IS31LT3938 HIGH VOLTAGE LED LIGHTING DRIVER WITH THREE LEVEL POWER SEQUENCING May 2015 GENERAL DESCRIPTION FEATURES IS31LT3938 LED driver IC is a peak current detection User configurable power sequencing levels buck converter which operates in constant off time 3% output current accuracy mode. It operates over a very wide input voltage Over current, temperature protection and short supply range of 10VDC to 450VDC or circuit protection 110VAC/220VAC. High efficiency (typical up to 95%) IS31LT3938 incorporates the special feature of three Higher MOS drive capability power sequencing levels by detecting OFF-ON cycles Wide input voltage range: 10VDC~450VDC or of the main power switch. When the switch is cycled 85VAC~ 265VAC within a 4 second period (typical) the device Linear and PWM dimming automatically switches the power level to the next step. Very few external components As a result, the input and output power of the luminaire may be adjusted depending on the desired amount of illumination and/or power consumption. There are APPLICATIONS multiple power levels that the engineer may configure, DC/DC or AC/DC constant current LED driver 2 steps or 3 steps, via the external pins DIM1 and DIM2. Signal and decorative lighting Backlight LED driver IS31LT3938 can also realize LED dimming using an external PWM signal. It can accept a PWM signal from 0% to 100% duty cycle. The LED current may also be adjusted linearly by applying an analog input voltage in the range of 0.5V to 2.5V. IS31LT3938 adopts a peak current mode control architecture, which eliminates the need for any additional loop compensation while maintaining a good degree of constant output current regulation. TYPICAL APPLICATION CIRCUIT Figure 1 Typical Application Circuit Lumissil Microsystems www.lumissil.com 1 Rev. C, 05/20/2015 IS31LT3938 PIN CONFIGURATION Package Pin Configurations SOP-8 PIN DESCRIPTION No. Pin Description These two pins configure the power sequencing levels as follows: 1 DIM1 DIM1=floatingDIM2=floating, no dimming (100% only) DIM1=floatingDIM2=GND , 100%-30%-100% DIM1=GNDDIM2=floating, 100%-50%-100% 2 DIM2 DIM1=GNDDIM2=GND, 100%-50%-20%-100% Linear and PWM dimming input pin. Linear dimming range: 0.5V to 2.5V. If V < 0.5V, GATE output is off. ADJ If 0.5V V 2.5V, V = V /10. ADJ CS TH ADJ If V > 2.5V, V = 0.25V. ADJ CS TH 3 ADJ When the pin is floating, there is an internal pull up to 4.0V (Typ.) and V = 0.25V. CS TH Recommended PWM dimming frequency range: 200Hz~1kHz. Note: During the start up (VIN voltage is rising), ADJ must not be connected to low (recommended floating). 4 GND Ground pin. All internal currents return through this pin. 5 GATE This pin connects to the external NMOSs gate. Current detect pin, uses an external resistor to sense the peak 6 CS inductor current. This pin sets the off time for the switch by connecting a resistor 7 TOFF between this pin and GND. 10V~450V supply voltage is connected to this pin via an external 8 VIN resistor. It is internally clamped and must be bypassed using a capacitor to GND. Lumissil Microsystems www.lumissil.com 2 Rev. C, 05/20/2015