® RT8525D Current Mode Boost Controller General Description Features The RT8525D 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 RT8525D input operating range is from 4.5V to 25V. z The RT8525D is an optimized design for wide output voltage range applications. The output voltage of the RT8525D can be adjusted by the FB pin. Ordering Information Programmable Soft-Start Time z Programmable Boost SW Frequency from 50kHz to 600kHz z Output Over Voltage Protection z Output Under Voltage Protection z 12-Lead WDFN Package z RoHS Compliant and Halogen Free z Applications Package Type QW : WDFN-12L 3x3 (W-Type) Lead Plating System G : Green (Halogen Free and Pb Free) Note : Richtek products are : RoHS compliant and compatible with the current require- z z z z LCD TV, Monitor Display Backlight LED Driver Application High Current High Output Voltage DC/DC Converters High Input Voltage DC/DC Converters Pin Configurations (TOP VIEW) ments of IPC/JEDEC J-STD-020. ` VDC VIN COMP SS FSW FAULT Suitable for use in SnPb or Pb-free soldering processes. Marking Information 0F= : Product Code 0F=YM DNN YMDNN : Date Code 1 2 3 4 5 6 GND RT8525D ` VIN Range : 4.5V to 25V 13 12 11 10 9 8 7 EN DRV GND ISW OVP FB WDFN-12L 3x3 Simplified Application Circuit L1 VIN CIN VDC ISW CDC M1 RSLP GND CC2 RFB1 FSW CC1 SS RSW CSS Chip Enable FB FAULT RFLT ROVP1 12V RFB2 OVP EN Copyright © 2012 Richtek Technology Corporation. All rights reserved. June 2012 VOUT RS COMP DS8525D-00 COUT RT8525D VIN DRV CVIN RC D1 COVP ROVP2 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT8525D 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 Frequency Adjust Pin. This pin allows setting the switching frequency with a resistor from 50kHz to 600kHz. 6 FAULT Open Drain Output for Fault Detection. 7 FB Feedback to Error Amplifier Input. 8 OVP Sense Output Voltage for Over Voltage Protection and Under Voltage Protection. 9 ISW External MOSFET Switch Current Sense Pin. Connect the current sense resistor between the external N-MOSFET switch and ground. 10, GND 13 (Exposed Pad) Ground of Boost Controller. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. 11 DRV Drive Output for the N-MOSFET. 12 EN Chip Enable (Active High). Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS8525D-00 June 2012 RT8525D Function Block Diagram FSW VIN VDC UVLO + OTP OVP/OUVP Logic 12V LDO FAULT Protection OSC + OC - EN S Q R Q + - DRV Blanking + - PWM Controller 2.5V 0.4V VOS GND OVP + - FAULT 0.1V - + EA - 4µA ISW 1.25V FB COMP SS Operation The RT8525D is a wide input operating voltage range and current mode step up controller. High voltage output and large output current are feasible by using an external NMOSFET. The error amplifier EA adjusts COMP voltage by comparing the feedback signal from the output voltage with the internal 1.25V reference. Blanking N-MOSFET current is measured by external RS. The slope compensator works together with sensing voltage of RSENSE to the ISW pin. There is need blanking time to avoid noise and parasitism effect. Fault Protection The protection functions include output over voltage, output under voltage, over temperature protection. The FAULT pin will be pulled low once a protection is triggered, and a suitable pulled-high RFLT is required. The detail description can refer to the Figure 2. Fault Protection Function Block. Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8525D-00 June 2012 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT8525D 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, OVP, ISW to GND ---------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C WDFN-12L 3x3 -------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) WDFN-12L 3x3, θJA -------------------------------------------------------------------------------------------------------WDFN-12L 3x3, 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 26.4V −0.3V to 13.2V −0.3V to 6V 1.667W 60°C/W 8.2°C/W 260°C 150°C −65°C to 150°C 2kV 200V (Note 4) Supply Input Voltage, VIN ------------------------------------------------------------------------------------------------ 4.5V to 25V Junction Temperature Range --------------------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range --------------------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VIN = 21V, CIN = 10μF, 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 ISHDN VEN = 0V -- 10 -- μA VUVLO VIN Rising -- 3.8 -- V -- 500 -- mV 11.4 12 12.6 V -- 500 -- mV -- 270 -- mA ΔVUVLO 13.5V < VIN < 16V, 1mA < ILOAD < 100mA Regulator Output Voltage VDC 16V < VIN < 20V, 1mA < ILOAD < 50mA 20V < VIN < 25V, 1mA < ILOAD < 20mA Dropout Voltage VDROP Short-Circuit Current Limit ISC VIN − VDC, VIN = 12V, ILOAD = 100mA VDC Short to GND Control Input EN Threshold Logic-High Voltage Logic-Low VIH 2 -- -- VIL -- -- 0.8 EN Sink Current IIH -- 5 -- VEN = 5V Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 V μA is a registered trademark of Richtek Technology Corporation. DS8525D-00 June 2012 RT8525D Parameter Shutdown Delay Symbol Test Conditions Min Typ Max Unit tSLEEP RSW = 56kΩ, EN = L, 12V Regular Shutdown 55 -- -- ms Shutdown Mode tSHDN RSW = 56kΩ, EN = L, IC Shutdown 110 -- -- ms -- 200 -- kHz -- 250 -- ns 90 -- -- % Sleeping Mode Boost Controller Switching Frequency fSW RSW = 56kΩ Minimum On-Time tMON Maximum Duty DMAX Feedback Voltage VFB -- 1.25 -- V ISLOPE, PK -- 50 -- μA ISS 3 4 5 μA Switching Slope Compensation Peak Magnitude of Slope Compensation Current Soft-Start Soft-Start Current Gate Driver RDS(ON)_N ISINK = 100mA (N-MOSFET) -- 1 -- Ω RDS(ON)_P ISOURCE = 100mA (P-MOSFET) -- 1.5 -- Ω Peak Sink Current IPEAKsk CLOAD = 1nF -- 2.2 -- A Peak Source Current IPEAKsr CLOAD = 1nF -- 2.55 -- A Rise Time tr CLOAD = 1nF -- 6 -- ns Fall Time tf CLOAD = 1nF -- 5 -- ns OCP Threshold VOCP Including Slope Compensation Magnitude -- 0.4 -- V VOUT OVP Threshold VOVP -- 2.5 -- V VOUT UVP Threshold Thermal Shutdown Temperature Thermal Shutdown Hysteresis VUVP -- 0.1 -- V TSD -- 150 -- °C ΔTSD -- 50 -- °C DRV On-Resistance Protection Function 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 © 2012 Richtek Technology Corporation. All rights reserved. DS8525D-00 June 2012 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT8525D Typical Application Circuit VIN 5V L1 10µH CIN 22µF 2 CVIN 1µF 1 RT8525D 11 DRV VIN VDC ISW CDC 3 COMP RC 5.6k CC1 27nF GND CC2 RSW 56k FAULT 12 EN Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 9 M1 RSLP 2.4k 10, 13 (Exposed Pad) OVP RFLT 6 100k VOUT 12V COUT 22µF x 2 RS 50m RFB1 43k FB 7 5 FSW 4 SS CSS 0.33µF Chip Enable D1 ROVP1 62k 12V RFB2 3k 8 COVP ROVP2 6k is a registered trademark of Richtek Technology Corporation. DS8525D-00 June 2012 RT8525D Typical Application Circuit 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) Boost Efficiency vs. Load Current Switching Frequency vs. Temperature 300 100 260 90 Efficiency (%) Switching Frequency (kHz)1 25 220 180 80 70 60 140 RSW = 56kΩ VIN = 5V, VOUT = 12V, RSW = 56kΩ 50 100 -50 -25 0 25 50 75 100 Temperature (°C) Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8525D-00 June 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 7 RT8525D Applications Information The RT8525D 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 RT8525D 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 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 Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 transient response. Select CC1 and CC2 to set the zero and pole to maintain loop stability. A typical compensation for the RT8525D is choosing 3kΩ for RC and 27nF for CC1. Soft-Start The soft-start of the RT8525D can be achieved by connecting a capacitor from the SS pin to GND. The builtin 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 soft-start 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, 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. DS8525D-00 June 2012 RT8525D 0.4 − DMAX × RSLP × 50μ IL, PK where IL, PK is peak inductor current, and DMAX is maximum duty. RS < Output Over Voltage Protection The output voltage can be clamped at the voltage level determined by the following equation : R VOUT (OVP) = VOVP × ⎛⎜ 1+ OVP1 ⎞⎟ , ⎝ ROVP2 ⎠ where VOVP = 2.5V (typ.) where ROVP1 and ROVP2 are the voltage divider connected to the OVP pin. Fault Protection 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 be under 0.25V. Then the protection function will perform 12V action 2 to turn off the driver. When protection function is released, the RT8525D will re-start. On the other hand, if the triggered protection is OVP, 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 OVP 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 OVP is released, the RT8525D will be in normal operation. Power MOSFET Selection 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 secondary. The VDC regulator in the RT8525D has a fixed output current limit to protect the IC and provide 12V DRV voltage for N-MOSFET switch gate driver. RFLT 100k FAULT 8k OUVP, OTP + OVP + Action 1 1.25V Node A - Comparator 1 + + Switch 1 Switch 2 0.25V - Action 2 Comparator 2 Figure 2. Fault Protection Function Block Inductor Selection The boundary value of the inductance L between Discontinuous Conduction Mode (DCM) and Continuous Conduction Mode (CCM) can be approximated by the following equation : 2 D × (1− D ) × VOUT L= 2 × fSW × IOUT where VOUT is the maximum output voltage, VIN is the minimum input voltage, fsw is the operating frequency, IOUT is the sum of current from all LED strings, Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8525D-00 June 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 selected with a saturated current rating greater than the peak current provided by the following equation : V ×I ILPK = OUT OUT + VIN × D × T 2×L η × VIN where η is the efficiency of the power converter. is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT8525D Diode Selection 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. ΔIL Input Current Output Current Time (1-D)TS 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 : D × IOUT ΔVOUT1 = η × COUT × fSW Finally, by taking ESR into consideration, the overall output ripple voltage can be determined as the following equation : D × IOUT ΔVOUT = IIN × ESR + η × COUT × fSW Inductor Current 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-12L 3x3 package, the thermal resistance, θJA, is 60°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) / (60°C/W) = 1.667W for WDFN-12L 3x3 package The maximum power dissipation depends on the operating ambient temperature for fixed T J(MAX) and thermal Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 is a registered trademark of Richtek Technology Corporation. DS8525D-00 June 2012 RT8525D resistance, θJA. The derating curve in Figure 4 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. Maximum Power Dissipation (W)1 1.80 Layout Considerations PCB layout is very important for designing switching power converter circuits. The following layout guides should be strictly followed for best performance of the RT8525D. Four-Layer PCB 1.65 ` 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 R FB1 and R FB2 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 1.50 1.35 1.20 1.05 0.90 0.75 0.60 0.45 0.30 0.15 0.00 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. CC2 VDC VIN COMP SS RC FSW CC1 FAULT 1 2 3 4 5 6 VIN GND CIN GND The compensation circuit should be kept away from the power loops and should be shielded with a ground trace to prevent any noise coupling. 13 12 11 10 9 8 7 EN DRV GND ISW OVP FB VIN RSLP VOUT D1 L1 M1 RS COUT GND RFB2 RFB1 GND 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. DS8525D-00 June 2012 is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT8525D Outline Dimension 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 0.150 0.250 0.006 0.010 D 2.950 3.050 0.116 0.120 D2 2.300 2.650 0.091 0.104 E 2.950 3.050 0.116 0.120 E2 1.400 1.750 0.055 0.069 e L 0.450 0.350 0.018 0.450 0.014 0.018 W-Type 12L DFN 3x3 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 12 DS8525D-00 June 2012