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ADD5201
High Efficiency, Eight-String, White LED Driver for LCD Backlight Applications
FEATURES
White LED driver based on inductive boost converter
Integrated 50 V MOSFET with 2.9 A peak current limit
Input voltage range: 6 V to 21 V
Maximum output adjustable up to 45 V
350 kHz to 1 MHz adjustable operating frequency
Built-in soft start for boost converter
Drives up to eight LED current sources
LED current adjustable up to 30 mA for each channel
Headroom control to maximize efficiency
Adjustable output dimming frequency: 200 Hz to 10 kHz
LED open/short fault protection
Selectable brightness control interface modes
PWM input
SMBus serial interface
Selectable dimming controls
Fixed delay PWM dimming control with 8-bit resolution
No delay PWM dimming control with 8-bit resolution
Phase shift PWM dimming control with 8-bit resolution
Direct PWM dimming control
DC current dimming mode with 8-bit resolution
General
Thermal shutdown
Undervoltage lockout
28-lead, 4 mm × 4 mm LFCSP
APPLICATIONS
Notebook PCs, UMPCs, and monitor displays
BLOCK DIAGRAM Figure 1.
GENERAL DESCRIPTION The ADD5201 is a white LED driver for backlight applications based on high efficiency, current mode, step-up converter tech-nology. It is designed with a 0.15 Ω, 2.9 A internal switch and a pin adjustable operating frequency between 350 kHz and 1 MHz. The ADD5201 contains eight regulated current sources for uniform brightness intensity. Each current source can be driven up to 30 mA.
The ADD5201 drives up to eight parallel strings of multiple series connected LEDs with a ±1.5% current regulation accuracy. The device provides an adjustable LED driving current up to 30 mA for each channel by an external resistor. The ADD5201 provides various brightness control methods. The LED dimming
with two external dimming mode selection pins. The device pro-vides a pin adjustable output dimming frequency range from 200 Hz to 10 kHz.
The ADD5201 operates over an input voltage range of 6 V to 21 V, but the device can function with a voltage as low as 5.4 V. The ADD5201 has multiple safety protection features to prevent damage during fault conditions. If any LED is open or short, the
device automatically disables the faulty current regulator. The internal soft start prevents inrush current during startup. A thermal shutdown protection prevents thermal damage.
The ADD5201 is available in a low profile, thermally enhanced,
TABLE OF CONTENTS Features .............................................................................................. 1
Applications ....................................................................................... 1
Block Diagram .................................................................................. 1
General Description ......................................................................... 1
Revision History ............................................................................... 2
Functional Block Diagram .............................................................. 3
Specifications ..................................................................................... 4
Step-Up Switching Regulator Specifications ............................. 4
LED Current Regulation Specifications .................................... 4
SMBus Specifications ................................................................... 5
General Specifications ................................................................. 5
Absolute Maximum Ratings ............................................................ 6
Thermal Resistance ...................................................................... 6
ESD Caution .................................................................................. 6
Pin Configuration and Function Descriptions ............................. 7
Typical Performance Characteristics ............................................. 8
Theory of Operation ...................................................................... 10
Current Mode, Step-Up Switching Regulator Operation ..... 10
Internal 3.3 V Regulator ............................................................ 10
Boost Converter Switching Frequency .................................... 10
Dimming Frequency (fPWM) Adjustment ................................. 10
Current Source ............................................................................ 10
Backlight Brightness Control .................................................... 11
PWM Dimming Mode .............................................................. 11
DC Current Dimming Mode .................................................... 12
Safety Features ............................................................................ 12
SMBus Interface.......................................................................... 13
SMBus Register Description ..................................................... 14
External Component Selection Guide ..................................... 16
Layout Guidelines....................................................................... 17
Typical Application Circuits ......................................................... 18
Outline Dimensions ....................................................................... 20
Ordering Guide ............................................................................... 20
REVISION HISTORY
4/12—Revision A: Initial Version SPECIFICATIONS VIN = 12 V, SHDN = high, TA = −25°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.
STEP-UP SWITCHING REGULATOR SPECIFICATIONS
Table 1. Typ 90 1.5
1 Test without ramp compensation; the current limit is guaranteed by design and/or correlation to static test. The current limit is dependent on the duty cycle. A maximum 1% deviation of R2/R1 for the OVP setting is considered. The allowable OVP level must not exceed the SW absolute maximum rating of 50 V when considering the OVP setting for the deviation of the resistors and the ADD5201 VOVPR deviation. See Figure 22 for more information.
LED CURRENT REGULATION SPECIFICATIONS
Table 2. Typ 1 Guaranteed by design. Test at TA = +25°C.
SMBus SPECIFICATIONS
Table 3. μs These specifications are guaranteed by design.
2 After this period, the first clock is generated.
GENERAL SPECIFICATIONS
Table 4.
ABSOLUTE MAXIMUM RATINGS TA = 25°C, unless otherwise noted.
Table 5. −0.3 V to +50 V
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.
THERMAL RESISTANCE θJA is specified for the worst-case conditions, that is, a device soldered in a circuit board for surface-mount packages.
Table 6. Thermal Resistance
ESD CAUTION PIN CONFIGURATION AND FUNCTION DESCRIPTIONS Figure 3. Pin Configuration
Table 7. Pin Function Descriptions
TYPICAL PERFORMANCE CHARACTERISTICS
Figure 10. Switching Waveforms, VIN = 7 V
Figure 11. Short-Circuit Protection Waveforms
Figure 13. Switching Waveforms, VIN = 21 V Figure 14. Open Load Protection Waveforms
THEORY OF OPERATION
CURRENT MODE, STEP-UP SWITCHING REGULATOR OPERATION The ADD5201 uses a current mode PWM boost regulator to provide the minimal voltage needed to enable the LED string to drive at the programmed LED current. The current mode regu-lation system allows fast transient response while maintaining a stable output voltage. By selecting the proper resistor-capacitor network from COMP to AGND, the regulator response can be
optimized for a wide range of input voltages, output voltages, and
Table 8. RFPWM and CFPWM Recommendations
