TFT- LCD DC-DC Converters with Operational Amplifiers EC9219 General Description The EC9219 include a high-performance step-up regulator, and high-current operational amplifiers for active-matrix thin-film transistor (TFT) liquid-crystal displays (LCDs). The step-up DC-DC converter provides the regulated supply voltage for the panel source driver ICs. The converter is a high-frequency (1.2MHz or 640KHZ) current-mode regulator with an integrated 18V n-channel MOSFET that allows the use of ultra-small inductors and ceramic capacitors. It provides fast transient response to pulsed loads while achieving efficiencies over 85%. The EC9219 includes one operational amplifier. These amplifiers are designed to drive the LCD backplane (VCOM) and/or the gamma-correction divider string. The devices feature high output current (±150mA), fast slew rate (17V/μs), wide bandwidth (12MHz), and rail-to-rail inputs and outputs The EC9219 are available in 14- pin thin TSOP packages with a maximum thickness of 1mm for ultra-thin LCD panels. Features Applications 2.6V to 5.5V Input Supply Range z z 1.2MHz or 640KHZ Current-Mode Step-Up Regulator z z Fast Transient Response to Pulsed Load z High-Accuracy Output Voltage ( 2% ) z Built-In 18V, 1.6A, 0.16Ω N-Channel MOSFET z High Efficiency (90%) z High-Performance Operational Amplifiers z 17V/μs Slew Rate z 12MHz, -3dB Bandwidth z Rail-to-Rail Inputs/Outputs z Thermal-Overload Protection z z Notebook Computer Displays , LCD Monitor Panels , Automotive Displays Ordering information PART NO MARKING PACKAGE EC9219I-G EC9219-G TSSOP14 Green Package EC9219G-G EC9219G TQFN16 Green Package P 1 / 14 2009/09/29 TFT- LCD DC-DC Converters with Operational Amplifiers EC9219 NAME Function OUT Operational-Amplifier Output IN + Operational-Amplifier Non-inverting Input SGND Analog ground. Comp Compensation pin. Output of the internal error amplifier. Capacitor and resistor from COMP pin to ground. Voltage feedback pin. Internal reference is 1.228V nominal. Connect a resistor divider from VOUT. VOUT =1.228V (1 + R3 / R8). See Typical FB Application Circuit. /SD Shutdown control pin. Pull SHDN low to turn off the device, and Soft-start Internal reference voltage control pin, Connect RC Delay circuit. PGND Power ground. LX Switch Pin. Connect the inductor/catch diode to LX and minimize the trace area for lowest EMI. Vin Analog power supply input pin. Freq Frequency Select Input. When FREQ is low, the oscillator frequency is set to 640kHz. When FREQ is high the frequency is 1.2MHz. SS Soft-start control pin. Connect a capacitor to control the converter start-up. Operational-Amplifier Power Input. Positive supply rail for the operational amplifiers. SUP Typically connected to DC-DC converter Output. Bypass SUP to SGND with a 0.1µF capacitor. NC IN - Operational-Amplifier Inverting Input P 2 / 14 2009/09/29 TFT- LCD DC-DC Converters with Operational Amplifiers EC9219 Absolute Maximum rating ( TA = 25℃ ) VIN to SGND......................................................-0.3V to +6V Comp, FB, SD , Freq to SGND ........................-0.3V to +6V PGND to SGND .......................................................... ±0.3V LX to PGND ....................................................-0.3V to +18V SUP,IN+,IN- to SGND .....................................-0.3V to +18V Out Maximum Continuous Output Current ...... ±150mA RMS LX Pin Current......................................................1.6A Operating Ambient Temperature ......... -40℃ to +85℃ Operating Junction Temperature........................ +125℃ Storage temperature ......................... -65℃ to +150℃ Lead Temperature ............................................+260℃ Stresses beyond those listed under “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 for extended periods may affect device reliability. Electrical Specifications VIN = 3V, VSUP = 10V ,FSEL = GND, TA =25℃ unless otherwise specified PARAMETER VIN Supply Range VIN Under voltage-Lockout Threshold SYMBOL VIN VUVLO Quiescent Current IIN Shutdown Supply Current IIN Input Low Level Input High Level VIL CONDITIONS MIN 2.6 TYP MAX 5.5 UNIT V 2.25 2.38 2.52 V SD = VIN,VFB=1.3, not switching 0.4 1 mA SD = VIN,VFB=COMP, switching 4 0.1 5 1 mA uA 0.3VIN V VIN rising ,typical hysteresis = 40mV SD = SGND include OP. SD , Freq ;VIN=３V to 5.5V VIH SD , Freq ;VIN=３V to 5.5V Hysteresis 0.7VIN SD , Freq ;VIN=３V to 5.5V Freq =VIN SD =VIN Temperature rising Freq Input Current SD Input Current Thermal Shutdown Hysteresis V 0.1VIN V 1 1 nA nA 130 30 °C °C Main STEP-UP REGULATOR Output Voltage Range Frequency Vmain fosc Maximum Duty Cycle D FB Regulation Voltage FB Line Regulation FB Input Bias Current Voltage Gain Swicth On-Resistance LX Leakage Current LX Current Limit Current-Sense Tran conductance VFB VIN 500 1000 85 85 1.222 Freq=GND Freq= VIN, Freq=GND Freq= VIN, load=50mA VIN=2.6V to 5.5V VFB=1.4 Av Rds(on) ILX FB to Comp VLX=18V Rcs 640 1200 90 90 1.24 18 750 1500 95 95 1.258 0.5 1 1000 160 1.8 2 250 0.047 V kHz kHz % % V % nA V/V mΩ uA A V/A OPEATIONAL AMPLIFERS SUP Supply Range SUP Supply Current Input Offset Voltage Input Bias Current Input Common-Mode Range Common-Mode Rejection Ratio Open-Loop Gain Output Voltage Swing ,High Output Voltage Swing ,Low Power-Supply Rejection Ratio Vsup Isup VOS IBIAS VCM CMRR AV VOH VOL PSRR 4.5 Buffer configuration ,no load OUT=4V,Vsup=8V OUT= Vsup/2 OUT= Vsup/2 0 50 75 Vsup-150 IOUT=5mA IOUT=-5mA 60 P 3 / 14 18 V 2.8 4 mA 2 20 50 Vsup mV nA V dB dB mV mV dB 70 100 Vsup-80 70 70 150 2009/09/29 TFT- LCD DC-DC Converters with Operational Amplifiers EC9219 PARAMETER Slew Rate SYMBOL SR -3dB Bandwidth Gain-Bandwidth Product GBP CONDITIONS Vin=4V,VIN+=6V,RL=2kΩ,CL=100 pF ,buffer configuration RL=2kΩ,CL=100 pF ,buffer configuration RL=2kΩ,CL=100pF buffer configuration MIN TYP MAX 10 17 V/µs 12 MHz 8 MHz Block Diagram EC9219 Figure 1 P 4 / 14 2009/09/29 UNIT TFT- LCD DC-DC Converters with Operational Amplifiers EC9219 Typical Application Circuit Q1 2N3906 D1 3 3 1 1 R1 2 0.1uF J1 1 VGFF= -6V/20mA 2 C1 1K C2 C3 0.1uF BAT54S 0.22uF D2 6.8V D3 Q2 2N3904 2 C4 3 J2 1 1 1 R2 2 3 0.1uF VGON= +18V/20mA 270 BAT54S C5 C6 0.1uF 0.22uF D4 18.8V VIN VDD=9.6V ±0.2VVDD 2 FM220 R3 87.6K_1% U1 LX VIN C14 0.1UF R7 NC R10 0 J5 1 CON1 J7 C15 47nF 8 9 FSLC 10 SS 11 VDD 12 13 14 LX GND IN /SHDN FREQ SS OPVCC OPVSUP INEC9219 J6 1 FB COMP OPGND IN+ OPOUT R4 NC 7 6 /SHDN 5 FB 4 COMP R6 0 R5 10.5K_1% 1 3 C17 0.1uF C10 C11 C12 C13 1 J4 CON1 VIN 3 2 C9 10uF/16V/1206 10UH D5 10uF/16V/1206 1 10uF/16V/1206 C8 LX 10uF/16V/1206 C7 10uF/10V/1206 10uF/10V/1206 CON1 L1 VIN 1 R13 12K_1% R11 1 R12 13K_1% 2 J3 VDD R9 20K C16 R8 13K_1% 10pF C18 6.8nF VCOM CON1 1 CON1 Figure 2 P 5 / 14 2009/09/29 TFT- LCD DC-DC Converters with Operational Amplifiers EC9219 Typical operating Characteristics Typical Application Circuit, Vin=3.3V, VMAIN=9.6 ,VGON=18V , VGOFF=-6V , OUT=6V , Freq=Vin TA=25℃ unless otherwise noted.) No-Load Supply Current vs. Input Voltage Freq=640kHz No-Load Supply Current vs. Input Voltage Freq=1.2MHz 0.8 0.8 0.7 0.6 No-Load Supply Current(mA) No-Load Supply Current(mA) 0.7 0.5 0.4 0.3 0.2 0.1 0.6 0.5 0.4 0.3 0.2 0.1 0 0 2.5 3 3.5 4 4.5 5 5.5 2.5 3 3.5 Input Voltage(V) 4 4.5 5 5.5 Input Voltage Output Voltage vs. Output Curren Efficiency vs. Output Current 10.1 95.00% 90.00% 10.05 85.00% Efficiency (%) Output Voltage(V) 10 9.95 80.00% 75.00% 3.3V 70.00% 5V 65.00% 9.9 60.00% 55.00% 9.85 50.00% 1 9.8 0 50 100 150 200 250 300 Output Current(mA) Vout=10V,Vin=3.3V,L=10uH, Freq=640KHz 10 100 1000 Output Current (mA) Vout=9.6V,L=10uH,Freq=640kHz FB Voltage vs. Temperature 1.257 FB Voltage(V) 1.252 1.247 1.242 1.237 1.232 1.227 1.222 -40 -20 0 20 40 60 80 100 120 140 Temperature(℃) P 6 / 14 2009/09/29 TFT- LCD DC-DC Converters with Operational Amplifiers EC9219 Start-up Waveform with Soft-start Start-up Waveform with Soft-start CH1: Vin CH1:Vin CH2:Output Voltage CH2:Output Voltage CH3:Inductor Current CH3:Inductor Current Vin=3.3V,Iout=10mA,Freq=640KHz, Vin=3.3V,Iout=200mA,Freq=640KHz, Vout=10.6V,Cout=30uF Start-up Waveform with Soft-start Vout=10.6V,Cout=30uF Start-up Waveform with Soft-start CH4: SHDN CH1:SHDN CH2:Output Voltage CH2:Output Voltage CH3:Inductor Current CH3:Inductor Current Vin=3.3V,Iout=10mA,Freq=640KHz, Vin=3.3V,Iout=200mA,Freq=640KHz, Vout=9.6V,Cout=30uF Vout=9.6V,Cout=30uF P 7 / 14 2009/09/29 TFT- LCD DC-DC Converters with Operational Amplifiers EC9219 Load-Transient Response SWITCHING WAVEFORM CH2: Output Voltage,AC-Coupled CH1:Output Voltage,AC-Coupled CH3:Load Current Ch3:Inductor Current Vin=3.3V,Vout=10V,Freq=640KHz Ch2:LX Switching Waveform Figure 7. Start-up Waveform with Soft-start Vin=3.3V,Vout=10V,Iout=200mA,Freq=640KHz,L=10uH Operational-Amplifier RAIL-TO-RAIL INPUT/OUTPU Operational-Amplifier Large-Signal Step Response CH1: Input signal CH1: Input signal CH2:Output signal CH2:Output signal VSUP:12V,RL:2K,CL:100P VSUP:12V,RL:2K,CL:100P P 8 / 14 2009/09/29 TFT- LCD DC-DC Converters with Operational Amplifiers EC9219 Typical Operating Circuit The EC9219 Typical Operating Circuit (Figure 2) is a complete power-supply system for TFT LCDs. The circuit generates a +9.6V source-driver supply and +18V and -6V gate-driver supplies. The input voltage range for the IC is from +2.6V to +5.5V. The listed load currents in Figure 1 are available from a +4.5V to +5.5V supply. Typical Operating Circuit recommended components,. Applications Information The EC9219 is a high frequency, high efficiency boost regulator operated at constant frequency PWM mode. The boost converter stores energy from an input voltage source and deliver it to a higher output voltage. The input voltage range is 2.6V to 5.5V and output voltage range is 5V to 18V The switching frequency is selectable between 640KHz and 1.2MHz allowing smaller inductors and faster transient response. An external compensation pin gives the user greater flexibility in setting output transient response and tighter load regulation. The converter soft-start characteristic can also be controlled by external C08 capacitor. The SHDN pin allows the user to completely shut-down the device. Main Step-Up Regulator The main step-up regulator employs a current-mode, fixed-frequency PWM architecture to maximize loop bandwidth and provide fast transient response to pulsed loads typical of TFT-LCD panel source drivers. The 1.2MHz switching frequency allows the use of low profile inductors and ceramic capacitors to minimize the thickness of LCD panel designs. The integrated high-efficiency MOSFET and soft-start function controls inrush currents. The output voltage can be set from VIN to 13V with an external resistive voltage-divider. The regulator controls the output voltage and the power delivered to the output by modulating the duty cycle (D) of the internal power MOSFET in each switching cycle. The duty cycle of the MOSFET is approximated by: D= VMAIN − VIN VMAIN Figure 1 shows the Functional Diagram of the step-up regulator. An error amplifier compares the signal at FB to 1.228V and changes the COMP output. The voltage at COMP sets the peak inductor current. As the load varies, the error amplifier sources or sinks current to the COMP output accordingly to produce the inductor peak current necessary to service the load. To maintain stability at high duty cycles, a slope-compensation signal is summed with the current-sense signal. On the rising edge of the internal clock, the controller sets a flip-flop, turning on the n-channel MOSFET and applying the input voltage across the inductor. The current through the inductor ramps up linearly, storing energy in its magnetic field. Once the sum of the current-feedback signal and the lope compensation exceeds the COMP voltage, the controller resets the flip-flop and turns off the MOSFET. Since the inductor current is continuous, a transverse potential develops across the inductor that turns on the diode (D1). The voltage across the inductor then becomes the difference between the output voltage and the input voltage. This discharge condition forces the current through the inductor to ramp back down, transferring the energy stored in the magnetic field to the output capacitor and the load. The MOSFET remains off for the rest of the clock cycle. P 9 / 14 2009/09/29 TFT- LCD DC-DC Converters with Operational Amplifiers EC9219 Operational Amplifiers The EC9219 has one operational amplifier. The operational amplifiers are typically used to drive the LCD backplane (VCOM) or the gamma-correction divider string. They feature 150mA output current, 17V/µs slew rate, and 12MHz bandwidth. The rail-to-rail input and output capability maximizes system flexibility. Frequency Selection The EC9219’s frequency can be user selected to operate at either 640kHz or 1.2MHz. Tie FREQ to GND for 640kHz operation. For a 1.2MHz switching frequency, tie FREQ to VIN. Under voltage Lockout (UVLO) The under voltage-lockout (UVLO) circuit compares the input voltage at VIN with the UVLO threshold to ensure the input voltage is high enough for reliable operation. The 100mV (typ) hysteresis prevents supply transients from causing a restart. Once the input voltage exceeds the UVLO rising threshold, startup begins. When the input voltage falls below the UVLO falling threshold, the controller turns off the main step-up regulator, turns off the outputs, and disables the switch control block; the operational amplifier outputs are high impedance. Thermal-Overload Protection Thermal-overload protection prevents excessive power dissipation from overheating the EC9219. When the junction temperature exceeds TJ = +135℃, a thermal sensor immediately activates the fault protection, which shuts down all outputs except the reference, allowing the device to cool down. Once the device cools down by approximately 30℃, and reactivate the device. The thermal-overload protection protects the controller in the event of fault conditions. For continuous operation, do not exceed the absolute maximum junction temperature rating of TJ = +125℃. Design Procedure Main Step-Up Regulator Inductor Selection The minimum inductance value, peak current rating, and series resistance are factors to consider when selecting the inductor. These factors influence the converter’s efficiency, maximum output load capability, transient-response time, and output voltage ripple. Size and cost are also important factors to consider. The maximum output current, input voltage, output voltage, and switching frequency determine the inductor value. Very high inductance values minimize the current ripple and therefore reduce the peak current, which decreases core losses in the inductor and RL losses in the entire power path. However, large inductor values also require more energy storage and more turns of wire, which increases size and can increase winding resistance losses in the inductor. Low inductance values decrease the size but increase the current ripple and peak current. Finding the best inductor involves choosing the best compromise between circuit efficiency, inductor size, and cost. The equations used here include a constant ICR(Inductor current ripple rate), which is the ratio of the inductor peak-to-peak ripple current to the average DC inductor current at the full load current. The best trade-off between inductor size and circuit efficiency for step-up regulators generally has an ICR between 0.3 and 0.5. However, depending on the AC characteristics of the inductor core material and ratio of inductor resistance to other power-path resistances, the best ICR can shift up or down. If the inductor resistance is relatively high, more ripple can be accepted to reduce the number of turns required and increase the wire diameter. If the inductor resistance is relatively low, increasing inductance to lower the peak current can decrease losses throughout the power path. If extremely thin high-resistance inductors are used, as is common for LCD-panel applications, the best ICR can increase to between 0.5 and 1.0. Once a physical inductor is chosen, higher and lower values of the inductor should be evaluated for efficiency improvements in typical operating regions. Calculate the approximate inductor value using the typical input voltage (VIN), the maximum output current (IMAIN(MAX)), the expected efficiency ( η TYP) taken from an appropriate curve in the Typical Operating Characteristics section, and an estimate of ICR based on the above discussion: P 10 / 14 2009/09/29 TFT- LCD DC-DC Converters with Operational Amplifiers EC9219 I2R is a registered trademark of Instruments for Research and Industry, Inc. Choose an available inductor value from an appropriate inductor family. Calculate the maximum DC input current at the minimum input voltage (VIN(MIN)) using conservation of energy and the expected efficiency at that operating point (⎜MIN) taken from the appropriate curve in the Typical Operating Characteristics: Calculate the ripple current at that operating point and the peak current required for the inductor: The inductor’s saturation current rating and the EC9219s’ LX current limit (ILIM) should exceed IPEAK, and the inductor’s DC current rating should exceed IIN(DC,MAX). For good efficiency, choose an inductor with less than 0.1Ω series resistance. Considering the Typical Operating Circuit, the maximum load current (IMAIN(MAX)) is 500mA with a 13V output and a typical input voltage of 5V. Choosing an ICR of 0.5 and estimating efficiency of 85% at this operating point: Using the circuit’s minimum input voltage (4.5V) and estimating efficiency of 80% at that operating point: The ripple current and the peak current are: Output-Capacitor Selection The total output voltage ripple has two components: the capacitive ripple caused by the charging and discharging of the output capacitance, and the ohmic ripple due to the capacitor’s equivalent series resistance (ESR). where IPEAK is the peak inductor current (see the Inductor Selection section). For ceramic capacitors, the output voltage ripple is typically dominated by VRIPPLE(C). The voltage rating and temperature characteristics of the output capacitor must also be considered. P 11 / 14 2009/09/29 TFT- LCD DC-DC Converters with Operational Amplifiers EC9219 Input-Capacitor Selection The input capacitor (CIN) reduces the current peaks drawn from the input supply and reduces noise injection into the IC. A 10μF ceramic capacitor is used in the Typical Applications Circuit (Figure 2) because of the high source impedance seen in typical lab setups. Actual applications usually have much lower source impedance since the step-up regulator often runs directly from the output of another regulated supply. Typically, CIN can be reduced below the values used in the Typical Applications Circuit. Ensure a low-noise supply at VIN by using adequate CIN. Alternately, greater voltage variation can be tolerated on CIN if VIN is decoupled from CIN using an RC low-pass filter. Rectifier Diode The EC9219s’ high switching frequency demands a high-speed rectifier. Schottky diodes are recommended for most applications because of their fast recovery time and low forward voltage. In general, a 2A Schottky diode complements the internal MOSFET well. Output-Voltage Selection The output voltage of the main step-up regulator can be adjusted by connecting a resistive voltage-divider from the output (VMAIN) to AGND with the center tap connected to FB (see Figure 2). Select R2 in the 10kΩ to 50kΩ range. Calculate R1 with the following equation: R3 = R8 × ( Vmain - 1) VFB where VFB, the step-up regulator’s feedback set point, is 1.228V. Place R3 and R8 close to the IC. Loop Compensation The EC9219 incorporates an trans conductance amplifier in its feedback path to allow the user some adjustment on the transient response and better regulation. The EC9219 uses current mode control architecture which has a fast current sense loop and a slow voltage feedback loop. The fast current feedback loop does not require any compensation. The slow voltage loop must be compensated for stable operation. The compensation network is a series RC network from COMP pin to ground. The resistor sets the high frequency integrator gain for fast transient response and the capacitor sets the integrator zero to ensure loop stability. For most applications, the compensation resistor in the range of 10K to 100K and the compensation capacitor in the range of 1nF to 0.22uF. PC Board Layout and Grounding Careful PC board layout is important for proper operation. Use the following guidelines for good PC board layout: z Minimize the area of high-current loops by placing the inductor, the output diode, and the output capacitors near the input capacitors and near the LX and PGND pins. The high-current input loop goes from the positive terminal of the input capacitor to the inductor, to the IC’s LX pin, out of PGND, and to the input capacitor’s negative terminal. The high-current output loop is from the positive terminal of the input capacitor to the inductor, to the output diode (D5), and to the positive terminal of the output capacitors, reconnecting between the output capacitor and input capacitor ground terminals. Connect these loop components with short, wide connections. Avoid using vias in the high-current paths. If vias are unavoidable, use many vias in parallel to reduce resistance and inductance. z Create a power-ground island (PGND) consisting of the input and output capacitor grounds, PGND pin, and any charge-pump components. Connect all of these together with short, wide traces or a small ground plane. Maximizing the width of the power-ground traces improves efficiency and reduces output voltage ripple and noise spikes. Create an analog ground plane (SGND) consisting of the SGND pin, all the feedback-divider ground connections, the COMP and SS capacitor ground connections. Connect the SGND and PGND islands. Make no other connections between these separate ground planes. P 12 / 14 2009/09/29 TFT- LCD DC-DC Converters with Operational Amplifiers EC9219 z z z z Place all feedback voltage-divider resistors as close to their respective feedback pins as possible. The divider’s center trace should be kept short. Placing the resistors far away causes their FB traces to become antennas that can pick up switching noise. Take care to avoid running any feedback trace near LX or the switching nodes in the charge pumps. Place the VIN pin bypass capacitors as close to the device as possible. The ground connection of the VIN bypass capacitor should be connected directly to the SGND pin with a wide trace. Minimize the length and maximize the width of the traces between the output capacitors and the load for best transient responses. Minimize the size of the LX node while keeping it wide and short. Keep the LX node away from feedback nodes (FB) and analog ground. Use DC traces to shield if necessary. Refer to the EC9219 DEMO BOARD for an example of proper PC board layout. Package Dimension TSSOP-14 Unit:mm P 13 / 14 2009/09/29 TFT- LCD DC-DC Converters with Operational Amplifiers EC9219 TQFN-16 P 14 / 14 2009/09/29