IS32LT3120 DUAL CHANNEL LINEAR LED DRIVER WITH FADE IN/FADE OUT DESCRIPTION ABSOLUTE MAXIMUM RATINGS The IS32LT3120 is a linear programmable current 45V power supply regulator consisting of 2 output channels capable of up Caution: Do not exceed the conditions listed above, otherwise to 200mA each. Each channel features an ON/OFF the board will be damaged. input pin to toggle the channel between the OFF condition and the source condition. PROCEDURE The device integrates 63 steps fade in and fade out algorithm (Gamma correction) which causes the output The IS32LT3120 evaluation board is fully assembled LED current to gradually ramp up to the full source and tested. Follow the steps listed below to verify value after the channels control pin is pulsed. The board operation. same controller causes the LED current to gradually Caution: Do not turn on the power supply until all connections ramp down to zero if the channels input control pin is are completed. pulsed while the output channel is on. 1) Connect the ground terminal of the power supply to the GND and the positive terminal to the VCC. Note: The V supply should be set close to the FEATURES CC IS32LT3120 minimal headroom voltage of 0.5V (V CC Voutx) for best thermal performance. The board can be Dual output channels source up to 200mA each operated with a larger headroom voltage as long as the Independent debounced ON/OFF control for each increase in package temperature is monitored. Exceeding channel the device package temperature specification will cause the device to enter thermal protection mode. Programmable current via a single external 2) The fade time of both channels is adjusted by the resistor variable resistor (RW1). Turn RW1 counter Programmable fade in, fade out via external clockwise to decrease fade time, and clockwise to resistor increase fade time. Once the desired fade time is - Pull down resistor value sets fade speed set, measure the resistor value across TP1 and - Gamma corrected fade in/out algorithm GND. Use this measured resistor value to replace Fault protection: the variable resistor RW1 and R3 (see schematic - LED string shorted to GND Figure 2). - Over temperature 3) The output current of both channels (OUT1 and SOP-8-EP packages OUT2) is adjusted by the variable resistor (RW2). Turn RW2 counter clockwise to decrease the Automotive grade - AEC-Q100 (pending) output current of both channels, and clockwise to Operating temperature range from -40C ~ +125C increase the output current of both channels. The test point TP2 can be used to detect the resistor value at the ISET pin. The final resistance can be QUICK START measured with an ohm meter across TP2 and GND pins. Use this measured resistor value to replace the variable resistor RW2 and R4 (see schematic Figure 2). 4) Momentary contact buttons (K1, K2) are used to individually enable/disable the Outx LED channels. Press K1 to enable the onboard LED string for channel 1. Press K2 to enable the onboard LED string for channel 2. In both cases wait for the LED string to be fully ON (fade time completed) before pressing the button (K1 or K2) to turn OFF the corresponding LED string. Always wait for completion of fade time before pressing either K1 or K2. 5) JP1 is used to connect the IS32LT3120 Out 1 (pin 4) to the onboard LED string (LED1, LED3 and Figure 1: Photo of IS32LT3120 Evaluation Board LED5). JP2 connects the device Out2 (pin 5) to the onboard LED string (LED2, LED4, LED6). Use one of the green terminal blocks to connect an RECOMMENDED EQUIPMENT external LED string. Remove the corresponding 12V,1A DC power supply jumper header (JP1 or JP2) to disable the onboard LED string. Lumissil Microsystems www.lumissil.com 1 Rev. A, 08/11/2014 IS32LT3120 DUAL CHANNEL LINEAR LED DRIVER WITH FADE IN/FADE OUT Note: Connecting an external LED string without JP3~JP6. Connecting the header to pins 2-3 removing the onboard string jumper header will drive both disables the corresponding LED, ie JP3 pins 2-3 onboard and external LED strings in parallel resulting in disables LED3. To enable all the LED3~LED6 lower current drive to both strings. connect JP3~JP6 to pins 1-2. 6) The on board LED string size can be adjusted . from 1 to 3 LEDs by using jumper headers ORDERING INFORMATION Part No. Temperature Range Package IS32LT3120-GRLA3-EB -40C ~ +125C (Automotive) SOP-8-EP, Lead-free Table 1: Ordering Information For pricing, delivery, and ordering information, please contact Lumissils analog marketing team at analog Lumissil.com or (408) 969-6600. EVALUATION BOARD OPERATION The device is protected from an output over current condition caused by an accidental short circuit of the IS32LT3120 evaluation board drives two strings of ISET pin, by internally limiting the maximum current in WLEDs. There are two variable resistors used for the event of an ISET short circuit to 260mA. adjusting the fade time (RW1), LED current (RW2). THERMAL ROLLOFF SETTING THE FADE TIME The output current of both channels will be equal to the The fade time, either in or out, for both channels is the set value so long as the die temperature of the IC same, and is set by a single external programming remains below 125C (Typical). If the die temperature resistor (R ). The fade time is programmable by TSET exceeds this threshold, the output current of the device Equation (1): will begin to reduce at a rate of 3%/C. t R 2.5 s (1) The roll off slope is related to ISET value. When TSET I =20mA, the roll off slope is about 3.7%. When SET For example, R =100k , fade time is about 0.25s. TSET I =200mA, the roll off slope is about 2.2% SET Note: In order to get the optimized effect, the recommended FAULT DETECTION fading time is between 1.5s (R =600k ) and 0.25s TSET (R =100k ). TSET An output shorted to GND fault is detected if the output voltage on a channel drops below the low voltage If the TSET pin is tied directly to GND, the fade in/out threshold V and remains below the threshold for t . function is canceled and the ramp time is about 73s, SCD FD The channel (OUTx) with the short condition will or instant on. However, the debounce feature of the reduce its output current to 20% of I . ENx pin is not disabled. SET When short condition is removed, output current will OUTPUT CURRENT SETTING recover to original value. A single programming resistor (R ) controls the ISET When output current is larger than limit value, about maximum output current for both output channels 260mA, the output current will be clamped. When the simultaneously. The programming resistor may be open fault condition is recovered, there will be a large computed using the following Equation: current pulse about 10s. 2000 R (10k R 100k ) ISET ISET I SET Lumissil Microsystems www.lumissil.com 2 Rev. A, 08/11/2014