MAX8790A

The MAX8790A is a high-efficiency driver for white lightemitting diodes (LEDs). It is designed for large liquidcrystal displays (LCDs) that employ an array of LEDs as the light source. A current-mode step-up controller drives up to six parallel strings of multiple series-connected LEDs. Each string is terminated with ballast that achieves ±1.5% current regulation accuracy, ensuring even brightness for all LEDs. The MAX8790A has a wide input-voltage range from 4.5V to 26V, and provides a fixed 20mA or adjustable 15mA to 27mA full-scale LED current.

Features of the MAX8790A are:(1)drives six parallel strings with multiple series-connected LEDs per string; (2)low 450mV feedback voltage at full current improves efficiency; (3)step-up controller regulates the output just above the highest led string voltage; (4)full-scale LED current adjustable from 15mA to 27mA, or preset 20mA; (5)wide 100:1 dimming range; (6)programmable dimming control: direct DPWM or analog dimming; (7)built-in PLL for synchronized dimming control; (8)open and short LED protections; (9)output overvoltage protection; (10)wide input voltage range from 4.5V to 26V; (11)external MOSFET allows a large number of LEDs per string; (12)500kHz/750kHz/1MHz switching frequency; (13)small, 20-pin, 4mm x 4mm thin QFN package.

The absolute maximum ratings of the MAX8790A can be summarized as:(1)ININ, SHDN, to GND:-0.3V to +28V;(2)storage temperature range:-65 to +150;(3)VCC, BRT, ENA, OSC, OV to GND:-0.3V to +6V;(4)junction temperature:+150;(5)operating temperature range:-40 to +85;(6)continuous power dissipation:1349mW.Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied.Exposure to absolute maximum rating conditions for extended periods may affect device reliability.The MAX8790A has multiple features to protect the controller from fault conditions. Separate feedback loops limit the output voltage if one or more LEDs fail open or short. During operation, if one of the feedback string voltages exceeds the VCC to 0.6V (typ) protection threshold, the controller shuts down and latches off after an internal timer expires. The controller MAX8790A features cycle-by-cycle current limit to provide consistent operation and soft-start capability. A thermal-shutdown circuit provides another level of protection.