AAT1451: Tablet PC High Efficiency White LED Driver Solution

Analogic’s AAT1451 is a four-way highly integrated high-efficiency white LED driver. The input voltage of the device is from 5V to 26V, which can be input from DC, cigarette lighter adapter or multiple lithium batteries, the integrated boost converter provides an output of up to 50V, the current of each LED string is programmable up to 30mA, and the total output current of 120mA can be driven Up to 481 LEDs with 93% efficiency. Mainly used in monitors, notebook and netbook computers, portable DVD players, portable TVs and white LED backlight drivers.

The AAT1451 supports up to 481 white LEDs at a total output current of 120mA through an external RSET resistor with four programmable precision sink currents up to 30mA (per string).

Its boost output voltage depends on the maximum total forward voltage of the LED string, with a wide range of LED characteristics. Each string is PWM dimmed and phase shifted by 90 degrees to reduce ripple current and capacitor size. The PWM input frequency range is 100Hz to 10kHz, and the dimming range is 256:1.

Figure 1 AAT1451 block diagram

The switching frequency of the integrated boost regulator is programmable from 600kHz to 1MHz by external resistors for best efficiency and minimal external L/C filtering components. Boost current mode control provides fast response to line and load transients. A comprehensive light load mode ensures maximum efficiency over the entire load range.

Fault-tolerant circuitry with the ability to shut down open and shorted LED strings extends the life of the system. A unique high voltage current source prevents damage caused by short-circuiting the LEDs. The FAULT pin indicates an LED shorted or overheated condition. The AAT1451 is available in a lead-free, thermally enhanced, 16-pin 3X4 TDFN package.

Figure 2 AAT1451 typical application circuit diagram

AAT1451 main features

• Input voltage range: 5V to 26V

• Integrated 50V boost converter

• Maximum output current: 120mA

• Programmable switching frequency

• 600kHz to 1MHz

• Up to 93% efficiency

• High efficiency light load mode

• Four white LED strings

• Programmable maximum sink current of 30mA (each)

Figure 3 AAT1451 evaluation board PCB layout

AAT1451 Evaluation Board Bill of Materials

• ±2% accuracy (22mA)

• ±1.5% matching (22mA)

• Direct PWM dimming

• Automatic Phase Shift

• Quick switch

• Integrated failsafe:

Independent shutdown of open/shorted LED strings

Overvoltage protection

Overheating protection

• Short LED and overtemperature fault indication

• Soft-start inrush current minimization

• TDFN34-16 ultra small package

• -40°C to +85°C temperature range

AAT1451 application:

• Monitoring

• Laptops and Netbooks

• Portable DVD player

• Portable TV

• White LED backlight