RT8560GQW

RT8560 High Voltage 4 Channel LED Driver General Description Features The RT8560 is a 60V 4-channel LED driver capable of delivering 30mA to each channel with 15 LEDs (3.6V per diode) total 60 LEDs with one driver. The RT8560 is a current mode boost converter opearated at 1MHz switching frequency, wide VIN range covers from 7V to 40V and the z High Voltage : VIN up to 40V, VOUT up to 60V, Driving up to 60 x 3.6V LEDs (15 each channel) z on-chip current switch is rated at 1.5A. z Channel Current Programmabe 4mA to 30mA 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 EN Pin VIN Under Voltage Lockout Over Temperature Protection Current Limiting Protection Small 20-Lead WQFN Package RoHS Compliant and Halogen Free The PWM output voltage loop selects and regulates the LED pin with the highest voltage string to 0.9V allowing voltage mismatches between LED strings. The RT8560 automatically detects and disconnects any unconnected and/or broken strings during operation from PWM loop to prevent VOUT 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 RT8560. Analog dimming is linearly controlled by an external voltage. With an on-chip output clampping amplifier and a 200kΩ resistor, PWM dimming signal is easily low-pass filtered to an analog dimming signal with one external capacitor for noise-free PWM dimming. A very high contrast ratio true digital PWM dimming can be achieved by driving EN 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 RT8560 is packaged with a tiny footprint package of WQFN-20L 4x4 packages. z z z z z z z Applications z z z UMPC and Notebook Computer Backlight GPS, Portable DVD Backlight Desk Lights and Room Lighting Ordering Information RT8560 Package Type QW : WQFN-20L 4x4 (W-Type) Lead Plating System G : Green (Halogen Free and Pb Free) 20 19 18 17 ` RoHS compliant and compatible with the current require- ` Suitable for use in SnPb or Pb-free soldering processes. LED3 LED2 LED1 GND GND z Richtek products are : (TOP VIEW) ments of IPC/JEDEC J-STD-020. 16 GND 1 15 GND GND SW SW 2 14 GND 4 z Note : Pin Configurations 3 z 13 12 21 11 6 7 8 9 VCC2 VCC1 RISET ACTL DCTL 5 10 LED4 VC SS OVP EN Marking Information For marking information, contact our sales representative directly or through a Richtek distributor located in your area. WQFN-20L 4x4 DS8560-01 April 2011 www.richtek.com 1 RT8560 Typical Application Circuit VIN 7V to 40V COUT3 1µF L 10µH VOUT 60V MAX D CVIN 10µF RVCC1 10 C2 15 LED String RT8560 R4 4, 5 SW LED1 7 VCC1 CVCC1 1µF R3 1k 5V R1 VOUT VIN : : : : COUT1 COUT2 18 LED4 15 RISET 5.36k OVP R2 RISET RVCC2 10 : : : : : : : : LED2 17 LED3 16 11 EN 12 : : : : 6 VCC2 8 5.36k RISET R5 1k ACTL 9 CVCC2 1µF ILED = 20mA × PWM Signal DCTL 10 14 VC 13 SS RVC 1.8k CVC 3.9nF GND 1, 2, 3, 19, 20, Exposed Pad (21) C1 0.1µF Figure 1. 1MHz, 20mA Full Scale Current Digital PWM Dimming Control VIN 7V to 40V COUT3 1µF L 10µH VOUT 60V MAX D CVIN 10µF RVCC1 10 C2 15 LED String RT8560 R4 4, 5 SW 7 VCC1 CVCC1 1µF 5V R3 1k R1 VOUT LED2 17 LED3 16 12 LED4 15 OVP RISET RVCC2 10 8 6 VCC2 ACTL 9 DCTL 10 CVCC2 1µF : : : : : : : : : : : : COUT1 COUT2 18 11 EN R2 VIN LED1 : : : : RISET 5.36k R5 1k ILED = 20mA × 5.36k RISET Analog Dimming 14 RVC 1.8k CVC 3.9nF VC 13 SS GND 1, 2, 3, 19, 20, Exposed Pad (21) C1 0.1µF Figure 2. 1MHz, 20mA Full Scale Current Analog Dimming Control www.richtek.com 2 DS8560-01 April 2011 RT8560 VIN 7V to 40V COUT3 1µF VOUT 60V MAX L 10µH D CVIN 10µF RVCC1 10 C3 15 LED String R4 4, 5 SW 7 VCC1 CVCC1 1µF R3 1k 5V R1 VOUT LED2 17 LED3 16 12 LED4 15 OVP RISET RVCC2 10 6 VCC2 CVCC2 1µF : : : : COUT1 COUT2 18 11 EN R2 VIN LED1 : : : : : : : : : : : : RT8560 RISET 5.36k 8 ILED = 20mA × 5.36k RISET ACTL 9 C2 0.1µF R5 1k DCTL 10 PWM Signal 14 VC 13 SS RVC 1.8k GND 1, 2, 3, 19, 20, Exposed Pad (21) C1 0.1µF CVC 3.9nF Figure 3. 1MHz, 20mA Full Scale Current PWM to Analog Dimming Control VIN 4V to 40V COUT3 1µF VAVDD 7V to 40V L 10µH VOUT 60V MAX D CVIN 10µF RVCC1 10 C2 15 LED String RT8560 R4 4, 5 5V R3 1k R1 VOUT : : : : : : : : COUT1 COUT2 18 11 EN 12 LED4 15 OVP RISET R2 VIN LED1 LED2 17 LED3 16 RVCC2 10 : : : : SW 7 VCC1 CVCC1 2.2µF : : : : 6 VCC2 CVCC2 1µF 8 ACTL 9 DCTL 10 RISET 5.36k ILED = 20mA × 5.36k RISET R5 1k PWM Signal 14 RVC 1.8k CVC 3.9nF VC 13 SS GND 1, 2, 3, 19, 20, Exposed Pad (21) C1 0.1µF Figure 4. Wide Range VIN Application by Connecting VCC1 to LCD Driver Power AVDD DS8560-01 April 2011 www.richtek.com 3 RT8560 Function Block Diagram SW OSC - VCC1 6.2V + 2.5V + - LED1 S + R OVP - R + - LED2 - EN 2V + + - Shutdown VCC2 VOUT Regulation Unit VC LED3 + - 6uA 5V SS LED4 1.2V DCTL + 1.2V 200k + - - ACTL www.richtek.com 4 + - RISET DS8560-01 April 2011 RT8560 Functional Pin Description Pin Number 1, 2, 3, 19, 20, 21 (Exposed Pad) 4, 5 Pin Name Pin Function GND Ground pin of the chip. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. SW PWM boost converter switch node. Bipolar power switch base current supply. Typical beta of the power NPN switch is approximately 70. VCC2 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. 6 VCC2 7 VCC1 Power supply of the chip. For good bypass, a low ESR capacitor is required. 8 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, ILED = 20mA × 5.36k for VACT L ≥ 1.2V. RISET 10 DCTL By adding a 0.1uF 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 EN Chip enable pin, when low chip is in shutdown mode. 12 OVP Over voltage protection. PWM boost converter turns off when VOVP goes higher than 2.5V. 13 SS Soft start pin, a capacitor of at least 10nF is required for soft start. 14 VC PWM boost converter loop compensation node. Channel 1 to Channel 4 LED current sink. Leave the pin unconnected if not used. 18, 17, 16, 15 DS8560-01 April 2011 LED1, LED2, LED3, LED4 www.richtek.com 5 RT8560 Absolute Maximum Ratings z z z z z z z z z z z z (Note 1) Supply Voltage, VCC1, VCC2 -----------------------------------------------------------------------------------------SW Pin Voltage at Switching Off -------------------------------------------------------------------------------------LED1, LED2, LED3, LED4 Pin ----------------------------------------------------------------------------------------EN Pin Voltage ------------------------------------------------------------------------------------------------------------RISET Pin Voltage -------------------------------------------------------------------------------------------------------ACTL, DCTL, OVP, SS, VC Pin Voltage ----------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C WQFN-20L 4x4 -----------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) WQFN-20L 4x4, θJA ------------------------------------------------------------------------------------------------------WQFN-20L 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 42V 65V 25V 20V 4V 8V 1.852W 54°C/W 7°C/W 150°C 260°C −65°C to 150°C 2kV 200V (Note 4) Supply Input Voltage, VCC1, VCC2 ---------------------------------------------------------------------------------- 7V to 40V Junction Temperature Range -------------------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range -------------------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VCC1 = 17V, TA = 25°C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit VCC1 UVLO Threshold VUVLO V CC1 Rising -- 6.2 6.5 V Supply Current IVCC1 VC ≤ 0.4V (Switching off) -- 4 7 mA Shutdown Current ISHDN VEN ≤ 0.7V -- 12 -- μA 2 -- 5 -- -- 0.8 2 -- 5 -- -- 0.15 Logic-High Voltage VEN_H EN Threshold Logic-Low Voltage VEN_L Logic-High Voltage VACTL_H ACTL Threshold Logic-Low Voltage VACTL_L EN Pin Input Current V V IEN VEN ≤ 5V -- -- 2 μA ILED 2V > VLED > 0.7V, RISET = 5.36kΩ, VACTL >1.28V 19 20 21 mA 2V > VLED > 0.7V, RISET = 5.36kΩ, VACTL >1.28V, Calculating (I(MAX) − I(MIN) / IAVERAGE x 100%) -- -- 3 % LED Current Programming LED Current LED´s Current Matching RISET Pin Voltage VRISET RISET = 5.36kΩ, VACTL > 1.28V -- 1.21 -- V Input Current of ACTL IACTL 0.3V ≤ VACTL ≤ 1.2V -- -- 2 μA To be continued www.richtek.com 6 DS8560-01 April 2011 RT8560 Parameter Symbol Test Conditions Min Typ Max Unit Threshold of ACTL VACTL LED Current Off -- 0.2 -- V Input Current of DCTL IDCTL 0.3V ≤ V DCTL ≤ 6V -- -- 1 μA Switching Frequency 840 1000 1160 kHz Maximum Duty Cycle -- 88 -- % Minimum On Time -- 200 -- ns -- 0.9 -- V -- 220 -- μA/V PWM Boost Converter Regulated VLED Amplifier gm Highest Voltage LED String GM Amplifier (gm) Output Current 2.4V > VC > 0.2V -- ±30 -- μA VC Threshold PWM Switch Off -- 0.7 -- V SW On Voltage ISW = 0.5A -- 0.4 -- V 1.2 1.5 -- A -- 2.5 -- V SW Current Limit ILIM OVP & Soft Start OVP Threshold VOVP OVP Input Current IOVP VOVP ≤ 2.5V -- -- 50 nA Soft Start Current ISS VSS = 0V -- 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 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. DS8560-01 April 2011 www.richtek.com 7 RT8560 Typical Operating Characteristics Efficiency vs. Input Voltage LED Current vs. Input Voltage 100 26 90 24 60LEDs LED Current (mA) 80 Efficiency (%) 70 60 50 40 30 20 22 20 LED1 LED2 LED3 LED4 18 16 14 12 10 0 10 8 12 16 20 24 28 32 36 40 8 12 16 24 1.24 23 1.22 22 28 32 36 40 1.20 V RISET (V) LED Current (mA) 24 VRISET vs. Temperature LED Current vs. Temperature 21 20 19 1.18 1.16 1.14 18 1.12 17 VIN = 12V 16 VIN = 12V 1.10 -40 -15 10 35 60 85 110 135 -40 1.24 18 1.23 16 LED Current (mA) 20 1.22 1.21 1.20 1.19 1.18 0 Input Voltage (V) www.richtek.com 8 100 120 6 1.15 28 80 32 36 40 ACTL = 200Hz ACTL = 1kHz ACTL = 10kHz ACTL = 20kHz ACTL = 30kHz 8 2 24 60 10 1.16 20 40 12 4 16 20 14 1.17 12 0 LED Current vs. ACTL PWM Duty Cycle VRISET vs. Input Voltage 1.25 8 -20 Temperature (°C) Temperature (°C) V RISET (V) 20 Input Voltage (V) Input Voltage (V) ACTL = 0V to 3V, VIN = 12V 0% 0 10% 10 20% 20 30% 30 40% 40 50% 50 60% 60 70% 70 80% 80 90% 90 100 % Duty Cycle (%) DS8560-01 April 2011 RT8560 LED Current vs. ACTL Voltage 25 20 20 LED Current (mA) LED Current (mA) LED Current vs. DCTL PWM Duty Cycle 25 DCTL = 200Hz DCTL = 1kHz DCTL = 10kHz 15 10 15 10 5 5 VIN = 12V DCTL = 0V to 3V, VIN = 12V 0 0 20 30 40 50 60 70 80 90 0 100 0.25 0.5 1 1.25 1.5 ACTL Voltage (V) Duty Cycle (%) Shutdown Current vs. Input Voltage Frequency vs. Input Voltage 1.10 40 1.08 35 Shutdown Current (uA) 1.06 Frequency (MHz) 0.75 1.04 1.02 1.00 0.98 0.96 0.94 30 25 20 15 10 0.92 5 0.90 0 VEN = 0V 8 10 12 14 16 18 20 22 24 8 12 16 Input Voltage (V) Switch Off Current vs. Input Voltage 24 28 32 36 40 SS Current vs. Temperature 5.0 10 4.9 9 4.8 8 4.7 7 SS Current (uA) Switch Off Current (mA) 20 Input Voltage (V) 4.6 4.5 4.4 4.3 6 5 4 3 2 4.2 4.1 1 VC = 0V VIN = 12V, CSS = 0.1uF 0 4.0 8 12 16 20 24 28 Input Voltage (V) DS8560-01 April 2011 32 36 40 -40 -20 0 20 40 60 80 100 120 Temperature (°C) www.richtek.com 9 RT8560 OVP Voltage vs. Temperature 2.50 9 2.48 8 2.46 7 2.44 OVP Voltage (V) SS Current (uA) SS Current vs. Input Voltage 10 6 5 4 3 2 2.42 2.40 2.38 2.36 2.34 1 CSS = 0.1uF 0 2.32 VIN = 12V 2.30 8 12 16 20 24 28 32 36 40 -40 Input Voltage (V) 0 20 40 60 80 100 120 Temperature (°C) OVP Voltage vs. Input Voltage Limit Current vs. Input Voltage 2.8 2.5 2.7 2.0 Limit Current (A) OVP Voltage (V) -20 2.6 2.5 2.4 1.5 1.0 0.5 2.3 2.2 0.0 8 12 16 20 24 28 32 36 40 8 10 12 14 16 18 20 22 24 26 28 30 32 Input Voltage (V) Input Voltage (V) ACTL Voltage vs. Temperature Power On from EN 0.40 ACTL Voltage (V) 0.35 VEN (2V/Div) 0.30 0.25 0.20 VOUT (20V/Div) 0.15 I IN (500mADiv) 0.10 0.05 VIN = 12V VIN = 12V, CSS = 0.1uF 0.00 -40 -20 0 20 40 60 80 100 120 Time (5ms/Div) Temperature (°C) www.richtek.com 10 DS8560-01 April 2011 RT8560 Line Transient Response OVP VIN (5V/Div) VIN (5V/Div) VOUT (20V/Div) SW (20V/Div) IOUT (50mA/Div) VIN = 10.8V to 13.2V, RISET = 4.8kΩ Time (50ms/Div) DS8560-01 April 2011 VIN = 12V, All LED Pin Open Time (2.5ms/Div) www.richtek.com 11 RT8560 Applications Information The RT8560 is a current mode boost converter operated at 1MHz to power up to 60 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 currentlimit protection features. VIN UVLO PWM EN VIN must be turned off early than EN and PWM signal Input UVLO Power Sequence Power-off sequence Abnormal Poweron sequence VIN UVLO PWM EN must be turned on late than VIN and PWM signal Soft-Start VOUT No Soft-Start If PWM turns on late VOUT Figure 6. Power-On Sequence Control by VIN EN and/or VIN should be pulled low once PWM pull low for over 10ms EN/VIN PWM Please refer to the below Figure 5 and 7. The recommended power-on sequence is that the PWM ready before EN and/or VIN ready. If not, the Soft-Start function will be disabled. As to power-off sequence, the EN/VIN must be pulled low within 10ms to prevent “Hard-Start” shown as Figure 7. EN VIN must be turned on late than EN and PWM signal Soft-Start The input operating voltage range of the RT8560 is 7V to 40V. An input capacitor at the VCC1 and VCC2 pin can reduce ripple voltage. It is recommended to use a ceramic 10uF 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 6.2V. Power-on sequence Abnormal Poweron sequence Power-off sequence Power-on sequence EN must be turned off early than VIN and PWM signal 10ms Figure 7. To Prevent “Hard-Start” Sequence Soft Start The RT8560 employs a soft start feature to limit the inrush current. The soft-start circuit prevents the excessive inrush current and input voltage droop. The soft-start time is determined by capacitor CSS connected to SS with a 7uA constant current to charge CSS. The value of capacitor CSS is user-defined to satisfy designer' requirement. LED connection No Soft-Start If PWM turns on late Figure 5. Power-On Sequence Control by EN The RT8560 equips 4 channel LED divers and each channel supports up to 15 LEDs. The 4 LED strings are connected from VOUT to pin 15, 16, 17 and 18 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 : ILED = 20mA × 5.36k RISET www.richtek.com 12 DS8560-01 April 2011 RT8560 Where, Over Voltage Protection VRISET is the voltage of the RISET pin (1.21V typ.) and the RISET is the resister between RISET pin and GND. The RT8560 equips over voltage protection (OVP) function. When the voltage at OVP pin reaches a threshold of approximately 2.5V, the MOSFET drive output (SW) will turn “OFF”. The MOSFET drive output (SW) will turn “ON” again once the voltage at OVP drops below the threshold of approximately 2.5V. This setting is the reference for the LED current at LED14 and represents the sensed LED current for each string. The DC/DC converter regulates the LED current according to the setting. So, the output voltage can be clamped at a certain voltage level and it can be calculated by the following equation : Brightness Control The RT8560 features both analog and digital dimming control. Analog dimming is linearly controlled by an external voltage (0.3V < VACTL < 1.2V). With an on-chip output clamping amplifier and a 200kΩ resistor, PWM dimming signal is easily low-pass filtered to an analog dimming signal with one external capacitor for noise-free 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 200Hz to 10kHz. Refer to Figure 8, the minimum dimming duty can be as low as 1% for the frequency range from 100Hz to 300Hz. For the dimming frequency from 300Hz to 1kHz, the duty is about 5%. If the frequency is increased to 1kHz to 30kHz, the duty will be about 10%. LED Current vs. ACTL PWM Duty Cycle 20 18 LED Current (mA) 16 VOUT, OVP = 2.5 × ⎛⎜ 1+ R1 ⎞⎟ ⎝ R2 ⎠ Where, R1 and R2 are the voltage divider connected to OVP 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. Current-limit Protection The RT8560 can limit the peak current to achieve over current protection. The RT8560 senses the inductor current of on period that flows through SW pin. The duty cycle depend on current signal and internal slope compensation compared with error signal. The internal N-MOSFET 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 N-MOSFET is on by the oscillator. 14 ACTL = 200Hz ACTL = 1kHz ACTL = 10kHz ACTL = 20kHz ACTL = 30kHz 12 10 8 6 4 2 ACTL = 0V to 3V, VIN = 12V 0 0% 0 10% 10 20% 20 30% 30 40% 40 50% 50 60% 60 70% 70 80% 80 90% 90 100 % Duty Cycle (%) Figure 8. LED Current vs. PWM Dimming Duty Cycle Over Temperature Protection The RT8560 has over temperature protection (OTP) function to prevent the excessive power dissipation from overheating. OTP will shut down the IC while junction temperature exceeds 150°C. Main converter starts switching once the junction temperature is cooled approximately 20°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 : L= DS8560-01 April 2011 (VOUT − VIN ) × VIN2 2 × IOUT × f × VOUT 2 www.richtek.com 13 RT8560 Where, Layout Guideline VOUT = maximum output voltage. 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, CVIN, COUT1 and COUT2 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. 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. ` Place L and D connected to SW pin as close as possible. The trace should be short and wide as possible. The inductor must be selected with a saturated current rating that is greater than the peak current provided by the following equation : IPEAK = VOUT × IOUT + VIN × T ⎛⎜ VOUT − VIN ⎞⎟ η × VIN 2 × L × ⎝ VOUT ⎠ ` It is recommended to place CVcc1 and CVcc2 close to VCC1 and VCC2 pins. ` Pin14 is the compensation point to adjust system stability. Place the compensation components to pin14 as close as possible, no matter the compensation is RC or capacitance. Where, η is the efficiency of the power converter. Diode Selection Place these components as close as possible. COUT1 COUT2 D VOUT 20 19 18 17 16 GND 1 15 GND GND 2 14 SW SW 4 13 12 21 5 6 L COUT3 GND 3 7 8 VCC2 VCC1 RISET 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. LED2 LED3 ` IOUT = sum of current from all LED strings. CVIN 9 11 10 ACTL DCTL f = operating frequency. GND GND LED1 VIN = minimum input voltage. LED4 CVC1 RVC VC GND SS OVP CVC2 Locate the compensation EN components to VC pin as close as possible. GND Capacitor Selection The input capacitor reduces current spikes from the input supply and minimizes noise injection to the converter. For most applications, a 10uF 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. VIN CVCC2 GND CVCC1 RVCC2 Locate the CVCC1 and CVCC2 as RVCC1 close as possible to V CC1 and VCC2 pin. Figure 9. PCB layout It is recommended to choose a ceramic capacitor bases on the output voltage ripple requirements. The minimum value of the output capacitor COUT is approximately given by the following equation : COUT = (VOUT − VIN ) × IOUT η × VRIPPLE × VOUT × f www.richtek.com 14 DS8560-01 April 2011 RT8560 Outline Dimension 1 1 2 2 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. Dimensions In Millimeters Dimensions In Inches Symbol Min 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 0.150 0.300 0.006 0.012 D 3.950 4.050 0.156 0.159 D2 2.650 2.750 0.104 0.108 E 3.950 4.050 0.156 0.159 E2 2.650 2.750 0.104 0.108 e L 0.500 0.350 0.020 0.450 0.014 0.018 W-Type 20L 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: 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. DS8560-01 April 2011 www.richtek.com 15