® RT8575 4-String White LED Driver with Boost Regulator General Description Features The RT8575 is a high efficiency LED driver with 40V I/O support. It is designed for LCD panel that employs an array of LEDs as the lighting source. An integrated switch current mode Boost controller drives four strings in parallel and supports up to 18 pieces of LEDs per string. The internal current sinks support typical ±1% current mismatching for excellent brightness uniformity in each LED string. To provide enough headroom for the operating of current sink, Boost controller monitors the minimum voltage of feedback pins and regulates an optimized output voltage for power efficiency. z Input Operating Voltage Range 4.2V to 24V z 60V Maximum Output Voltage Adjustable Switching Frequency : 150kHz to 500kHz Support Up to 4 LED Strings 50mA to 150mA LED Current Per Channel 1% Typical LED Current Accuracy 1% Typical LED Current Matching Programmable Over Voltage Protection Built-in Soft-Start, OTP LED Short/Open Detection RoHS Compliant and Halogen Free The RT8575 has a wide input voltage operating range from 4.2V to 24V and provides adjustable 50mA to 150mA LED current. The internal 150mΩ, 60V power switch with current-mode control provides cycle-by-cycle over current protection. RT8575 also integrates PWM dimming function for accurate LED current control. The input PWM dimming frequency can operate from 120Hz to 1kHz without inducing any inrush current in LEDs or inductor. The switching frequency of RT8575 is adjustable from 150kHz to 500kHz, which allows the trade-off between efficiency and component size. Applications The RT8575 is available in WDFN-16L 5x5 and DIP-16 (BW) packages to achieve optimized solution for PCB space. z z z z z z z z z z White LED Backlighting Ordering Information RT8575 Package Type QW : WDFN-16L 5x5 (W-Type) N : DIP-16 (BW) 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 J-STD-020. ` Suitable for use in SnPb or Pb-free soldering processes. Simplified Application Circuit D1 L1 VIN VOUT CIN1 COUT R1 LX VIN CIN2 RT8575 ROVP2 ISET Chip Enable EN CCOMP RT RSW : : : : : : GND Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8575-00 January 2013 : : : CH1 CH2 CH3 CH4 COMP RCOMP : : : RISET PWM PWM Signal ROVP1 OVP is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT8575 Marking Information Pin Configurations (TOP VIEW) RT8575GQW RT8575GQW : Product Number RT8575 GQW YMDNN CH1 CH2 CH3 CH4 AGND ISET COMP RT YMDNN : Date Code 16 15 1 2 3 4 14 13 PGND 5 6 7 12 11 10 17 8 9 OVP PGND PGND LX LX VIN EN PWM WDFN-16L 5x5 RT8575GN RichTek RT8575 GNYMDNN RT8575GN : Product Number EN 14 PWM YMDNN : Date Code VIN 2 13 RT LX 3 12 COMP GND 4 11 GND OVP 5 10 ISET CH1 6 9 CH4 CH2 7 8 CH3 DIP-16 (BW) Functional Pin Description Pin No. Pin Name Pin Function WDFN-16L 5x5 DIP-16 (BW) 1 to 4 6 to 9 5 -- AGND Analog Ground. 6 10 ISET LED current is set by the value of the resistor RISET connected from the ISET pin to ground. Do not short the ISET pin. VISET is typically 1V. 7 12 COMP 8 13 RT 9 14 PWM 10 1 EN Chip Enable (Active High). Note that this pin is high impedance. There should be a 100kΩ pull low resistor connected to GND when the control signal is floating. 11 2 VIN Power Supply Input. 12, 13 3 LX The Switching Pin for Boost Converter. 14, 15, 17 (Exposed Pad) -- PGND 16 5 OVP -- 4, 11 GND CH1 to CH4 Current Sink for LED. (Connect to GND, if not used) Compensation Pin for Error Amplifier. Connect a compensation network to ground. Switching Frequency Selection Input. The switching frequency is adjustable from 150kHz to 500kHz. Dimming Control Input. Power Ground of Boost Converter. The exposed pad must be soldered to a large PCB and connected to PGND for maximum power dissipation. Over Voltage Protection for Boost Converter. The detecting threshold is 1.2V. Ground. Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS8575-00 January 2013 RT8575 Function Block Diagram OVP RT + OTP 1.2V - OSC VIN 5V LDO LX S Q R Q OCP EN + PWM Controller PGND + - LED Open & Short Detection + COMP - PWM VREF 4 Mini LED Selection …… CH1 CH2 CH4 + - 1V + + - - …… + - AGND (Only for WDFN Package) ISET Operation The RT8575 integrates 4 linear LED drivers and a Boost converter. When EN is High and VIN is higher than the voltage of UVLO, the RT8575 will start operation and detect which channels are using. If the channel is connected to ground, it would be defined as un-used channel. And the diver of this channel will be turned off after the un-used checking. Then, RT8575 will enter the soft-start mode. VISET will increase to be 1V slowly, which represents that the ILED also increases slowly. Beside that the OCP is clamped Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8575-00 January 2013 at lower level, just prevents a large inrush current. RT8575 will choose the min. value of VLED as the feedback voltage of Boost converter, the un-used channel is out of the list. During normal operation, when LED string is defined as short, the driver of that channel will be turned off. In order to protect the system, “SHORT” status of the channel should only be released by re-start of the system. When LED string is defined as open, the driver of that channel will be turned off, and auto-recovery when “OPEN” is released. is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT8575 Absolute Maximum Ratings z z z z z z z z z (Note 1) Supply Input Voltage, VIN to GND -------------------------------------------------------------------------------------EN, ISET, COMP, OVP, RT to GND -----------------------------------------------------------------------------------CH1 to CH4, LX to GND -------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C WDFN-16L 5x5 -------------------------------------------------------------------------------------------------------------DIP-16 (BW) ----------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) WDFN-16L 5x5, θJA -------------------------------------------------------------------------------------------------------WDFN-16L 5x5, θJC -------------------------------------------------------------------------------------------------------DIP-16 (BW), θJA ----------------------------------------------------------------------------------------------------------DIP-16 (BW), θJC ----------------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------------------Junction Temperature -----------------------------------------------------------------------------------------------------Storage Temperature Range --------------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Model) ----------------------------------------------------------------------------------------------MM (Machine Model) ------------------------------------------------------------------------------------------------------ Recommended Operating Conditions z z z −0.3V to 44V −0.3V to 44V −0.3V to 66V 3.47W 1.8W 28.8°C/W 4.4°C/W 55.7°C/W 8.3°C/W 260°C 150°C −65°C to 150°C 2kV 200V (Note 4) Supply Input Voltage, VIN ------------------------------------------------------------------------------------------------ 4.2V to 24V Junction Temperature Range --------------------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range --------------------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VIN = 19V, CIN2 = 1μF, TA = 25°C, unless otherwise specified) Parameter Symbol Input Supply Voltage VIN Under Voltage Lockout Threshold VUVLO Under Voltage Lockout Hysteresis DVUVLO VIN Rising Typ Max Unit 4.2 -- 24 V -- 3.8 -- V -- 500 -- mV IVCC COMP = 0V, Not Switching -- 2.5 -- COMP = 2V, Switching -- 3.3 -- ISHDN VIN = 4.5V, EN = 0 -- -- 20 Logic-High VIH VIN = 4.2V to 24V 2 -- -- Logic-Low VIL VIN = 4.2V to 24V -- -- 0.8 120 -- 1k Hz 224 280 336 kHz -- 0.15 -- Ω -- 220 -- ns -- 92 -- % 2.8 3.3 3.8 A Shutdown Current PWM Dimming Frequency FPWM Switching Frequency FOSC RSW = 51.1kΩ LX On-Resistance (N-MOSFET) RLX VIN > 4.5V Minimum On-Time TMON Maximum Duty DMAX LX Current Limit ILIM VCOMP = 2V, Switching Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 Min IVCC_SW Quiescent Current EN, PWM Input Voltage Test Conditions mA μA V is a registered trademark of Richtek Technology Corporation. DS8575-00 January 2013 RT8575 Parameter Symbol Test Conditions Min Typ Max Unit LED Current Accuracy ILEDA 0.4V < CHx < 2V, RISET = 7.5kΩ 116.4 120 123.6 mA LED Current Matching ILEDM 0.4V < CHx < 2V, RISET = 7.5kΩ -- ±1 ±3 % ISET Pin Voltage VISET -- 1 -- V OVP Threshold VOVP 1.17 1.2 1.23 V Thermal Shutdown Temperature TOTP -- 150 -- °C Thermal Shutdown Hysteresis TOTP_hys -- 20 -- °C Un-Connected LED Detection VUSE -- 0.2 -- V Opened LED Protection VOLP -- 0.1 -- V Shorted LED Protection VSLP -- 5.6 -- V Shutdown Delay Time TSD -- 28 -- ms Un-Connection fOSC = 280kHz Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and 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 may affect device reliability. Note 2. θJA is measured at TA = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC is measured at the exposed pad of the package. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8575-00 January 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT8575 Typical Application Circuit L1 22µH VIN 4.2V to 24V CIN1 47μF/35V D1 R1 10 CIN2 1µF COUT 47μF/100V LX VIN RT8575 OVP Chip Enable EN COVP 100pF VOUT 60V(MAX) ROVP1 300k ROVP2 6.2k : : : : : : : : : : : : ILED 150mA (MAX) PGND GND AGND PWM PWM Signal RCOMP 0 CCOMP 100nF COMP RT RSW 51.1k ISET RISET 7.5k Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 CH1 CH2 CH3 CH4 is a registered trademark of Richtek Technology Corporation. DS8575-00 January 2013 RT8575 Typical Operating Characteristics Efficiency vs. Input Voltage 100 90 90 Efficiency (%) Efficiency (%) Efficiency vs. Input Voltage 100 80 70 60 80 70 60 6S4P, ILEDx = 120mA, fOSC = 280kHz, PWM = 3.3V 14S4P, ILEDx = 120mA, fOSC = 280kHz, PWM = 3.3V 50 50 12 14 15 17 18 20 21 23 24 4 5 6 Input Voltage (V) LED Current vs. Input Voltage 9 10 11 12 LED Current vs. Input Voltage 160 150 150 CH1 CH2 CH3 CH4 140 130 LED Current (mA) LED Current (mA) 8 Input Voltage (V) 160 120 110 100 14 LEDs per channel, RISET = 7.5kΩ, fOSC = 280kHz, PWM = 3.3V 90 CH1 CH2 CH3 CH4 140 130 120 110 100 6 LEDs per channel, RISET = 7.5kΩ, fOSC = 280kHz, PWM = 3.3V 90 80 80 0 5 10 15 20 25 30 4 5 6 Input Voltage (V) 7 8 9 10 11 12 Input Voltage (V) LED Current vs. Temperature LED Current vs. Dimming Duty 120 160 150 100 LED1 LED2 LED3 LED4 140 130 120 LED Current (mA) LED Current (mA) 7 110 100 90 fOSC 14S4P, RISET = 7.5kΩ, = 280kHz, VIN = 19V, PWM = 3.3V 80 200Hz 500Hz 1kHz 80 60 40 20 14S4P, fOSC = 280kHz, VIN = 19V 0 -50 -25 0 25 50 75 100 Temperature (°C) Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8575-00 January 2013 125 0 10 20 30 40 50 60 70 80 90 100 Dimming Duty (%) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT8575 Quiescent Current vs. Input Voltage 5.0 1.35 4.5 Quiescent Current (mA) OVP Voltage (V) OVP Voltage vs. Input Voltage 1.40 1.30 1.25 1.20 1.15 1.10 4.0 3.5 2.5 2.0 1.0 0.5 1.00 0.0 6 8 10 12 14 16 18 20 22 Not Switching 1.5 1.05 4 Switching 3.0 VIN = 19V, fOSC = 280kHz 4 24 6.5 9 Input Voltage (V) 14 16.5 19 21.5 24 Input Voltage (V) Quiescent Current vs. Temperature LED Current vs. RISET 5.0 160 4.5 140 4.0 3.5 LED Current (mA) Quiescent Current (mA) 11.5 Switching 3.0 2.5 2.0 Not Switching 1.5 1.0 0.5 VIN = 19V, fOSC = 280kHz 0.0 120 100 80 60 40 20 VIN = 19V 0 -40 -20 0 20 40 60 80 100 125 5 7.5 10 12.5 15 17.5 Temperature (°C) RISET (k Ω ) Switching Frequency vs. RSW Line Transient Response 20 Switching Frequency (kHz)1 600 500 400 300 200 100 VIN = 19V VIN (4V/Div) IOUT (200mA/Div) fOSC = 280kHz, VIN = 17.1V to 20.9V, PWM = 3.3V, RISET = 7.5kΩ 0 20 30 40 50 60 70 80 90 100 110 120 130 Time (25ms/Div) RSW (k Ω ) Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 is a registered trademark of Richtek Technology Corporation. DS8575-00 January 2013 RT8575 Power Off from PWM Power On from PWM VPWM (5V/Div) VPWM (5V/Div) VOUT (50V/Div) VLX (50V/Div) VOUT (50V/Div) VLX (50V/Div) IOUT (300mA/Div) IOUT (300mA/Div) fOSC = 280kHz, VIN = 19V, 14S4P, EN = 3.3V, Dimming Duty = 50%, Dimming Frequency = 200Hz fOSC = 280kHz, VIN = 19V, 14S4P, EN = 3.3V, Dimming Duty = 50%, Dimming Frequency = 200Hz Time (10ms/Div) Time (10ms/Div) Power On from EN Power Off from EN VEN (5V/Div) VEN (5V/Div) VOUT (50V/Div) VLX (50V/Div) VOUT (50V/Div) VLX (50V/Div) IOUT (300mA/Div) IOUT (300mA/Div) fOSC = 280kHz, VIN = 19V, 14S4P, PWM = 3.3V fOSC = 280kHz, VIN = 19V, 14S4P, PWM = 3.3V Time (5ms/Div) Time (5ms/Div) Power On from VIN Power Off from VIN VIN (12V/Div) VIN (12V/Div) VOUT (50V/Div) VLX (50V/Div) VOUT (50V/Div) VLX (50V/Div) IOUT (300mA/Div) fOSC = 280kHz, 14S4P, PWM = EN = 3.3V Time (5ms/Div) Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8575-00 January 2013 IOUT (300mA/Div) fOSC = 280kHz, 14S4P, PWM = EN = 3.3V Time (5ms/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT8575 Application Information The RT8575 is a general purpose 4-CH LED driver capable of delivering an adjustable 50mA to 150mA LED current. The IC is a current mode Boost converter integrated with a 60V/4A power switch and can cover a wide VIN range from 4.2V to 24V. The switching frequency is adjustable by an external resistor from 150kHz to 500kHz. The part integrates built-in soft-start, with PWM dimming control; moreover, it provides over voltage, over temperature, short LED and cycle-by-cycle over current protection features. Compensation Supply Voltage Capacitor Selection LED Connection The RT8575 equips a built-in LDO linear regulator to provide the internal logic of IC power. The output of LDO is the pin out of VIN. The VIN pin is recommended to connect at least a 1μF/25V bypass capacitor. The bypass capacitor should be used with X5R or X7R type, to assure the bypass capacitance remains stable in over voltage or over temperature. The RT8575 equips 4-CH LED drivers and each channel supports up to 18 LEDs (Vf = 3V). The LED strings are connected from the output of the Boost converter to pin CHx (x = 1 to 4) respectively. If one of the current sink channels is not used, the CHx pin should be connected to GND. If the un-used channel is not connected to GND, it will be considered that the LED string is opened, the channel will turn light when the LED string is recovering connected. Soft-Start The RT8575 equips a soft-start feature to prevent high inrush current during start-up. The soft-start function prevents excessive input current and input voltage droop during power on state. LED Current Setting LED current of each channel can be calculated by following equation : ILED ≅ 900 RISET Where the RISET resistor is connected between the ISET pin and GND. This setting is the reference for the LED current at the LED pin and represents the sensed LED current for each string. The LED driver regulates the LED current according to the setting. Switching Frequency The LED driver switching frequency is adjusted by the external resistor, RSW. The switching frequency can be calculated by the following equation : 9 fOSC ≅ 14.3 × 10 RSW Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 The regulator loop can be compensated by adjusting the external components connected to the COMP pin. The COMP pin is the output of the internal error amplifier. The compensation capacitor will adjust the integrator zero to maintain stability and the resistor value will adjust the frequency integrator gain for fast transient response. Typical values of the compensation components are RCOMP = 0Ω, CCOMP = 100nF. Over Voltage Protection The RT8575 integrates over voltage protection. When the voltage at the OVP pin rises above the threshold voltage of approximately 1.2V, The internal switch will be turned off. Once the voltage of OVP pin drop below its threshold voltage, the internal switch will be turned on again. The output voltage can be clamped at a certain voltage level and can be calculated by the following equations : R VOUT(OVP) ≅ VOVP × ⎛⎜ 1+ OVP1 ⎞⎟ ⎝ ROVP2 ⎠ where VOVP = 1.2V (typ.). ROVP1 and ROVP2 are the resistors in the voltage divider connected to the 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 strings in normal operation. It is suggested to use near 300kΩ for ROVP1, and use a 100pF bypass capacitor at ROVP2. Current Limit Protection The RT8575 can limit the peak current to achieve over current protection. The RT8575 senses the inductor current during the “ON” period that flows through the LX is a registered trademark of Richtek Technology Corporation. DS8575-00 January 2013 RT8575 pin. The duty cycle depends on the current signal and internal slope compensation in comparison with the error signal. The internal switch of Boost converter will be turned off when the peak current value of inductor current is larger than the threshold current 3.3A (typ.). In the “OFF” period, the inductor current will be decreased until the internal switch is turned on by the oscillator. Short LED Protection Brightness Control Open LED Protection The RT8575 features a digital dimming control scheme. A very high contrast ratio true digital PWM dimming is achieved by driving the PWM pin with a PWM signal. The recommended PWM frequency is 120Hz to 1kHz. The LED current can be approximately 100% proportional to duty cycle, but the linearity is not ideal on the high frequency and lower duty ratio. If the CHx pin voltage is low at 0.1V, the LED driver will determine whether the channel is open. The CHx pin voltage will not be regulated and not latch, until the CHx pin is recovering connected, the CHx pin will start normal work again. If all CHx pins are open (floating), the output voltage will be clamped to the setting voltage of OVP (VOUT(OVP)). Over Temperature Protection Power On/Off Sequence The RT8575 has over temperature protection function to prevent the IC from overheating due to excessive power dissipation. The OTP function will shut down the IC when junction temperature exceeds 150°C. When junction temperature cools down to 130°C (TOTP_hys = 20°C), the LED driver will return to normal work. LED driver is without power sequence concern. Mode1, Mode2 and Mode3 are different power sequences respectively. There is no concern in the above condition. VIN The RT8575 integrates Short LED Protection (SLP). If one or more of the CH1 to CH4 pin voltages exceeds the threshold of approximately 5.6V during normal operation, the channels will be closed and latch. If the LED of all channels is shorted circuit, the internal switch of Boost converter will be turned off. VIN VOUT VOUT EN EN PWM PWM Power On Mode1 Power Off Mode1 VIN VIN VOUT VOUT EN EN PWM PWM Power On Mode2 Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8575-00 January 2013 Power Off Mode2 is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT8575 VIN VIN UVLO UVLO VOUT VOUT EN EN PWM PWM Power On Mode3 Power Off Mode3 Figure 1. Power On/Off Sequence Shutdown Delay Time Inductor Selection The EN shutdown delay is about 32ms, it is in intended to prevent the glitch of EN. When EN has glitch happening (Tglitch < 32ms), the IC will not need to recover soft-start again. But the LED current sources will be closed immediately. And after about 32ms, the IC will be shut down. Please refer to the Figure 2. The value of the inductance, L, can be approximated by the following equation, where the transition is from Discontinuous Conduction Mode (DCM) to Continuous Conduction Mode (CCM) : EN TEN < 32ms L= The duty cycle, D, can be calculated as the following equation : D= ILED VISET VLX TEN < 32ms TEN ≈ 32ms D × (1− D)2 × VOUT 2 × fOSC × IOUT VOUT − VIN VOUT Where VOUT is the maximum output voltage, VIN is the minimum input voltage, fOSC is the operating frequency, and IOUT is the sum of current from all LED strings. The Boost converter operates in DCM over the entire input voltage range when the inductor value is less than this value, L. With an inductance greater than L, the converter operates in CCM at the minimum input voltage and may be discontinuous at higher voltages. EN The inductor must be selected with a saturated current rating that is greater than the peak current as provided by the following equation : ILED IPEAK = VISET VOUT × IOUT VIN × D × TOSC + 2×L η × VIN where η is the efficiency of the power converter. VLX Diode Selection TEN > 32ms Figure 2. Shutdown Delay Time Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 Schottky diodes are recommended for most applications because of their fast recovery time and low forward voltage. Power dissipation, reverse voltage rating, and pulsating is a registered trademark of Richtek Technology Corporation. DS8575-00 January 2013 RT8575 peak current are important parameters for consideration when making a Schottky diode selection. Make sure that the diode's peak current rating exceeds IPEAK and reverse voltage rating exceeds the maximum output voltage. ΔIL Input Current Inductor Current Input Capacitor Selection Low ESR electrolytic capacitors are recommended for input capacitor applications. Low ESR will effectively reduce the input voltage ripple caused by switching operation. A 47μF/35V is sufficient for most applications. Nevertheless, this value can be decreased for lower output current requirement. Another consideration is the voltage rating of the input capacitor must be greater than the maximum input voltage. Output Capacitor Selection Output ripple voltage is an important index for estimating the performance. This portion consists of two parts, one is the ESR voltage of output capacitor, the other part is formed by charging and discharging process of output capacitor. Refer to Figure 3, evaluate ΔVOUT1 by ideal energy equalization. According to the definition of Q, the Q value can be calculated as following equation : ⎡ ⎤ Q = 1 × ⎢⎛⎜ IIN + 1 ΔIL − IOUT ⎞⎟ + ⎛⎜ IIN − 1 ΔIL − IOUT ⎞⎟ ⎥ 2 ⎣⎝ 2 2 ⎠ ⎝ ⎠⎦ V × IN × 1 = COUT × ΔVOUT1 VOUT fOSC where fOSC is the switching frequency, and ΔIL is the inductor ripple current. Move COUT to the left side to estimate the value of ΔVOUT1 as the following equation : ΔVOUT1 = D × IOUT η × COUT × fOSC Then, take the ESR into consideration, the ESR voltage can be determined as the following equation : I V × D × TOSC ⎞ ΔVESR = ⎛⎜ OUT + IN ⎟ × RESR 1 − D 2L ⎝ ⎠ Finally, the total output ripple ΔVOUT is combined from the ΔVOUT1 and ΔVESR. In the general application, the output capacitor is recommended to use a 47μF/63V electrolytic capacitor. Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8575-00 January 2013 Output Current Time (1-D)TS Output Ripple Voltage (ac) Time ΔVOUT1 Figure 3. The Output Ripple Voltage without the Contribution of ESR 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 dissipation 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, the maximum junction temperature is 125°C. The junction to ambient thermal resistance, θJA, is layout dependent. For WDFN-16L 5x5 package, the thermal resistance, θJA, is 28.8°C/W on a standard JEDEC 51-7 four-layer thermal test board. For DIP-16 (BW) package, the thermal resistance, θJA, is 55.7°C/W on a standard JEDEC 51-7 four-layer thermal test board. The maximum power dissipation at TA = 25°C can be calculated by the following formula : PD(MAX) = (125°C − 25°C) / (28.8°C/W) = 3.47W for WDFN-16L 5x5 package is a registered trademark of Richtek Technology Corporation. www.richtek.com 13 RT8575 PD(MAX) = (125°C − 25°C) / (55.7°C/W) = 1.8W for DIP-16 (BW) package The maximum power dissipation depends on the operating ambient temperature for fixed T J(MAX) and thermal resistance, θJA. The derating curve in Figure 4 allow the designer to see the effect of rising ambient temperature on the maximum power dissipation. Layout Consideration PCB layout is very important for designing switching power converter circuits. The following layout guides should be strictly followed for best performance of the RT8575. ` The power components, L1, D1, CIN1 and COUT must be placed as close as possible to reduce power loop. The PCB trace between power components must be as short and wide as possible. ` Place L1 and D1 as close as possible to LX pin. The trace should be as short and wide as possible. ` The compensation circuit (RCOMP, CCOMP) should be kept away from the power loops and should be shielded with a ground trace to prevent any noise coupling. Place the compensation components as close as possible to COMP pin. ` The LED current setting resistor (RISET) should be kept away from the power loops and should be shielded with a ground trace. Place the LED current resistor as close as possible to ISET pin. Maximum Power Dissipation (W)1 4.0 Four-Layer PCB 3.5 WDFN-16L 5x5 3.0 2.5 DIP-16 (BW) 2.0 1.5 1.0 0.5 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 4. Derating Curve of Maximum Power Dissipation Locate the CIN2 as close to VIN as possible. The compensation circuit and RISET resistor should be kept away from the power loops and should be shielded with a ground trace to prevent any noise coupling. GND COUT VOUT CIN2 RT8575 EN 14 PWM RSW VIN D1 VIN L1 2 13 3 12 COMP RT R1 RCOMP LX CCOMP VIN CIN1 GND 4 11 OVP 5 10 ISET CH1 6 9 CH4 CH2 7 8 CH3 GND RISET GND Place the power components as close as possible. The traces should be wide and short especially for the high-current loop. Figure 5. PCB Layout Guide for DIP-16 (BW) Package Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 14 is a registered trademark of Richtek Technology Corporation. DS8575-00 January 2013 RT8575 Place the power components as close as possible. The traces should be wide and short especially for the high-current loop. VOUT 16 OVP CH1 The compensation circuit and RISET resistor should be kept away from the power loops and should CH2 be shielded with a ground trace to prevent any noise coupling. CH3 2 15 PGND 3 14 PGND CH4 4 D1 PGND AGND COUT RT8575 13 PGND LX L1 VIN LX AGND 5 12 ISET 6 11 VIN RCOMP COMP 7 10 EN RT 8 9 RISET CCOMP CIN1 R1 VIN CIN2 RRT Separate power ground (PGND) and analog ground (AGND). Connect AGND and PGND islands at a single end. Make sure there are no other connections between these separate ground planes. PWM Locate the CIN2 as close to VIN as possible. PGND The exposed pad of the chip should be connected to ground plane for thermal consideration. Figure 6. PCB Layout Guide for WDFN-16L 5x5 Package Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8575-00 January 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 15 RT8575 Outline Dimension Symbol Dimensions In Millimeters Dimensions In Inches Min. Max. Min. Max. A 3.700 4.320 0.146 0.170 A1 0.381 0.710 0.015 0.028 A2 3.200 3.600 0.126 0.142 b 0.360 0.560 0.014 0.022 b1 1.143 1.778 0.045 0.070 b2 2.920 3.100 0.115 0.122 C 0.204 0.360 0.008 0.014 D 18.800 19.300 0.740 0.760 E 6.200 6.600 0.244 0.260 E1 7.320 7.920 0.288 0.312 E2 8.350 9.250 0.329 0.364 2.540 e L 3.000 0.100 3.600 0.118 0.142 16-Lead DIP (BW) Plastic Package Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 16 is a registered trademark of Richtek Technology Corporation. DS8575-00 January 2013 RT8575 2 1 2 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 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 0.200 0.300 0.008 0.012 D 4.900 5.100 0.193 0.201 D2 4.350 4.450 0.171 0.175 E 4.900 5.100 0.193 0.201 E2 3.650 3.750 0.144 0.148 e L 0.500 0.350 0.020 0.450 0.014 0.018 W-Type 16L DFN 5x5 Package Richtek Technology Corporation 5F, No. 20, Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries. DS8575-00 January 2013 www.richtek.com 17