RT8561C High Voltage 8-CH LED Driver General Description Features The RT8561C is a 40V 8-CH LED driver capable of delivering 30mA to each channel with 10 LEDs (3.6V per diode), for a total of 80 LEDs with one driver. The RT8561C is a current mode boost converter that operates at 1MHz, with a wide VIN range from 4.5V to 24V and an on chip z High Voltage : VIN up to 24V, VOUT up to 40V z Programmable Channel Current from 10mA to 30mA and Matched to 1.5% Current Mode PWM 1MHz Boost Converter Easy and High Accuracy Digital Dimming by PWM Signal Programmable Soft-Start Automatic Detection of Unconnected and/or Broken Channel Programmable Over Voltage Protection Disconnects LED in Shutdown No Power Sequence Concern VIN Under Voltage Lockout Over Temperature Protection Current Limiting Protection Small 24-Lead WQFN Package RoHS Compliant and Halogen Free z z current switch rated at 2.5A. The PWM output voltage loop regulates the LED pins to 0.6V with an auto adjustment circuit allowing voltage mismatches between LED strings. The RT8561C automati cally detects and disconnects any unconnected and/or broken strings during operation from the PWM loop to prevent VOUT from over voltage. z z z z z z The 1.5% matched LED currents on all channels can be simply programmed with a resistor or a current sink. A very high contrast ratio true digital PWM dimming can be achieved by driving the PWM pin with a PWM signal. z z z z Other protection features include programmable output over voltage protection, LED current limit, PWM switch current limit and thermal shutdown. Applications The RT8561C is available in a WQFN-24L 4x4 package. z z z UMPC and Notebook Computer Backlight GPS, Portable DVD Backlight Desk Lights and Room Lighting Ordering Information Pin Configurations LX 23 LX 24 GND Lead Plating System G : Green (Halogen Free and Pb Free) GND (TOP VIEW) GND Package Type QW : WQFN-24L 4x4 (W-Type) GND RT8561C 22 21 20 19 Note : LED1 1 18 VCC Richtek products are : LED2 2 17 CREG LED3 3 16 LED8 LED4 4 15 LED7 LED5 5 14 LED6 OVP 6 13 EN 25 Marking Information E4= : Product Code E4=YM DNN YMDNN : Date Code DS8561C-00 April 2011 VC 7 8 9 10 11 12 NC Suitable for use in SnPb or Pb-free soldering processes. ACTL ` SS ments of IPC/JEDEC J-STD-020. GND RISET RoHS compliant and compatible with the current require- NC ` WQFN-24L 4x4 www.richtek.com 1 RT8561C Typical Application Circuit VIN 4.5V to 24V C5 10µF C6 1µF LED1 7 VC R1 1.8k LED2 LED7 LED8 17 CREG 9 SS ... ::: : : : 8 x 10 LED String : : 1 2 15 16 R2 OVP 6 RISET 10 VOUT R3 C4 0.1µF 21, 22, 23, 24, 25 (Exposed Pad) C7 : : : : ... 11 ACTL PWM Signal R7 ... R6 1k LX 19, 20 VCC R5 1k 13 EN 5V C2 3.9nF : : : : RT8561C 18 C3 4.7µF D1 C1 10µF R4 10 C8 VOUT 40V MAX L1 10µH RISET 4.75k ILED (mA) = 20 x 4.75 RISET (kΩ ) GND Note : Due to the limitation of maximum duty, 5V input can support typically to VOUT = 33V. Figure 1. 1MHz, 20mA Full Scale Current PWM Dimming Control Function Block Diagram LX OSC VCC - 4.2V + R OVP - + - - 1.6V + EN - R + 1.2V CREG LED1 S + LED2 Shutdown + - 5V LDO VOUT Regulation Unit VC . . . LED7 + 5V - 5µA SS LED8 + ACTL + GND - - RISET www.richtek.com 2 DS8561C-00 April 2011 RT8561C Functional Pin Description Pin No. Pin Name 1, 2, 3, 4, 5 LED1, LED2, LED3, LED4, LED5 Channel 1 to Channel 5 LED current sink. Leave the pin unconnected if not used. 6 OVP Over Voltage Protection. PWM boost converter turns off when VOVP goes higher than 1.2V. 7 VC PWM boost converter loop compensation node. 8 NC No Internal Connection. 9 SS Soft Start Pin, a capacitor of at least 10nF is required for soft start. 10 RISET A resistor or a current from DAC on this pin programs the full LED current. 11 ACTL Analog/Digital dimming control. When using analog dimming, ILED (mA) = 20 x 4.75 for VACTL ≥ 1.2V. RISET (k Ω) 12 NC No Internal Connection. 13 EN Chip enable pin, when pulled low, chip is in shutdown mode. LED6, LED7, LED8 Channel 6 to Channel 8 LED current sink. Leave the pin unconnected if not used. 17 CREG 4.7μF capacitor should be placed on this pin to stabilize the 5V output of the internal regulator. This regulator is for chip internal use only. 18 VCC Power supply of the chip. For good bypass, a low ESR capacitor is required. LX PWM boost converter switch node. GND Ground pin of the chip. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. 14, 15, 16 19, 20 21, 22, 23, 24, 25 (Exposed Pad) DS8561C-00 April 2011 Pin Function www.richtek.com 3 RT8561C Absolute Maximum Ratings z z z z z z z z z z z (Note 1) Supply Voltage, VCC ----------------------------------------------------------------------------------------------------LX Pin Voltage at Switching Off ---------------------------------------------------------------------------------------LED1 to LED8 Pin --------------------------------------------------------------------------------------------------------ACTL, EN ------------------------------------------------------------------------------------------------------------------OVP -------------------------------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C WQFN-24L 4x4 -----------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) WQFN-24L 4x4, θJA ------------------------------------------------------------------------------------------------------WQFN-24L 4x4, θJC -----------------------------------------------------------------------------------------------------Junction Temperature ----------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Mode) ---------------------------------------------------------------------------------------------MM (Machine Mode) ------------------------------------------------------------------------------------------------------ Recommended Operating Conditions z z z 28V 50V 50V 24V −0.3V to 5.5V 1.923W 52°C/W 7°C/W 150°C 260°C −65°C to 150°C 2kV 200V (Note 4) Supply Input Voltage, VCC ---------------------------------------------------------------------------------------------- 4.5V to 24V Junction Temperature Range -------------------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range -------------------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VCC = 17V, TA = 25°C, unless otherwise specified) Parameter Symbol Supply Current IVCC VIN Under Voltage Lockout Threshold VUVLO Shutdown Current ISHDN EN Threshold Voltage ACTL Threshold Voltage Test Conditions Min Typ Max Unit VC ≤ 0.2V (Switching off) -- 3 5 mA VIN Rising -- 4.2 4.5 Hysteresis -- 0.3 -- VEN = 0V -- -- 10 1.6 -- 5 -- -- 0.65 1.3 -- 5 -- -- 0.65 Logic-High VEN_H Logic-Low VEN_L Logic-High VACTL_H Logic-Low EN Pin Input Current VACTL_L V μA V V IEN VEN ≤ 5V -- -- 0.1 μA ILED 2V > VLED > 0.6V, RISET = 4.75kΩ 19 20 21 mA 2V > VLED > 0.6V, RISET = 4.75kΩ Calculating (I (MAX) − I(MIN)) / IAverage x 100% -- -- 1.5 % 1.17 1.2 1.23 V LED Current Programming LED Current LEDs Current Matching RISET Pin Voltage VRISET 3.6kΩ ≤ RISET ≤ 9.6kΩ, VACTL > 1.2V Input Current of ACTL IACTL VACTL = 1.3V -- 1 2 μA Un-connection -- 0.1 -- V VLED Threshold To be continued www.richtek.com 4 DS8561C-00 April 2011 RT8561C Parameter Symbol Test Conditions Min Typ Max Unit 0.8 1 1.2 MHz -- 100 -- ns 0.5 0.6 0.7 V PWM Boost Converter Switching Frequency Minimum On Time Regulated VLED Highest Voltage LED String Amplifier (gm) Output Current 2.4V > VC > 0.2V -- ±15 -- μA VC Threshold PWM Switch Off 0.1 0.2 -- V -- 0.3 0.5 Ω I LIM 2.5 -- -- A OVP Threshold VOVP 1.1 1.2 1.3 V OVP Input Current I OVP VOVP ≤ 3V -- -- 50 nA Soft Start Current I SS VSS ≤ 2.5V 3 5 8 μA -- 150 -- °C -- 20 -- °C LX RDS(ON) LX Current Limit OVP & Soft Start Thermal Shutdown Temperature Thermal Shutdown Hysteresis TSD 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 2. θJA is measured in the natural convection at TA = 25°C on a high effective four layers thermal conductivity test board of JEDEC 51-7 thermal measurement standard. The case point of θJC 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. DS8561C-00 April 2011 www.richtek.com 5 RT8561C Typical Operating Characteristics Efficiency vs. Input Voltage LED Current vs. Input Voltage 100 22.0 90 21.2 LED Current (mA) 80 Efficiency (%) 21.6 80LEDs 70 60 50 40 30 20.8 20.4 LED1 LED2 LED3 LED4 LED5 LED6 LED7 LED8 20.0 19.6 19.2 20 18.8 10 18.4 18.0 0 4 6 8 10 12 14 16 18 20 22 4 24 6 8 10 14 16 18 20 22 24 Input Voltage (V) Input Voltage (V) VRISET vs. Temperature LED Current vs. Temperature 24 1.24 23 1.22 22 1.20 21 VRISET (V) LED Current (mA) 12 20 19 1.18 1.16 1.14 18 1.12 17 VIN = 12V VIN = 12V 1.10 16 -50 -25 0 25 50 75 100 -50 125 -25 0 25 50 75 100 125 Temperature (°C) Temperature (°C) LED Current vs. PWM Duty Cycle VRISET vs. Input Voltage 25 1.25 1.24 20 LED Current (mA) 1.23 VRISET (V) 1.22 1.21 1.20 1.19 1.18 15 PWM = 200Hz PWM = 1kHz PWM = 10kHz PWM = 30kHz 10 5 1.17 1.16 VPWM = 0V to 3V, VIN = 12V 0 1.15 4 6 8 10 12 14 16 Input Voltage (V) www.richtek.com 6 18 20 22 24 0 0 0.1 10 0.2 20 0.3 1 30 0.4 40 0.5 50 0.6 60 0.7 70 0.8 80 0.9 90 100 Duty Cycle (%) DS8561C-00 April 2011 RT8561C Shutdown Current vs. Temperature Shutdown Current vs. Input Voltage 6 Shutdown Current (μA)1 Shutdown Current (μA)1 10 8 6 4 2 4 6 8 10 12 14 16 18 20 22 4 3 2 1 VIN = 12V, VEN = 0V VEN = 0V 0 5 0 -50 24 -25 0 50 75 100 125 Temperature (°C) Input voltage (V) Switch Off Current vs. Input Voltage SS Current vs. Temperature 4.0 8.0 3.8 7.6 3.6 7.2 3.4 6.8 SS Current (μA) Switch Off Current (mA) 25 3.2 3.0 2.8 2.6 6.4 6.0 5.6 5.2 4.8 2.4 2.2 4.4 VCOMP = 0V VIN = 12V, CSS = 0.1μF 4.0 2.0 4 6 8 10 12 14 16 18 20 22 -50 24 -25 0 25 50 75 100 125 Temperature (°C) Input Voltage (V) OVP Voltage vs. Temperature SS Current vs. Input Voltage 6.0 1.30 1.28 1.26 OVP Voltage (V) SS Current (μA) 5.8 5.6 5.4 5.2 1.24 1.22 1.20 1.18 1.16 1.14 CSS = 0.1μF 5.0 1.12 VIN = 12V 1.10 4 6 8 10 12 14 16 18 Input Voltage (V) DS8561C-00 April 2011 20 22 24 -50 -25 0 25 50 75 100 125 Temperature (°C) www.richtek.com 7 RT8561C OVP Voltage (V) OVP Voltage vs. Input Voltage Line Transient Response 1.4 14V 1.2 12V 1.0 10V 0.8 IOUT (100mA/Div) 0.6 0.4 0.2 VIN VIN = 10.8V to 13.2V 0.0 4 6 8 10 12 14 16 18 20 22 24 Time (50ms/Div) Input Voltage (V) Power On from EN EN (2V/Div) VOUT (20V/Div) LX (20V/Div) I IN (100mADiv) VIN = 12V Time (10ms/Div) www.richtek.com 8 DS8561C-00 April 2011 RT8561C Applications Information The RT8561C is a current mode boost converter operating at 1MHz to power up to 80 white LEDs with a programmable current for uniform intensity. The part integrates current sources, soft-start, and easy analog and digital dimming control. The protection block provides the circuitry for over temperature, over voltage and current limit protection features. Input UVLO The input operating voltage range of the RT8561C is 4.5V to 24V. An input capacitor at the VCC pin can reduce ripple voltage. It is recommended to use a ceramic 10μF or larger capacitor as the input capacitor. This IC provides an Under Voltage Lockout (UVLO) function to enhance the stability during startup. If VIN is close to VOUT and smaller than VOUT, 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 RT8561C features digital dimming control scheme. A very high contrast ratio true digital PWM dimming can be achieved by driving the ACTL pin with a PWM signal at the recommended PWM frequency range from 100Hz to 10kHz. Dimming frequency can be sufficiently adjusted from 100Hz to 30kHz. However, LED current cannot be 100% proportional to duty cycle especially for high frequency and low duty ratio because of physical limitation caused by inductor rising time. Refer to Table 1 and Figure 2. Soft-Start The RT8561C employs a soft-start feature to limit the inrush current. The soft-start circuit prevents excessive inrush current and input voltage droop. The soft-start time is determined by the capacitor, C4, which is connected to the SS pin with 5μA constant current. The value of capacitor C4 is user defined to satisfy the designer's requirement. LED Connection The RT8561C provides an 8-CH LED driver with each channel capable of supporting up to 10 LEDs. The 8 LED strings are connected from VOUT to pins 1, 2, 3, 4, 5, 14, 15, and 16 respectively. If one of the LED channels is not in use, the LED pin should be tied to ground directly. Table 1. Dimming Frequency (Hz) 100 < fPWM ≤ 200 200 < fPWM ≤ 500 500 < fPWM ≤ 1k 1k < fPWM ≤ 2k 2k < fPWM ≤ 5k 5k < fPWM ≤ 10k 10k < f PWM ≤ 20k Duty (Min.) 0.16% 0.40% 0.80% 1.60% 4.00% 8.00% 16.00% Duty (Max.) 100% 100% 100% 100% 100% 100% 100% Note : The minimum duty in Table 1 is based on the application circuit and does not consider the deviation of current linearity. LED Current vs. PWM Duty Cycle 25 Setting and Regulation of LED Current The LED current can be calculated by the following equation : ILED (mA) = 20 x 4.75 RISET (kΩ) where, RISET is the resistor between the RISET pin and GND. This setting is the reference for the LED current at LED1 to LED8 and represents the sensed LED current for each string. The DC/DC converter regulates the LED current according to the setting. DS8561C-00 April 2011 LED Current (mA) 20 15 PWM = 200Hz PWM = 1kHz PWM = 10kHz PWM = 30kHz 10 5 VPWM = 0V to 3V, VIN = 12V 0 0 0 0.1 10 0.2 20 0.3 1 30 0.4 40 0.5 50 0.6 60 0.7 70 0.8 80 0.9 90 100 Duty Cycle (%) Figure 2. LED Current vs. PWM Dimming Duty Cycle www.richtek.com 9 RT8561C Over Voltage Protection The RT8561C equips an Over Voltage Protection (OVP) function. When the voltage at the OVP pin reaches a threshold of approximately 1.2V, the MOSFET driver output (LX) will be turned “OFF”. The MOSFET driver output (LX) will be turned “ON” again once the voltage at OVP drops below the threshold voltage 1.2V. Thus, the output voltage can be clamped at a certain voltage level as shown in the following equation : VOUT, OVP = VOVP × ⎛⎜ 1+ R2 ⎞⎟ ⎝ R3 ⎠ Hence, even when VIN is ready, the control circuit will still wait for the arrival of PWM and EN before the LEDs can react : VIN VOUT EN ACTL Figure 3. EN/ACTL Prior to VIN where R2 and R3 are the resistors in a voltage divider connected to the OVP pin. VOVP is typically 1.2V. 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. UVLO VIN UVLO VOUT EN ACTL Current Limit Protection The RT8561C can limit the peak current to achieve over current protection. The RT8561C senses the inductor current through the LX pin during the switch on period. The duty cycle depends on the current sense signal summed up with the internal slope compensation and compared to the VC signal. The internal N-MOSFET 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 beginning cycle. Figure 4. VIN Tums Off Prior to EN/ACTL VIN VOUT EN ACTL Figure 5. EN Prior to ACTL Signal Over Temperature Protection The RT8561C has an Over Temperature Protection (OTP) function to prevent excessive power dissipation from overheating the device. The OTP will shut down switching operation when the junction temperature exceeds 150°C. The main converter will start switching again once the junction temperature cools down approximately by 20°C. VIN VOUT EN Power Sequence The RT8561C can apply these power on/off sequences among VLED, EN and ACTL as shown in the charts below. www.richtek.com 10 ACTL Figure 6. EN Prior to ACTL Signal DS8561C-00 April 2011 RT8561C Diode Selection VIN VOUT EN ACTL Figure 7. ACTL Prior to EN Signal Schottky diode is a good choice for an asynchronous boost converter due to its small forward voltage. However, when selecting a Schottky diode, important parameters such as power dissipation, reverse voltage rating and pulsating peak current should all be taken into consideration. Choose a suitable diode with reverse voltage rating greater than the maximum output voltage. Capacitor Selection VIN_POK LED_ON ACTL EN Figure 8 Inductor Selection The value of the output inductor (L), where the transition from discontinuous to continuous mode occurs is approximated by the following equation : L= (VOUT − VIN ) × VIN2 2 × IOUT × f × VOUT 2 where, VOUT = maximum output voltage. VIN = minimum input voltage. f = operating frequency. IOUT = 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 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 saturation current rating greater than the peak current provided by the following equation : IPEAK = VOUT × IOUT + VIN × T ⎛⎜ VOUT − VIN ⎞⎟ η × VIN 2 × L ⎝ VOUT ⎠ DS8561C-00 April 2011 The input capacitor reduces current spikes from the input supply and minimizes noise injection into the converter. For most applications, a 10μF 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. It is recommended to choose a ceramic capacitor based on the output voltage ripple requirements. The minimum value of the output capacitor COUT is approximately given by the following equation : (VOUT − VIN ) × IOUT COUT = η × VRIPPLE × VOUT × f Thermal Considerations For continuous operation, do not exceed absolute maximum junction temperature. The maximum power dissipation depends on the thermal resistance of the IC package, PCB layout, rate of surrounding airflow, and difference between junction and ambient temperature. The maximum power dissipaton can be calculated by the following formula : PD(MAX) = (TJ(MAX) − TA) / θJA where TJ(MAX) is the maximum junction temperature, TA is the ambient temperature, and θJA is the junction to ambient thermal resistance. For recommended operating condition specifications of RT8561C, the maximum junction temperature is 125°C and TA is the ambient temperature. The junction to ambient thermal resistance, θJA, is layout dependent. For WQFN24L 4x4 packages, the thermal resistance, θJA, is 52°C/ W on a standard JEDEC 51-7 four-layer thermal test board. The maximum power dissipaton at TA = 25°C can be calculated by the following formula : www.richtek.com 11 RT8561C PD(MAX) = (125°C − 25°C) / (52°C/W) = 1.923W for WQFN-24L 4x4 package 17 LED3 3 LED4 4 LED5 5 OVP 6 8 9 10 11 12 ACTL NC 25 R1 C2 0.00 GND 50 75 100 125 LX 18 GND GND C6 2 0.40 Ambient Temperature (°C) 19 1 C8 25 20 LED2 1.20 0 21 LED1 7 0.80 GND GND 22 LX GND 23 RISET 1.60 24 VIN L SS 2.00 C1 NC Four-Layer PCB GND D VC Maximum Power Dissipation (W)1 2.40 VOUT C5 GND The maximum power dissipation depends on the operating ambient temperature for fixed T J(MAX) and thermal resistance, θJA. For the RT8561C package, the derating curve in Figure 9 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. Place these components as close as possible. R4 VCC 16 Locate the C6 as CREG close to VCC pin as LED8 possible. 15 LED7 14 LED6 13 EN Locate the compensation components to VC pin as close as possible. Figure 10. PCB Layout Guide Figure 9. Derating Curve for RT8561C Package 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 L1, D1, CVIN1, COUT1 and COUT2 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 these trace during operation. ` Place L1 and D1 connected to LX pin as close as possible. The trace should be short and wide as possible. ` Recommend place CVIN2 close to VCC pin. ` Pin7 is the compensation point to adjust system stability. Place the compensation components to pin7 as close as possible, no matter the compensation is RC or capacitance. www.richtek.com 12 DS8561C-00 April 2011 RT8561C Outline Dimension D2 D SEE DETAIL A L 1 E E2 e b 1 2 DETAIL A Pin #1 ID and Tie Bar Mark Options A A3 A1 Symbol 1 2 Note : The configuration of the Pin #1 identifier is optional, but must be located within the zone indicated. Dimensions In Millimeters Min Dimensions In Inches Max Min Max A 0.700 0.800 0.028 0.031 A1 0.000 0.050 0.000 0.002 A3 0.175 0.250 0.007 0.010 b 0.180 0.300 0.007 0.012 D 3.950 4.050 0.156 0.159 D2 2.300 2.750 0.091 0.108 E 3.950 4.050 0.156 0.159 E2 2.300 2.750 0.091 0.108 e L 0.500 0.350 0.020 0.450 0.014 0.018 W-Type 24L QFN 4x4 Package Richtek Technology Corporation Richtek Technology Corporation Headquarter Taipei Office (Marketing) 5F, No. 20, Taiyuen Street, Chupei City 5F, No. 95, Minchiuan Road, Hsintien City Hsinchu, Taiwan, R.O.C. Taipei County, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611 Tel: (8862)86672399 Fax: (8862)86672377 Email: [email protected] 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. DS8561C-00 April 2011 www.richtek.com 13