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Four-String White LED Driver Data Sheet ADD5205 Rev. 0 Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 ©2011 Analog Devices, Inc. All rights reserved.
FEATURES
White LED driver based on inductive boost converter Input voltage range: 2.8 V to 18 V Internal compensation
1 MHz fixed operating frequency
28 V fixed overvoltage protection
Built-in soft start for boost converter Drives up to 4 LED current sources LED current adjustable up to 25 mA for each channel DC current level brightness control with PWM input LED open fault protection General Thermal shutdown Undervoltage lockout 12-lead, 3 mm × 3 mm × 0.75 mm LFCSP package
APPLICATIONS
Smart PCs, PMPs, tablet PCs, UMPCs, and notebooks FUNCTIONAL BLOCK DIAGRAM STEP-UP SWITCHING REGULATOR 4-CHANNEL CURRENT SOURCES BRIGHTNESS CONTROL LOGIC UNDERVOLTAGE LOCKOUT SOFT START THERMAL PROTECTION OVERVOLTAGE PROTECTION AUTODISABLE FOR LED OPEN 09858-001 Figure 1. GENERAL DESCRIPTION The ADD5205 is a white LED driver for backlight applications based on high efficiency, current mode, step-up converter technology. It is designed with a 0.3 Ω internal switch and 1 MHz fixed operating frequency. The ADD5205 contains four regulated constant current sources for uniform brightness intensity. Each current source is capable of driving up to 25 mA. The ADD5205 has four parallel strings of multiple series connected LEDs with ±2% current matching. The device provides adjustable current sources that drive up to 25 mA using an external resistor. The LED current can be controlled by a PWM signal input on the PWM pin. An internal circuit translates the PWM signal to an analog signal with an external capacitor and linearly controls the LED current. The ADD5205 has multiple safety protection features to prevent any damage during fault conditions. If one or more LEDs are open, the device disables the faulty current regulator automatically. The internal soft start prevents inrush current during startup. A thermal shutdown protection feature prevents thermal damage. The ADD5205 is available in a low profile, thermally enhanced 3 mm × 3 mm × 0.75 mm, 12-lead lead frame chip scale package (LFCSP) and is specified over the temperature range of −25°C to +85°C.
Rev. 0 | Page 2 of 16 TABLE OF CONTENTS
REVISION HISTORY
8/11—Revision 0: Initial Version
Figure 2. Functional Block Diagram
Rev. 0 | Page 4 of 16 SPECIFICATIONS VIN = 3.7 V , SHDN = high, TA = −25°C to +85°C, unless otherwise noted. Typical values are at TA = 25°C. Table 1. Parameter Symbol Test Conditions/Comments Min Typ Max Unit SUPPLY Input Voltage Range VIN 2.8 18 V Quiescent Current IQ V IN = 2.8 V to 18 V, not switching 3.4 mA Shutdown Supply Current ISD VIN = 2.8 V to 18 V, SHDN = 0 V 1 μA SWITCH On Resistance RDS(ON) I SW = 100 mA 0.3 Ω Switch Current Limit ICL 1.9 A Leakage Current ILKG 1 μA OSCILLATOR Switching Frequency fOSC 1 MHz Maximum Duty Cycle DMAX 90 % SOFT START Soft Start Time1 1.5 ms CURRENT SOURCE ISET Pin Voltage VSET 1.26 V C_FILTER Pin Voltage VC_FILTER Duty = 100% 0.22 V Adjustable LED Current1 I LED 25 mA Constant Current Sink of 20 mA2 I LED20 R SET = 130 kΩ 19.6 20 20.6 mA Headroom Voltage of 20 mA2 V HR20 R SET = 130 kΩ 0.66 V Current Matching Between Strings2 ILED = 20 mA −2 +2 % LED Current Accuracy of 20 mA2 ILED = 20 mA −3 +3 % Current Source Leakage Current 1 μA SHUTDOWN CONTROL SHDN Voltage High VSHDN_HIGH VIN = 2.8 V to 18 V 1.5 6 V SHDN Voltage Low VSHDN_LOW VIN = 2.8 V to 18 V 0.6 V PWM Control PWM Input Frequency Range1 0.1 kHz PWM Voltage High VPWM_HIGH V IN = 2.8 V to 18 V 1.5 V PWM Voltage Low VPWM_LOW V IN = 2.8 V to 18 V 0.6 V 1 Guaranteed by design. 2 Tested at TA = 25°C.
Rev. 0 | Page 5 of 16 VIN = 3.7 V , SHDN = high, TA = −25°C to +85°C, unless otherwise noted. Typical values are at TA = 25°C. Table 2. Parameter Symbol Test Conditions/Comments Min Typ Max Unit THERMAL PROTECTION Thermal Shutdown Threshold1 TSD 160 °C Thermal Shutdown Hysteresis1 TSD HYST 30 °C UVLO UVLO Rising Threshold VUVLOR V IN rising 2.5 V UVLO Falling Threshold VUVLOF V IN falling 2 V OVERVOLTAGE PROTECTION Overvoltage Threshold on OVP Pin VOVP 28 V 1 Guaranteed by design.
TA = 25°C, unless otherwise noted. soldered in a circuit board for surface-mount packages. Table 4. Thermal Resistance
- CONNECT THE EXPOSED PADDLE TO GROUND.
Figure 3. Pin Configuration Table 5. Pin Function Descriptions 1 VIN Supply Input Pin. Bypassed with a capacitor to ground. 2 SHDN Shutdown Control Pin for Enabling IC. Active low. 4 SW Drain Connection of the Internal Power FET Pin. 7 ISET Full-Scale LED Current Set Pin. A resistor from this pin to ground sets the LED current up to 25 mA. filter with an internal resistor. connected to LEDs as a default channel. EPAD Connect the exposed paddle to ground.
wide range of input voltages, output voltages, and load conditions. type of LEDs) for four channels from a supply of 5 V to 18 V . up to 25 mA by an external resistor. In this mode, the maximum LED current is set by the value of RSET. Figure 14. DC Current Dimming Timing voltage lockout (UVLO), and thermal protection. inrush current at startup. The soft start time is typically 1.5 ms. this condition, OLP is activated. An undervoltage lockout circuit is included with built-in hysteresis. shuts down when VIN falls below 2 V (typical). cool. The device self starts when the TJ of the die falls below 130°C.
the output through the output diode during the switch-off time. current and lower series resistance for a given physical size. Solve for the inductance value (L). greater than the maximum dc input current to the regulator. ILPK is the peak inductor current. ILAVG is the input average current. Table 6 shows a list of recommend inductors. Table 6. Recommended Inductors as close as possible to the ADD5205. 4.7 μF or greater capacitor is preferred. be rated for a reverse voltage greater than the output voltage used. than the peak inductor current.
Rev. 0 | Page 12 of 16 LAYOUT GUIDELINES When designing a high frequency, switching, regulated power supply, layout is very important. Using a good layout can solve many problems associated with these types of supplies. The main problems are loss of regulation at high output current and/or large input-to-output voltage differentials, excessive noise on the output and switch waveforms, and instability. Using the following guidelines can help minimize these problems. Make all power (high current) traces as short, direct, and thick as possible. It is good practice on a standard printed circuit board (PCB) to make the traces an absolute minimum of 15 mil (0.381 mm) per ampere. Place the inductor, output capacitors, and output diode as close to each other as possible. This helps reduce the EMI radiated by the power traces that is due to the high switching currents through them. This also reduces lead inductance and resistance, which in turn reduces noise spikes, ringing, and resistive losses that produce voltage errors. The grounds of the IC, input capacitors, output capacitors, and output diode (if applicable), should be connected close together, directly to a ground plane. It is also a good idea to have a ground plane on both sides of the PCB. This reduces noise by reducing ground loop errors and by absorbing more of the EMI radiated by the inductor. Due to how switching regulators operate, there are two power states: on and off. During each state, there is a current loop made by the power components currently conducting. Place the power components so that the current loop is conducting in the same direction during each of the two states. This prevents magnetic field reversal caused by the traces between the two half cycles and reduces radiated EMI. Layout Procedure Use the following general guidelines when designing PCBs:
- Keep CIN close to the VIN and GND leads of the ADD5205.
- Keep the high current path from CIN (through L1) to the SW and GND leads as short as possible.
- Keep the high current path from CIN (through L1), D1, and COUT as short as possible.
- Keep high current traces as short and wide as possible.
- Place the COVP as close as possible to the OVP pin.
- Place the LED current setting resistors as close as possible to each pin to prevent noise pickup.
- Avoid routing noise sensitive traces near high current traces and components, especially the LED current setting node (ISET).
- Use a thermal pad size that is the same dimension as the exposed pad on the bottom of the package. Heat Sinking When using a surface-mount power IC or external power switches, the PCB can often be used as the heat sink. This is done by using the copper area of the PCB to transfer heat from the device. Users should maximize this area to optimize thermal performance.
Figure 15. Typical Application Circuit
0.05 MAX
0.02 NOM
0.20 REF
0.20 MIN
COMPLIANT TOJEDEC STANDARDS MO-229-WEED-4. Figure 16. 12-Lead Lead Frame Chip Scale Package [LFCSP_WQ]
Rev. 0 | Page 15 of 16 NOTES
Rev. 0 | Page 16 of 16 NOTES ©2011 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D09858-0-8/11(0)