® RT8577A High Voltage 4-CH LED Driver General Description Features The RT8577A is an 4-CH LED driver capable of delivering 120mA for each channel. The RT8577A is a current mode boost converter with an adjustable switching frequency via the RT pin from 200kHz to 2.1MHz and a wide VIN range from 5.5V to 40V. Wide Input Supply Voltage Range : 5.5V to 40V Adjustable Boost Controller Switching Frequency from 200kHz to 2.1MHz Programmable Channel Current Channel Current Matching : ±1.5% External Dimming Control Boost MOSFET Over Current Protection Automatic LED Open/Short Protection to Avoid Output Over Voltage VCC Under Voltage Lockout Adjustable Over Voltage Protection Thermal Shutdown Protection Abnormal Status Indicator for OVP/Short/OTP Condition AEC-Q100 Grade 3 Certification RoHS Compliant and Halogen Free The PWM output voltage loop selects and regulates the LED pin with the highest voltage string to 0.6V, hence allowing voltage mismatches between LED strings. The RT8577A automatically detects and disconnects any unconnected and/or broken strings during operation from PWM loop to prevent VOUT from over voltage. The 1.5% matched LED currents on all channels are simply programmed with a resistor. A very high contrast ratio true digital PWM dimming can be achieved by driving the PWM pin with a PWM signal. When an abnormal situation (OVP/short/OTP) occurs, a status signal will be sent to the system to shut down the IC. Applications Ordering Information Package Type QW : WQFN-20L 5x5 (W-Type) Lead Plating System G : Green (Halogen Free and Pb Free) Pin Configurations (TOP VIEW) Suitable for use in SnPb or Pb-free soldering processes. Marking Information RT8577AGQW : Product Number VC 19 18 17 16 GND 1 15 STATUS GND 2 14 VCC GND 3 13 NC LED3 4 12 CREG LED4 5 11 DRV GND 21 6 7 8 9 10 EN YMDNN : Date Code OVP RT8577A GQW YMDNN 20 SEN PWM ments of IPC/JEDEC J-STD-020. NC RoHS compliant and compatible with the current require- RT LED1 Richtek products are : LED2 Note : RISET RT8577A Automotive Infotainment LCD TV, Monitor Display Backlight LED Driver Application General Purpose Constant Current Source WQFN-20L 5x5 Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS8577A-01 December 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT8577A Functional Pin Description Pin No. Pin Name 1, 2, 3, GND 21 (Exposed pad) 4, 5 LED4, LED3 Pin Function Ground. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. Channel 3 and Channel 4 LED Current Sinks. Leave the pins unconnected if not used. Over-Voltage Detection Input. The Boost converter turns off when VOVP goes higher than 2V. LED Current Set Pin. A resistor or a current from DAC on this pin programs the full LED current. 6 OVP 7 RISET 8 RT Switching Frequency Set. Connect a resistor between RT and GND to set the boost converter switching frequency. 9 EN Enable Control Input. When EN is pulled low, the chip will be shut down. 10 SEN Current Sense Input. During normal operation, this pin senses the voltage across the external inductor current sensing resistor for peak current mode control and also to limit the inductor current during every switching cycle. 11 DRV Boost Converter Power Switch Gate Output. This pin drives the external power N-MOSFET device. 12 CREG Regulator Output for Chip Internal use Only. A 1F capacitor should be placed on this pin to stabilize the 5V output of the internal regulator. NC No Internal Connection. 14 VCC Power Supply of the Chip. For good bypass, a low ESR capacitor close to the pin is required. 15 STATUS Status Indicator Output. This pin will be pulled to low if fault happens. 16 VC PWM Boost Converter Loop Compensation Node. 17 PWM Dimming Control Input. 19 LED1 Channel 1 LED Current Sink, Leave this pin unconnected if it is not used. 20 LED2 Channel 2 LED Current Sink, Leave this pin unconnected if it is not used. 13, 18 Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS8577A-01 December 2015 RT8577A Function Block Diagram DRV SEN OSC RT VCC STATUS OVP - UVLO S + OTP R OVP + 2V LED Short R - LED1 - 1.2V + + - Shutdown + - CREG 5V LDO VC 5V VOUT Regulation Unit PWM ………………… EN LED4 + - + GND - RISET Operation The RT8577A integrated a current-mode Boost PWM controller and 4 LED drivers. When EN and PWM are high and VIN is higher than the UVLO threshold voltage, the controller starts operation. In normal operation, the DRV pin turns high when the gate driver is set by the oscillator and the DRV pin turns low when the gate driver is reset by the current comparator. When the DRV pin turns high to turn on the external MOSFET, the inductor current will rise up. Once the SEN pin voltage reaches the level of the VC pin, the current comparator will reset the gate driver and turn off the MOSFET. The DRV pin is then set to high again by OSC and repeats in the next switching cycle. The oscillator frequency can be set by an external resistor at the RT pin. Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS8577A-01 December 2015 The output voltage of the Boost converter supports LED current and regulation voltage at the LEDx pin. The LED current is set by an external resistor at the RISET pin. A PWM dimming function is provided to control the LED brightness through the PWM pin. If OVP, OTP or shorted LED happens, the STATUS pin will be pulled to low as a fault indicator. is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT8577A Absolute Maximum Ratings (Note 1) Supply Voltage, VCC, STATUS ----------------------------------------------------------------------------------------LED1 to LED4 --------------------------------------------------------------------------------------------------------------PWM, EN, DRV, SEN, VC, RT, CREG, OVP, RISET -------------------------------------------------------------Power Dissipation, PD @ TA = 25°C WQFN-20L 5x5 ------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) WQFN-20L 5x5, θJA -------------------------------------------------------------------------------------------------------WQFN-20L 5x5, θJC ------------------------------------------------------------------------------------------------------Junction Temperature -----------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------------------Storage Temperature Range --------------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Model) ----------------------------------------------------------------------------------------------MM (Machine Model) ------------------------------------------------------------------------------------------------------ Recommended Operating Conditions −0.3V to 45V −0.3V to 50V −0.3V to 5.6V 3.54W 28.2°C/W 7.1°C/W 150°C 260°C −65°C to 150°C 2kV 200V (Note 4) Supply Voltage, VCC -----------------------------------------------------------------------------------------------------LED1 to LED4 --------------------------------------------------------------------------------------------------------------ILED1 to ILED4 ----------------------------------------------------------------------------------------------------------------Junction Temperature Range --------------------------------------------------------------------------------------------Ambient Temperature Range --------------------------------------------------------------------------------------------- 5.5V to 40V 45V 20mA to 120mA −40°C to 125°C −40°C to 85°C Electrical Characteristics (VCC = 12V, TA = 25°C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit Supply Voltage Supply Current IVCC Switching Off -- 5 -- mA Shutdown Current ISHDN VEN 0.7V -- 10 -- A VDD LDO Output VCREG 4.5 5 5.5 V VDD LDO Capability ICREG 30 -- -- mA VCC UVLO Threshold VUVLO VCC Rising -- 4.5 -- Hysteresis -- 0.3 -- EN Threshold Voltage V Logic-High VENH 1.5 -- -- Logic-Low VENL -- -- 0.8 RISET = 15k, VPWM 1.2V ILED = 80mA ILED = (20mA, 120mA) Note6 76 80 84 mA ILEDx ILED_AVE 100% ILED_AVE -- 1.5 3 % V LED Current Programming LED Current Accuracy LED Current Matching (Note5) Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 is a registered trademark of Richtek Technology Corporation. DS8577A-01 December 2015 RT8577A Parameter Symbol Test Conditions Min Typ Max Unit LED1 to LED4 Regulation Voltage ILED = 80mA -- 0.86 -- V VLED Threshold No Connection -- 0.1 -- V -- 1.2 -- V RISET Pin Voltage Dimming Logic-High VPWMH 1.2 -- -- Logic-Low VPWML -- -- 0.52 1.8 2.1 2.4 MHz RRT = Open -- 200 -- kHz Working -- 40 60 ns 80 -- -- % 0.3 0.5 0.6 V Gate Driver Source 1.5 2.5 3 A Gate Driver Sink 2.5 3 4 A 1.9 2 2.1 V -- 7 -- V -- 150 -- C -- 20 -- C -- -- 0.5 V PWM Threshold Voltage V PWM Boost Controller Switching Frequency Minimum On Time f SW (Note 5) Maximum Duty Cycle SEN Current Sense Limit tON RRT = 20k (Note 5) Dmax (Note 5) Input Current Limit OVP, SCP, OTP OVP Threshold (Note 5) VOVP SCP Threshold VSCP Thermal Shutdown Temperature TSD Thermal Shutdown Hysteresis TSD STATUS Low Voltage VSTATUS LED1 to LED4 Lockout Temperature Point Resume Temperature Point Open Drain at 10mA 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. Note 5. Electrical items with mark indicate performance guaranteed by design with correlation data (TA = −40°C to 85°C) Note 6. The LED current matching at 20mA and 120mA is guaranteed by design and not production tested. Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS8577A-01 December 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT8577A Typical Application Circuit L1 10µH VIN 5.5V to 40V R1 D1 CIN 20µF CVCC 1µF MSW RF1 100 RSENSE 100m External PWM Enable RC 560 CC 0.22µF 10 STATUS RISET RT 9 EN 16 : : : : RSTATUS 100k 15 : : : …… : : : : : : : : : COUT 4.7µF x 6 VIN FLT 7 RISET 9.1k 8 RRT 56k CREG 12 CREG 1µF VC GND 1, 2, 3, 21 (Exposed Pad) ILED (Note 6) RISET 120mA 10k 80mA 15k 20mA 68k Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 19 LED1 20 LED2 4 LED3 5 LED4 SEN 11 DRV RPWM 1k 17 PWM RENA 1k ROVP1 100k RT8577A CF 1nF RDRV 5 ROVP2 2.1M OVP 6 14 VCC VOUT 45V (MAX) is a registered trademark of Richtek Technology Corporation. DS8577A-01 December 2015 RT8577A Timing Diagram Power On/Off Sequence LED driver is without power sequence concern. Mode1, Mode2 and Mode3 are different power sequences respectively. There is no concern in the above condition. Mode1 : Delay Time of PWM vs VOUT VIN VOUT EN 100ns PWM Mode2 : Delay Time of EN vs VOUT VIN VOUT 100µs EN PWM Mode3 : Delay Time of VIN vs VOUT VIN UVLO UVLO VOUT EN PWM Figure 1. Power On/Off Sequence Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS8577A-01 December 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT8577A Typical Operating Characteristics LED Current vs. Input Voltage LED Current vs. PWM Duty Cycle 160 120 100 LED Current (mA) LED Current (mA) 140 120 LED1 LED2 LED3 LED4 100 80 80 PWM = 200Hz PWM = 1kHz PWM = 10kHz 60 40 20 48LEDs, RISET = 10kΩ VIN = 12V, 48LEDs, RISET = 10kΩ 60 0 8 10 12 14 16 18 20 22 24 26 28 0 10 20 30 40 50 60 70 80 90 Input Voltage (V) PWM Duty Cycle (%) Efficiency vs. Input Voltage Start up with Minimum PWM Duty 100 100 Efficiency (%) 95 90 VOUT (10V/Div) 85 VIN (5V/Div) 80 IOUT (50mA/Div) 75 PWM (2V/Div) 48LEDs, RISET = 10kΩ 70 8 10 12 14 16 18 20 22 24 26 f = 400Hz, PWM Duty = 1% Time (50ms/Div) 28 Input Voltage (V) OVP Protection LED Short Delay Time VIN = 12V, Short 3LEDs, 48LEDs, RISET = 10kΩ OVP (1V/Div) OVP Trigger by LED remove, VIN = 12V, VOUT = 48LEDS VLEDx (10V/Div) VOUT (5V/Div) STATUS (5V/Div) STATUS (5V/Div) DRV (5V/Div) DRV (5V/Div) Time (100μs/Div) Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 IOUT (100mA/Div) Time (25μs/Div) is a registered trademark of Richtek Technology Corporation. DS8577A-01 December 2015 RT8577A LED Short Protection LED Short Protection IOUT (100mA/Div) IOUT (100mA/Div) STATUS (5V/Div) Before Short STATUS (5V/Div) VLEDx (10V/Div) VLEDx (10V/Div) DRV (5V/Div) DRV (5V/Div) VIN = 12V, Short 3LEDs Time (2.5ms/Div) Power On from EN Power Off from EN EN (2V/Div) DRV (5V/Div) DRV (5V/Div) I IN (1A/Div) I IN (1A/Div) VIN = 12V, 48LEDs, RISET = 10kΩ VIN = 12V, 48LEDs, RISET = 10kΩ Time (10ms/Div) Time (25ms/Div) Power On from VIN Power Off from VIN VIN (10V/Div) VIN (10V/Div) DRV (5V/Div) DRV (5V/Div) VIN = 12V, 48LEDs, RISET = 10kΩ Time (10ms/Div) Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS8577A-01 VIN = 12V, Short 3LEDs Time (2.5ms/Div) EN (2V/Div) I IN (1A/Div) After Short December 2015 I IN (1A/Div) VIN = 12V, 48LEDs, RISET = 10kΩ Time (25ms/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT8577A Power On from PWM Power Off from PWM PWM (2V/Div) PWM (2V/Div) DRV (5V/Div) DRV (5V/Div) I IN (1A/Div) I IN (1A/Div) VIN = 12V, 48LEDs, RISET = 10kΩ Time (10ms/Div) Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 VIN = 12V, 48LEDs, RISET = 10kΩ Time (10ms/Div) is a registered trademark of Richtek Technology Corporation. DS8577A-01 December 2015 RT8577A Application information The RT8577A is an 4-CH driver controller that delivers well matched LED current to each channel of LED strings. The external N-MOSFET current source will accommodate the power dissipation difference among channels resulting from the forward voltage difference between the LED strings. With high speed current source N-MOSFET drivers, the RT8577A features highly accurate current matching, while also providing very fast turn-on and turn-off times. This allows a very narrow minimum on or off pulse. The RT8577A integrates adjustable switching frequency and provides circuitry for over temperature, over voltage, under voltage and current limit protection. Compensation The regulator loop can be compensated by adjusting the external components connected to the VC pin. The VC 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 RC = 560Ω, CC = 0.22μF. LED Connection The RT8577A equips 4-CH LED drivers and each channel supports up to 15 LEDs. The LED strings are connected from the output of the boost converter to pin LEDx (x = 1 to 4) respectively. If one of the LED channel is not in use, the LED pin should be opened directly. Setting and Regulation of LED current The LED current can be calculated by the following equation : 1200 ILED 40mA < ILED 120mA RISET ILED 1360 20mA < ILED 40mA RISET where RISET is the resistor between the RISET pin and GND. This setting is the reference for the LED current at pin LEDx and represents the sensed LED current for each string. The DC/DC converter regulates the LED current according to the setting. Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS8577A-01 December 2015 Over Voltage Protection The RT8577A integrates Over Voltage Protection (OVP) . When the voltage at the OVP pin rises above the threshold voltage of approximately 2V, the internal switch will be turned off and STATUS pin will be pulled to low. The internal switch will be turned on again once the voltage at the OVP pin returns to normal range. The output voltage can be clamped at a certain voltage level and can be calculated by the following equations : R VOUT(OVP) = VOVP 1 + OVP2 ROVP1 where ROVP1 and ROVP2 are the resistors in the resistive 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. Suggested value for ROVP2 is up to 3.6MΩ to prevent loading effect. LED Short Circuit Protection The RT8577A integrates LED Short Circuit Protection (SCP). If one of the LED1 to LED4 pin voltages exceeds a threshold of approximately 7V during normal operation, the STATUS pin will be pulled low for a fault signal. STATUS The RT8577A provides a fault status indicator with an open drain STATUS pin. If fault condition (LED Short/OVP/OTP) occurs, the STATUS will be reset after VIN or EN is reapplied. Setting the Switching Frequency The RT8577A switching frequency is programmable from 200kHz to 2.1MHz by adjusting the oscillator resistor, RRT. The switching frequency can be calculated by the following equation : fSW 200k + 38 109 RRT is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT8577A Current Limit Protection Over Temperature Protection The RT8577A can sense the RSENSE voltage between the SEN pin and GND to achieve over current protection. The boost converter senses the inductor current during the on period. The duty cycle depends on the current signal and internal slope compensation compared with the error signal. The external switch will be turned off when the current signal is larger than the internal slope compensation. In the off period, the inductor current will decrease until the internal switch is turned on by the oscillator. The current limit value can be calculated by the following equation : 0.5V Current Limit (A) RSENSE The RT8577A has over temperature protection function to prevent the IC from overheating due to excessive power dissipation. The IC will shut down and the STATUS pin will be pulled low when junction temperature exceeds 150°C. Main converter starts switching after junction temperature cools down by approximately 20°C. Inductor Selection 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) : 2 L= Brightness Control The RT8577A 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 100Hz to 10kHz, but the 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. Please refer to Table 1. Table 1. Dimming Frequency (Hz) Duty (Min.) 100 < f PWM 500 0.2% 500 < f PWM 1k 0.4% 1k < f PWM 2k 0.8% 2k < f PWM 5k 1.5% 5k < f PWM 10k 3% Duty (Max.) 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. Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 D 1 D VOUT 2 f IOUT The duty cycle can be calculated as the following equation : V VIN D = OUT VOUT where VOUT is the maximum output voltage, VIN is the minimum input voltage, f 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. The inductor must be selected with a saturated current rating that is greater than the peak current as provided by the following equation : V I V D T IPEAK = OUT OUT IN η VIN 2L where η is the efficiency of the power converter. is a registered trademark of Richtek Technology Corporation. DS8577A-01 December 2015 RT8577A Schottky diodes are recommended for most applications because of their fast recovery time and low forward voltage. Power dissipation, reverse voltage rating, and pulsating 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. Capacitor Selection The input capacitor reduces current spikes from the input supply and minimizes noise injection to the converter. For general applications, six 4.7μF ceramic capacitors are 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. packages, the thermal resistance, θJA, is 28.2°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 / (28.2°C/W) = 3.54W for WQFN-20L 5x5 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 2 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. 4.0 Maximum Power Dissipation (W)1 Diode Selection It is recommended to choose a ceramic capacitor based on the output voltage ripple requirements. The minimum value of the output capacitor, COUT, can be calculated by the following equation : COUT = IOUT D VOUT f Four-Layer PCB 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 where ΔVOUT is the peak-to-peak ripple voltage at the output. 0 25 50 75 100 125 Ambient Temperature (°C) Figure 2. Derating Curve of Maximum Power Dissipation 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 : Layout Considerations Careful PCB layout is very important for designing switching power converter circuits. The following layout guidelines should be strictly followed for best performance of the RT8577A. The power components L1, D1, CIN, COUT must be placed as close as possible to the IC to reduce current loop. The PCB trace between power components must be as short and wide as possible. The compensation circuit should be kept away from the power loops and shielded with a ground trace to prevent any noise coupling. Place the compensation components, RC and CC, as close as possible to pin 9. The exposed pad of the chip should be connected to ground plane for thermal consideration. 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 and TA is the ambient temperature. The junction to ambient thermal resistance, θJA, is layout dependent. For WQFN-20L 5x5 Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS8577A-01 December 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 13 RT8577A OVP Protection VIN PWM Delay time 50µs STATUS Status latch until EN goes low VOUT OVP 2V OVP EN SW Frequency = 2.1MHz Time DRV Short Protection VIN PWM ILEDX(1) 10µs 10µs ILEDX(2) Delay time 50µs STATUS Status latch until EN goes low VLEDX(1) LED SHORT VLEDX(2) EN 7V SW Frequency = 2.1MHz DRV Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 14 Time is a registered trademark of Richtek Technology Corporation. DS8577A-01 December 2015 RT8577A OTP Function 130°C 150°C Thermal 150°C 130°C STATUS VOUT DRV Protection Functions Description LED Short Detect VLEDx voltage. Triggered if VLEDx 7V. Protection Behavior V If one of LED1 to LED4 pin voltages exceeds a threshold of approximately 7V during normal operation, the STATUS pin will be pulled to low for a fault signal. Internal switching does not stop. OVP Use OVP pin voltage for detection. Triggered if OVP pin voltage 2V. V OTP Triggered if TJ 150C V STATUS pin is used as fault indicator. Fault and pull low. V Fault Indicator Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS8577A-01 December 2015 The internal switch will be turned off and STATUS pin will be pulled to low. The Internal switch will be turned on again once the voltage at the OVP pin returns to normal range. The IC will shut down and the STATUS pin will be pulled to low when junction temperature exceeds 150C and IC returns to normal operation when temperature falls to 130C. If fault condition (LED short, OVP or OTP) occurs, the STATUS pin will be pulled to low. It will be reset after VIN or EN is re-applied. is a registered trademark of Richtek Technology Corporation. www.richtek.com 15 RT8577A Locate the CVCC as close to VCC as possible. CVCC CC PGND LED1 NC PWM VC 20 19 18 17 16 VIN GND 1 15 GND 2 14 STATUS R1 VCC GND 3 13 NC LED3 4 12 CREG LED4 5 11 DRV GND 21 VIN L1 RISET 9 D1 VOUT MSW 10 CF SEN 8 EN 7 RISET RT OVP 6 COUT RDRV RF1 AGND CIN + 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. The PGND should be wide and short enough to connect ground plane. LED2 RC RSENSE Place the power components as Close as possible. The traces should be wide and short especially for the high current loop. PGND RRT AGND The exposed pad of the chip should be connected to ground plane for thermal consideration. 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. Figure 3. PCB Layout Guide Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 16 is a registered trademark of Richtek Technology Corporation. DS8577A-01 December 2015 RT8577A Outline Dimension 1 2 DETAIL A Pin #1 ID and Tie Bar Mark 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 0.250 0.350 0.010 0.014 D 4.900 5.100 0.193 0.201 D2 3.100 3.200 0.122 0.126 E 4.900 5.100 0.193 0.201 E2 3.100 3.200 0.122 0.126 e L 0.650 0.500 0.026 0.600 0.020 0.024 W-Type 20L QFN 5x5 Package Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS8577A-01 December 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 17 RT8577A Richtek Technology Corporation 14F, No. 8, Tai Yuen 1st 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. www.richtek.com 18 DS8577A-01 December 2015