IS31LT3948 PFM MODE BOOST LED DRIVER WITH THE EXTERNAL NMOS February 2015 GENERAL DESCRIPTION FEATURES The IS31LT3948 is a PFM step-up DC-DC converter Wide input voltage range: 5V~100V designed for driving the white LED arrays for large Constant current output limited only by external size LCD panel backlighting applications. It can component selection (Note) deliver stable constant output current from a few No loop compensation required milliamps up to 2A, programmed via an external Internal over-voltage protection resistor. Internal over-temperature protection The IS31LT3948 utilizes a control scheme in which Operating temperature range -40C to +85C the output is automatically adjusted to the optimum (IS31LT3948-GRLS2-TR) output voltage for the system, maximizing the Operating temperature range -40C to +125 C efficiency. Furthermore, the control scheme is (IS31LT3948-GRLS4-TR) inherently stable removing the need to provide SOP-8 package additional loop compensation. Note: The maximum output current is determined by The device features external PWM dimming, which V /V ratio as well as the external components. If OUT IN allows the flexible control of the back-lighting output current and V /V ratio is high, high current OUT IN luminance. components of inductor and NMOS are needed. The IS31LT3948 has a wide input voltage range from 5V to 100V (Note). An integrated OVP circuit APPLICATIONS protects the chip and the system even under no-load TV monitor backlighting conditions. Notebook The chip is assembled in SOP-8 package. It Automotive operates from 5V to 100V over two temperature Street lamp ranges of -40C to +85C and -40C to +125C. LED lighting Note: The IS31LT3948 has an internal 5V shunt regulator connected to the VCC pin. A dropping resistor must be connected between the VCC pin and VIN to limit current flow. VIN voltages above 100V are allowed but care must be taken to ensure that the output voltage remains greater than VIN, and that the NMOS voltage rating is sufficiently large. TYPICAL APPLICATION CIRCUIT Figure 1 Typical Application Circuit Lumissil Microsystems www.lumissil.com 1 Rev. D, 01/21/2015 IS31LT3948 PIN CONFIGURATIONS Package Pin Configuration (Top View) SOP-8 PIN DESCRIPTIONS No. Pin Description 1 VCC Positive power supply input pin. Internally clamped at 5V (Typ.). Off time setting pin. An external resistor connected to this pin forms 2 TOFF an RC discharge path to generate a constant minimum off time of the NMOS. Enable and input peak current control pin. Pulled up to 4.5V internally to set V =0.24V when ADJ is floating. If V <0.5V, CS TH ADJ NMOS will always shutdown. If 0.5 V 2.4V, V = V /10. If ADJ CS TH ADJ 3 ADJ V >2.4V, V =0.24V. ADJ CS TH Note: During the start up (V voltage is rising), ADJ must not be CC connected to low (recommended floating). 4 GND Ground. 5 GATE Drivers output for the gate of the external NMOS. 6 CS Current sense input for the boost, peak current control loop. Feedback voltage input pin. Used to regulate the current of LEDs by 7 FB keeping V =0.3V. FB Overvoltage protection input pin, if the voltage of OVP exceed 1V, 8 OVP gate will always shutdown. Lumissil Microsystems www.lumissil.com 2 Rev. D, 01/21/2015