Wide Input Voltage, Fault Tolerant, Independently Controlled
Multi-Channel LED Driver with I2C interface
A8517
FEATURES AND BENEFITS (continued)
□ Cycle-by-cycle switch current limit
□ Overtemperature, and output overvoltage and undervoltage
protection
• Thermal warning and derating of LED current at higher
temperatures
• Buffered PWM dimming control for all channels to facilitate
localized dimming applications
• Polyphase PWM dimming: LED currents staggered to reduce
light flickering and input ripple current
• Synchronize boost switching frequency: 400 kHz to 2.3 MHz
to allow operation below or above the AM band
• Programmable frequency dithering to reduce EMI
• Typical LED current accuracy of 0.7%, and LED-to-LED
matching accuracy of 0.8%
DESCRIPTION (continued)
The control loop is optimized to achieve very high dimming ratios
using only PWM control, to react smoothly to supply voltage
transients and step changes, and to eliminate night flash in display
backlightapplicationswhenstartingupatverylowPWMdutycycle.
The A8517 detects and protects against a wide variety of fault
conditions, and two-way communication allows fault status to be
reported.Itprovidesprotectionagainstoutputshortandovervoltage,
open or shorted diode, open or shorted LED pin, shorted boost
switch or inductor, and IC overtemperature. A dual cycle-by-cycle
current limit protects the internal switch against switch overcurrent.
Ifrequired, theICcandriveanexternalPFETasaninput-disconnect
switch that is triggered by integrated current sense.
• Protection Features
□ Open/shorted LED pin detection
□ Programmable LED string short detection
□ Open/shorted external components (including boost
inductor, Schottky diode, FSET resistor and so forth)
□ Input overcurrent protection against output to GND short
SELECTION GUIDE
Operating Ambient
Temperature Range
Leadframe
Part Number
Package
Packing [1]
Plating
TA (°C)
28-pin TSSOP with exposed
thermal pad
A8517KLPTR-T
–40 to 125
4000 pieces per 13-in. reel
100% matte tin
1 Contact Allegro™ for additional packing options.
Table of Contents
Boost Frequency Dithering
Polyphase Grouping
Boost Output Voltage Regulation
Output Hysteresis
Soft Start Timing
22
23
24
24
24
24
26
27
31
38
39
39
40
41
43
45
58
A-1
A-1
A-2
A-4
Features and Benefits
Description
1
1
Applications
1
Package
1
Typical Application Drawing
Selection Guide
1
2
Input Disconnect Switch
System Failure Detection and Protection
Fault Handling
Application Information
Programming Information
I2C Interface Description
Timing Considerations
I2C Command Write to the A8517
I2C Command Read from the A8517
Register Map
Register Field Reference
Package Outline Drawing
Appendix A
Specifications
3
Absolute Maximum Ratings
Thermal Characteristics
Functional Block Diagram
Pinout Diagram and Terminal List Table
Electrical Characteristics
Characteristic Performance
Fault Handling
Input Overcurrent Protection
Switch Overcurrent Protection
LED String Open Fault Detection
3
3
4
5
6
9
14
14
15
15
Protection Against Open/Missing BOOST Diode 16
Power Stage Transfer Function
Output to Control Transfer Function
Stabilizing the Closed Loop System
Functional Description
Enabling the IC
17
17
18
22
PWM Dimming
Measuring Feedback Loop Gain, Phase Margin A-7
Output Current and Voltage
Allegro MicroSystems, LLC
115 Northeast Cutoff
2
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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