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Preliminary RT9287 Boost Converter for OLED Power with Dual LDO General Description The RT9287 integrates a boost converter for OLED power and a Dual LDO for camera image sensor power. To achieve high efficiency, the boost converter optimizes its operating frequency for small LC filters value and reduces the operating current. Moreover, the internal soft-start function reduces the inrush current. For the Dual LDO part, it possesses functions of 2% accuracy, dual channel, low dropout voltage (240mV@300mA), low noise, low ground current and low dropout regulator sourcing up to 300mA at each channel. For battery-powered devices, it provides near zero shutdown current. Moreover, it also integrates functions such as current limiting, over temperature, output short circuit, 27A low ground current per LDO and short circuit thermal folded back protection. When output short circuit occurs, the RT9287 reduces its over temperature protection trip point to provide maximum safety to users. The RT9287 is available in WDFN-10L 3x3 package. Features Boost Converter VIN Operating Range : 2.7V to 5.5V Maximum Output Voltage Up to 20V Output Current up to 100mA at VOUT = 12V. Low Shutdown Supply Current Minimize the External Component Small LC Filter Internal Soft Start Dual LDO Wide Operating Voltage Ranges : 2.7V to 5.5V Low-Noise for RF Application No Noise Bypass Capacitor Required Fast Response in Line/Load Transient TTL-Logic-Controlled Shutdown Input Low Temperature Coefficient Dual LDO Outputs (300mA/300mA) Ultra-low Quiescent Current 27A/LDO High Output Accuracy 2% Short Circuit Protection Thermal Shutdown Protection Current Limit Protection Short Circuit Thermal Folded Back Protection RoHS Compliant and 100% Lead (Pb)-Free Ordering Information RT9287Package Type QW : WDFN-10L 3x3 (W-Type) Operating Temperature Range P : Pb Free with Commercial Standard G : Green (Halogen Free with Commercial Standard) LDO Output Voltage : VOUT1/VOUT2 MG : 2.80V/1.80V Applications Camera Phone OLED Power Pin Configurations (TOP VIEW) VDD1 EN1 EN2 ENB FB 1 2 3 4 5 10 9 8 7 9 Note : Richtek Pb-free and Green 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. 100% matte tin (Sn) plating. GND 11 VLDO1 VLDO2 GND VDD2 LX WDFN-10L 3x3 Marking Information For marking information, contact our sales representative directly or through a Richtek distributor located in your area, otherwise visit our website for detail. DS9287-01 August 2007 www.richtek.com 1 RT9287 Typical Application Circuit Preliminary L1 4.7uH to 22uH V IN + 2.7V to 5.5V D1 SS0520 V OUT 12V R1 910k C2 1uF/16V C1 1uF 7 4 V IN 1 C IN 1uF Chip Enable 2 3 RT9287 VDD2 ENB VDD1 LX 6 FB 5 VLDO1 10 C OUT1 1uF 9 8 C OUT2 1uF R2 105k V FB = 1.235V (typ.) V OUT1 VOUT = R1 + R2 x VFB R2 VFB = 1.235 (typ.) R2 > 100k EN1 EN2 VLDO1 GND V OUT2 Functional Pin Description Pin No. 1 2 3 4 Pin Name VDD1 EN1 EN2 ENB LDO Power Input Voltage. LDO Channel 1 Enable. (Active High). LDO Channel 2 Enable. (Active High). Boost Enable (Active High). Voltage sensing input to trigger the function of over voltage protection. Note that this pin is high impedance. There should be a pull low 100k resistor connected to GND when the control signal is floating. Boost Feedback Reference Voltage Pin. Series connect a resistor between WLED and ground as a current sense. Sense the current feedback voltage to set the current rating. Boost Switch Pin. Connect this Pin to inductor and catch diode. Minimize the track area to reduce EMI. Boost Supply Input Voltage Pin. Bypass 1F capacitor to GND to reduce the input noise. GND pin should be soldered to PCB board and connected to GND. LDO Channel 2 Output Voltage. LDO Channel 1 Output Voltage. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. Pin Function 5 6 7 8 9 10 Exposed Pad (11) FB LX VDD2 GND VLDO2 VLDO1 GND www.richtek.com 2 DS9287-01 August 2007 Preliminary Function Block Diagram RT9287 1.2MHz OSC Current Bias BandGap ibias VREF OCP 750mA PWM Logic LX + ENB Timer 5ms Soft Start + - Protection Circuit VDD2 UVLO Buffer FB VREF EN1 Shutdown and Logic Control VREF - VDD1 + MOS Driver VLDO1 Current-Limit and Thermal Protection Error Amplifier EN2 Shutdown and Logic Control VREF - + MOS Driver VLDO2 Current-Limit and Thermal Protection GND Error Amplifier DS9287-01 August 2007 www.richtek.com 3 RT9287 Absolute Maximum Ratings Preliminary (Note 1) Supply Input Voltage, VDD ----------------------------------------------------------------------------------------------- -0.3V to 7V LX Input Voltage ----------------------------------------------------------------------------------------------------------- -0.3V to 22V The Other Pins ------------------------------------------------------------------------------------------------------------- -0.3V to 6V Power Dissipation, PD @ TA = 25C WDFN-10L 3x3 -----------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 4) WDFN-10L 3x3, JA -----------------------------------------------------------------------------------------------------WDFN-10L 3x3, JC -----------------------------------------------------------------------------------------------------Junction Temperature ----------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------------ESD Susceptibility (Note 2) HBM (Human Body Mode) ---------------------------------------------------------------------------------------------MM (Machine Mode) -----------------------------------------------------------------------------------------------------0.926W 108C/W 8.2C/W 150C 260C -65C to 150C 2kV 200V Recommended Operating Conditions (Note 3) Supply Input Voltage Range -------------------------------------------------------------------------------------------- 2.7V to 5.5V Junction Temperature Range -------------------------------------------------------------------------------------------- -40C to 125C Ambient Temperature Range ------------------------------------------------------------------------------------------- -40C to 85C Electrical Characteristics (VDD2 = 3.7V, VDD1 = VOUT + 1V, VEN = VIN, CIN = COUT = 1A, TA = 25C, unless otherwise specified) Parameter Boost System Supply Input Operating Voltage Range Under Voltage Lockout Quiescent Current Supply Current Shut Down Current Line Regulation Oscillator Operating Frequency Maximum Duty Cycle Reference Voltage Feedback Reference Voltage MOSFET On Resistance of MOSFET OCP Enable Voltage Low Enable Voltage High Symbol Test Condition Min Typ Max Units VDD2 VDD2 IDD2 IDD2 IDD2 VFB = 1.5V, No switch VFB = 0V, Switch VENB < 0.4V VDD2 = 3.0V to 4.3V fOSC 2.7 ------85 -2.2 300 2 -3 1.2 -1.235 0.75 750 --- 5.5 ---1 ---1.296 --0.4 -- V V A mA A % MHz % V mA V V VREF RDS(ON) 1.173 ---1.5 VEN_L VEN_H To be continued www.richtek.com 4 DS9287-01 August 2007 Preliminary Parameter Dual LDO Input Voltage Dropout Voltage (Note 5) V DD1 V DROP V LDO1, V LDO2 V V LINE V LOAD IQ ISHDN V IH V IL TSD TSD TSD f = 100Hz PSRR ILOAD = 10mA PSRR PSRR ILOAD = 150mA f = 1kHz f = 10kHz f = 100Hz f = 1kHz f = 10kHz IOUT = 1mA V DD1 = (V LDO1,2 + 0.3V) to 5.5V or V DD1 > 2.7V, whichever is larger 1mA < IOUT < 300mA RLOAD = 1 V EN1, 2 > 1.5V V EN1, 2 < 0.4V V DD = 2.7V to 5.5V, Power On V DD = 2.7V to 5.5V, Shutdown V DD = 2.7V to 5.5V IOUT = 150mA IOUT = 300mA 2.7 --1.2 -2 --330 --1.5 ------------120 240 ----450 58 ---100 165 40 40 65 60 50 65 50 50 Symbol Test Condition Min Typ RT9287 Max 5.5 --3.6 +2 0.2 0.6 700 80 1 -0.4 ----------Units V mV mV V % % % mA A A V V ppm/C C C C dB dB dB dB dB dB Output Voltage Range VLDO1,2 Accuracy Line Regulation Load Regulation Current Limit Quiescent Current Shutdown Current EN1,2 Threshold Output Voltage TC Thermal Shutdown Thermal Shutdown Hysteresis Thermal Shutdown Hysteresis Note 1. Stresses listed as the above "Absolute Maximum Ratings" may cause permanent damage to the device. These are for stress ratings. 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 for extended periods may remain possibility to affect device reliability. Note 2. Devices are ESD sensitive. Handling precaution recommended. Note 3. The device is not guaranteed to function outside its operating conditions. Note 4. JA is measured in the natural convection at T A = 25C on a low effective thermal conductivity test board of JEDEC 51-3 thermal measurement standard. The case point of JC is on the expose pad for the WDFN package. Note 5. The dropout voltage is defined as VIN -VOUT, which is measured when VOUT is VOUT(NORMAL) - 100mV. DS9287-01 August 2007 www.richtek.com 5 RT9287 Preliminary Typical Operating Characteristics Boost Efficiency vs. Input Voltage 88 86 Boost Efficiency vs. Load Current 86 VOUT = 12V 84 Efficiency (%) 82 80 78 76 VOUT = 15V Efficiency (%) 84 82 80 78 76 ILOAD = 20mA 3 3.2 3.4 3.6 3.8 4 4.2 4.4 74 5 VIN = 3.7V, VOUT = 15V 10 15 20 25 30 35 40 Input Voltage (V) Load Current (mA) Boost Feedback Voltage vs. Input Voltage 1.2400 Boost Feedback Voltage vs. Load Current 1.243 1.242 Feedback Voltage (V) Feedback Voltage (V) VOUT = 15V, ILOAD = 20mA 1.2395 1.241 1.240 1.239 1.238 1.237 1.2390 1.2385 1.2380 VIN = 3.7V, VOUT = 15V 1.236 3.8 4 4.2 4.4 1.2375 3 3.2 3.4 3.6 0 10 20 30 40 50 Input Voltage (V) Load Current (mA) Boost Feedback Voltage vs.Temperature 1.2390 1.2385 Boost Normal Operation VIN (100mV/Div) VOUT (100mV/Div) ILX (200mA/Div) VLX (10V/Div) Feedback Voltage (V) 1.2380 1.2375 1.2370 1.2365 1.2360 VIN = 3.7V, ILOAD = 20mA 1.2355 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 VIN = 3V, VOUT = 15V, ILOAD = 20mA Time (500ns/Div) Temperature (C) www.richtek.com 6 DS9287-01 August 2007 Preliminary RT9287 Boost Normal Operation Boost Normal Operation VIN (100mV/Div) VOUT (100mV/Div) ILX (200mA/Div) VLX (10V/Div) VIN = 3.7V, VOUT = 15V, ILOAD = 20mA VIN (100mV/Div) VOUT (100mV/Div) ILX (200mA/Div) VLX (10V/Div) VIN = 4.5V, VOUT = 15V, ILOAD = 20mA Time (500ns/Div) Time (500ns/Div) LDO 1 Output Voltage vs. Temperature 2.90 2.88 1.90 1.88 LDO 2 Output Voltage vs. Temperature Output Voltage (V) 2.83 2.80 2.78 2.75 2.73 2.70 Output Voltage (V) 2.85 1.85 1.83 1.80 1.78 1.75 1.73 VIN = VEN1 = 4.3V -50 -25 0 25 50 75 100 125 VIN = VEN2 = 4.3V 1.70 -50 -25 0 25 50 75 100 125 Temperature (C) Temperature (C) LDO Quiescent Current vs. Temperature 70 350 300 LDO Dropout Voltage vs. Load Current Quiescent Current (uA) Dropout Voltage (mV) 66 85C 25C -40C 250 200 150 100 50 62 58 54 50 VIN = VEN1 = VEN2 = 4.3V -50 -25 0 25 50 75 100 125 0 0 50 100 150 200 250 300 Temperature (C) Load Current (mA) DS9287-01 August 2007 www.richtek.com 7 RT9287 LDO PSRR 0 -10 -20 -30 Preliminary LDO Line Transient Response VIN 4.8 (V) PSRR (dB) -40 -50 -60 -70 -80 -90 -100 10 0.01 100 0.1 ILOAD = 10mA ILOAD = 100mA 3.8 ILOAD = 0mA VOUT1 (20mV/Div) VOUT2 (20mV/Div) Both ILOAD = 1mA, VIN = 3.8V to 4.8V 1000 1 10000 10 100000 100 1000000 1000 Time (250s/Div) Frequency (kHz) Frequency (Hz) LDO Line Transient Response VIN 4.8 (V) 3.8 LDO Load Transient Response IOUT (100mA/Div) VOUT1 (20mV/Div) VOUT2 (20mV/Div) Both ILOAD = 10mA, VIN = 3.8V to 4.8V ILOAD = 10mA to 100mA, VIN = VEN = 4.3V VOUT1 (20mV/Div) VOUT2 (20mV/Div) Time (250s/Div) Time (250s/Div) LDO Load Transient Response LDO Power On from EN IOUT (200mA/Div) VOUT1 (100mV/Div) VOUT2 (100mV/Div) ILOAD = 10mA to 350mA, VIN = VEN = 4.3V VEN (2V/Div) VOUT1 (2V/Div) VOUT2 (2V/Div) Both ILOAD = 100mA, VIN = 5V Time (250s/Div) Time (10s/Div) www.richtek.com 8 DS9287-01 August 2007 Preliminary RT9287 Cross Talk LDO Power Off from EN VEN (2V/Div) VOUT1 (2V/Div) VOUT2 (2V/Div) Both ILOAD = 100mA, VIN = 5V I Boost (10mA/Div) VOUT1 (50mV/Div) VOUT2 (50mV/Div) VIN = VEN = 4.3V Time (250s/Div) Time (10s/Div) DS9287-01 August 2007 www.richtek.com 9 RT9287 Application Information Boost Converter Power Sequence Preliminary phone. The inductor should have low core loss at 1MHz and low DCR for better efficiency. The inductor saturation current rating should be considered to cover the inductor peak current. Capacitor Selection Input and output ceramic capacitors of 1F are recommended for boost regulator. For better voltage filtering, ceramic capacitors with low ESR are recommended. X5R and X7R types are suitable because they have better temperature characteristics. Diode Selection The RT9287 must take notice of the power sequence. The power sequence of RT9287 has to VDD2 early than ENB or else the RT9287 maybe fall into the unknown state to result in RT9287 turn off. VDD2 > 2.7V VDD2 ENB > 1.5V ENB ENB < 0.4V VOUT Figure 1 LED Current Control As shown in Figure 2, the RT9287 regulates the LED current by setting the current sense resistor (R SET) connected between FB pin and ground. The reference voltage of FB pin is 1.235V in typical. The LED current (ILED) can be calculated by the following Equation. ILED = VREF / RSET (1) Schottky diode is suitable for RT9287 because of its low forward voltage and fast reverse recovery. Using Schottky diode can get better efficiency. The high speed rectification is also a good characteristic of Schottky diode for high switching frequency. Current rating of the diode must meet the root mean square of the peak current and output average current multiplication as following : ID (RMS) IOUT x IPEAK The reverse breakdown voltage of the diode should be higher than the output voltage. Output Voltage Control For fixed output voltage application, the output voltage can be adjusted by the divider circuit on FB pin. Figure 3 shows a 2-level voltage control circuit for OLED application. The output voltage can be calculated by the following equations. Table 1 is the recommended resistance for different conditions. VOUT = RA x {(FB/RB) + (FB-GPIO)/RGPIO} + FB (3) In order to have an accurate LED current, a precision resistor is preferred (1% is recommended). L1 4.7uH to 22uH + VIN 2.7V to 5.5V C1 1uF RT9287 7 VDD2 LX 6 FB 5 RSET D1 SS0520 C2 1uF/16V ILED VENB>1.5V 4 ENB VENB<0.4V 8 GND As GPIO = 0V, VOUT = RA x {(1.235/RB) + (1.235/RGPIO)} + 1.235 (4) Figure 2. Application for Driving 3 Series WLEDs Inductor Selection The recommended value of the inductor is from 10H to 22H for 4 to 5 WLEDs applications. For 3WLEDs, the recommended value of the inductor is from 4.7H to 22H. Small size and better efficiency are the major concerns for portable devices, just as RT9287's application for mobile www.richtek.com 10 As GPIO = 2.8V, VOUT = RA x {(1.235/RB) + (1.235-2.8)/RGPIO} + 1.235 (5) As GPIO = 1.8V, VOUT = RA x {(1.235/RB) + (1.235-1.8)/RGPIO} + 1.235 (6) For Efficiency Consideration set RA = 990k. DS9287-01 August 2007 Preliminary Table 1. Suggested Resistance for Output Voltage Control RB RGPIO RA Conditions (k) (k) (k) Case A : Normal Voltage = 16V 990 102 445 (GPIO = 0V) Dimming Voltage = 12V (GPIO = 1.8V) Case B : Normal Voltage = 16V 990 94 690 (GPIO = 0V) Dimming Voltage = 12V (GPIO = 2.8V) L1 4.7uH to 22uH + VIN 2.7V to 5.5V C1 1uF RT9287 7 VDD2 LX 6 FB 5 C2 RA RGPIO OLED D1 SS0520 VOUT RT9287 capacitor values. Output capacitor of larger capacitance can reduce noise and improve load transient response, stability, and PSRR. The output capacitor should be located not more than 0.5 inch from the VOUT pin of the LDO and returned to a clean analog ground. Region of Stable COUT ESR vs. Load Current 100 Region of Stable OUT ESR () Region of Stable CCOUT ESR () VIN = 5V, CIN = COUT1 = COUT2 = 1uF/X7R 10 Unstable Range 1 0.1 Stable Range 0.01 GPIO Simulation Verify 0.001 0 50 100 150 200 250 300 Load Current (mA) VENB>1.5V 4 ENB VENB<0.4V 8 GND Figure 4. Stable Cout ESR Range Thermal protection limits power dissipation in LDO. When the operating junction temperature exceeds a certain temperature, the OTP circuit starts the thermal shutdown function and turns the pass element off. The pass element turns on again after the junction temperature is cooled down. The RT9287 lowers its OTP trip level from 170C to 110C when output short circuit occurs (VOUT < 0.4V) as shown in Figure 5. It reduces operating junction temperature and provides maximum safety to customer while output short circuit occurring. VOUT Short to GND RB Figure 3. Application Circuit for 2-level Output Voltage Control Dual LDO Like any low-dropout regulator, the external capacitors used with the RT9287 must be carefully selected for regulator stability and performance. Using a capacitor whose value is > 1F on the LDO input and the amount of capacitance can be increased without limit. The input capacitor must be located a distance of not more than 0.5 inch from the input pin of the IC and returned to a clean analog ground. Any high quality ceramic or tantalum capacitor can be used for this part. The capacitor with larger value and lower ESR (equivalent series resistance) provides better PSRR and line-transient response. The output capacitor must meet both requirements for minimum amount of capacitance and ESR in all applications. The LDO is designed specifically to work with low ESR ceramic output capacitor in space-saving and performance consideration. Using a ceramic capacitor whose value is at least 1F with ESR is > 20m on the LDO output ensures stability. The LDO still works well with other kinds of output capacitor due to the wide stable ESR range. Figure 4 shows the curves of allowable ESR range as a function of load current for various output DS9287-01 August 2007 0.4V VOUT IOUT TSD 170 C 110 C OTP Trip Point 110 C IC Temperature 80 C Figure 5. Short Circuit Thermal Folded Back Protection when Output Short Circuit Occurs (Patent) www.richtek.com 11 RT9287 Thermal Considerations Preliminary Layout Guide The exposed pad and GND should be connected to a strong ground plane for heat sinking and noise prevention. Traces should be kept as short as possible. LX node copper area should be minimized for reducing EMI. The Dual LDO input capacitor C1 must be located a distance of not more than 0.5 inch from the VDD1 pin and returned to ground plane. The Boost input capacitor C2 should be placed as closed as possible to Pin 7. The Dual LDO output capacitor C3 and C4 must be located a distance of not more than 0.5 inch from the VLDO1 and VLDO2 pin and returned to ground plane. FB node copper area should be minimized and kept far away from noise sources (LX). Feedback resistance R2 should be placed as closed as possible to Pin 5. The input capacitors C1 and C2 must be located a distance of not more than 0.5 inch from the VDD1 and VDD2 Pin. C1 The output capacitors C3 and C4 should be located not more than 0.5 inch from the VOUT pin of the LDO . C3 The maximum power dissipation depends on the thermal resistance of IC package, PCB layout, the rate of surroundings airflow and temperature difference between junctions to ambient. The maximum power dissipation can be calculated by following formula : PD(MAX) = ( TJ(MAX) - TA ) / JA Where T J(MAX) is the maximum operation junction temperature, TA is the ambient temperature and the JA is the junction to ambient thermal resistance. For recommended operating conditions specification of the RT9287, where TJ(MAX) is the maximum junction temperature of the die and TA is the maximum ambient temperature. The junction to ambient thermal resistance JA is layout dependent. For WDFN-10L 3x3 packages, the thermal resistance JA is 60C/W on the standard JEDEC 51-7 four-layers thermal test board. The maximum power dissipation at TA = 25C can be calculated by following formula : PD(MAX) = ( 125C - 25C) / (60C/W) = 1.667W for WDFN-10L 3x3 packages The maximum power dissipation depends on operating ambient temperature for fixed TJ(MAX) and thermal resistance JJ(MAX). For RT9287 packages, the Figure 6 of derating curves allows the designer to see the effect of rising ambient temperature on the maximum power allowed. 1.8 VDD1 EN1 EN2 ENB R1 FB R2 1 2 3 4 5 10 9 VLDO1 VLDO2 GND VDD2 LX D1 VOUT C2 L1 C4 GND 8 7 9 Maximum Power Dissipation (W) 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0 25 50 75 100 125 Ground Plane FB node copper area should be minimized and keep far away from noise sources (LX). R1 and R2 should be placed as close as RT9287. C5 The exposed pad and GND should be connected to a strong ground plane for heat sinking and noise prevention. Figure 7 Ambient Temperature (C) Figure 6. Derating Curves for RT9287 Packages www.richtek.com 12 DS9287-01 August 2007 Preliminary Outline Dimension D2 RT9287 D L E E2 SEE DETAIL A 1 e A A1 A3 b 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 A A1 A3 b D D2 E E2 e L Dimensions In Millimeters Min 0.700 0.000 0.175 0.180 2.950 2.300 2.950 1.500 0.500 0.350 0.450 Max 0.800 0.050 0.250 0.300 3.050 2.650 3.050 1.750 Dimensions In Inches Min 0.028 0.000 0.007 0.007 0.116 0.091 0.116 0.059 0.020 0.014 0.018 Max 0.031 0.002 0.010 0.012 0.120 0.104 0.120 0.069 W-Type 10L DFN 3x3 Package Richtek Technology Corporation Headquarter 5F, No. 20, Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611 Richtek Technology Corporation Taipei Office (Marketing) 8F, No. 137, Lane 235, Paochiao Road, Hsintien City Taipei County, Taiwan, R.O.C. Tel: (8862)89191466 Fax: (8862)89191465 Email: marketing@richtek.com DS9287-01 August 2007 www.richtek.com 13 |
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