IS32LT3125/IS32LT3125A SINGLE CHANNEL LINEAR CURRENT LED DRIVER DESCRIPTION QUICK START The IS32LT3125/3125A is a linear programmable current regulator consisting of a single output channel capable of 250mA. It features an EN pin to enable and disable the output channels current source. It supports PWM dimming via EN pin or power supply modulation (PSM). The UV pin can be used to set external VCC undervoltage lockout threshold via a resistor divider. An external resistor programs the current level for the channel current source. In addition, IS32LT3125/3125A integrates fault protection for LED open/short, ISET pin open/short and over temperature condition for robust operation. Detection of these failures is reported by the FAULTB pin. When a fault is detected the device will disable itself and output an open drain low signal. Multiple devices can have their Figure 1: Photo of IS32LT3125/IS32LT3125A Evaluation Board FAULTB pins connected to create a one-fail-all-fail condition. Under a fault condition, the IS32LT3125 will sink 30mA I current, while the IS32LT3125A will sink RECOMMENDED EQUIPMENT CC a lower 2mA (Max.) I . CC 12V,1A DC power supply The IS32LT3125/3125A is targeted at the automotive market with end applications to include interior and exterior lighting. For 12V automotive applications the ABSOLUTE MAXIMUM RATINGS low dropout driver can support one to several LEDs on the output channel. 42V power supply Caution: Do not exceed the conditions listed above, otherwise Both devices are offered in a small thermally enhanced the board will be damaged. SOP-8-EP package. PROCEDURE FEATURES The IS32LT3125/IS32LT3125A evaluation board is Single channel, sources up to 250mA fully assembled and tested. Follow the steps listed 5.0V to 28V input supply voltage range below to verify board operation. - Withstand 42V load dump Caution: Do not turn on the power supply until all connections External resister sets source current are completed. Programmable VCC undervoltage lockout to 1) Connect the ground terminal of the power supply match the LED stack for High Side PWM operation to the GND and the positive terminal to the Vin. Shared fault flag for multiple devices operation 2) The evaluation board supports several current Fault protection with flag output: levels, selected by R5, R6, R7, R8, R9 see table - LED string open/short below. The final resistance can be measured with - OUT pin short to VCC/GND an ohm meter across ISET and GND pins. For - ISET pin open/short jumpers (R5~R9) Closed=1 and Open=0. - Thermal shutdown R5 R6 R7 R8 R9 R (k )I (mA) ISET OUT - I set to 30mA under fault condition CC (IS32LT3125 only) 0 0 0 0 0 - 0 External C capacitor keeps fault status during STOR 1 0 0 0 0 8 250 start/stop operation SOP-8-EP package 0 1 0 0 0 13 153 AEC-Q100 Qualified 0 0 1 0 0 20 100 Operating temperature range from -40C ~ +125C 0 0 0 1 0 39 51 0 0 0 0 1 82 24 3) There is one LED string on board and can be adjusted from 1 to 3 LEDs by jumpers, JP2 and Lumissil Microsystems www.lumissil.com 1 Rev. A, 07/07/2020 IS32LT3125/IS32LT3125A SINGLE CHANNEL LINEAR CURRENT LED DRIVER JP3. Open JP1 to disable the LED string on external PWM signal on EN test point. board. Note: JP4 connects EN pin to VCC via R2 resistor. If JP4 is not opened, the external PWM source may be damaged by 4) If external LED string is used, please make sure high voltage. JP1 is open. Connect the anode of the external 6) FAULTB terminal is fault reporting pin. In the LED string to OUT and cathode to GND. event of LED string open/short, ISET pin Note: Connecting an external LED string without open/short or thermal shutdown fault condition, removing the onboard JP1 jumper header will drive both on board and external LED strings in parallel resulting in the FAULTB will pull low for reporting. Once the lower current drive to the LED string. fault condition is removed, the FAULTB pin goes 5) To support PWM dimming, open JP4 and apply an back high. ORDERING INFORMATION Part No. Temperature Range Package IS32LT3125 -GRLA3-EB -40C ~ +125C (Automotive) SOP-8-EP, Lead-free IS32LT3125A-GRLA3-EB 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 can be in the range of 100Hz to 300Hz, (200Hz Typ.) and input capacitor, C , should be low value (0.1uF VCC IS32LT3125/IS32LT3125A evaluation board drives typical) to ensure rapid discharge during PSM low one string of WLEDs (default is 3 LED in series). It can period. be dimmed via PWM on power line or by digitally CSTOR OPERATION driving the EN pin. The output current is set by a single reference resistor (R ) and capable of 250mA. ISET To keep the IC operating normally during condition of PSM when V goes to zero, C capacitor provides CC STOR OUTPUT CURRENT SETTING the keep-alive current needed to power the digital counter and the fault flag circuits. A capacitor value of A single resistor (R ) controls the maximum output ISET 2.2F is recommended. The keep-alive time could be current for the channel. The resistor value for a specific roughly calculated by the following Equation (2): current level is calculated using the following Equation (1): 2.5V C STOR t (2) alive 2000 I CST R (1) ISET I SET EN PIN OPERATION (8kR 80k ) ISET The voltage at the EN pin must be higher than V to EN enable the IC and below (V -V ) to disable the IC. R need to be chosen 1% accuracy resistor with EN ENHY ISET The EN pin of the IS32LT3125/IS32LT3125A can good temperature characteristic to ensure stable accept a PWM signal to implement LED dimming. LED output current. average current may be computed using the following The device is protected from an output overcurrent Equation (3). condition caused by a too low value R , by internally ISET limiting the maximum current to 300mA (Typ.). If ISET I I D (3) LED MAX PWM pin is open, the output will be off and FAULTB will be pulled low. I is computed using Equation (1) and D is the MAX PWM duty cycle. To guarantee a reasonably good dimming POWER SUPPLY MODULATION DIMMING effect, recommend PWM frequency in the range of 100Hz ~ 1kHz. Driving the EN pin with a PWM signal The IS32LT3125/IS32LT3125A can operate with can effectively adjust the LED intensity. The PWM Power Supply Modulation (PSM) where the devices signal voltage levels must meet the EN pin input power supply is pulse width modulated to achieve LED voltage levels, V . Pull up to VCC via a 10K resister dimming. The IS32LT3125/IS32LT3125A stability is EN when EN pin is unused do not leave it floating. not affected by operation with PSM. To get better dimming linearity, the recommended PSM frequency Lumissil Microsystems www.lumissil.com 2 Rev. A, 07/07/2020