Freescale MC34844 10-channel LED TV backlight driver solution

Freescale’s MC34844/A is a 10-channel LED backlight driver with integrated power supply. The operating voltage is 7.0-28V, and it can drive 160 10-channel parallel LED strings. Each string is current matched to within ±2% and programmable via the I2C/SM bus interface. LED brightness dimming 256 levels, programmable to 65,000:1 (256:1 PWM, 256:1 current DAC), integrated DC/DC converter efficiency is 90%, MC34844 LED current up to 50mA per channel, MC34844A per channel LED current is up to 80mA, mainly used in HDTVs up to 43 inches wide, notebook computers, GPS screens, etc. This article describes the MC34844/A key features, block diagram, various application circuits, and the KIT34844AEPEVBE evaluation board key features, circuit diagram, and bill of materials.

10 Channel LED Backlight Driver with Integrated Power Supply

The 34844/A is a high efficiency, LED driver for use in backlighting LCD displays from 10″ to 20″+. Operating from supplies of 7.0 to 28 V, the MC34844/A is capable of driving up to 160 LEDs in 10 parallel strings . Current in the 10 strings is matched to within ±2%, and can be programmed via the I2C/SM Bus interface.

The 34844/A also includes a Pulse Width Monitor (PWM) generator for LED dimming. The LEDs can be dimmed to one of 256 levels, programmed through the I2C/SM Bus interface. Up to 65,000:1 (256:1 PWM, 256 :1 Current DAC) dimming ratio.

The integrated boost converter generates the minimum output voltage required to keep all LEDs illuminated with the selected current, providing the highest efficiency possible.

The 34844 has an integrated boost self-clocks at a default frequency of 600 kHz, but may be programmed via I2C to 150/300/600/1200 kHz. The PWM frequency can be set from 100 Hz to 25 kHz, or can be synchronized to an external input. If not synchronized to another source, the internal PWM rate outputs on the CK pin. This enables multiple devices to be synchronized together.

The 34844A has a default boost frequency of 320 kHz, but may be programmed via I2C to 160/320/650/1300 kHz. The PWM frequency can be set from 110 Hz to 27 kHz, or can be synchronized to an external input. If not synchronized to another source, the internal PWM rate outputs on the CK pin. This enables multiple devices to be synchronized together.

The 34844/A also supports optical/temperature closed loop operation and also features LED over-temperature protection, LED short protection, and LED open circuit protection. The IC also includes over-voltage protection, over-current protection, and under-voltage lockout .

Main features of MC34844:

•Input voltage of 7.0 to 28 V

• 2.5 A integrated boost FET

•Up to 50 mA on the 34844 LED current per channel

•Up to 80 mA on the 34844A LED current per channel

•90% efficiency (DC:DC)

•I2C/SM Bus interface

•10 channel current mirror with ±2% current matching

•Boost output voltage up to 60V, with Dynamic Headroom Control (DHC)

•PWM frequency programmable or synchronizable from 100 to 25,000 Hz for the 34844

•PWM frequency programmable or synchronizable from 110 to 27,000 Hz for the 34844A

•32-Ld 5x5x1.0mm TQFN Package

MC34844 application:

•Monitors and HDTV – up to 42 inch

•Personal Computer Notebooks

• GPS Screens

•Small screen Televisions
Freescale MC34844 10-channel LED TV backlight driver solution
figure 1. MC34844 Simplified Block Diagram
Freescale MC34844 10-channel LED TV backlight driver solution
figure 2. MC34844 Simplified Application Block Diagram (SM-Bus Mode)
Freescale MC34844 10-channel LED TV backlight driver solution
image 3. MC34844A Simplified Application Block Diagram (Manual Mode)
Freescale MC34844 10-channel LED TV backlight driver solution
Figure 4. MC34844 artificial mode application circuit diagram (single wire control)
Freescale MC34844 10-channel LED TV backlight driver solution
Figure 5. MC34844 artificial mode application circuit diagram (two-wire control)
Freescale MC34844 10-channel LED TV backlight driver solution
Image 6. MC34844 SM bus mode application circuit diagram
Freescale MC34844 10-channel LED TV backlight driver solution
Figure 7. MC34844 SM master-slave connection circuit diagram
Freescale MC34844 10-channel LED TV backlight driver solution
Figure 8. MC34844A High Output Application Circuit (Artificial Mode): Conditions: VIN = 60-72V, VOUT = 120 V, Load = 40S8P, ILED = 60 mA, OVP = 125 V, fSW = 300

KIT34844AEPEVBE Evaluation Board

The KIT34844AEPEVBE Evaluation board supports the 34844/A, which is a high efficiency, LED driver for use in backlighting LCD displays from 10″ to 20″+. Operating from supplies of 7.0 to 28V, the MC34844/A is capable of driving up to 160 LEDs in 10 parallel strings. Current in the 10 strings is matched to within ±2%, and can be programmed via the I2C/SM Bus interface.

The 34844/A also includes a Pulse Width Monitor (PWM) generator for LED dimming. The LEDs can be dimmed to one of 256 levels, programmed through the I2C/SM Bus interface. Up to 65,000:1 (256:1 PWM, 256 :1 Current DAC) dimming ratio.

The integrated boost converter generates the minimum output voltage required to keep all LEDs illuminated with the selected current, providing the highest efficiency possible.
Freescale MC34844 10-channel LED TV backlight driver solution
Figure 9. KIT34844AEPEVBE Evaluation Board Outline Drawing

Key features of the KIT34844AEPEVBE evaluation board:

Input voltage of 7.0 to 28V

2.5A integrated boost FET

Up to 50 mA on the 34844 LED current per channel

Up to 80 mA on the 34844A LED current per channel

90% efficiency (DC:DC)

I2C/SM Bus interface

10 channel current mirror with ±2% current matching

Boost output voltage up to 60V, with Dynamic Headroom Control (DHC)

PWM frequency programmable or synchronizable from 100 to 25,000 Hz for the 34844

PWM frequency programmable or synchronizable from 110 to 27,000 Hz for the 34844A

32-Ld 5x5x1.0mm TQFN Package

KIT34844AEPEVBE evaluation board operating parameters:

•Input Voltage (Vin) = 24V +/- 10%

•LED Load = 16 Leds x 10 Channels

•Expected Output Voltage (Vout) = around 47V

•Duty Cycle = All range.

•PWM Minimum Pulse Width = 400ns

•LED Current = 60mA

• HW OVP = 53V

•Boost Frequency = 330KHz (Typ)

•PWM Freq= 200 Hz to 25KHz (5V), or 100% Duty Cycle

•Master Mode
Freescale MC34844 10-channel LED TV backlight driver solution
Figure 10. KIT34844AEPEVBE Evaluation Board Circuit Diagram
KIT34844AEPEVBE Evaluation Board Bill of Materials:

For details, see:
http://cache.freescale.com/files/analog/doc/user_guide/KT34844AUG.pdf?fpsp=1

The Links:   PT76S16 LB121S03-TL01