RT8532 RICHTEK | Alldatasheet
Document overview
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Technical content
Features
Wide Input Voltage : VIN 2.5V to 24V High Output Voltage : VOUT up to 43V Programmable Full Channel Current from 5mA to 50mA and Matched to 2% Channel Current Regulation with ±±±±±3% Accuracy Direct PWM Dimming up to 20kHz and Minimum On-Time to 500ns PWM to Mixed Analog and PWM Dimming up to 20kHz with Maximum 9 bit Resolution Built-In Soft Start to Prevent Inrush Current without External Capacitor Disconnects LED in Shutdown Strings Open Detection Current Limit Protection Programmable Over Voltage Protection Over Temperature Protection 20-Lead WQFN Package RoHS Compliant and Halogen Free Simplified Application Circuit OVP LED1 LED2 LED3 ISET VIN VOUTVIN LED4 COMP CIN L1 D1 AGND RT8532 ROVP1 ROVP2 COUT LX RCOMP CCOMP RISET PGND PWM LED5 LED6 PWM Signal EN Chip Enable CC RFSW FREQ MIXMIX COVP
www.richtek.com DS8532-04 January 2014 ©Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Functional Pin Description Pin No. Pin Name Pin Function 1 EN Chip Enable (Active High). There is an internal pull low resistor 400k for the EN pin.
2 FREQ
Switching Frequency of Boost Converter Setting. Connect a resistor between this pin and AGND to set the switching frequency. FSW SW 25R1 . 1 6 k F( M H z )
3 ISET
LED Current Setting. LED current is set by the resistor R IS ET connected from the ISET pin to ground. LED ISET 240Im A Rk
4 MIX
Dimming Mode Selection. There is an internal pull high 400k resistor connected to VDC. Floating or pulling high for 25% Mixed mode dimming, pulling low for direct PWM mode dimming. Recommended to mixed mode for high LED efficiency. 5 AGND Analog Ground of LED Driver. 6, 7, 8, 9, 10, LED6 to LED1 Current Sink for LED String. (Leave the pin unconnected or short to GND, if not used.) 12 OVP Over Voltage Protection Sense Input. The detecting threshold is 1.2V (typ.). 13, 14 PGND Power Ground of Boost Converter. 15, 16 LX Switching Pin of Boost Converter. 17 PWM PWM Dimming Control Input. 18 VDC Internal Regulator Voltage. Connect a capacitor from this pin to ground. 19 VIN Power Supply Input. 20 COMP Compensation Note for Boost Converter. Connect a compensation network to this pin for stability. (Exposed Pad) GND Ground. The Exposed Pad must be Soldered to a Large PCB and Connected to GND for Maximum Power Dissipation.
Ordering Information
Note : Richtek products are : RoHS compliant and compatible with the current require- ments of IPC/JEDEC J-STD-020. Suitable for use in SnPb or Pb-free soldering processes. Pin Configurations WQFN-20L 3x3 (TOP VIEW) Marking Information Package Type QW : WQFN-20L 3x3 (W-Type) RT8532 Lead Plating System G : Green (Halogen Free and Pb Free) MIX ISET EN FREQ LX PGND OVP PGND LED6 LED5 LED3 COMP VIN PWM VDC 17181920 9876 GND 115 LX AGND LED1 LED2 LED4 89=YM DNN 89= : Product Code YMDNN : Date Code
DS8532-04 January 2014 www.richtek.com ©Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Function Block Diagram Operation Enable Control When VIN is higher than the UVLO voltage and EN pin input voltage is higher than rising threshold, the VDC will be regulated around 3.8V if VIN is higher than 3.8V. OSC The switching frequency is adjustable by the external resistor connected between the FREQ pin and GND. PWM Controller This controller includes some logic circuit to control LX N-MOSFET on/off. This block controls the minimum on time and max duty of LX. OCP & OTP When LX N-MOSFET peak current is higher than 2.5A (typically), the LX N-MOSFET is turned off immediately and resumed again at next clock pulse. When the junction temperature is higher than 150 °C (typically), the LX N- MOSFET will be turned off until the temperature is lower than the 120°C (typically). OVP When OVP pin voltage is higher than 1.2V, the LX N-MOSFET is turned off immediately to protect the LX N-MOSFET. Minimum LED Selection This block detects all LEDx voltage and select a minimum voltage to EA (Error Amplifier). This function can guarantee the lowest of LED pin voltage is around 600mV and V OUT can be boost to the highest forward voltage of LED strings. LED Open Detection If the voltage at LEDx pin is lower than 100mV, this channel is defined as open channel and the Minimum LED Selection function will discard it to regulate other used channels in proper voltage. OSC 0.6V OCP LDO PWM Controller Mini LED Selection - 1.2V ……+ PWM VIN OVP ISET COMP LED1 LED2 AGND LED6 LX R SQ Q PGND FREQ PWMO Generator EN PWM-to-DC LED Open Detection MIX MUX DAC GND VDC OTP
www.richtek.com DS8532-04 January 2014 ©Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation.
Electrical Characteristics
Recommended Operating Conditions (Note 4) Absolute Maximum Ratings (Note 1) Power Dissipation, PD @ TA = 25°C Package Thermal Resistance (Note 2) ESD Susceptibility (Note 3) (VIN = 5V, TA = 25 °C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit VIN Quiescent Current IVIN PWM = COMP = 0V , Not Switching -- 3 -- mA IVIN_SW PWM = COMP = 2V , Switching -- 4 -- VIN Shutdown Current I SHDN VIN = 4.5V, EN = 0V -- -- 10 A VIN Under Voltage Lockout Threshold VUVLO VIN Rising -- 2.3 -- V VIN Falling -- 2.1 -- PWM Dimming Frequency f PWM 0.1 -- 20 kHz Control Input EN, PWM Input Voltage High V IH VIN = 2.5V to 24V 1.3 -- 24 V Low V IL VIN = 2.5V to 24V -- -- 0.5 Boost Converter Switching Frequency f SW RFSW = 22k 0.8 1 1.2 MHz RFSW = 51k 0.4 0.5 0.6 LX On Resistance (N-MOSFET) RLX V IN > 4.5V 0.18 0.2 0.22
DS8532-04 January 2014 www.richtek.com ©Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. 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. θ JA is measured at T A = 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. Parameter Symbol Test Conditions Min Typ Max Unit Minimum On-Time t ON(MIN) F SW = 1MHz 40 60 80 ns Maximum Duty D MAX F SW = 1MHz 90 93 96 % LX Current Limit I LIM 2.2 2.5 2.8 A Regulated VLEDx V LEDx Highest LED String, ILED = 20mA 0.5 0.6 0.7 V Low Dropout Linear Regulator LDO Output Voltage Range V DC 3.6 3.8 4 V LED Current Programming LED Current Accuracy I LEDA 2V > VLEDx > 0.5V, RISET = 12k 19.4 20 20.6 mA LED Current Matching I LEDM 2V > VLEDx > 0.5V, RISET = 12k, Formulated by (ILEDx IAVG) / IAVG x 100% -- -- 2 % ISET Pin Voltage V ISET 0.76 1 1.24 V Fault Protection OVP Threshold V OVP 1.16 1.2 1.24 V OVP UVLO Threshold V OVPF -- 50 -- mV Thermal Shutdown Temperature TSD -- 150 -- C OTP Hysteresis T OTP_Hys -- 30 -- C LED Pin Under Voltage Threshold VLSD Un-Connection -- 0.1 -- V
©Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Figure 1. For General Application Circuit Figure 2. For Low Input Voltage Application Circuit
17 PWM
DS8532-04 January 2014 www.richtek.com ©Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Typical Operating Characteristics fSW vs. RFSW 200 400 600 800 1000 1200 1400 1600 1800 2000 0 20 40 60 80 100 120 140 RFSW (kohm) fSW (kHz)
9 LEDs per channel
(kΩ) Efficiency vs. Input Voltage 100 4 8 12 16 20 24 Input Voltage (V) Efficiency (%) 54 LEDs, fSW = 500kHz, PWM = 3.3V LED Current vs. PWM Duty Cycle 0 2 04 06 08 0 1 0 0 PWM Duty Cycle (%) LED Current (mA)
9 LEDs per channel, fSW = 500kHz
LED Current vs. Input Voltage 4 8 12 16 20 24 Input Voltage (V) Output Current (mA) 9 LEDs per channel, fSW = 500kHz, PWM = 3.3V LED1 LED2 LED3 LED4 LED5 LED6 VDC vs. Temperature 2.0 2.5 3.0 3.5 4.0 4.5 5.0 -50 -25 0 25 50 75 100 125 Temperature (°C) VDC (V) LED Current vs. Temperature -50 -25 0 25 50 75 100 125 Temperature (°C) LED Current (mA) 9 LEDs per channel, fSW = 500kHz, PWM = 3.3V
www.richtek.com DS8532-04 January 2014 ©Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Line Transient Response Time (2.5ms/Div) ILED (20mA/Div) VIN (10V/Div) VIN = 12V to 18V, fSW = 500kHz, PWM = 3.3V Time (10ms/Div) Power On from EN VEN (5V/Div) VOUT (20V/Div) ILED (20mA/Div) VLX (20V/Div) VIN = 12V, fSW = 500kHz, PWM = 3.3V OVP Threshold Voltage vs. Input Voltage 1.0 1.1 1.2 1.3 1.4 4 8 12 16 20 24 Input Voltage (V) OVP Threshold Voltage (V) Quiescent Current vs. Input Voltage 1.5 1.8 2.0 2.3 2.5 3 5 8 1 01 31 51 82 02 32 5 Input Voltage (V) Quiescent Current (mA ) Not Switching Time (10ms/Div) Power On in PWM Mode VEN (5V/Div) VIN (10V/Div) ILED (20mA/Div) VPWM (5V/Div) VIN = 12V, fSW = 500kHz Time (10ms/Div) Power On in Mixed Mode VPWM (5V/Div) VIN (20V/Div) ILED (20mA/Div) VEN (5V/Div) VIN = 12V, fSW = 500kHz
DS8532-04 January 2014 www.richtek.com ©Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation.
Application Information
The RT8532 is a general purpose 6-CH LED driver capable of delivering an adjustable 5mA to 50mA LED current. The IC is a current mode boost converter integrated with a 43V/2.5A power switch and can cover a wide VIN range from 2.5V to 24V. The part integrates both built-in soft- start and with PWM dimming control; moreover, it provides over voltage, over temperature and current limiting protection features. It also integrates PWM and mixed mode dimming function for accurate LED current control. The PWM dimming frequency can operate from 100Hz to 20kHz without inducing any inrush current in LED or inductor. Input Capacitor Selection Low ESR ceramic capacitors are recommended for input capacitor applications. Low ESR will effectively reduce the input ripple voltage caused by the switching operation. Two 2.2μF low ESR ceramic capacitors are sufficient for most applications. Nevertheless, this value can be decreased for applications with lower output current requirement. Another consideration is the voltage rating of the input capacitor, which must be greater than the maximum input voltage. Output Capacitor Selection Output ripple voltage is an important index for estimating chip performance. This portion consists of two parts. One is the product of the inductor current ripple with the ESR of the output capacitor, while the other part is formed by the charging and discharging process of the output capacitor. As shown in Figure 3, ΔV OUT1 can be evaluated based on the ideal energy equalization. According to the definition of Q, the Q value can be calculated as the following equation : where f SW is the switching frequency and ΔIL is the inductor ripple current. Move COUT to the left side to estimate the value of ΔVOUT1 according to the following equation : IN L OUT IN L OUT IN OUT OUT1 OUT SW 11 1QI I I I I I22 2 V 1 C VVf Finally, taking ESR into account, the overall output ripple voltage can be determined by the following equation : Figure 3. The Output Ripple Voltage without the The inductor value depends on the maximum input current.
www.richtek.com DS8532-04 January 2014 ©Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. LED ISET 240Im A Rk where RISET is the resistor between the ISET pin and GND. This setting is the reference for the LED current at LED1 to LED6 and represents the sensed LED current for each string. The DC/DC converter regulates the LED current according to the setting. PWM Mode and Mixed Mode Brightness Dimming The RT8532 allows two ways of controlling the LED brightness. PWM Mode Dimming : When the MIX pin is connected to GND, the dimming mode operates in PWM Mode. During the PWM dimming, the current source turn-on/off is synchronized with the PWM signal. The LED current frequency is equivalent to PWM input frequency. Mixed Mode Dimming : If the MIX pin is floating or tied to VDC, the dimming mode operates in Mixed Mode. In this mode the PWM and I LED dimming cycle will delay by 2 periods. First cycle delay is required for the period, while the second cycle delay is for the duty rate calculation. (a) When 25% ≤ PWM duty ≤ 100%, the current source outputs are DC dimming, and the PWM duty cycle modulates the amplitude of the currents. (b) When PWM Duty < 25%, the DC dimming will translate to DC-PWM dimming to control the LED current. In this state, the LED current is fixed at 0.25 x ISET, and the dimming duty is 4 x PWM duties. The minimum D/A Converter is 512 steps resolution for I LED regulation. where VOUT is the maximum output voltage, V IN is the minimum input voltage, f SW is the switching frequency, and IOUT is the sum of current from all LED strings. LED Soft-Start Function The soft-start time of the LED boost converter, defined as the period from EN to set I OUT, is several tens of milliseconds according to the difference of PWM or Mixed mode. The LED starts up after V IN, PWM and EN signals are all ready. The soft-start inrush peak current must be less than 2.5A. LED Driver Compensation The control 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 capacitors, C C and CCOMP, will adjust the integrator zero and pole respectively to maintain stability. Moreover, the resistor, R COMP, will adjust the mid-band gain for fast transient response. Diode Selection Schottky diodes D1 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 I PEAK and reverse voltage rating exceeds the maximum output voltage. IN OUT IN OUT OUT SW VD V VL1
0.4 V I f
where η is the efficiency of the boost converter, IIN(MAX) is the maximum input current and IRIPPLE is the inductor ripple current. The input peak current can be obtained by adding the maximum input current with half of the inductor ripple current as shown in the following equation : I PEAK = 1.2 x IIN(MAX) Note that the saturated current of inductor must be greater than IPEAK. The inductance can eventually be determined according to the following equation : Setting and Regulation of LED Current The LED current can be calculated by the following equation :
©Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. The RT8532 features the digital dimming control scheme. the recommended PWM frequency is 100Hz to 10kHz. by inductor rising time. Please refer to Table 1 and Table2. Table 1. Mixed Dimming Mode Table 2. PWM Dimming Mode the junction temperature should be kept below 125°C. threshold of approximately 1.2V, the driver will turn off. OVP2 to reduce loading effect. turns off all LED driver functions.
©Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. be strictly followed for best performance of the RT8532. through these trace during operation. trace should be short and wide as possible. Place the input capacitor C1 close to VIN pin. Figure 4. Derating Curve of Maximum Power Dissipation on the maximum power dissipation.
©Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Figure 5. PCB Layout Guide trace to prevent any noise coupling.
www.richtek.com DS8532-04 January 2014 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 furnish ed 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 infringeme nts 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 R ichtek or its subsidiaries. Outline Dimension 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 0.250 0.006 0.010 D 2.900 3.100 0.1 14 0.122 D2 1.650 1.750 0.065 0.069 E 2.900 3.100 0.1 14 0.122 E2 1.650 1.750 0.065 0.069 e 0.400 0.016 L 0.350 0.450 0.014 0.018 W-Type 20L QFN 3x3 Package Note : The configuration of the Pin #1 identifier is optional, but must be located within the zone indicated. DETAIL A Pin #1 ID and Tie Bar Mark Options 2 2