RT8560. High Voltage 4 Channel LED Driver. General Description. Features. Applications

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1 High Voltage 4 Channel LED Driver General Description The RT5 is a V 4channel LED driver capable of delivering 3mA to each channel with LEDs (3.V per diode) total LEDs with one driver. The RT5 is a current mode boost converter opearated at 1MHz switching frequency, wide range covers from 7V to 4V and the onchip current switch is rated at 1.5A. The PWM output voltage loop selects and regulates the LED pin with the highest voltage string to.9v allowing voltage mismatches between LED strings. The RT5 automatically detects and disconnects any unconnected and/or broken strings during operation from PWM loop to prevent from over voltage. The 3% matched LED currents on all channels are simply programmed with a resistor or a current sink. Both analog dimming and digitally controlled PWM dimming are supported by RT5. Analog dimming is linearly controlled by an external voltage. With an onchip output clampping amplifier and a kω resistor, PWM dimming signal is easily lowpass filtered to an analog dimming signal with one external capacitor for noisefree PWM dimming. A very high contrast ratio true digital PWM dimming can be achieved by driving pin to PWM shutdown the chip or by driving ACTL pin. Other protecting features include programmable PWM output over voltage protection, LED curren limit, PWM switch current limit and thermal shutdown. The RT5 is packaged with a tiny footprint package of WQFNL 4x4 packages. Pin Configurations (TOP VIEW) VC SS VCC VCC1 LED RISET ACTL DCTL WQFNL 4x4 Features High Voltage up to 4V, up to V, Driving up to x 3.V LEDs ( each channel) Channel Current Programmabe 4mA to 3mA and Matched to 3% Accuracy Current Mode PWM 1MHz 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 Digital Dimming Providing High Accuracy Digital Dimming by PWM at ACTL Pin or Pin Under Voltage Lockout Over Temperature Protection Current Limiting Protection Small Lead WQFN Package RoHS Compliant and Halogen Free Applications UMPC and Notebook Computer Backlight GPS, Portable DVD Backlight Desk Lights and Room Lighting Ordering Information RT5 Package Type QW WQFNL 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 JSTD. Suitable for use in SnPb or Pbfree soldering processes. Marking Information For marking information, contact our sales representative directly or through a Richtek distributor located in your area. 1

2 Typical Application Circuit 7V to 4V L µh C OUT3 D V MAX R VCC1 C VCC1 R VCC R VC 1.k C VC 3.9nF C VIN µf C 5V R1 R4 R3 R C VCC C1. 4, 5 7 VCC1 11 VCC VC 13 SS LED String RT5 1 LED 17 1 RISET ACTL 9 DCTL R5 C OUT1 I LED = ma PWM Signal 1,, 3, 19,, Exposed Pad (1) C OUT Figure 1. 1MHz, ma Full Scale Current Digital PWM Dimming Control 7V to 4V L µh C OUT3 D V MAX R VCC1 C VCC1 R VCC R VC 1.k C VC 3.9nF C VIN µf C 5V R1 R4 R3 R C VCC C1. 4, 5 7 VCC1 11 VCC 13 VC SS LED String RT5 1 LED 17 1 RISET ACTL 9 DCTL R5 C OUT1 C OUT I LED = ma Analog Dimming 1,, 3, 19,, Exposed Pad (1) Figure. 1MHz, ma Full Scale Current Analog Dimming Control

3 7V to 4V L µh C OUT3 D V MAX R VCC1 C VCC1 R VCC R VC 1.k C VC 3.9nF C VIN µf C3 5V R1 R4 R3 R C VCC C1. 4, 5 7 VCC1 11 VCC 13 VC SS LED String RT5 1 LED 17 1 RISET ACTL 9 DCTL R5 C OUT1 I LED = ma R PWM Signal 1,, 3, 19,, Exposed Pad (1) C OUT ISET C. Figure 3. 1MHz, ma Full Scale Current PWM to Analog Dimming Control V AVDD 7V to 4V 4V to 4V L µh C OUT3 D V MAX R VCC1 C VCC1.µF R VCC R VC 1.k C VC 3.9nF C VIN µf C 5V R1 R4 R3 R C VCC C1. 4, 5 7 VCC1 11 VCC 13 VC SS LED String RT5 1 LED 17 1 RISET ACTL 9 DCTL R5 C OUT1 I LED = ma PWM Signal 1,, 3, 19,, Exposed Pad (1) C OUT Figure 4. Wide Range VIN Application by Connecting VCC1 to LCD Driver Power AVDD 3

4 4 Function Block Diagram R R S.V.5V ua V Shutdown 5V LED DCTL SS VC VCC1 OSC k ACTL RISET 1.V 1.V VCC Regulation Unit

5 Functional Pin Description Pin Number Pin Name Pin Function 1,, 3, 19,, 1 (Exposed Pad) RT5 Ground pin of the chip. The exposed pad must be soldered to a large PCB and connected to for maximum power dissipation. 4, 5 PWM boost converter switch node. VCC Bipolar power switch base current supply. Typical beta of the power NPN switch is approximately 7. VCC can be connected either to VCC1 or to a separate lower voltage, as low as 3V, for better system efficiency and/or heat concern. A good bypass is necessary. 7 VCC1 Power supply of the chip. For good bypass, a low ESR capacitor is required. RISET A resistor or a current from DAC on this pin programs the full LED current. 9 ACTL Analog/Digital dimming control. When using analog dimming, I LED = ma for VACTL 1.V. R ISET DCTL By adding a.1uf filtering capacitor on ACTL pin, the PWM dimming signal on DCTL pin will be averaged out and converted into analog dimming signal on ACTL pin. 11 Chip enable pin, when low chip is in shutdown mode. Over voltage protection. PWM boost converter turns off when V goes higher than.5v. 13 SS Soft start pin, a capacitor of at least nf is required for soft start. VC PWM boost converter loop compensation node. 1, 17, 1,, LED,, Channel 1 to Channel 4 LED current sink. Leave the pin unconnected if not used. 5

6 Absolute Maximum Ratings (Note 1) Supply Voltage, VCC1, VCC 4V Pin Voltage at Switching Off 5V, LED,, Pin 5V Pin Voltage V RISET Pin Voltage 4V ACTL, DCTL,, SS, VC Pin Voltage V Power Dissipation, P T A = 5 C WQFNL 4x4 1.5W Package Thermal Resistance (Note ) WQFNL 4x4, θ JA 54 C/W WQFNL 4x4, θ JC 7 C/W Junction Temperature C Lead Temperature (Soldering, sec.) C Storage Temperature Range 5 C to C ESD Susceptibility (Note 3) HBM (Human Body Mode) kv MM (Machine Mode) V Recommended Operating Conditions (Note 4) Supply Input Voltage, VCC1, VCC 7V to 4V Junction Temperature Range Ambient Temperature Range 4 C to 5 C 4 C to 5 C Electrical Characteristics (V CC1 = 17V, T A = 5 C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit V CC1 UVLO Threshold V UVLO V CC1 Rising..5 V Supply Current I VCC1 VC.4V (Switching off) 4 7 ma Shutdown Current I SHDN V.7V μa LogicHigh Voltage V _H 5 Threshold LogicLow Voltage V _L. ACTL LogicHigh Voltage V ACTL_H 5 Threshold LogicLow Voltage V ACTL_L. V V Pin Input Current I V 5V μa LED Current Programming LED Current I LED V > V LED >.7V, = Ω, V ACTL >1.V 19 1 ma LED s Current Matching V > V LED >.7V, = Ω, V ACTL >1.V, Calculating (I (MAX) I (MIN) / I AVERAGE x %) 3 % RISET Pin Voltage V RISET = Ω, V ACTL > 1.V 1.1 V Input Current of ACTL I ACTL.3V V ACTL 1.V μa To be continued

7 Parameter Symbol Test Conditions Min Typ Max Unit Threshold of ACTL V ACTL LED Current Off. V Input Current of DCTL I DCTL.3V V DCTL V 1 μa PWM Boost Converter Switching Frequency 4 11 khz Maximum Duty Cycle % Minimum On Time ns Regulated V LED Highest Voltage LED String.9 V Amplifier gm GM μa/v Amplifier (gm) Output Current.4V > V C >.V ±3 μa VC Threshold PWM Switch Off.7 V On Voltage I =.5A.4 V Current Limit I LIM A & Soft Start Threshold V.5 V Input Current I V.5V 5 na Soft Start Current I SS V SS = V 7 μa Note 1. 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 517 thermal measurement standard. The case point of θ JC is on the expose pad for the WQFN package. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. 7

8 Typical Operating Characteristics Efficiency vs. Input Voltage LED Current vs. Input Voltage Efficiency (%) LEDs LED Current (ma) LED LED Current vs. Temperature 1.4 V RISET vs. Temperature 3 1. LED Current (ma) VRISET (V) VIN = V Temperature ( C) 1. VIN = V Temperature ( C) VRISET (V) V RISET vs. Input Voltage LED Current (ma) LED Current vs. ACTL PWM Duty Cycle ACTL = Hz ACTL = Hz ACTL = khz ACTL = khz ACTL = 3kHz ACTL = V to 3V, VIN = V % % % 3% 4% 5% % 7% % 9% % Duty Cycle (%)

9 5 LED Current vs. DCTL PWM Duty Cycle 5 LED Current vs. ACTL Voltage LED Current (ma) DCTL = Hz DCTL = Hz DCTL = khz LED Current (ma) 5 5 DCTL = V to 3V, VIN = V Duty Cycle (%) ACTL Voltage (V) VIN = V 1. Frequency vs. Input Voltage 4 Shutdown Current vs. Input Voltage Frequency (MHz) Shutdown Current (ua) V = V Switch Off Current vs. Input Voltage SS Current vs. Temperature Switch Off Current (ma) SS Current (ua) VC = V 1 VIN = V, CSS =.1uF 4 4 Temperature ( C) 9

10 SS Current vs. Input Voltage Voltage vs. Temperature SS Current (ua) Voltage (V) CSS =.1uF.3 VIN = V Temperature ( C) Voltage vs. Input Voltage Limit Current vs. Input Voltage Voltage (V)..5.4 Limit Current (A) ACTL Voltage vs. Temperature Power On from V (V/Div) ACTL Voltage (V).5... VOUT (V/Div) I IN (5mADiv).5 VIN = V. 4 4 Time (5ms/Div) VIN = V, CSS =.1uF Temperature ( C)

11 Line Transient Response (5V/Div) (5V/Div) (V/Div) I OUT (5mA/Div) VIN =.V to 13.V, RISET = 4.kΩ Time (5ms/Div) (V/Div) VIN = V, All LED Pin Open Time (.5ms/Div) 11

12 Applications Information The RT5 is a current mode boost converter operated at 1MHz to power up to 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 7V to 4V. An input capacitor at the VCC1 and VCC pin can reduce ripple voltage. It is recommended to use a ceramic uf 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 around.v. Power Sequence Please refer to the below Figure 5 and 7. The recommended poweron sequence is that the PWM ready before and/or VIN ready. If not, the SoftStart function will be disabled. As to poweroff sequence, the /VIN must be pulled low within ms to prevent HardStart shown as Figure 7. VIN PWM VOUT Poweron sequence must be turned on late than VIN and PWM signal SoftStart Poweroff sequence must be turned off early than VIN and PWM signal Abnormal Poweron sequence Figure 5. PowerOn Sequence Control by UVLO No SoftStart If PWM turns on late Poweron sequence VIN PWM VOUT VIN must be turned off early than and PWM signal SoftStart Poweroff sequence VIN must be turned on late than and PWM signal Abnormal Poweron sequence UVLO No SoftStart If PWM turns on late Figure. PowerOn Sequence Control by VIN /VIN PWM ms and/or VIN should be pulled low once PWM pull low for over ms Figure 7. 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 with a 7uA constant current to charge C SS. The value of capacitor C SS is userdefined to satisfy designer' requirement. LED connection The RT5 equips 4 channel LED divers and each channel supports up to LEDs. The 4 LED strings are connected from VOUT to pin, 1, 17 and 1 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 I LED = ma

13 Where, V RISET is the voltage of the RISET pin (1.1V typ.) and the is the resister between RISET pin and. This setting is the reference for the LED current at 4 and represents the sensed LED current for each string. The DC/DC converter regulates the LED current according to the setting. Brightness Control The RT5 features both analog and digital dimming control. Analog dimming is linearly controlled by an external voltage (.3V < V ACTL < 1.V). With an onchip output clamping amplifier and a kω resistor, PWM dimming signal is easily lowpass filtered to an analog dimming signal with one external capacitor for noisefree PWM dimming. A very high contrast ratio true digital PWM dimming can be achieved by driving ACTL pin with a PWM signal and suggest PWM frequency is from Hz to khz. Refer to Figure, the minimum dimming duty can be as low as 1% for the frequency range from Hz to 3Hz. For the dimming frequency from 3Hz to Hz, the duty is about 5%. If the frequency is increased to Hz to 3kHz, the duty will be about %. LED Current (ma) LED Current vs. ACTL PWM Duty Cycle ACTL = Hz ACTL = Hz ACTL = khz ACTL = khz ACTL = 3kHz ACTL = V to 3V, VIN = V % % % 3% 4% 5% % 7% % 9% % Duty Cycle (%) Figure. LED Current vs. PWM Dimming Duty Cycle Over Voltage Protection The RT5 equips over voltage protection () function. When the voltage at pin reaches a threshold of approximately.5v, the MOSFET drive output () will turn OFF. The MOSFET drive output () will turn ON again once the voltage at drops below the threshold of approximately.5v. So, the output voltage can be clamped at a certain voltage level and it can be calculated by the following equation R1, =.5 1 R Where, R1 and R are the voltage divider connected to pin. 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. Currentlimit Protection The RT5 can limit the peak current to achieve over current protection. The RT5 senses the inductor current of on period that flows through pin. The duty cycle depend on current signal and internal slope compensation compared with error signal. The internal NMOSFET will be turned off when the current signal is large than internal slope compensation. In the off period, the inductor current will be descended until the internal NMOSFET is on by the oscillator. Over Temperature Protection The RT5 has over temperature protection (OTP) function to prevent the excessive power dissipation from overheating. OTP will shut down the IC while junction temperature exceeds C. Main converter starts switching once the junction temperature is cooled 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 (V V ) V L = I f V OUT IN IN OUT OUT 13

14 Where, = maximum output voltage. = minimum input voltage. f = operating frequency. I OUT = sum of current from all LED strings. The boost converter operates in discontinuous mode over the entire input voltage range when the L1 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 saturated current rating that is greater than the peak current provided by the following equation VOUT IOUT VIN T VOUT VIN I PEAK = η VIN L VOUT Where, η is the efficiency of the power converter. Diode Selection Schottky diode is a good choice for an asynchronous Boost converter due to the small forward voltage. However, power dissipation, reverse voltage rating and pulsating peak current are the important parameters for Schottky diode selection. 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 uf 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 for designing power switching converter circuits. Some recommended layout guides that should be strictly be followed are shown as follows The power components L, D, C VIN, C OUT1 and C OUT must be placed as close as possible to reduce the ac current loop. The PCB trace between power components must be as short and wide as possible due to large current stream flows through these traces during operation. Place L and D connected to pin as close as possible. The trace should be short and wide as possible. It is recommended to place C Vcc1 and C Vcc close to V CC1 and V CC pins. Pin is the compensation point to adjust system stability. Place the compensation components to pin as close as possible, no matter the compensation is RC or capacitance. Place these components as close as possible. C OUT C OUT3 C OUT1 D C VIN L C VCC R VCC R VCC VC SS VCC VCC1 RISET C VCC1 LED ACTL DCTL Figure 9. PCB layout R VC Locate the C VCC1 and C VCC as close as possible to V CC1 and V CC pin. C VC1 C VC Locate the compensation components to VC pin as close as possible. 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 VIN ) IOUT C OUT = η V V f RIPPLE OUT

15 Outline Dimension 1 1 DETAIL A Pin #1 ID and Tie Bar Mark Options Note The configuration of the Pin #1 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..3.. D D E E e.5. L WType L QFN 4x4 Package Richtek Technology Corporation Headquarter 5F, No., Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel (3)5579 Fax (3)5511 Richtek Technology Corporation Taipei Office (Marketing) 5F, No. 95, Minchiuan Road, Hsintien City Taipei County, Taiwan, R.O.C. Tel ()7399 Fax ()7377 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.