Datasheet AD8240 (Analog Devices)

LED Driver/Monitor AD8240 FEATURES FUNCTIONAL BLOCK DIAGRAM PWM input for LED brightness control VPL V US SHUNT BASE O Open LED detection 5 6 7 8 Latch-off overcurrent protection RSENSE Constant voltage regulated output V 1 SENSE 10k
Ω
Supply range: 9 V to 27 V Regulated voltage range: 12.5 V to 27 V Operating current: 300 µA Shutdown current: 10 µA 5V 2 REFERENCE R1 Temperature range −40°C to +125°C 350k
Ω
LATCH-OFF 8-lead MSOP package DRIVER PWM 3 R2 250k
Ω
GENERAL DESCRIPTION AD8240
001
4
0-
GND
The AD8240 LED driver/monitor, in combination with an 04824- external transistor, supplies a constant 12 V to drive LED Figure 1. lamps. This allows cost-effective LED lamp monitoring and
PRODUCT HIGHLIGHTS
short-circuit protection. The output is regulated at 12 V when 1. Partial LED lamp failure detection. the supply voltage is between 12.5 V and 27 V. Allows for compliance with automotive regulations A CMOS compatible, level-dependent, digital input can be used for turn signal functionality detection and minimum for PWM control of the LED brightness. VO is turned on when brightness, as well as running/brake light minimum the PWM input is high and turned off when the input is low. brightness compliance. The AD8240 is designed to work with a PWM frequency up 2. Current limiting/latch-off protection. to 500 Hz, and a typical PWM range from 5% to 95%. Limiting and latching off the LED current protects vehicle wiring and prevents lamp damage Open LED detection is accomplished by measuring the change in LED lamp current caused by an open LED(s) through the use 3. PWM input. of an internal high-side current-sense amplifier that amplifies Provides brightness control. the voltage across an external current shunt. The voltage across 4. Constant voltage output. the shunt resistor is amplified to a level that can be measured by Saves cost by minimizing wiring and system design a microcontroller A/D converter or a comparator. The ability to complexity. measure the change in LED lamp current is the key benefit of 5. Drives an external transistor for low power operation. constant-voltage LED lamp driving. Providing for an external power transistor allows the The output is current-limited by latching off the output voltage AD8240 to be a low cost solution in a small package. A when the current reaches a preset level. The current limit is set more efficient design is made possible when the system by selecting the value of the external current shunt that causes designer can select a power device with specifications the output of the sense amplifier to slightly exceed the 5 V that match the application requirements. reference level when the current exceeds a maximum level. 6. Linear regulation. When the sense amplifier output exceeds 5 V, it trips an internal Minimizes EMI, which allows faster system integration, comparator that causes the driver to latch off the output voltage. qualification, and time to market. Additionally, costs are The latch is reset during the next PWM cycle. The overcurrent reduced by eliminating the inductor required for a condition can also be detected by a microcontroller or external switching design. Because of the power-saving nature of comparator by measuring the sense amplifier output. LED lamps as compared to incandescent lamps, a switching driver is typically not required.
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Document Outline FEATURES GENERAL DESCRIPTION FUNCTIONAL BLOCK DIAGRAM PRODUCT HIGHLIGHTS SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS PRODUCT DESCRIPTION LINEAR REGULATOR (BLOCK A) HIGH-SIDE CURRENT-SENSE AMPLIFIER WITH OPEN LED DETECTION (B COMPARATOR WITH LATCH-OFF OVERCURRENT PROTECTION (BLOCK C) INTELLIGENT DRIVER (BLOCK D) USING/EVALUATING THE AD8240 LED DRIVER MONITOR SETUP Shunt Resistor Selection Circuit Configuration CONTROLLING THE LED LAMP USING/EVALUATING THE VSENSE OUTPUT Using/Evaluating the Short-Circuit Protection Feature ADVANTAGES OF DRIVING LED LAMPS WITH CONSTANT VOLTAGE BACKGROUND MONITORING THE LEDS DRIVING AUTOMOTIVE LEDS Constant Current Constant Voltage OUTLINE DIMENSIONS ORDERING GUIDE