A8521: Wide Input Voltage Range, High Efficiency Fault Tolerant LED Driver


The A8521 is a multi-output white LED driver for small-size LCD backlighting. It integrates a current-mode boost converter with internal power switch and four current sinks. The boost converter can drive up to 48 LEDs, 12 LEDs per string, at 80 mA. The LED sinks can be paralleled together to achieve even higher LED currents, up to 320 mA. The A8521 can operate with a single power supply, from 5 to 40 V, which allows the part to withstand load dump conditions encountered in automotive systems.

The A8521 can drive an external P-FET to disconnect the input supply from the system in the event of a fault. The A8521 provides protection against output short and overvoltage, open or shorted diode, open or shorted LED pin, shorted boost switch or inductor, shorted FSET or ISET resistor, and IC overtemperature. A dual level cycle-by-cycle current limit function provides soft start and protects the internal current switch against high current overloads.

The A8521 has a synchronization pin that allows PWM switching frequencies to be synchronized in the range of 580 kHz to 2.3 MHz. The high switching frequency allows the A8521 to operate above the AM radio band.

It is very similar to the A8514, with a slight modification to the current sinks which allows it to operate a very low PWM threshold. This is sometimes needed for applications such as Head Up Display (HUD).

The A8521 is provided in a 20-pin TSSOP package (suffix LP) with an exposed pad for enhanced thermal dissipation. It is lead (Pb) free, with 100% matte tin lead frame plating.

This part is discontinued. Samples are no longer available. Date of status change: September 1, 2016. Recommended Substitutions: For existing customer transition, and for new customers or new applications, contact Allegro Sales.

Top Features

  • AEC-Q100 Qualified
  • Wide input voltage range of 5 to 40 V for start/stop, cold crank and load dump requirements
  • Fully integrated LED current sinks and boost converter with 60 V DMOS
  • Sync function to synchronize boost converter switching frequency up to 2.3 MHz, allowing operation above the AM band
  • Excellent input voltage transient response
  • Single resistor primary OVP minimizes VOUT leakage
  • Internal secondary OVP for redundant protection
  • LED current of 80 mA per channel
  • Drives up to 12 series LEDs in 4 parallel strings
  • 0.7% to 0.8% LED to LED matching accuracy
  • PWM and analog dimming inputs
  • 5000:1 PWM dimming at 200 Hz
  • Provides driver for external PMOS input disconnect switch
  • Extensive protection against:
    • Shorted boost switch or inductor
    • Shorted FSET or ISET resistor
    • Shorted output
    • Open or shorted LED pin
    • Open boost Schottky
    • Overtemperature (OTP)

Part Number Specifications and Availability

Part Number Package Type Temperature RoHS
Part Composition /
RoHS Data
Comments Samples Check Stock
A8521KLPTR-T 20-lead TSSOP -40°C to 125°C Yes View Data Discontinued Contact your
local sales rep
Distributor Stock

Allegro’s products are not to be used in any devices or systems, including but not limited to life support devices or systems, in which a failure of Allegro’s product can reasonably be expected to cause bodily harm.