® RT8525 Boost Controller with Dimming Control General Description Features The RT8525 is a wide input operating voltage range step up controller. High voltage output and large output current are feasible by using an external N-MOSFET. The RT8525 input operating range is from 4.5V to 29V. z Programmable Soft-Start Time z Programmable Boost SW Frequency from 50kHz to 600kHz z Output Over Voltage Protection z Output Under Voltage Protection z 14-Lead SOP Package z RoHS Compliant and Halogen Free z The RT8525 is an optimized design for wide output voltage range applications. The output voltage of the RT8525 can be adjusted by the FB pin. The PWMI pin can be used as a digital input, allowing WLED brightness control with a logic-level PWM signal. Applications Ordering Information z RT8525 z Note : VIN Range : 4.5V to 29V Package Type S : SOP-14 Lead Plating System G : Green (Halogen Free and Pb Free) LCD TV, Monitor Display Backlight LED Driver Application Pin Configurations (TOP VIEW) VDC VIN COMP SS FSW AGND PWMI 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. Marking Information 14 2 13 3 12 4 11 5 10 6 9 7 8 DRV PGND EN ISW OOVP FB FAULT SOP-14 RT8525GS : Product Number RT8525 GSYMDNN YMDNN : Date Code Typical Application Circuit VIN 24V CIN 100µF 2 VIN CVIN 1µF RC 33k CC1 27nF L1 33µH RT8525 14 DRV 1 VDC CDC 1µF 3 COMP CC2 RSW 56k 5 FSW 4 SS CSS 0.33µF Chip Enable 12 EN Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8525-01 March 2012 D1 ISW PGND RSLP 11 2.4k 13 FB 9 7 PWMI RFLT 8 100k FAULT OOVP 10 AGND 6 M1 RS 50m RFB1 117k PWMI 12V COVP VOUT 50V COUT 100µF x 2 ROVP1 150k RFB2 3k ROVP2 6k is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT8525 Functional Pin Description Pin No. Pin Name Pin Function 1 VDC Output of Internal Pre-Regulator. 2 VIN IC Power Supply. 3 COMP Compensation for Error Amplifier. Connect a compensation network to ground. 4 SS External Capacitor to Adjust Soft-Start Time. 5 FSW 6 AGND Frequency Adjust Pin. This pin allows setting the switching frequency with a resistor from 50kHz to 600kHz. Analog Ground. 7 PWMI External Digital Input for Dimming Function. 8 FAULT Open Drain Output for Fault Detection. 9 FB Feedback to Error Amplifier Input. 10 OOVP Sense Output Voltage for Over Voltage Protection and Under Voltage Protection. 11 ISW External MOSFET Switch Current Sense Pin. Connect the current sense resistor between the external N-MOSFET switch and ground. 12 EN Chip Enable (Active High). 13 PGND Power Ground of Boost Controller. 14 DRV Drive Output for the N-MOSFET. Function Block Diagram FSW VIN VDC UVLO + OTP OOVP/OUVP Logic 12V LDO OSC + OC - EN PWMI PGND S Q R Q + - DRV Blanking VOS PWM Controller 2.5V 0.4V + - FAULT Protection OOVP + - FAULT 0.1V - + EA - AGND 4µA ISW 1.25V FB COMP SS Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS8525-01 March 2012 RT8525 Absolute Maximum Ratings z z z z z z z z z (Note 1) VIN to GND -----------------------------------------------------------------------------------------------------------------VDC, DRV, FAULT to GND ----------------------------------------------------------------------------------------------EN, COMP, SS, FSW, FB, OOVP, ISW, PWMI to GND --------------------------------------------------------Power Dissipation, PD @ TA = 25°C SOP-14 ---------------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) SOP-14 , θJA ---------------------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------Junction Temperature ----------------------------------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM -------------------------------------------------------------------------------------------------------------------------MM ---------------------------------------------------------------------------------------------------------------------------- Recommended Operating Conditions z z z −0.3V to 32V −0.3V to 13.2V −0.3V to 6V 1.000W 100°C/W 260°C 150°C −65°C to 150°C 2kV 200V (Note 4) Supply Input Voltage, VIN ----------------------------------------------------------------------------------------------- 4.5V to 29V Junction Temperature Range -------------------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range -------------------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VIN = 21V, VOUT = 50V, TA = 25°C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit Input Power Supply Quiescent Current IQ No Switching, RSW = 56kΩ -- 1.3 2 mA Shutdown Current Under Voltage Lockout Threshold Under Voltage Lockout Hysteresis 12V Regulator I SHDN VEN = 0V -- 10 -- μA VUVLO VIN Rising -- 3.8 -- V -- 500 -- mV 11.4 12 12.6 V -- 500 -- mV -- 270 -- mA Logic-High VIH 2 -- -- Logic-Low -- -- 0.8 ΔVUVLO Regulator Output Voltage VDC Dropout Voltage VDROP 13.5V < VIN < 16V, 1mA < I LOAD < 100mA 16V < VIN < 20V, 1mA < I LOAD < 50mA 20V < VIN < 29V, 1mA < I LOAD < 20mA VIN − VDC, VIN = 12V, I LOAD = 100mA Short-Circuit Current Limit I SC VDC Short to GND Control Input EN Threshold Voltage EN Sink Current Sleeping Mode Shutdown Delay Shutdown Mode VIL I IH VEN = 5V -- 5 -- μA t SLEEP RSW = 56kΩ, EN = L, 12V Regular Shutdown 55 -- -- ms t SHDN RSW = 56kΩ, EN = L, IC Shutdown 110 -- -- ms Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8525-01 March 2012 V is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT8525 Parameter Symbol Test Conditions Min Typ Max Unit -- 200 -- kHz -- 250 -- ns 90 -- -- % 1.225 1.25 1.275 V ISLOPE, PK -- 50 -- μA ISS 3 4 5 μA Boost Controller Switching Frequency f SW Minimum On-Time tMON Maximum Duty D MAX Feedback Voltage VFB R SW = 56kΩ Switching Slope Compensation Peak Magnitude of Slope Compensation Current Soft-Start Soft-Start Current Gate Driver R DS(ON)_N ISINK = 100mA (N-MOSFET) -- 1 -- Ω R DS(ON)_P ISOURCE = 100mA (P-MOSFET) -- 1.5 -- Ω Peak Sink Current IPEAKsk C LOAD = 1nF -- 2.2 -- A Peak Source Current IPEAKsr C LOAD = 1nF -- 2.55 -- A Rise Time tr C LOAD = 1nF -- 6 -- ns Fall Time tf C LOAD = 1nF -- 5 -- ns DRV On-Resistance PWM Dimming Control PWMI Threshold Voltage Logic-High VPWMI_H 2 -- -- Logic-Low VPWMI_L -- -- 0.8 -- 0.4 -- V V Protection Function OCP Threshold VOCP Including Slope Compensation Magnitude VOUT OVP Threshold VOVP 2.375 2.5 2.625 V VOUT UVP Threshold Thermal Shutdown Temperature Thermal Shutdown Hysteresis VUVP -- 0.1 -- V TSD -- 150 -- °C ΔTSD -- 50 -- °C 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 low effective thermal conductivity single-layer test board per JEDEC 51-3. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions.. Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 is a registered trademark of Richtek Technology Corporation. DS8525-01 March 2012 RT8525 Typical Operating Characteristics Quiescent Current vs. Temperature 3.0 2.5 2.5 Quiescent Current (mA) Quiescent Current (mA) Quiescent Current vs. Input Voltage 3.0 2.0 1.5 1.0 0.5 No Switching 9 14 19 24 1.5 1.0 0.5 No Switching 0.0 0.0 4 2.0 -50 29 -25 0 Feedback Voltage vs. Input Voltage 75 100 125 Feedback Voltage vs. Temperature 1.5 1.5 1.4 1.4 Feedback Voltage (V) Feedback Voltage (V) 50 Temperature (°C) Input Voltage (V) 1.3 1.2 1.1 1.0 1.3 1.2 1.1 1.0 4 9 14 19 24 29 -50 -25 0 25 50 75 100 125 Temperature (°C) Input Voltage (V) Switching Frequency vs. Temperature Boost Efficiency vs. Load Current 300 100 260 90 Efficiency(%) Switching Frequency (kHz)1 25 220 180 140 80 70 60 RSW = 56kΩ 100 VIN = 24V, VOUT = 50V 50 -50 -25 0 25 50 75 100 Temperature (°C) Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8525-01 March 2012 125 0 0.4 0.8 1.2 1.6 2 Load Current (A) is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT8525 Applications Information The RT8525 is a wide input operating voltage range step up controller. High voltage output and large output current are feasible by using an external N-MOSFET. The protection functions include output over voltage, output under voltage, over temperature and current limiting protection. Boost Output Voltage Setting The regulated output voltage is set by an external resistor divider according to the following equation : R VOUT = VFB × ⎛⎜ 1+ FB1 ⎞⎟ , where VFB = 1.25V (typ.) ⎝ RFB2 ⎠ The recommended value of RFB2 should be at least 1kΩ for saving sacrificing. Moreover, placing the resistor divider as close as possible to the chip can reduce noise sensitivity. Boost Switching Frequency The RT8525 boost driver switching frequency is able to be adjusted by a resistor RSW ranging from 18kΩ to 220kΩ. The following figure illustrates the corresponding switching frequency within the resistor range. Switching Frequency vs. RSW 600 f SW (kHz) 500 400 300 200 100 VIN = 24V, VOUT = 50V, COUT = 100μF x 2, L1 = 33μH, while the recommended value for compensation is as follows : RC = 33kΩ, CC1 = 27nF. Soft-Start The soft-start of the RT8525 can be achieved by connecting a capacitor from the SS pin to GND. The built-in soft-start circuit reduces the start-up current spike and output voltage overshoot. The external capacitor charged by an internal 4μA constant charging current determines the softstart time. The SS pin limits the rising rate of the COMP pin voltage and thereby limits the peak switch current. The soft-start interval is set by the soft-start capacitor according to the following equation : tSS ≅ CSS × 5 × 105 A typical value for the soft-start capacitor is 0.33μF. The soft-start capacitor is discharged when EN voltage falls below its threshold after shutdown delay or UVLO occurs. Slope Compensation and Current Limiting A slope compensation is applied to avoid sub-harmonic oscillation in current-mode control. The slope compensation voltage is generated by the internal ramp current flow through a slope compensation resistor RSLP. The inductor current is sensed by the sensing resistor RS. Both of them are added and presented on the ISW pin. The internal ramp current is rising linearly form zero at the beginning of each switching cycle to 50μA in maximum on-time of each cycle. The slope compensation resistor RSLP can be calculated by the following equation : ( VOUT − VIN ) × RS RSLP > 2 × L × 50μ × fSW where RS is current sensing resistor, L is inductor value, 0 0 50 100 150 200 250 RSW (kΩ) Figure 1. Boost Switching Frequency Boost Loop Compensation The voltage feedback loop can be compensated by an external compensation network consisted of RC, CC1 and CC2. Choose RC to set high frequency gain for fast transient response. Select CC1 and CC2 to set the zero and pole to maintain loop stability. For typical application, Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 and fSW is boost switching frequency. The current flow through inductor during charging period is detected by a sensing resistor RS. Besides, the slope compensation voltage also attributes magnitude to ISW. As the voltage at the ISW pin is over 0.4V, the DRV will be pulled low and turn off the external N-MOSFET. So that the inductor will be forced to leave charging stage and enter discharging stage to prevent over current. The current limiting can be calculated by the following equation: is a registered trademark of Richtek Technology Corporation. DS8525-01 March 2012 RT8525 RS < 0.4 − DMAX × RSLP × 50μ IL, PK be under 0.25V. Then the protection function will perform action 2 to turn off the driver. When protection function is released, the RT8525 will re-start. where IL, PK is peak inductor current, and DMAX is maximum duty. On the other hand, if the triggered protection is OOVP, the voltage at node A will be decided by voltage divider composed of RFLT and the internal 8kΩ resistor. This voltage must be designed between 0.25V and 1.25V by choosing RFLT appropriately. Once the OOVP turns on the Switch 2, the divided FAULT voltage will activate action 1 to turn off the driver without resetting soft-start. Therefore, when protection function OOVP is released, the RT8525 will be in normal operation. Output Over Voltage Protection The output voltage can be clamped at the voltage level determined by the following equation : R VOUT (OOVP) = VOOVP × ⎛⎜ 1+ OVP1 ⎞⎟ , R OVP2 ⎠ ⎝ where VOOVP = 2.5V (typ.) where ROVP1 and ROVP2 are the voltage divider connected to the OOVP pin. Power MOSFET Selection Fault Protection For the applications operating at high output voltage, switching losses dominate the overall power loss. Therefore, the power N-MOSFET switch is typically chosen for drain voltage, VDS, rating and low gate charge. Consideration of switch on-resistance RDS(ON) is usually The FAULT pin will be pulled low once a protection is triggered, and a suitable pulled-high RFLT is required. The suggested RFLT is 100kΩ if the pulled-high voltage was 12V. The following figure illustrates the fault protection function block. If one of the OUVP and OTP occurs, the switch 1 will be turned on, and the voltage at node A will secondary. The VDC regulator in the RT8525 has a fixed output current limit to protect the IC and provide 12V DRV voltage for N-MOSFET switch gate driver. 12V RFLT 100k FAULT 8k OUVP, OTP Action 1 1.25V Node A - Comparator 1 + + OOVP Switch 1 Switch 2 + + 0.25V - Action 2 Comparator 2 Figure 2. Fault Protection Function Block Inductor Selection fsw is the operating frequency, The boundary value of the inductance L between Discontinuous Conduction Mode (DCM) and Continuous Conduction Mode (CCM) can be approximated by the following equation : IOUT is the sum of current from all LED strings, 2 D × (1− D ) × VOUT 2 × fSW × IOUT where L= VOUT is the maximum output voltage, VIN is the minimum input voltage, Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8525-01 March 2012 and D is the duty cycle calculated by the following equation : V − VIN D = OUT VOUT The boost converter operates in DCM over the entire input voltage range if the inductor value is less than the boundary value L. With an inductance greater than L, the converter operates in CCM at the minimum input voltage and may transit to DCM at higher voltages. The inductor must be is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT8525 selected with a saturated current rating greater than the peak current provided by the following equation : ILPK = VOUT × IOUT VIN × D × T + 2×L η × VIN ΔIL Input Current Inductor Current where η is the efficiency of the power converter. Output Current Diode Selection Time Schottky diodes are recommended for most applications because of their fast recovery time and low forward voltage. The power dissipation, reverse voltage rating and pulsating peak current are the important parameters for Schottky diode selection. Make sure that the diode's peak current rating exceeds ILPK, and reverse voltage rating exceeds the maximum output voltage. Capacitor Selection Output ripple voltage is an important index for estimating the performance. This portion consists of two parts, one is the product of input current and ESR of output capacitor, another 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 : ⎡ ⎤ V Q = 1 × ⎢⎛⎜ IIN + 1 ΔIL − IOUT ⎞⎟ + ⎛⎜ IIN − 1 ΔIL − IOUT ⎞⎟ ⎥ × IN 2 ⎣⎝ 2 2 ⎠ ⎝ ⎠ ⎦ VOUT × 1 = COUT × ΔVOUT1 fSW where fSW 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 × fSW Finally, by taking ESR into consideration, the overall output ripple voltage can be determined as the following equation : ΔVOUT = IIN × ESR + D × IOUT η × COUT × fSW Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 (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 SOP-14 packages, the thermal resistance, θJA, is 100°C/ W on a standard JEDEC 51-3 single-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) / (100°C/W) = 1.000W for SOP-14 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 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. is a registered trademark of Richtek Technology Corporation. DS8525-01 March 2012 RT8525 Maximum Power Dissipation (W)1 1.1 Layout Considerations Single-Layer PCB 1.0 PCB layout is very important for designing switching power converter circuits. The following layout guides should be strictly followed for best performance of the RT8525. 0.9 0.8 0.7 0.6 ` The power components L1, D1, CIN, COUT, M1 and RS must be placed as close as possible to reduce current loop. The PCB trace between power components must be as short and wide as possible. ` Place components RFB1, RFB2, ROVP1 and ROVP2 close to IC as possible. The trace should be kept away from the power loops and shielded with a ground trace to prevent any noise coupling. ` The compensation circuit 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 to the COMP pin as close as possible, no matter the compensation is RC, CC1 or 0.5 0.4 0.3 0.2 0.1 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 4. Derating Curve of Maximum Power Dissipation CC2. Place the power components as close as possible. The traces should be wide and short especially for the high-current loop. The compensation circuit PGND should be kept away from the power loops and should be shielded with a ground trace to prevent any noise coupling. 14 VDC 2 13 VIN 3 12 COMP 4 11 RC SS CC2 5 10 FSW CC1 9 6 AGND 7 8 PWMI VIN VIN CIN D1 L1 VOUT COUT DRV M1 PGND PGND RS EN R SLP ISW ROVP2 OOVP FB ROVP1 RFB2 AGND FAULT RFB1 AGND is suggested that connect to PGND from the sense resistor RS for better stability. VOUT The feedback voltage divider resistors must near the feedback pin. The divider center trace must be shorter and avoid the trace near any switching nodes. Figure 5. PCB Layout Guide Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8525-01 March 2012 is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT8525 Outline Dimension H A M J B F C I D Dimensions In Millimeters Dimensions In Inches Symbol Min Max Min Max A 8.534 8.738 0.336 0.344 B 3.810 3.988 0.150 0.157 C 1.346 1.753 0.053 0.069 D 0.330 0.508 0.013 0.020 F 1.194 1.346 0.047 0.053 H 0.178 0.254 0.007 0.010 I 0.102 0.254 0.004 0.010 J 5.791 6.198 0.228 0.244 M 0.406 1.270 0.016 0.050 14–Lead SOP Plastic 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. www.richtek.com 10 DS8525-01 March 2012