MAX1542-MAX1543

19-2741; Rev 0; 4/03 KIT ATION EVALU E AILABL AV TFT LCD DC-to-DC Converter with Operational Amplifiers General Description Features o Ultra-High-Performance Step-Up Regulator Fast Transient Response to Pulsed Load Using Current-Mode Control Architecture High-Accuracy Output Voltage (1.3%) Built-In 14V, 1.2A, 0.2Ω N-Channel Power MOSFET with Lossless Current-Sensing High Efficiency (85%) 8-Step Current-Controlled Digital Soft-Start o Two High-Performance Operational Amplifiers 150mA Output Short-Circuit Current 7.5V/µs Slew Rate 12MHz -3dB Bandwidth Rail-to-Rail Inputs/Outputs Unity Gain Stable o Logic-Controlled High-Voltage Switch with Adjustable Delay o Timer Delay Latch FB Fault Protection o Thermal Protection o 2.6V to 5.5V Input Operating Voltage Range o 3.6mA (Switching), 0.45mA (Not Switching) Quiescent Current o Ultra-Thin 20-Pin Thin QFN Package (5mm x 5mm x 0.8mm) MAX1542/MAX1543 The MAX1542/MAX1543 include a high-performance boost regulator and two high-current operational amplifiers for active matrix, thin-film transistor (TFT), liquidcrystal displays (LCDs). Also included is a logiccontrolled, high-voltage switch with adjustable delay. The MAX1543 includes an additional high-voltage load switch and features pin-selectable boost regulator switching frequency. The step-up DC-to-DC converter is a high-frequency 640kHz (MAX1543)/1.2MHz (MAX1542/MAX1543) current-mode regulator with a built-in power MOSFET that allows the use of ultra-small inductors and ceramic capacitors. It provides fast transient response to pulsed loads while producing efficiencies over 85%. The two easy-to-use, high-performance operational amplifiers can drive the LCD backplane (VCOM) and/or the gamma correction divider string. The devices feature high short-circuit current (150mA), fast slew rate (7.5V/µs), wide bandwidth (12MHz), and Rail-to-Rail® inputs and outputs. The MAX1542/MAX1543 are available in 20-pin thin QFN packages with a maximum thickness of 0.8mm for ultra-thin LCD panel design. Applications Notebook Computer Displays LCD Monitor Panels PDAs Car Navigation Displays Pin Configurations DRN CTL DEL FB Ordering Information PART MAX1542ETP MAX1543ETP TEMP RANGE -40°C to +85°C -40°C to +85°C PIN-PACKAGE 20 Thin QFN (5mm x 5mm) 20 Thin QFN (5mm x 5mm) TOP VIEW 20 19 18 17 COMP COM SRC I.C. PGND AGND 1 2 3 4 5 NEG2 10 16 15 14 FREQ IN LX SUP POS2 MAX1543 13 12 11 6 7 8 OUT1 POS1 THIN QFN (5mm x 5mm) Pin Configurations continued at end of data sheet. NEG1 OUT2 9 Rail-to-Rail is a registered trademark of Nippon Motorola, Ltd. 1 ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. TFT LCD DC-to-DC Converter with Operational Amplifiers MAX1542/MAX1543 ABSOLUTE MAXIMUM RATINGS IN, CTL, COMP, FB, DEL, FREQ (MAX1543) to AGND ...............................................................-0.3V to +6V COMP, FB, DEL to AGND .............................-0.3V to (IN + 0.3V) PGND to AGND ..................................................................±0.3V LX to PGND ............................................................-0.3V to +14V SUP, POS1, NEG1, OUT1, POS2, NEG2, OUT2 to AGND .......................................-0.3V to +14V POS1, NEG1, OUT1, POS2, NEG2, OUT2 to AGND ......................................-0.3V to (SUP + 0.3V) SRC, COM to AGND...............................................-0.3V to +30V SRC to COM ...........................................................-0.3V to +30V SRC to DRN (MAX1543).........................................-0.3V to +30V COM to AGND ...........................................-0.3V to (SRC + 0.3V) DRN (MAX1543) to AGND .........................-0.3V to (SRC + 0.3V) DRN (MAX1543) to COM.........................................-30V to +30V MAX1542 COM RMS Output Current ...............................+75mA MAX1543 COM RMS Output Current ...............................±50mA OUT1, OUT2 Continuous Output Current.........................±75mA Continuous Power Dissipation (TA = +70°C) 20-Pin Thin QFN 5mm x 5mm (derate 20.8mW/°C above +70°C) .............................1667mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature .....................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C 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 CHARACTERISTICS (VIN = 3V, VSUP = 8V, VSRC = 28V, FREQ = IN (MAX1543), PGND = AGND = 0, TA = 0°C to +85°C, typical values at TA = +25°C, unless otherwise noted.) PARAMETER IN Supply Range IN Undervoltage Lockout Threshold IN Quiescent Current Duration to Trigger Fault Condition Thermal Shutdown MAIN STEP-UP REGULATOR Output Voltage Range Operating Frequency Oscillator Maximum Duty Cycle FREQ Input Low Voltage FREQ Input High Voltage FREQ Pulldown Current FB Regulation Voltage FB Fault Trip Level FB Load Regulation FB Line Regulation VFB MAX1543, VIN = 2.6V to 5.5V MAX1543, VIN = 2.6V to 5.5V MAX1543, VFREQ = 1.0V No load VFB falling 0 ≤ IMAIN ≤ full load VIN = 2.6V to 5.5V TA = +85°C TA = 0°C to +85°C 0.7 x VIN 3.5 1.224 1.222 0.96 5 1.240 1.240 1 -1 -0.08 ±0.15 6.5 1.256 1.258 1.04 VMAIN MAX1542 fOSC MAX1543 FREQ = AGND FREQ = IN VIN 1020 512 1020 82 1200 600 1200 87 13 1380 768 1380 92 0.3 x VIN % V V µA V V % %/V kHz V SYMBOL VIN VUVLO IIN VIN rising VIN falling VFB = 1.3V, LX not switching VFB = 1.1V, LX switching MAX1542 MAX1543 Rising edge Hysteresis FREQ = AGND FREQ = IN CONDITIONS MIN 2.6 2.3 2.2 2.5 2.35 0.45 3.6 55 51 55 160 15 °C ms TYP MAX 5.5 2.7 2.5 0.65 6.5 UNITS V V mA 2 _______________________________________________________________________________________ TFT LCD DC-to-DC Converter with Operational Amplifiers ELECTRICAL CHARACTERISTICS (continued) (VIN = 3V, VSUP = 8V, VSRC = 28V, FREQ = IN (MAX1543), PGND = AGND = 0, TA = 0°C to +85°C, typical values at TA = +25°C, unless otherwise noted.) PARAMETER FB Input Bias Current FB Transconductance FB Voltage Gain LX On-Resistance LX Leakage Current LX Current Limit Current-Sense Transresistance MAX1542 Soft-Start Period Soft-Start Step Size OPERATIONAL AMPLIFIERS SUP Supply Range SUP Supply Current Input Offset Voltage Input Bias Current Input Common-Mode Voltage Range Common-Mode Rejection Ratio Open-Loop Gain IOUT_ = 100µA Output Voltage Swing High VOH IOUT_ = 5mA Output Voltage Swing Low Short-Circuit Current Output Source-and-Sink Current Power-Supply Rejection Ratio Slew Rate -3dB Bandwidth Gain-Bandwidth Product GBW RL = 10kΩ, CL =10pF, buffer configuration Buffer configuration PSRR VOL IOUT_ = -100µA IOUT_ = -5mA To VSUP/2 Source Sink 50 50 40 60 100 7.5 12 8 VSUP 15 VSUP 150 VSUP ISUP VOS IBIAS VCM CMRR 0 ≤ VNEG_, VPOS_ ≤ VSUP Buffer configuration, VPOS_ = 4V, no load VCM = VSUP/2, TA = +25°C NEG1, NEG2, POS1, POS2 0 50 90 125 VSUP 2 mV VSUP 80 2 80 150 140 15 150 mV mA mA dB V/µs MHz MHz 4.5 1.3 0 +1 13.0 1.9 12 ±50 VSUP V mA mV nA V dB dB tSS MAX1543 FREQ = AGND FREQ = IN RLX(ON) ILX ILIM VLX = 13V VFB = 1V, duty cycle = 65% 1.2 0.30 SYMBOL VFB = 1.5V ∆ICOMP = 5µA FB to COMP CONDITIONS MIN -40 75 160 700 210 0.01 1.5 0.50 14 13 14 ILIM / 8 A ms 400 20 1.8 0.65 TYP MAX +40 280 UNITS nA µS V/V mΩ µA A Ω MAX1542/MAX1543 Buffer configuration, VPOS_ = 4V, |∆VOS| < 10mV DC, 6V ≤ VSUP ≤ 13V, VNEG_, VPOS_ = VSUP/2 POSITIVE GATE-DRIVER TIMING AND CONTROL SWITCHES DEL Capacitor Charge Current During startup, VDEL = 1V 4 5 6 µA _______________________________________________________________________________________ 3 TFT LCD DC-to-DC Converter with Operational Amplifiers MAX1542/MAX1543 ELECTRICAL CHARACTERISTICS (continued) (VIN = 3V, VSUP = 8V, VSRC = 28V, FREQ = IN (MAX1543), PGND = AGND = 0, TA = 0°C to +85°C, typical values at TA = +25°C, unless otherwise noted.) PARAMETER DEL Turn-On Threshold DEL Discharge Switch OnResistance CTL Input Low Voltage CTL Input High Voltage CTL Input Leakage Current CTL-to-SRC Propagation Delay SRC Input Voltage Range SRC Input Current ISRC VDRN = 8V, CTL = IN, VDEL = 1.5V MAX1542 MAX1543 70 100 15 90 5 15 30 350 1000 SYMBOL VTH(DEL) During UVLO, VIN = 2.2V VIN = 2.6V to 5.5V VIN = 2.6V to 5.5V CTL = AGND or IN 2 -1 100 28 130 180 30 150 10 30 60 1800 µA Ω Ω Ω µA +1 CONDITIONS MIN 1.178 TYP 1.240 20 0.6 MAX 1.302 UNITS V Ω V V µA ns V VDRN = 8V, CTL = AGND, VDEL = 1.5V DRN Input Current SRC to COM Switch OnResistance DRN to COM Switch OnResistance (MAX1543) COM to PGND Switch OnResistance (MAX1543) IDRC RSRC(ON) RDRN(ON) RCOM(ON) VDRN = 8V, CTL = AGND, VDEL = 1.5V, MAX1543 VDEL = 1.5V, CTL = IN MAX1542 MAX1543 VDEL = 1.5V, CTL = AGND VDEL = 1.1V ELECTRICAL CHARACTERISTICS (VIN = 3V, VSUP = 8V, VSRC = 28V, FREQ = IN (MAX1543), PGND = AGND = 0, TA = -40°C to +85°C, unless otherwise noted.) PARAMETER IN Supply Range IN Undervoltage Lockout Threshold IN Quiescent Current MAIN STEP-UP REGULATOR Output Voltage Range Operating Frequency FB Regulation Voltage FB Fault Trip Level FB Line Regulation FB Transconductance LX On-Resistance RLX(ON) VMAIN MAX1542 fOSC VFB MAX1543 No load VFB falling VIN = 2.6V to 5.5V ∆ICOMP = 5µA 75 FREQ = AGND FREQ = IN VIN 1000 512 1000 1.215 0.96 13 1400 768 1400 1.260 1.04 0.15 300 400 V V %/V µS mΩ kHz V SYMBOL VIN VUVLO IIN VIN rising VIN falling VFB = 1.3V, LX not switching VFB = 1.1V, LX switching CONDITIONS MIN 2.6 2.3 2.2 TYP MAX 5.5 2.7 2.5 0.65 6.5 UNITS V V mA 4 _______________________________________________________________________________________ TFT LCD DC-to-DC Converter with Operational Amplifiers ELECTRICAL CHARACTERISTICS (continued) (VIN = 3V, VSUP = 8V, VSRC = 28V, FREQ = IN (MAX1543), PGND = AGND = 0, TA = -40°C to +85°C, unless otherwise noted.) PARAMETER LX Current Limit Current-Sense Transresistance OPERATIONAL AMPLIFIERS SUP Supply Range SUP Supply Current Input Offset Voltage Input Bias Current Input Common-Mode Voltage Range VSUP ISUP VOS IBIAS VCM IOUT_ = 100µA Output Voltage Swing High VOH IOUT_ = 5mA Output Voltage Swing Low Short-Circuit Current Output Source-and-Sink Current VOL IOUT_ = -100µA IOUT_ = -5mA To VSUP/2 Source Sink 50 50 40 Buffer configuration, VPOS_ = 4V, no load VCM = VSUP/2, TA = +25ºC NEG1, NEG2, POS1, POS2 0 VSUP 15 mV VSUP 150 15 150 mV mA mA 4.5 13.0 2.1 12 ±50 VSUP V mA mV nA V SYMBOL ILIM CONDITIONS VFB = 1V, duty cycle = 65% MIN 1.2 0.30 TYP MAX 1.8 0.65 UNITS A Ω MAX1542/MAX1543 Buffer configuration, VPOS_ = 4V, | ∆VOS | < 10mV During startup, VDEL = 1.0V VTH (DEL) VIN = 2.6V to 5.5V VIN = 2.6V to 5.5V VDRN = 8V, CTL = IN, VDEL = 1.5V MAX1542 MAX1543 POSITIVE GATE-DRIVER TIMING AND CONTROL SWITCHES DEL Capacitor Charge Current DEL Turn-On Threshold CTL Input Low Voltage CTL Input High Voltage SRC Input Voltage Range SRC Input Current ISRC 4 1.178 2 28 130 180 30 150 10 30 60 350 1800 µA Ω Ω Ω µA 6 1.302 0.6 µA V V V V VDRN = 8V, CTL = AGND, VDEL = 1.5V DRN Input Current SRC to COM Switch OnResistance DRN to COM Switch OnResistance (MAX1543) COM to PGND Switch OnResistance (MAX1543) IDRN RSRC(ON) RDRN(ON) RCOM(ON) VDRN = 8V, CTL = AGND, VDEL = 1.5V, MAX1543 VDEL = 1.5V, CTL = IN MAX1542 MAX1543 VDEL = 1.5V, CTL = AGND VDEL = 1.1V _______________________________________________________________________________________ 5 TFT LCD DC-to-DC Converter with Operational Amplifiers MAX1542/MAX1543 Typical Operating Characteristics (VIN = 3.3V, VMAIN = 8V, fOSC = 1.2MHz, TA = +25°C, unless otherwise noted.) STEP-UP REGULATOR EFFICIENCY vs. LOAD CURRENT (VMAIN = 8V) MAX1542 toc01 STEP-UP REGULATOR EFFICIENCY vs. LOAD CURRENT (VMAIN = 8V) 90 85 EFFICIENCY (%) 80 75 70 65 60 55 50 7.5 1 10 100 1000 VIN = 5V VIN = 2.7V VIN = 3.3V MAX1543 fOSC = 640kHz L = 10µH VIN = 5V MAX1542 toc02 STEP-UP REGULATOR OUTPUT VOLTAGE vs. LOAD CURRENT (VMAIN = 8V) MAX1542 toc03 95 90 85 EFFICIENCY (%) 80 75 70 65 60 55 50 1 10 100 VIN = 2.7V MAX1543 fOSC = 1.2MHz L = 4.7µH VIN = 5V VIN = 3.3V 95 8.1 8.0 OUTPUT VOLTAGE (V) 7.9 7.8 7.7 7.6 VIN = 3.3V fOSC = 1.2MHz 1 10 100 1000 1000 LOAD CURRENT (mA) LOAD CURRENT (mA) LOAD CURRENT (mA) STEP-UP REGULATOR SUPPLY CURRENT vs. SUPPLY VOLTAGE MAX1542 toc04 STEP-UP REGULATOR SUPPLY CURRENT vs. TEMPERATURE MAX1542 toc05 SWITCHING FREQUENCY vs. INPUT VOLTAGE MAX1543 IMAIN = 200mA SWITCHING FREQUENCY (kHz) 1200 MAX1542 toc06 0.7 0.6 SUPPLY CURRENT (mA) 0.5 0.4 0.3 0.2 0.1 0 2.5 NO LOAD fOSC = 1.2MHz R1 = 75kΩ R2 = 13.7kΩ SUP DISCONNECTED 3.0 3.5 4.0 VIN (V) 4.5 5.0 CURRENT INTO INDUCTOR CURRENT INTO IN PIN 2.0 NO LOAD VIN = 3.3V fOSC = 1.2MHz R1 = 75kΩ R2 = 13.7kΩ SUP DISCONNECTED CURRENT INTO INDUCTOR 0.8 CURRENT INTO IN PIN 0.4 1400 1.6 SUPPLY CURRENT (mA) 1.2 1000 FREQ = IN 800 FREQ = AGND 600 0 5.5 -40 -15 10 35 60 85 TEMPERATURE (°C) 400 2.5 3.0 3.5 4.0 VIN (V) 4.5 5.0 5.5 SUP SUPPLY CURRENT vs. SUP VOLTAGE NO LOAD BUFFER CONFIGURATION POS_ = VSUP/2 MAX1542 toc07 SUP SUPPLY CURRENT vs. TEMPERATURE VSUP = 13V MAX1542 toc08 1.75 2.0 1.50 1.6 ISUP (mA) ISUP (mA) VSUP = 8V 1.25 1.2 1.00 VSUP = 5V 0.75 4.5 6.0 7.5 9.0 VSUP (V) 10.5 12.0 13.5 0.8 -40 -15 10 35 60 85 TEMPERATURE (°C) NO LOAD BUFFER CONFIGURATION VPOS = VSUP/2 6 _______________________________________________________________________________________ TFT LCD DC-to-DC Converter with Operational Amplifiers Typical Operating Characteristics (continued) (VIN = 3.3V, VMAIN = 8V, fOSC = 1.2MHz, TA = +25°C, unless otherwise noted.) OPERATIONAL AMPLIFIER FREQUENCY RESPONSE FOR VARIOUS CLOAD MAX1542 toc09 MAX1542/MAX1543 OPERATIONAL AMPLIFIER OVERSHOOT vs. LOAD CAPACITANCE VSUP = 8V RL = 10kΩ AV = 1 POS_ = 4V ±50mV MAX1542 toc10 20 100pF 1000pF 0 56pF 15pF 100 10 MAGNITUDE (dB) 80 OVERSHOOT (%) RISING EDGE 60 FALLING EDGE -10 40 -20 -30 VSUP = 8V AV = 1 RL = 10kΩ 100 1k 10k 100k FREQUENCY (Hz) 20 0 1 100 LOAD CAPACITANCE (pF) 1000 OPERATIONAL AMPLIFIER OUTPUT HIGH VOLTAGE vs. LOAD MAX1542 toc11 OPERATIONAL AMPLIFIER OUTPUT LOW VOLTAGE vs. LOAD VSUP = 8V AV = 1 120 VOL (mV) MAX1542 toc12 160 VSUP = 8V AV = 1 120 VSUP - VOUT (mV) 160 80 80 40 40 0 0 2 4 6 8 10 IOUT_ (mA) 0 0 2 4 6 8 10 IOUT_ (mA) POWER-SUPPLY REJECTION RATIO vs. FREQUENCY MAX1542 toc13 OPERATIONAL AMPLIFIER SETTLING TIME vs. STEP SIZE 450 400 SETTLING TIME (ns) 350 300 250 200 150 100 VMAIN AC-COUPLED 100mV/div FALLING EDGE VSUP = 8V AV = +1 RL = 10kΩ CL = 10pF VCM = 4V MAX1542 toc14 STEP-UP REGULATOR LOAD-TRANSIENT RESPONSE MAX1542 toc15 120 100 80 PSRR (dB) 60 40 20 0 VSUP = 8V 0.1 1 10 100 1k 500 RISING EDGE 200mA IMAIN 200mA/div IL 500mA/div 20mA 50 0 10k 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 STEP SIZE (V) FREQUENCY (Hz) 40µs/div L = 4.7µH RCOMP = 120kΩ CCOMP = 470pF _______________________________________________________________________________________ 7 TFT LCD DC-to-DC Converter with Operational Amplifiers MAX1542/MAX1543 Typical Operating Characteristics (continued) (VIN = 3.3V, VMAIN = 8V, fOSC = 1.2MHz, TA = +25°C, unless otherwise noted.) STEP-UP REGULATOR PULSED LOAD-TRANSIENT RESPONSE MAX1542 toc16 STARTUP SEQUENCE MAX1542 toc17 VIN 2V/div IMAIN 1A/div IL 500mA/div VMAIN 100mV/div AC-COUPLED VMAIN 8V/div L = 4.7µH RCOMP = 120kΩ CCOMP = 470pF 10µs/div 1ms/div VGOFF 5V/div VCOM 10V/div HEAVY-LOAD SOFT-START WAVEFORMS MAX1542 toc18 TIMER DELAY LATCH RESPONSE TO OVERLOAD MAX1542 toc19 OPERATIONAL AMPLIFIER RAIL-TO-RAIL I/O PERFORMANCE MAX1542 toc20 VIN 5V/div VMAIN 5V/div VMAIN 5V/div IL 2A/div VPOS1 5V/div IL 500mA/div VOUT1 5V/div VCOM 20V/div 10ms/div VSUP = 8V BUFFER CONFIGURATION 100µs/div VOUT1 5V/div RLOAD = 10Ω 2ms/div OPERATIONAL AMPLIFIER LOAD-TRANSIENT RESPONSE MAX1542 toc21 OPERATIONAL AMPLIFIER LARGE-SIGNAL STEP RESPONSE MAX1542 toc22 4V VOUT1 1V/div AC-COUPLED 4V VPOS1 500mV/div AC-COUPLED +50 0 -50 BUFFER CONFIGURATION 1µs/div 1µs/div IOUT1 50mA/div VSUP = 8V AV = 10 VOUT1 2V/div 8 _______________________________________________________________________________________ TFT LCD DC-to-DC Converter with Operational Amplifiers Typical Operating Characteristics (continued) (VIN = 3.3V, VMAIN = 8V, fOSC = 1.2MHz, TA = +25°C, unless otherwise noted.) OPERATIONAL AMPLIFIER LARGE-SIGNAL STEP RESPONSE MAX1542 toc23 MAX1542/MAX1543 OPERATIONAL AMPLIFIER SMALL-SIGNAL STEP RESPONSE MAX1542 toc24 POS_ 50mV/div AC-COUPLED VOUT_ 1V/div CHI AMPL 4.86V CHI + OVER 4.970% OUT_ 50mV/div AC-COUPLED AV = 1 1µs/div VSUP = 8V, AV = 1 200ns/div CH2 + OVER 6.234% CH2 - OVER 2.352% Pin Description PIN MAX1542 1 2 3, 15, 20 — 4 5 6 7 8 9 10 11 12 13 MAX1543 1 2 — 3 4 5 6 7 8 9 10 11 12 13 NAME COM SRC N.C. I.C. PGND AGND POS1 NEG1 OUT1 OUT2 NEG2 POS2 SUP LX FUNCTION Internal High-Voltage MOSFET Switch Common Terminal. Do not allow the voltage on COM to exceed VSRC. Switch Input. Source of the internal high-voltage P-channel MOSFET. Bypass SRC to PGND with a minimum of 0.1µF close to the pins. No Connection. Not internally connected. Internal Connection. Make no connection to this pin. Power Ground. PGND is the source of the main boost N-channel power MOSFET. Connect PGND to the output capacitor ground terminals through a short, wide PC board trace. Connect to analog ground (AGND) underneath the IC. Analog Ground. Connect to power ground (PGND) underneath the IC. Operational Amplifier 1 Noninverting Input Operational Amplifier 1 Inverting Input Operational Amplifier 1 Output Operational Amplifier 2 Output Operational Amplifier 2 Inverting Input Operational Amplifier 2 Noninverting Input Operational Amplifier Power Input. Positive supply rail for the OUT1 and OUT2 amplifiers. Typically connected to VMAIN. Bypass SUP to AGND with a 0.1µF capacitor. Power MOSFET N-Channel Drain and Switching Node. Connect the inductor and catch diode to LX and minimize the trace area for lowest EMI. _______________________________________________________________________________________ 9 TFT LCD DC-to-DC Converter with Operational Amplifiers MAX1542/MAX1543 Pin Description (continued) PIN MAX1542 14 — MAX1543 14 15 NAME IN FREQ FUNCTION Supply Voltage. IN can range from 2.6V to 5.5V. Oscillator Frequency Select Input. Pull FREQ low or leave it unconnected for 640kHz operation. Connect FREQ high for 1.2MHz operation. This input has a 5µA pulldown current. Step-Up Converter Feedback Input. Regulates to 1.24V (nominal). Connect a resistordivider from the output (VMAIN) to FB to analog ground (AGND). Place the resistor-divider within 5mm of FB. Step-Up Regulator Error Amplifier Compensation Point. Connect a series RC from COMP to AGND. See the Loop Compensation section for component selection guidelines. High-Voltage Switch Delay Input. Connect a capacitor from DEL to AGND to set the highvoltage switch startup delay. A 5µA current source charges CDEL. For the MAX1542, the high-voltage switch between SRC and COM is disabled until VDEL exceeds 1.24V. Following the delay period, CTL controls the state of the high-voltage switch. For the MAX1543, the switches between SRC, COM, and DRN are disabled and a 1kΩ pulldown between COM and PGND is enabled until VDEL exceeds 1.24V. Following the delay period, the 1kΩ pulldown is released and CTL controls the state of the high-voltage switches (see the Delay Control Circuit section). High-Voltage Switch Control Input. When CTL is high, the high-voltage switch between COM and SRC is on and the high-voltage switches between COM and DRN (MAX1543) are off. When CTL is low, the high-voltage switch between COM and SRC is off and the high-voltage switches between COM and DRN (MAX1543) are on. CTL is inhibited by the undervoltage lockout and when VDEL is less than 1.24V. Switch Input. Drain of the internal high-voltage back-to-back P-channel MOSFETs connected to COM. 16 16 FB 17 17 COMP 18 18 DEL 19 19 CTL — 20 DRN Typical Application Circuits The MAX1542 typical application circuit (Figure 1) and the MAX1543 typical application circuit (Figure 2) generate an +8V source driver supply and approximately +22V and -7V gate driver supplies for TFT displays. The input voltage is from +2.6V to +5.5V. Table 1 lists recommended components and Table 2 lists contact information for component suppliers. Main Step-Up Converter The MAX1542/MAX1543 main step-up converter switches at 1.2MHz or 640kHz (MAX1543 only) (see the Oscillator Frequency (FREQ) section). The devices employ a current-mode, fixed-frequency, pulse-width modulation (PWM) architecture to maximize loop bandwidth providing fast transient response to pulsed loads found in source drivers for TFT LCD panels. The highswitching frequency also allows the use of low-profile inductors and capacitors to minimize the thickness of LCD panel designs. The integrated high-efficiency MOSFET and the IC’s built-in digital soft-start function reduce the number of external components required while controlling inrush current. The output voltage of the main step-up converter (VMAIN) can be set from VIN to 13V with an external resistive voltage-divider at FB. Detailed Description The MAX1542/MAX1543 include a high-performance step-up regulator, two high-current operational amplifiers, and startup timing and level-shifting functionality useful for active matrix TFT LCDs. Figure 3 shows the MAX1542/MAX1543 functional diagram. 10 ______________________________________________________________________________________ TFT LCD DC-to-DC Converter with Operational Amplifiers MAX1542/MAX1543 Table 1. Component List DESIGNATION C1 C8, C9 D1 D2, D3, D4 L1 DESCRIPTION 10µF ±10%, 6.3V X5R ceramic capacitor 4.7µF ±10%, 10V X5R ceramic capacitors 1A, 30V Schottky diode 200mA, 100V dual ultra-fast diodes 4.7µH, 1.3A inductor PART TDK C3216X5R0J106K TDK C3225X5R1A475K Toshiba CRS02 Fairchild MMBD4148SE Sumida CLS5D11HP-4R7 Table 2. Component Suppliers SUPPLIER Inductors Sumida USA Capacitors TDK Diodes Fairchild Toshiba 888-522-5372 949-455-2000 408-822-2104 949-859-3963 www.fairchildsemi.com www.toshiba.com/taec/ 847-803-6100 847-803-6296 www.component.tdk.com 847-956-0666 847-956-0702 www.sumida.com PHONE FAX WEBSITE The regulator controls the output voltage and the power delivered to the outputs by modulating the duty cycle (D) of the power MOSFET in each switching cycle. The duty cycle of the MOSFET is approximated by: V −V D ≈ MAIN IN VMAIN The device regulates the output voltage through a combination of an error amplifier, two comparators, and several signal generators (Figure 3). The error amplifier compares the signal at FB to 1.24V and varies the COMP output. The voltage at COMP determines the current trip point each time the internal MOSFET turns on. 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 currentsense signal. Short-Circuit Current Limit The MAX1542/MAX1543 operational amplifiers limit short-circuit current to ±150mA if the output is directly shorted to SUP or AGND. In such a condition, the junction temperature of the IC rises until it reaches the thermal shutdown threshold, typically +160 ° C. Once it reaches this threshold, the IC shuts down and remains inactive until IN falls below VUVLO. Driving Pure Capacitive Loads The operational amplifiers are typically used to drive the LCD backplane (VCOM) or the gamma correction divider string. The LCD backplane consists of a distributed series capacitance and resistance, a load easily driven by the operational amplifiers. However, if the operational amplifiers are used in an application with a pure capacitive load, steps must be taken to ensure stable operation. As the operational amplifier’s capacitive load increases, the amplifier bandwidth decreases and gain peaking increases. A small 5Ω to 50Ω resistance placed between OUT_ and the capacitive load reduces peaking but reduces the amplifier gain. An alternative method of reducing peaking is the use of a snubber circuit. A 150Ω and 10nF (typ) shunt load, or snubber, does not continuously load the output or reduce amplifier gain. Operational Amplifiers The MAX1542/MAX1543 include two operational amplifiers that are typically used to drive the LCD backplane VCOM and/or the gamma correction divider string. The operational amplifiers feature ±150mA output short-circuit current, 7.5V/µs slew rate, and 12MHz bandwidth. The rail-to-rail inputs and outputs maximize flexibility. ______________________________________________________________________________________ 11 TFT LCD DC-to-DC Converter with Operational Amplifiers MAX1542/MAX1543 C4 0.1µF C3 0.1µF G_OFF -7V AT 20mA D4 G_ON +22V AT 20mA C2 0.1µF D2 C5 0.1µF D3 C6 0.1µF C7 0.1µF VMAIN VIN 2.6V TO 5.5V C1 10µF L1 4.7µF D1 +8V AT 250mA R1 75kΩ C8 4.7µF C9 4.7µF IN COMP LX FB SUP R8 100kΩ C11 220pF R2 13.7kΩ R5 40kΩ R3 40kΩ MAX1542 POS1 POS2 SRC CTL COM DEL PGND NEG1 OUT1 NEG2 OUT2 AGND R6 40kΩ R4 40kΩ TO VCOM BACKPLANE C10 33nF Figure 1. MAX1542 Typical Application Circuit Delay Control Circuit A capacitor from DEL to AGND selects the switch control block supply startup delay. After the input voltage exceeds VUVLO, a 5µA current source charges CDEL. Once the capacitor voltage exceeds the turn-on threshold (1.24V) COM can be connected to SRC, depending on the state of CTL. Before startup and when IN is less than VUVLO, DEL is internally connected to AGND to discharge CDEL. Select CDEL using the following equation: CDEL = (DELAY TIME) × 5µA 1.24 V CTL controls the P-channel MOSFET, between COM and SRC. A high at CTL turns on Q1 between SRC and COM, and a low at CTL turns Q1 off (Figure 4). MAX1543 Control Block Switch The switch control input (CTL) is not activated until the input voltage (VIN) exceeds VUVLO (2.5V) and VDEL exceeds the turn-on voltage (1.24V). During UVLO or when DEL is below the turn-on threshold, COM is pulled low to PGND through Q3 and a 1kΩ resistance. Once activated, CTL controls the COM MOSFETs, switching COM between SRC and DRN. A high at CTL turns on Q1 and disables Q2. A low at CTL turns on Q2 and turns off Q1 (Figure 4). MAX1542 Control Block Switch The switch control input (CTL) is not activated until VDEL exceeds the turn-on voltage (1.24V) and the input voltage (VIN) exceeds VUVLO (2.5V). Once activated, 12 Undervoltage Lockout (UVLO) The UVLO comparator of the MAX1542/MAX1543 compares the input voltage at IN with the UVLO threshold ______________________________________________________________________________________ TFT LCD DC-to-DC Converter with Operational Amplifiers MAX1542/MAX1543 C4 0.1µF G_OFF -7V AT 20mA VIN 2.6V TO 5.5V C1 10µF IN FREQ COMP R8 100kΩ C11 220pF L1 4.7µF D1 R1 75kΩ LX FB SUP R5 40kΩ POS1 POS2 CTL SRC NEG1 OUT1 NEG2 OUT2 AGND R6 40kΩ R4 40kΩ R3 40kΩ R2 13.7kΩ C8 4.7µF C3 0.1µF C2 0.1µF D2 C5 0.1µF C6 0.1µF D4 G_ON +22V AT 20mA D3 C7 0.1µF VMAIN +8V AT 250mA C9 4.7µF MAX1543 C10 33nF COM DRN DEL PGND TO VCOM BACKPLANE Figure 2. MAX1543 Typical Application Circuit (2.5V rising, 2.35V falling, typ) to ensure that the input voltage is high enough for reliable operation. The 150mV (typ) hysteresis prevents supply transients from causing a restart. Once the input voltage exceeds the UVLO threshold, startup begins. When the input voltage falls below the UVLO threshold, the controller turns off the N-channel MOSFET, the switch control block turns off Q1, and the operational amplifier outputs float. For the MAX1543, the switch control block also turns off Q2 and turns on Q3 when the input voltage falls below the UVLO threshold (Figure 4). Fault Protection Once the soft-start routine is complete, if the output of the main regulator is below the fault detection threshold, the MAX1542/MAX1543 activate the fault timer. If the fault condition continuously exists throughout the fault timer duration, the MAX1542/MAX1543 set the fault latch, which shuts down the device. After removing the fault condition, cycle the input voltage (IN) below VUVLO to clear the fault latch and reactivate the device. Digital Soft-Start The MAX1542/MAX1543 digital soft-start period duration is 14ms (typ). During this time, the MAX1542/ MAX1543 directly limit the peak inductor current, allowing from zero up to the full current-limit value in eight equal current steps (ILIM/8). The maximum load current is available after output voltage reaches the full regulation threshold (which terminates soft-start), or after the soft-start timer expires. 13 Oscillator Frequency (FREQ) The MAX1542 internal oscillator is preset to 1.2MHz. The internal oscillator frequency is pin programmable for the MAX1543. Connect FREQ to ground or leave it unconnected for 640kHz operation and connect it to VIN for 1.2MHz operation. FREQ has a 5µA (typ) pulldown current. ______________________________________________________________________________________ TFT LCD DC-to-DC Converter with Operational Amplifiers MAX1542/MAX1543 COMP ERROR AMPLIFIER FB 1.24V CLOCK ERROR COMPARATOR CONTROL AND DRIVER LOGIC SOFTSTART IN LX N PGND FREQ* OSCILLATOR SLOPE COMPENSATION ∑ CURRENT SENSE AGND 5µA SUP EXT* NEG1 5µA OUT1 SWITCH CONTROL (SEE FIGURE 4) NEG2 OUT2 POS1 POS2 MAX1542 MAX1543 DEL *MAX1543 ONLY. SRC COM DRN* CTL Figure 3. Functional Diagram Thermal-Overload Protection Thermal-overload protection prevents excessive power dissipation from overheating the MAX1542/MAX1543. When the junction temperature exceeds TJ = +160°C, a thermal sensor immediately activates the fault protection, which shuts down the device, allowing the IC to cool. The input voltage must fall (below VUVLO) to clear the fault latch and reactivate the controller. 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 = +150°C. Applications Information Inductor Selection The primary considerations in inductor selection are inductor physical shape, circuit efficiency, and cost. The factors that determine the inductance value are input voltage, output voltage, switching frequency, and maximum output current. Final inductor selection includes ensuring the chosen inductor meets the application’s peak current and RMS current requirements. Very high inductance values minimize the current ripple and therefore reduce the peak current, which decreases core losses in the inductor and I2R losses in the circuit’s entire power path. However, large inductance 14 ______________________________________________________________________________________ TFT LCD DC-to-DC Converter with Operational Amplifiers MAX1542/MAX1543 IN 5µA 2.5V N MAX1542 MAX1543 SRC Q1 DEL REF P COM P CTL Q2 1kΩ P DRN Q3 N MAX1543 ONLY Figure 4. Switch Control values also require more energy storage and more turns of wire, which increase physical size and can increase I2R losses in the inductor. Low inductance values decrease the physical 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, LIR, which is the ratio of the inductor peak-to-peak ripple current to the average DC inductor current at the full output current. The best trade-off between inductor size and circuit efficiency for step-up converters generally has an LIR 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 LIR 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 LIR can increase to between 0.5 and 1.0. Once a physical inductor is chosen, higher and lower values of that 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 (ηTYP) taken from an appropriate curve in the T ypical Operating Characteristics, and an estimate for LIR based on the above paragraphs: L ≅ VIN2 x ηTYP x (VMAIN − VIN ) / (VMAIN2 x LIR x IMAIN(MAX) x fOSC ) 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 ______________________________________________________________________________________ 15 TFT LCD DC-to-DC Converter with Operational Amplifiers operating point (ηMIN) taken from an appropriate curve in the Typical Operating Characteristics: IIN(DC,MAX) = IMAIN(MAX) ✕ VMAIN / (VIN(MIN) ✕ ηMIN) Calculate the ripple current at that operating point and the peak current required for the inductor: IRIPPLE = VIN(MIN) ✕ (VMAIN -VIN(MIN)) / (L ✕ fOSC ✕ VMAIN) IPEAK = IIN(DC,MAX) + (IRIPPLE) / 2 The inductor ’ s saturation current rating and the MAX1542/MAX1543s ’ L X current limit (I LIM ) should exceed I PEAK and the inductor ’ s DC current rating should exceed IIN(DC,MAX). For reasonable efficiency, choose an inductor with less than 0.5Ω series resistance. Considering the Typical Application Circuits, the maximum load current (IMAIN(MAX)) is 200mA with an 8V output and a typical input voltage of 3.3V. Choosing an LIR of 0.6 and estimating efficiency of 85% at this operating point: L = (3.3V)2 ✕ 0.85 ✕ (8V - 3.3V) / ((8V)2 ✕ 0.6 ✕ 0.2A ✕ 1.2MHz) = 4.7µH Using the circuit’s minimum input voltage (2.7V) and estimating efficiency of 80% at that operating point, IIN(DC,MAX) = (0.2A ✕ 8V / (2.7V ✕ 0.8)) = 741mA The ripple current and the peak current are: IRIPPLE = 2.7V ✕ (8V - 2.7V) / (4.7µH ✕ 1.2MHz ✕ 8V) = 317mA IPEAK = 741mA + (317mA / 2) = 900mA MAX1542/MAX1543 Input Capacitor Selection The input capacitor (CIN) reduces the current peaks drawn from the input supply and reduces noise injection into the device. A 10µF ceramic capacitor is used in the Typical Application Circuits (Figures 1 and 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 Application Circuits. Ensure a lownoise supply at IN by using adequate CIN. Output Voltage The MAX1542/MAX1543 operate with an adjustable output from VIN to 13V. Connect a resistive voltage-divider to FB ( Typical Application Circuits ) from the output (VMAIN) to AGND. Select the resistor values as follows: V  R1 = R2  MAIN − 1  VFB  where VFB, the step-up converter feedback set point, is 1.24V. Since the input bias current into FB is typically zero, R2 can have a value up to 100kΩ without sacrificing accuracy, although lower values provide better noise immunity. Connect the resistor-divider as close to the IC as possible. Loop Compensation Choose RCOMP to set the high-frequency integrator gain for fast transient response. Choose CCOMP to set the integrator zero to maintain loop stability. For low-ESR output capacitors, use the following equations to obtain stable performance and good transient response: RCOMP ≅ CCOMP ≅ 500 x VIN x VOUT x COUT L x IMAIN(MAX) VOUT x COUT 10 x IMAIN(MAX) x RCOMP 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): VRIPPLE = VRIPPLE(ESR) + VRIPPLE(C) VRIPPLE(ESR) ≅ IPEAK x RESR(COUT) , and V I −V  VRIPPLE(C) ≅ MAIN  MAIN IN  COUT  VMAIN × ƒ OSC  where I PEAK 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. To further optimize transient response, vary RCOMP in 20% steps and CCOMP in 50% steps while observing transient response waveforms. Charge Pumps Selecting the Number of Charge-Pump Stages For highest efficiency, always choose the lowest number of charge-pump stages that meet the output requirements. Figures 5 and 6 show the positive and 16 ______________________________________________________________________________________ TFT LCD DC-to-DC Converter with Operational Amplifiers MAX1542/MAX1543 POSITIVE CHARGE-PUMP OUTPUT VOLTAGE vs. VMAIN 60 VD = 0.3V TO 1V 50 -10 40 2-STAGE CHARGE-PUMP 30 20 10 1-STAGE CHARGE-PUMP 0 2 4 6 8 VMAIN (V) 10 12 14 -40 -45 2 4 6 8 VMAIN (V) 10 12 14 VD = 0.3V TO 1V G_OFF (V) G_ON (V) -15 -20 -25 -30 -35 2-STAGE CHARGE-PUMP 3-STAGE CHARGE-PUMP 3-STAGE CHARGE-PUMP -0 -5 1-STAGE CHARGE-PUMP NEGATIVE CHARGE-PUMP OUTPUT VOLTAGE vs. VMAIN Figure 5. Positive Charge-Pump Output Voltage vs. VMAIN Figure 6. Negative Charge-Pump Output Voltage vs. VMAIN negative charge-pump output voltages for a given VMAIN for one-, two-, and three-stage charge pumps, based on the following equations: G _ ON = VMAIN + n(VMAIN − VD ) G _ OFF = − n(VMAIN − VD ) where G_ON is the positive charge-pump output voltage, G_OFF is the negative charge-pump output voltage, n is the number of charge-pump stages, and VD is the voltage drop across each diode. VD is the forward voltage drop of the charge-pump diodes. Flying Capacitors Increasing the flying capacitor (C3, C4, and C5) value increases the output current capability. Increasing the capacitance indefinitely has a negligible effect on output current capability because the internal switch resistance and the diode impedance limit the source impedance. A 0.1µF ceramic capacitor works well in most low-current applications. The flying capacitor’s voltage rating must exceed the following: VCX > n ✕ VMAIN Where n is the stage number in which the flying capacitor appears, and VMAIN is the main output voltage. For example, the two-stage positive charge pump in the Typical Application Circuits (Figures 1 and 2) where VMAIN = 8V contains two flying capacitors. The flying capacitor in the first stage (C5) requires a voltage rat- ing greater than 8V. The flying capacitor in the second stage (C4) requires a voltage rating greater than 16V. Charge-Pump Output Capacitor Increasing the output capacitance or decreasing the ESR reduces the output ripple voltage and the peak-topeak transient voltage. With ceramic capacitors, the output voltage ripple is dominated by the capacitance value. Use the following equation to approximate the required capacitor value: COUT ≥ ILOAD 2 × FOSC × VRIPPLE where VRIPPLE is the acceptable peak-to-peak outputvoltage ripple. Charge-Pump Rectifier Diodes To maximize the available output voltage, use Schottky diodes with a current rating equal to or greater than two times the average charge-pump input current. If the loaded charge-pump output voltage is greater than required, some or all of the Schottky diodes can be replaced with low-cost silicon switching diodes with an equivalent current rating. The charge-pump input current is: ICP _ IN = ICP _ OUT × n where n is the number of charge-pump stages. ______________________________________________________________________________________ 17 TFT LCD DC-to-DC Converter with Operational Amplifiers MAX1542/MAX1543 Power Dissipation The MAX1542/MAX1543s’ maximum power dissipation depends on the thermal resistance from the IC die to the ambient environment and the ambient temperature. The thermal resistance depends on the IC package, PC board copper area, other thermal mass, and airflow. The MAX1542/MAX1543, with their exposed backside pad soldered to 1in2 of PC board copper, can dissipate about 1.7W into +70°C still air. More PC board copper, cooler ambient air, and more airflow increase the possible dissipation while less copper or warmer air decreases the IC’s dissipation capability. The major components of power dissipation are the power dissipated in the step-up converter and the power dissipated by the operational amplifiers. Step-Up Converter The largest portions of power dissipation in the step-up converter are the internal MOSFET, inductor, and the output diode. If the step-up converter has 90% efficiency, about 3% to 5% of the power is lost in the internal MOSFET, about 3% to 4% in the inductor, and about 1% in the output diode. The rest of the 1% to 3% is distributed among the input and output capacitors and the PC board traces. If the input power is about 3W, the power lost in the internal MOSFET is about 90mW to 150mW. Operational Amplifiers The power dissipated in the operational amplifiers depends on their output current, the output voltage, and the supply voltage: PDSOURCE = IOUT _(SOURCE) × (VSUP − VOUT _ ) PDSINK = IOUT _(SINK ) × VOUT _ where IOUT_(SOURCE) is the output current sourced by the operational amplifier, and IOUT_(SINK) is the output current that the operational amplifier sinks. In a typical case where the supply voltage is 8V and the output voltage is 4V with an output source current of 30mA, the power dissipated is 120mW. Minimize the area of high-current loops by placing the inductor, output diode, and output capacitors near the input capacitors and near LX and PGND. The high-current input loop goes from the positive terminal of the input capacitor to the inductor, to the IC’s LX pin, out PGND, and to the input capacitor negative terminal. The high-current output loop is from the positive terminal of the input capacitor to the inductor, to the catch diode (D1), to the positive terminal of the output capacitors, reconnecting between the output capacitor and input capacitor ground terminals. Connect these loop components together 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. 2) Create a power ground island (PGND) consisting of the input and output capacitor grounds, PGND pin, and the SRC bypass capacitor and other chargepump 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 island (AGND) consisting of the AGND pin, FB divider, the operation amplifier dividers, the COMP and DEL capacitor ground connections, and the device’s exposed backside pad. Connect the AGND and PGND islands by connecting the PGND pin directly to the exposed backside pad. Make no other connections between these separate ground planes. 3) Place the feedback voltage-divider resistors close to FB. 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. Avoid running the feedback trace near LX or the switching nodes in the charge pumps. 4) Minimize the length and maximize the width of the traces between the output capacitors and the load for best transient response. 5) Minimize the size of the LX node while keeping it wide and short. Keep the LX node away from the feedback node (FB) and analog ground. Use DC traces as shields if necessary. Refer to the MAX1543 Evaluation Kit for an example of proper board layout. Layout Procedure Careful PC board layout and routing are required for high-frequency switching power supplies to achieve good regulation, high efficiency, and stability. Use the following guidelines for good PC board layout: 1) Place the input capacitors close enough to the IC to provide adequate bypassing (within 1.5cm). Connect the input capacitors to IN with a wide trace. 18 ______________________________________________________________________________________ TFT LCD DC-to-DC Converter with Operational Amplifiers Pin Configurations (continued) COMP N.C. CTL DEL Chip Information TRANSISTOR COUNT: 2508 PROCESS: BiCMOS MAX1542/MAX1543 TOP VIEW 20 19 18 17 COM SRC N.C. PGND AGND 16 FB 1 2 3 4 5 10 15 14 N.C. IN LX SUP POS2 MAX1542 13 12 11 6 7 8 POS1 NEG1 OUT1 OUT2 9 THIN QFN ______________________________________________________________________________________ NEG2 19 TFT LCD DC-to-DC Converter with Operational Amplifiers MAX1542/MAX1543 Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.) 0.15 C A D2 C L D b D2/2 0.10 M C A B PIN # 1 I.D. D/2 0.15 C B k PIN # 1 I.D. 0.35x45 E/2 E2/2 E (NE-1) X e C L E2 k L DETAIL A e (ND-1) X e C L C L L L e 0.10 C A 0.08 C e C A1 A3 PROPRIETARY INFORMATION TITLE: PACKAGE OUTLINE 16, 20, 28, 32L, QFN THIN, 5x5x0.8 mm APPROVAL DOCUMENT CONTROL NO. REV. 21-0140 C 1 2 COMMON DIMENSIONS EXPOSED PAD VARIATIONS NOTES: 1. DIMENSIONING & TOLERANCING CONFORM TO ASME Y14.5M-1994. 2. ALL DIMENSIONS ARE IN MILLIMETERS. ANGLES ARE IN DEGREES. 3. N IS THE TOTAL NUMBER OF TERMINALS. 4. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO JESD 95-1 SPP-012. DETAILS OF TERMINAL #1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE ZONE INDICATED. THE TERMINAL #1 IDENTIFIER MAY BE EITHER A MOLD OR MARKED FEATURE. 5. DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.25 mm AND 0.30 mm FROM TERMINAL TIP. 6. ND AND NE REFER TO THE NUMBER OF TERMINALS ON EACH D AND E SIDE RESPECTIVELY. 7. DEPOPULATION IS POSSIBLE IN A SYMMETRICAL FASHION. 8. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS. 9. DRAWING CONFORMS TO JEDEC MO220. 10. WARPAGE SHALL NOT EXCEED 0.10 mm. PROPRIETARY INFORMATION TITLE: PACKAGE OUTLINE 16, 20, 28, 32L, QFN THIN, 5x5x0.8 mm APPROVAL DOCUMENT CONTROL NO. REV. 21-0140 C 2 2 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 20 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products. QFN THIN.EPS