New Industry Products

LED Backlight Driver with Integrated LCD Bias for Automotive Infotainment

August 22, 2018 by Paul Shepard

Automotive infotainment designers can now upgrade to bigger, higher resolution displays with greater ease, reduced cost and smaller solution size with the MAX20069 from Maxim Integrated Products, Inc. The MAX20069 provides the industry's first solution integrating four I2C-controlled, 150mA LED backlight drivers and a four-output thin-film-transistor liquid-crystal display (TFT-LCD) bias in a single chip. The IC can reduce design footprint up to one-third compared to the closest competitor's parts

Automotive displays are growing larger and more sophisticated as vehicle manufacturers lure buyers with greater information and entertainment options. Market research suggests a 39 percent compound annual growth rate for the 8-inch display market in vehicle instrument clusters, center stack and heads-up display systems.

Instrument clusters are expected to migrate to 12.3-inch displays soon. As a result, automotive infotainment system designers will require power solutions with precision, flexibility and small overall solution size to meet increasingly complex system requirements.

MAX20069 supports larger screen sizes and higher resolution by providing positive analog supply voltage (PAVVD) and negative analog supply voltage (NAVDD), both of which are required for low-temperature polysilicon panels (LTPS) that deliver higher resolution and lower cost than amorphous silicon panels now currently in use.

The IC also supports the high currents that next-generation displays require, with 150mA per channel in the four-channel LED driver for 8-inch or larger displays and higher resolutions. MAX20069 operates over the minus 40°C to 105°C ambient temperature range and is available in a 6mm x 6mm TQFN package.

The MAX20069 is a highly integrated TFT power supply and LED backlight driver IC for automotive TFT-LCD applications. The IC integrates one buck-boost converter, one boost converter, two gate-driver supplies, and a boost/SEPIC converter that can power one to four strings of LEDs in the display backlight.

The source-driver power supplies consist of a synchronous boost converter and an inverting buck-boost converter that can generate voltages up to +18V and down to -7V. The positive source driver can deliver up to 150mA, while the negative source driver is capable of 100mA. The positive source-driver supply regulation voltage (VPOS) is set by connecting an external resistor-divider on FBP or through I2C.

The negative source-driver supply voltage (VNEG) is always tightly regulated to -VPOS (down to a minimum of -7V). The source-driver supplies operate from an input voltage between 2.8V and 5.5V

The gate-driver power supplies consist of regulated charge pumps that generate up to +28V and -21.5V and can deliver up to 3mA each.

The IC features a quad-string LED driver that operates off a separate input voltage (VBATT) and can power up to four strings of LEDs with 150mA (max) of current per string. The IC features logic-controlled pulse-width-modulation (PWM) dimming, with minimum pulse widths as low as 500ns with the option of phase shifting the LED strings with respect to each other.

When phase shifting is enabled, each string is turned on at a different time, reducing the input and output ripple as well as audible noise. With phase shifting disabled, the current sinks turn on simultaneously and parallel connection of current sinks is possible.

The startup and shutdown sequences for all power domains are controlled using one of the seven preset modes, which are selectable through a resistor on the SEQ pin or through the I2C interface. The MAX20069 is available in a 40-pin (6mm x 6mm) TQFN package with an exposed pad, and operates over the -40°C to +105°C ambient temperature range.

Key features

  • 4-Output TFT-LCD Bias Power
    • 8V to 5.5V Input for the TFT-LCD Section
    • Integrated 440kHz or 2.2MHz Boost and Buck-Boost Converters
    • Positive and Negative 3mA Gate Voltage Regulators with Adjustable Output Voltage
    • Flexible Resistor-Programmable Sequencing through the SEQ Pin
    • Undervoltage Detection on All Outputs
    • Low Quiescent Current Standby Mode
  • 4-Channel LED Backlight Driver
    • Up to 150mA Current per Channel
    • 5V to 42V Input Voltage Range
    • Integrated Boost/SEPIC Controller (440kHz or 2.2MHz)
    • Dimming Ratio 10,000:1 at 200Hz
    • Adaptive Voltage Optimization to Reduce Power Dissipation in the LED Current Sinks
    • Open-String, Shorted-LED, and Short-to-GND Diagnostics
  • Low EMI
    • Phase-Shift Dimming of LED Strings
    • Spread Spectrum on LED Driver and TFT
    • Selectable Switching Frequency
  • I2C Interface for Control and Diagnostics
    • Fault Indication through the FLTB pin and I2C
  • Overload and Thermal Protection
  • -40°C to +105°C Ambient Temperature Operation
  • 40-Pin (6mm x 6mm) TQFN Package with Exposed Pad

Key Advantages

  • High Integration: Reduces design footprint, providing TFT-LCD bias with four rails plus four 150mA LED backlight drivers.
    • Single board supports panels from multiple manufacturers through a resistor or I2C programmable sequencing to further reduce solution size
    • Utilizes 25 percent of the microcontroller (MCU) register bits versus closest competitor's solution, eliminating the need for a more powerful and costlier MCU in display design
  • Performance: Delivers twice the dimming ratio compared to the closest competitor's offering, maintaining panel readability during transition to different light conditions; MAX20069 supports increased resolution through a 10,000:1 pulse-width modulation (PWM) dimming ratio at 200Hz
  • Safety and Built-in Diagnostics: An easy-to-use I2C interface quickly pinpoints problems, directing the microcontroller to adjust to conditions or alert the driver of a failure
  • Electromagnetic Interference (EMI) Mitigation: 2.2MHz switching frequency, spread spectrum and phase-shift capabilities help mitigate interference and emissions

"Automotive manufacturers are using more screens, larger panels and brighter displays across several vehicle lines to support a safer and more engaging experience on the road," said Szukang Hsien, executive business manager, Automotive Business Unit, Maxim Integrated. "Maxim's integrated LED backlight driver and TFT-LCD bias solution supports newer panel types to help automotive manufacturers adopt lower cost yet higher resolution panels with smaller solution size and a high level of integration."

Availability and Pricing

The MAX20069 is available at Maxim's website for $4.40 (1000-up, FOB USA); also available from select authorized distributors. The MAX20069EVKIT# evaluation kit is available for $45.