ANALOG DEVICES LT8386 60V, 3A Silent Switcher Synchronous Step-Up LED Driver Owner’s Manual
- June 6, 2024
- Analog Devices
Table of Contents
ANALOG DEVICES LT8386 60V, 3A Silent Switcher Synchronous Step-Up LED
Driver
LT8386
60V, 3A Silent Switcher Synchronous Step-Up LED Driver
DESCRIPTION
Demonstration circuit DC3008A is a 60V 3A Silent Switcher synchronous step-up LED driver featuring the LT®8386. It drives a single string of LEDs at 500mA up to 45V when VIN is between 4V and 40V. It runs down to 4VIN with reduced ILED and can withstand VIN as high as 50V, but has overvoltage lockout (OVLO) set for 45V for this application. DC3008A runs at 340kHz switching fre-quency. Spread spectrum frequency modulation (SSFM) can be turned on with a simple jumper, reducing EMI. DC3008A comes with low EMI features including opti-mized layout, SSFM and input EMI filter.
It is protected against both open and short LED condi-tions and reports the faults. The LT8386 boost converter has an input voltage range from 4V to 56V. Its internal synchronous 3.3A 60V switches allow up to 52V of LEDs (with adjusted FB resistors) on the output with room for over voltage protection and overshoot during an open LED event. It has adjustable switching frequency between 200kHz and 2MHz. It can be synchronized to an exter-nal source or programmed with SSFM for low EMI. The PWMTG high-side PWM MOSFET driver assists with short-circuit protection and versatility. LT8386 can be configured as a boost, boost-buck, or buck mode LED driver and maintain all of its low EMI, PWM dimming, and fault diagnostic features.
The LT8386 can be PWM dimmed with an external PWM signal or an internally- generated PWM signal. DC3008A has a jumper that can be set to switch between internally-generated PWM signal, externally-generated PWM signal, and no PWM signal (100% ON). It can be analog dimmed with a control voltage on its control pin (CTRL).
When run with both PWM dimming and SSFM, the SSFM aligns itself with the PWM
signal for flicker-free operation.
Small ceramic input and output capacitors are used to save space and cost. The
board is designed with small, high frequency capacitors on both sides of the
VOUT pins for a reduction in emissions. The open LED overvoltage protection
uses the IC’s constant voltage regulation loop to regulate the output to
approximately 57V if the LED string is opened. The output current can be
monitored through the ISMON test point.
Undervoltage and overvoltage lockout can be adjusted on the circuit with a few
simple resistor choices. There is an EMI filter on the input of DC3008A.
Please follow the recommend layout and four-layer thickness of DC3008A for low
EMI applications.
The LT8386 data sheet gives a complete description of the part, operation and
applications information. The data sheet must be read in conjunction with this
demo man-ual for demonstration circuit DC3008A. The LT8386JV is assembled in a
28-lead plastic 4mm x 5mm LQFN pack-age with a thermally-enhanced GND pad.
Proper board layout is essential for maximum thermal performance. See the data
sheet section Layout Considerations.
Design files for this circuit board are available.
All registered trademarks and trademarks are the property of their respective owners.
PERFORMANCE SUMMARY
Specifications are at TA = 25°C
BOARD PHOTO
QUICK START PROCEDURE
NOTE: Make sure that the voltage applied to VIN does not exceed 50V.
The DC3008A is easy to set up to evaluate the performance of the LT8386. Refer
to Figure 1 for proper measurement equipment setup and follow the procedure
below.
- With power off, connect a string of one or two LEDs that runs with a forward voltage less than or equal to 45V at 500mA to the LED+ and LED– GND terminals.
- Connect the EN/UVLO terminal to GND.
- For always-on LED operation: Set JP1 to “ON” and JP2 to “EXT/ON”.
- With power off, connect the input power supply to the VIN and GND terminals.
- Turn the input power supply on and make sure the voltage is between 4V and 45V to start operation.
- Release the EN/UVLO-to-GND connection.
- Observe the LED string running at the programmed LED current.
- To change the brightness with analog dimming, sim-ply attach a voltage source to the CTRL test point and set the voltage between 0V and 2V. See data sheet for details.
- To change brightness with internally-generated PWM dimming, change the JP1 and JP2 jumpers to “INT”. Adjust the voltage of the PWM pin by changing the position of the VR1 potentiometer.
- To change brightness with external PWM dimming, set JP1 to “EXT” and JP2 to “EXT/ON”. Keep LED wire length to a minimum to achieve the highest dimming ratios. Attach a 0V-3V rectangular waveform with vary-ing duty cycle to the PWM test point.
- To enable spread spectrum frequency modulation, set JP3 to “SSFM”. Setting JP3 to “NO SSFM” turns off SSFM. Setting JP3 to “SYNC” connects the pin to the SYNC test point. The converter can be synchronized to an external clock by connecting one to the SYNC test point in this setting. Please see the datasheet for details.
QUICK START PROCEDURE
Figure 1. Test Procedure Setup Drawing for DC3008A
TEST RESULTS
Figure 2.
DC3008A efficiency with and without EMI filters. DC3008A is assembled with EMI
filters.
Figure 3. DC3008A 43VLED string – ILED v. VIN. Below 7VIN, ILED
scales back based upon ISWPK. 
Figure 4. DC3008A ILED Load
Transient with CTRL Input with SSFM OFF, ILED transient is between 200mA and
500mA using a voltage input to the CTRL pin.
Figure 5.
The LT8386 can achieve dimming ratios of 10000:1 at 100Hz with an EMI filter
on the output. With the output EMI filter removed, the LT8386 can achieve
25,000:1 or higher PWM dimming ratio. 
Figure 6. DC3008A LT8386 thermal
image with 500mA, 45V LEDs, SSFM ON, and (a) 9VIN, (b) 12VIN 
Figure 7.
DC3008A bode plots with 43V, 500mA LED string (a) 12VIN and (b) 9VIN
Figure
8. Average and Peak Conducted Emissions Performance Using Current Method with
CISPR25 Class 5 Limits. Addition of the
shield can reduce CE average from 30MHz to 108MHz further below the limits.
14VIN, 43VLED, 500mA, SSFM ON, with no ferrite clamp on output cables to
LEDs 
Figure 9. Average and Peak Conducted Emissions Performance Using Voltage
Method with CISPR25 Class 5 Limits. For reduced AM
band CE results, use a larger L2, C10, or C24, or add on the EMI shield.
14VIN, 43VLED, 500mA, SSFM ON, with no ferrite clamp on output cables to
LEDs 
Figure 10. Average and Peak Radiated Emissions Performance with CISPR25
Class 5 Limits. DC3008A passes all radiated emissions without requiring the
EMI shield. 14VIN, 43VLED, 500mA, SSFM ON, with no ferrite clamp on output
cables to LEDs
EMISSIONS SHIELD (OPTION)
For the ultimate lowest emissions, an EMI shield can be attached to DC3008A. The PCB was fabricated with placeholders for six shield clips which can hold a 44mm x 44mm metal shield. Part numbers for an example shield are provided in the Parts List below in the Hardware list.
The top silkscreen picture (Figure 11) shows the place-holders for the six surface mount shield clips. Then the emissions of the board can be tested with and without the removable clip-shield.
Figure
11. EMI shield clips can be soldered to the six placeholders on the PCB. A
square 44mm x 44mm outline shows where the EMI shield fits onto the PCB.
PARTS LIST
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.
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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ANALOG DEVICES LT8386 60V, 3A Silent Switcher Synchronous Step-Up LED
Driver
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