RT8562. High Voltage 8 Channel LED Driver. General Description. Features. Applications. Pin Configurations. Ordering Information. Marking Information

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1 High Voltage Channel LED Driver General Description The RT5 is a 40V channel LED driver capable of delivering 0mA to each channel with 0 LEDs (.V per diode), total of 0 LEDs with one driver. The RT5 is a current mode boost converter opearated at MHz, wide V IN range covers from V to 4V and the onchip current switch is rated at.5a. The output voltage loop regulates the LED pins to 0.V with an autoadjustment circuit allowing voltage mismatches between LED strings. The RT5 automatically detects and disconnects any unconnected and/or broken strings during operation from loop to prevent from over voltage. The.5% matched LED currents on all channels are simply programmed with a resistor or a current sink. Both analog dimming and digitally controlled dimming are supported by RT5. Analog dimming is linearly controlled by an external voltage. A very high contrast ratio true digital dimming can be achieved by driving pin with a signal. Other protecting features include programmable output over voltage protection, LED curren limit, switch current limit and thermal shutdown. Features High Voltage V IN up to 4V, up to 40V, Driving up to 0 x.v LEDs (0 each channel) Channel Current Programmabe 0mA to 0mA and Matched to.5% Current Mode MHz Boost Converter Easy Analog and Digital Dimming Control Programmable Soft Start Automatic Detecting Unconnected and/or Broken Channel Programmable Over Voltage Protection Disconnects LED in Shutdown Providing High Accuracy Digital Dimming by Signal V IN Under Voltage Lockout Over Temperature Protection Current Limiting Protection Small 4Lead WQFN Package RoHS Compliant and Halogen Free Applications UMPC and Notebook Computer Backlight GPS, Portable DVD Backlight Desk Lights and Room Lighting The RT5 is packaged with a tiny footprint package of WQFN4L 4x4 packages. Ordering Information RT5 Package Type QW WQFN4L 4x4 (WType) Lead Plating System G Green (Halogen Free and Pb Free) Note Richtek products are RoHS compliant and compatible with the current requirements of IPC/JEDEC JSTD0. Suitable for use in SnPb or Pbfree soldering processes. Pin Configurations NC SS NC 4 5 (TOP VIEW) CH VDC CH COMP CH5 NC LX CH4 LX P P CH CH Marking Information WQFN4L 4x4 For marking information, contact our sales representative directly or through a Richtek distributor located in your area.

2 Typical Application Circuit V IN V to 4V Signal R.k C.9nF 5V C 4.7µF 0 R4 C µf R k C 0µF R5 k C4 0.µF COMP 4 VDC SS L 0µH RT5 LX 9 LX 5 CH 4 CH 7 5, Exposed Pad (5) C5 0µF R R x 4.75 LED (ma) = R (kω) I D R7... R 4.75k C7 40V MAX... 0 LED String Figure. MHz, ma Full Scale Current Dimming Control V IN V to 4V Analog Dimming R.k C.9nF C 4.7µF R4 0 5V C µf R k C 0µF R5 k C4 0.µF COMP 4 VDC SS L 0µH RT5 LX 9 LX 5 CH 4 CH 7 5, Exposed Pad (5)... R 4.75k C5 0µF R R x 4.75 LED (ma) = R (kω) I D R7 C7 40V MAX... 0 LED String Figure. MHz, ma Full Scale Current Analog Dimming Control

3 V IN 4V to V V AVDD V to 4V R.k 5V Analog Dimming C.9nF R4 0 R5 k R k C 4.7µF C7 µf C 0µF C.µF C4 0.µF COMP 4 VDC SS L 0µH RT5 LX 9 LX 5 CH 4 CH 7 5, Exposed Pad (5) C5 0µF x 4.75 ILED (ma) = R (kω) Note. Due to the limitaion of maximum duty, 5V input can support typically to = V.. Due to the limitaion of maximum duty, 4V input can support typically to = V. D R7... R 4.75k C R R 40V MAX... 0 LED String Figure. Wide Range V IN Application by Connecting VCC Pin to LCD Driver Power AVDD Function Block Diagram LX, LX 5.V.V OSC S R R CH VDC.V Shutdown 5V LDO... COMP 5uA Regulation Unit 5V SS CH

4 Functional Pin Description Pin No. Pin Name Pin Function Chip enable pin, when pulled low, chip is in shutdown mode., 4, NC No Internal Connection. SS Soft Start Pin, a capacitor of at least 0nF is required for soft start. 5, 5 (Exposed Pad) Ground pin of the chip. The exposed pad must be soldered to a large PCB and connected to for maximum power dissipation. Analog/Digital dimming control. When using analog dimming, I x 4.75 LED (ma) = for V.V. R (kω) A resistor or a current from DAC on this pin programs the full LED current. 0, 9,, 7 CH5 to CH Channel 5 to Channel LED current sink. Leave the pin unconnected if not used. 5, 4,, CH to CH4 Channel to Channel 4 LED current sink. Leave the pin unconnected if not used. Over Voltage Protection. boost converter turns off when V goes higher than.v. 7, P, P Power Ground (LX/LX power return). 9, LX, LX boost converter switch node. COMP boost converter loop compensation node. Power supply of the chip. For good bypass, a low ESR capacitor is required. 4 VDC Put μf capacitor on this pin to stabilize the 5V output of the internal regulator. This regulator is for chip internal use only. Absolute Maximum Ratings (Note ) Supply Voltage, V LX, LX Pin Voltage at Switching Off 45V CH to CH Pin 5V,, Pin Voltage 0.V to 5.5V Power Dissipation, P T A = 5 C WQFN4L 4x4.9W Package Thermal Resistance (Note ) WQFN4L 4x4, θ JA 5 C/W WQFN4L 4x4, θ JC 7 C/W Junction Temperature 50 C Lead Temperature (Soldering, 0 sec.) 0 C Storage Temperature Range 5 C to 50 C ESD Susceptibility (Note ) HBM (Human Body Mode) kv MM (Machine Mode) 0V Recommended Operating Conditions (Note 4) Supply Input Voltage, V to 4V Junction Temperature Range 40 C to 5 C Ambient Temperature Range 40 C to 5 C 4

5 Electrical Characteristics (V IN = 7V, T A = 5 C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit Supply Current I COMP 0.V (Switching off) 5 ma V IN Under Voltage Lockout V IN Rising V Threshold UVLO V V IN Falling 4.9 Shutdown Current I SHDN V 0.7V 0 μa Pin Input Current I V 5V 0. μa High Level V _H. 5 Logic Input Low Level V _L High Level V _H. 5 Logic Input Low Level V_L 0.5 V V LED Current Programming LED Current I CHx V > V CHx > 0.V, R = 4.75kΩ, V >.V 9 ma LEDs Current Matching V > V CHx > 0.V, R = 4.75kΩ, V >.V, Calculating (I (MAX) I (MIN) ) / I Average x 00%.5 % Pin Voltage V.kΩ R 9.kΩ, V >.V.7.. V Input Current of I 0.V V PW M.V μa Threshold of V LED Current Off 0. V V CHx Threshold Unconnection 0. V Boost Converter Switching Frequency 0.. MHz Minimum On Time 00 ns Regulated V CHx Highest Voltage LED String V Amplifier (gm) Output Current.4V > COMP > 0.V ±5 μa COMP Threshold Switch Off V LX, LX R DS(ON) Ω LX, LX Current Limit I LIM.5 A SW Maximum Duty % & Soft Start Threshold V... V Input Current I V V 50 na Soft Start Current I SS V SS.5V 5 μa Thermal Shutdown Temperature T SD 50 C Thermal Shutdown Hysteresis C Note. Stresses listed as the above Absolute Maximum Ratings may cause permanent damage to the device. These are for stress ratings. Functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may remain possibility to affect device reliability. Note. θ JA is measured in the natural convection at T A = 5 C on a high effective four layers thermal conductivity test board of JEDEC 57 thermal measurement standard. The case point of θ JC is on the expose pad for the WQFN package. Note. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. 5

6 Typical Operating Characteristics 00 Efficiency vs. Input Voltage LED Current vs. Input Voltage Efficiency (%) LEDs LED Current (ma) 4 4 CH CH CH4 CH5 CH CH LED Current vs. Temperature.4 V vs. Temperature. LED Current (ma) 9 V (V) = V Temperature ( C) = V Temperature ( C).5 V vs. Input Voltage 5 LED Current vs. Duty Cycle V (V) LED Current (ma) = 0Hz = khz = 0kHz = 0kHz V = 0V to V, = V Duty Cycle (%)

7 LED Current vs. Analog Voltage Frequency vs. Input Voltage LED Current (ma) Frequency (khz) = V Analog Voltage(V) Shutdown Current vs. Input Voltage Switch Off Current vs. Input Voltage Shutdown Current (ua) 4 Switch Off Current (ma) V = 0V..0 COMP = 0V SS Current vs. Temperature SS Current vs. Input Voltage SS Current (ua) SS Current (ua) = V, CSS = 0.μF CSS = 0.μF Temperature ( C) Input Volatge (V) 7

8 Voltage vs. Temperature Voltage vs. Input Volatge Voltage (V) Voltage (V) = V Temperature ( C) SWOFF Threshold Voltage vs. Temperature SWOFF Threshold Voltage (V) = V Temperature ( C) Power On from (5V/Div) I OUT (00mA/Div) Line Transient Response Time (50ms/Div) = 0.V to.v V (V/Div) V IN (0V/Div) (50V/Div) (V/Div) LX, LX (50V/Div) IIN (500mADiv) = V, CSS = 0.μF = V, All LED Pin Open Time (0ms/Div) Time (.5ms/Div)

9 Applications Information The RT5 is a current mode boost converter operating at MHz to power up to 0 white LEDs with a programmable current for uniform intensity. The part integrates current sources, softstart, and easy analog and digital dimming control. The protection block provides the circuitry for overtemperature, overvoltage and currentlimit protection features. Input UVLO The input operating voltage range of the RT5 is V to 4V. An input capacitor at the pin can reduce ripple voltage. It is recommended to use a ceramic 0uF or larger capacitance as the input capacitor. This IC provides an under voltage lockout (UVLO) function to enhance the stability when startup. The UVLO threshold of input rising voltage is set at 5.V typically with a 0.7V hysteresis. Power Sequence Please refer to the below Figure 4 and 5. The recommended poweron sequence is that the ready before and/or ready. If not, the SoftStart function will be disabled. As to poweroff sequence, the / must be pulled low within 0ms to prevent HardStart shown as Figure. VOUT Poweron sequence must be turned on late than and signal SoftStart Poweroff sequence must be turned off early than and signal Abnormal Poweron sequence Figure 4. PowerOn Sequence Control by UVLO No SoftStart If turns on late Poweron sequence VOUT must be turned off early than and signal SoftStart Poweroff sequence must be turned on late than and signal Abnormal Poweron sequence UVLO No SoftStart If turns on late Figure 5. PowerOn Sequence Control by / 0ms and/or should be pulled low once pull low for over 0 ms Figure. To Prevent HardStart Sequence Soft Start The RT5 employs a soft start feature to limit the inrush current. The softstart circuit prevents the excessive inrush current and input voltage droop. The softstart time is determined by capacitor C SS connected to SS pin with 5uA constant current to charge C SS. The value of capacitor C SS is userdefined to satisfy the designer's requirement. The recommended softstart capacitor is 0.uF. LED connection The RT5 equips channel LED drivers and each channel supports up to 0 LEDs. The LED strings are connected from VOUT to pin 7,, 9, 0,,, 4, and 5 respectively. If one of the LED channel is not used, the LED pin should be opened directly. Setting and Regulation of LED current The LED current can be calculated by the following equation x 4.75 I LED(mA) = R (kω) 9

10 Where, the R is the resister between pin and. This setting is the reference for the LED current at CH to CH and represents the sensed LED current for each string. The DC/DC converter regulates the LED current according to the setting. If V IN is close to and smaller than, the control loop may turn on the power switch with minimum on time and then skip cycles to maintain LED current regulation. Brightness Control The RT5 features both analog and digital dimming control. Analog dimming is linearly controlled by an external voltage (0.V to.v) at pin. A very high contrast ratio true digital dimming can be achieved by driving pin with a signal and the recommended frequency is 00Hz to 0kHz. Dimming frequency can be sufficiently adjusted from 00Hz to 0kHz. However, LED current cannot be 00% proportional to duty cycle especially for high frequency and low duty ratio because of physical limitation caused by inductor rising time. Refer to Figure 7, the minimum dimming duty can be as low as % for the frequency range from 00Hz to 00Hz. For the dimming frequency from 00Hz to khz, the duty is about 5%. If the frequency is increased to khz to 0kHz, the duty will be about 0%. LED Current (ma) LED Current vs. Duty Cycle V = 0V to V, = V Duty Cycle (%) = 0Hz = khz = 0kHz = 0kHz Figure 7. LED Current vs. Dimming Duty Cycle Over Voltage Protection The RT5 equips over voltage protection () function. When the voltage at the pin reaches a threshold of approximately.v, the MOSFET driver output (LX, LX) will be turned OFF. The MOSFET driver output (LX, LX) will be turned ON again once the voltage at drops below the threshold voltage.v. So, the output voltage can be clamped at a certain voltage level and it can be calculated by the following equation V R OUT, = V R Where R and R are the voltage divider connected to pin. V is typically.v. If at least one string is in normal operation, the controller will automatically ignore the open strings and continue to regulate the current for the string(s) in normal operation. Current Limit Protection The RT5 can limit the peak current to achieve over current protection. RT5 senses the inductor current through LX, LX pins in the switchon period. The duty cycle depends on the current sense signal summing with the internal slope compensation compared to the COMP signal. The internal NMOSFET will be turned off when the current signal is larger than the COMP signal. In the off period, the inductor current will descend. The internal MOSFET is turned on by the oscillator in the next begining cycle. Over Temperature Protection The RT5 has over temperature protection (OTP) function to prevent the excessive power dissipation from overheating. The OTP will shut down switching operation while the junction temperature exceeds 50 C. Main converter starts switching when junction temperature cooling down approximately C. Inductor Selection The value of the output inductor (L), where the transition from discontinuous to continuous mode occurs is approximated by the following equation (VOUT ) L = I f V OUT OUT

11 Where, = maximum output voltage. V IN = minimum input voltage. f = operating frequency. I OUT = sum of current from all LED strings. η is the efficiency of the power converter. The boost converter operates in discontinuous mode over the entire input voltage range when the L inductor value is less than this value L. With an inductance greater than L, the converter operates in continuous mode at the minimum input voltage and may be discontinuous at higher voltages. The inductor must be selected with a saturation current rating greater than the peak current provided by the following equation OUT OUT IN OUT IN I PEAK = V I V T V V η L VOUT Diode Selection Schottky diode is a good choice for an asynchronous Boost converter due to the small forward voltage. However, for power dissipation, reverse voltage rating and pulsating peak current are the important parameters of Schottky diode consideration. Choose a suitable diode whose reverse voltage rating is greater than the maximum output voltage. Capacitor Selection The input capacitor reduces current spikes from the input supply and minimizes noise injection to the converter. For most applications, a 0uF ceramic capacitor is sufficient. A value higher or lower may be used depending on the noise level from the input supply and the input current to the converter. Layout Guideline PCB layout is very important to design power switching converter circuits. The following layout guide lines should be strictly followed for best performance of the RT5. The power components L, D, C, C OUT and C OUT must be placed as close as possible to reduce the ac current loop. The PCB trace between power components must be short and wide as possible due to large current flow through these trace during operation. Place L and D connected to LX pin as close as possible. The trace should be short and wide as possible. It is recommend to place C close to pin. Pin is the compensation point to adjust system stability. Place the compensation components to pin as close as possible. Locate the compensation components to COMP pin as close as possible. Locate the C as close to pin as possible. NC SS NC R4 C 4 5 CH VDC CH COMP CH5 NC LX CH4 LX 7 C VC 4 C R L Figure V IN C Place power components as close as possible. D C OUT P P CH CH C OUT It is recommended to choose a ceramic capacitor bases on the output voltage ripple requirements. The minimum value of the output capacitor C OUT is approximately given by the following equation (VOUT V IN) IOUT C OUT = η V V f RIPPLE OUT

12 Outline Dimension D D SEE DETAIL A L E E A A A e b DETAIL A Pin # ID and Tie Bar Mark Options Note The configuration of the Pin # identifier is optional, but must be located within the zone indicated. Symbol Dimensions In Millimeters Dimensions In Inches Min Max Min Max A A A b D D E E e L WType 4L QFN 4x4 Package Richtek Technology Corporation Headquarter 5F, No., Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel ()5579 Fax ()55 Richtek Technology Corporation Taipei Office (Marketing) 5F, No. 95, Minchiuan Road, Hsintien City Taipei County, Taiwan, R.O.C. Tel ()799 Fax ()777 marketing@richtek.com Information that is provided by Richtek Technology Corporation is believed to be accurate and reliable. Richtek reserves the right to make any change in circuit design, specification or other related things if necessary without notice at any time. No third party intellectual property infringement of the applications should be guaranteed by users when integrating Richtek products into any application. No legal responsibility for any said applications is assumed by Richtek.