IS31LT3954-GRLS4-TR ISSI

IS31LT3954 CONSTANT-CURRENT 3-AMPERE PWM DIMMABLE BUCK REGULATOR LED DRIVER WITH OUTPUT FAULT REPORTING September 2021 GENERAL DESCRIPTION FEATURES The IS31LT3954 is a DC-to-DC switching converter Wide input voltage supply from 4.5V to 38V that integrates an N-channel MOSFET to operate in a - Withstand 40V load dump buck configuration. The device can operate from a True average output current control wide input voltage between 4.5V and 38V and 3A maximum output over operating temperature provides a constant current of up to 3A for driving a range single LED or multiple series connected LEDs. Cycle-by-cycle current limit The external resistor, R , is used to set a constant ISET Integrated high-side MOSFET switch LED output current, while allowing the output voltage Dimming via direct logic input or power supply to be automatically adjusted for a variety of LED voltage configurations. Internal control loop compensation The IS31LT3954 operates in a fixed frequency mode Under-voltage lockout (UVLO) and thermal during switching. There is an external resistor shutdown protection connected between the VCC and TON pins used to 2A low power shutdown configure the on-time (switching frequency). The Spread spectrum to optimize EMI switching frequency is dithered for spread spectrum Robust fault protection and reporting function: operation which will spread the electromagnetic - Pin-to-GND short energy into a wider frequency band. This function is - Component open/short faults helpful for optimizing EMI performance. - Adjacent pin-to-pin short A logic input PWM signal applied to the enable (EN) - LED open/short pin will adjust the average LED current. The LED - Thermal shutdown brightness is proportional to the duty cycle of the PWM signal. APPLICATIONS True average output current operation is achieved General high brightness LED lighting with fast transient response by using cycle-by-cycle, Architecture lighting controlled on-time method. Dimmable lights The IS31LT3954 is available in an SOP-8-EP Pool lighting package with an exposed pad for enhanced thermal dissipation. It operates from 4.5V to 38V over the temperature range of -40C to +125C. TYPICAL APPLICATION CIRCUIT Figure 1 Typical Application Circuit Lumissil Microsystems www.lumissil.com 1 Rev. F, 09/01/2021 IS31LT3954 PIN CONFIGURATION Package Pin Configuration (Top View) SOP-8-EP PIN DESCRIPTION No. Pin Description Power supply input. Connect a bypass capacitor CIN to ground. 1 VCC The path from CIN to GND and VCC pins should be as short as possible. On-time setting. Connect a resister from this pin to VCC pin to 2 TON set the regulator controlled on-time. Logic input for enable and PWM dimming. Pull up above 1.4V to 3 EN/PWM enable and below 0.4V to disable. Input a 100Hz~20kHz PWM signal to dim the LED brightness. Drive output current sense feedback. Set the output current by 4 FB connecting a resister from this pin to the ground. Open drain diagnostic pin. Active low to indicate fault 5 FAULTB conditions. 6 GND Ground. Internal MOSFET gate driver bootstrap. Connect a 0.1F X7R 7 BOOT ceramic capacitor from this pin to LX pin. Internal high-side MOSFET switch output. Connect this pin to 8 LX the inductor and Schottky diode. Thermal Pad Connect to GND. Lumissil Microsystems www.lumissil.com 2 Rev. F, 09/01/2021