.3kΩ, SSFM = OFF

R5 = 45.3kΩ, SSFM = ON

R1 = 25mΩ, 8V < V

< 36V, V

LED

= 7.2V, V

CTRL

= 2V

R7 = 1MΩ, R8 = 124kΩ

12V V

, 2MHz, 2 LEDs, SSFM = OFF

Rev. 0

DEMO MANUAL DC2987A

BOARD PHOTO

Figure 1. DC2987A Board Photo

Rev. 0

DEMO MANUAL DC2987A

QUICK START PROCEDURE

NOTE: Make sure that the voltage applied to V

does not

exceed 36V.

The DC2987A is easy to set up to evaluate the performance

of the LT3935. Refer to Figure 1 for proper measurement

equipment setup and follow the procedure below.

1. With power off, connect a string of one or two LEDs

that runs with a forward voltage less than or equal to

8V at 4A to the LED

and LED

–

GND terminals.

2. Connect the EN/UVLO terminal to GND.

3. For always-on LED operation: Set JP3 to ON.

With power off, connect the input power supply to the

and GND terminals.

Turn the input power supply on and make sure the

voltage is between 8V and 36V to start operation.

6. Release the EN/UVLO-to-GND connection.

7. Observe the LED string running at the programmed

LED current.

8. To change the brightness with analog dimming, sim-

ply adjust the VR1 potentiometer or attach a volt-

age source to the CTRL terminal and set the voltage

between 0V and 2V. See data sheet for details.

9. To change brightness with external PWM dimming,

set JP3 to EXT. Connect LEDs between LED

and LED

–

PWM terminals. Keep LED wire length to a minimum

to achieve higher dimming ratios. Attach a 0V to 3V

rectangular waveform with varying duty cycle to the

PWM terminal.

10.

To enable spread spectrum frequency modulation,

set JP2 to SSFM

Figure 2. Test Procedure Setup Drawing for DC2987A

Rev. 0

DEMO MANUAL DC2987A

TEST RESULTS

Figure 3. DC2987A Efficiency vs Input Voltage with 2MHz

and 2 LEDs at 7.4V

LED

4A with SSFM Off

Figure 4. DC2987A High Performance External PWM Dimming

with LEDs Connected Between LED

and LED

–

PWM with SSFM

Off, 12V

and 7.4V

LED

Figure 5. DC2987A 50% to 100% I

LED

Load Transient with

CTRL Input with SSFM Off, 12V

and 7.4V

LED

PWM

5V/DIV

LED

2A/DIV

5µs/DIV

= 12V, V

LED

= 7.4V, I

LED

= 4A

= 2MHz + SSFM ON

100Hz EXTERNAL PWM DIMMING

WIRE LENGTH OF 15cm BETWEEN LED

AND LED

–

PWM

Figure 6. The LT3935 Can Achieve Dimming Ratios of

10000:1 at 100Hz

Figure 7. PWM Dimming Has Linear Behavior at High Dimming

Ratios. Connect LED String to LED

and LED

–

PWM to Use the

MOSFET for Highest Dimming Ratio

Rev. 0

DEMO MANUAL DC2987A

EMISSION RESULTS

Figure 8. Average and Peak Conducted Emissions Performance Using Current Method with CISPR25 Class 5 Limits

Figure 9. Average and Peak Conducted Emissions Performance Using Voltage Method with CISPR25 Class 5 Limits

Figure 10. Average and Peak Radiated Emissions Performance with CISPR25 Class 5 Limits

Rev. 0

DEMO MANUAL DC2987A

PARTS LIST

ITEM

QTY

REFERENCE

C1, C2

C3, C22

C5, C24

C8, C11

C10

C12

C15

C13, C14, C20, C23

C17

C25, C26

FB1, FB2

FB3, FB4, FB5, FB6

R2, R4

R13

R10

R14

R17

R18

VR1

PART DESCRIPTION

CAP., X7R, 0.1µF, 50V, 10% 0402, AEC-Q200

CAP., X7R, 1µF, 50V, 10% 0805, AEC-Q200

CAP., X7R, 6.8µF, 16V, 10% 1206, AEC-Q200

CAP., X5R, 2.2µF, 25V, 10% 0402, AEC-Q200

CAP., C0G/NP0, 150pF, 25V, 5% 0402

CAP., X7R, 1000pF, 25V, 10% 0402

CAP., X7R, 0.1µF, 16V, 10% 0402

CAP., X7R, 0.01µF, 16V, 10% 0603

IND., 1µH

RES., 0.025Ω, 1/2W, 1% 0805, AEC-Q-200

RES., 45.3k, 1/16W, 1% 0402, AEC-Q200

RES., 10k, 1/16W, 1% 0402, AEC-Q200

RES., 1M, 1/16W, 1% 0402, AEC-Q200

RES., 124k, 1/16W, 1% 0402, AEC-Q200

IC., LT3935, LQFN-28, 5mm × 4mm

CAP., OPTION, ALUM. ELECT., SMD

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

CAP., OPTION, 0402

CAP., OPTION, 0603

FERRITE BEAD, 120Ω, 0805

FERRITE BEAD, OPTION, 0805

XSTR., MOSFET, N-CH, 20V, 4.7A, SOT23-3

RES., 34k, 1/16W, 1% 0402

RES., 169k, 1/16W, 1% 0402, AEC-Q200

RES., 1MΩ, 1/16W, 1% 0402, AEC-Q200

RES., 100k, 1/16W, 5% 0402, AEC-Q200

RES., 2M, 1/16W, 1% 0402, AEC-Q200

RES., OPTION, 0402

RES., 0Ω, 1/10W, 0603, AEC-Q200

TRIMMER 100k 0.25W SMD

VISHAY, CRCW06030000Z0EA

BOURNS, 3314J-1-104E

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

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

WURTH ELEKTRONIK, 62000621121

SULLINS CONNECTOR SOLUTIONS, NRPN022PAEN-RC

WURTH ELEKTRONIK, 6

NEXPERIA, PMV28UNEAR

BOURNS, CR0402-FX-3402GLF

VISHAY, CRCW0402169KFKED

VISHAY, CRCW04021M00FKED

VISHAY, CRCW0402100KJNED

VISHAY, CRCW04022M00FKED

MURATA, BLM21PG121SH1D

MURATA, GCM32EC71H106KA03L

MANUFACTURER/PART NUMBER

MURATA, GCM155R71H104KE02D

MURATA, GCM21BR71H105KA03L

TDK, CGA5L1X7R1C685K160AC

MURATA, GRT155R61E225KE13D

AVX, 04023A151JAT2A

AVX, 04023C102KAT2A

AVX, 0402YC104KAT2A

AVX, 0603YC103KAT2A

WURTH ELEKTRONIK, 74438357010

SUSUMU, KRL1220E-M-R025-F-T1

VISHAY, CRCW040245K3FKED

VISHAY, CRCW040210K0FKED

VISHAY, CRCW04021M00FKED

VISHAY, CRCW0402124KFKED

ANALOG DEVICES, LT3935JV#PBF

Required Circuit Components

Additional Demo Circuit Components

Hardware: For Demo Circuit Only

E1, E2, E10, E11, E13, E15TESTPOINT, TURRET, 0.094" PBF

E3, E4, E6, E7, E12, E14

JP1, JP2

JP3

XJP1, XJP3, XJP6

TESTPOINT, TURRET, 0.061" PBF

HEADER 3 PIN 0.079 DOUBLE ROW

HEADER 2 PIN 0.079 DOUBLE ROW

SHUNT, .079" CENTER

Rev. 0

DEMO MANUAL DC2987A

SCHEMATIC DIAGRAM

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.

Rev. 0

DEMO MANUAL DC2987A

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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