LX1990

LX1990 TM ® Dual Programmable LED Current Sink DESCRIPTION KEY FEATURES W WW . Microsemi . C OM The LX1990 is a dual output current sink optimized for driving light emitting diodes. This low cost bipolar IC enables precise current regulation in LED display lighting applications, yet requires far fewer parts than discrete solutions. The LX1990 is supplied in a micro-miniature 6 lead MLP package featuring a 3 x 3 mm footprint, a profile of less than 1mm, and much improved thermal performance. Its two output sink currents are accurately matched and require only one resistor to program. Program current is only 1% of the output currents, and quiescent current is low, providing a very high efficiency driver for battery-powered displays. The LX1990 is based on a currentmirror architecture that transfers a reference current produced at the ISET pin to each of two open-collector current sinking outputs. The output stages multiply this reference current by 100 to sink independently regulated currents up to 30 mA. Light output from LED’s is proportional to average current through them; they can easily produce a brightness range of 500:1. However, color of emitted light is shifted by current amplitude. Color shift at low light levels can be reduced by driving the LED’s with a constant peak current while dimming with duty cycle control. This is achieved by driving the ISET resistor with a PWM signal. A 500:1 brightness range can be achieved by choosing 270 Hz as the PWM frequency (to avoid optical beating with 50/60 Hz room lights) and pulse width from 3.7 milliseconds to 7.4 microseconds. The LX1990 features a shutdown mode via the Enable pin. In this mode the LX1990 consumes less than 1µA and holds the two open collector output stages off. This pin may also be used to pulse width modulate output current. See applications section for dimming details. • Programmable Sink Current 0.1 to 30mA x 2 Channels • Replaces Discrete Transistor Circuitry With A Single Package • 300mV Maximum Current Sink Dropout Voltage at 20mA • 2.7 to 5.5V Power Supply Input • IOUT Compliance Voltage from 0.1 to 10VDC • Enable Input With