19-3699; Rev 1; 9/05 Step-Up Regulator with Switch Control and Operational Amplifier for TFT LCD The MAX8758 includes a high-performance step-up regulator, a high-speed operational amplifier, and a logiccontrolled, high-voltage switch-control block with programmable delay. The device is optimized for thin-film transistor (TFT) liquid-crystal display (LCD) applications. The step-up DC-DC regulator provides the regulated supply voltage for the panel source driver ICs. The converter is a high-frequency (640kHz/1.2MHz), current-mode regulator with an integrated 14V n-channel power MOSFET. The high-switching frequency allows the use of ultra-small inductors and ceramic capacitors. The current-mode control architecture provides fast transient response to pulsed loads. The regulator achieves efficiencies over 85% by bootstrapping the supply rail of the internal gate driver from the step-up regulator output. The step-up regulator features undervoltage lockout (UVLO), soft-start, and internal current limit. The high-current operational amplifier is designed to drive the LCD backplane (VCOM). The amplifier features high output current (±150mA), fast slew rate (7.5V/µs), wide bandwidth (12MHz), and rail-to-rail inputs and outputs. The MAX8758 is available in a 24-pin, 4mm x 4mm, thin QFN package with a maximum thickness of 0.8mm for ultra-thin LCD panels. The device operates over the -40°C to +85°C temperature range. Features ♦ 1.8V to 5.5V Input Voltage Range ♦ Input Undervoltage Lockout ♦ 0.5mA Quiescent Current ♦ 640kHz/1.2MHz Current-Mode Step-Up Regulator Fast Transient Response High-Accuracy Output Voltage (1.5%) Built-In 14V, 2.5A, 115mΩ MOSFET High Efficiency Programmable Soft-Start Current Limit with Lossless Sensing Timer-Delay Fault Latch ♦ High-Speed Operational Amplifier ±150mA Output Current 7.5V/µs Slew Rate 12MHz, -3dB Bandwidth Rail-to-Rail Inputs/Outputs ♦ Dual-Mode™, Logic-Controlled, High-Voltage Switch with Programmable Delay ♦ Thermal-Overload Protection ♦ 24-Pin, 4mm x 4mm, Thin QFN Package Simplified Operating Circuit Applications Notebook Displays VGOFF LCD Monitors VIN VMAIN Ordering Information LX IN PART MAX8758ETG MAX8758ETG+ TEMP RANGE PIN-PACKAGE -40°C to +85°C 24 Thin QFN-EP* 4mm x 4mm -40°C to +85°C FB GND FREQ SHDN PGND COMP 24 Thin QFN-EP* 4mm x 4mm MAX8758 OUT LDO SUPB *EP = Exposed pad. +Denotes lead-free package. SS POSB Pin Configuration appears at end of data sheet. MODE NEGB OUTB DualMode is a trademark of Maxim Integrated Products, Inc. FROM TCON TO VCOM BACKPLANE THR CTL DRN DLP GON SRC VGON ________________________________________________________________ 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. 1 MAX8758 General Description MAX8758 Step-Up Regulator with Switch Control and Operational Amplifier for TFT LCD ABSOLUTE MAXIMUM RATINGS IN, SHDN, CTL, LDO to GND ...................................-0.3V to +6V SUPB, LX, OUT to GND..........................................-0.3V to +14V OUTB, NEGB, POSB to GND ..................-0.3V to (SUPB + 0.3V) THR, DLP, MODE, FREQ, COMP, FB, SS to GND..............................................-0.3V to VLDO + 0.3V PGND to GND ......................................................-0.3V to + 0.3V SRC to GND ..........................................................-0.3V to + 30V GON, DRN to GND ....................................-0.3V to VSRC + 0.3V GON RMS Current Rating................................................± 50mA OUTB RMS Current Rating ..............................................± 60mA LX RMS Current Rating .........................................................1.6A Continuous Power Dissipation (TA = +70°C) 24-Pin, 4mm x 4mm Thin QFN (derate 16.9mW/°C above +70°C) ..........................1349.1mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +160°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 = V SHDN = +3V, OUT = +10V, FREQ = GND, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS IN Input Voltage Range MIN TYP 1.8 MAX UNITS 5.5 V IN Quiescent Current VIN = 3V, VFB = 1.5V 27 40 µA IN Undervoltage Lockout IN rising, 200mV hysteresis, LX remains off below this level 1.3 1.75 V LDO Output Voltage 6V ≤ VOUT ≤ 13V, ILDO = 12.5mA, VFB = 1.5V (Note1) 4.8 5.0 5.2 V LDO Undervoltage Lockout Voltage LDO rising, 200mV hysteresis 2.4 2.7 3.0 V OUT Supply Voltage Range (Note 1) 13.0 V OUT Overvoltage Fault Threshold 4.5 13.2 13.6 OUT Undervoltage Fault Threshold 14.0 V 1.4 V VFB = 1.5V, no load 0.5 2.0 VFB = 1.1V, no load 4 10.0 Shutdown Supply Current (Total of IN, OUT, and SUPB) VIN = VOUT = VSUPB = 3V 4 10 Thermal Shutdown Temperature rising, 15°C hysteresis OUT Supply Current +160 mA µA °C STEP-UP REGULATOR Operating Frequency Oscillator Maximum Duty Cycle FREQ = GND 512 600 768 FREQ = IN 1020 1200 1380 FREQ = GND 91 95 99 FREQ = IN 88 92 96 1.228 1.24 1.252 V 0.96 1.0 1.04 V FB Regulation Voltage FB Fault Trip Level Duration to Trigger Fault Condition FB Load Regulation Falling edge FREQ = GND 43 51 64 FREQ = IN 47 55 65 0 < ILOAD < 200mA, transient only -1 FB Line Regulation VIN = 1.8V to 5.5V FB Input Bias Current VFB = 1.3V FB Transconductance ΔI = 5µA at COMP FB Voltage Gain FB to COMP 700 LX On-Resistance ILX = 200mA 115 2 -0.15 75 kHz % ms % -0.08 +0.15 %/V 125 200 nA 160 280 µS 200 mΩ _______________________________________________________________________________________ V/V Step-Up Regulator with Switch Control and Operational Amplifier for TFT LCD (VIN = V SHDN = +3V, OUT = +10V, FREQ = GND, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS LX Leakage Current VLX = 13V LX Current Limit 65% duty cycle MIN TYP MAX UNITS µA 0.01 20 2.0 2.5 3.0 A Current-Sense Transresistance 0.19 0.3 0.40 V/A SS Source Current 3.0 4.0 5.5 µA 0.6 V POSITIVE GATE DRIVER TIMING AND CONTROL SWITCHES CTL Input Low Voltage CTL Input High Voltage CTL Input Leakage Current VIN = 1.8V to 5.5V VIN = 1.8V to 2.4V 1.4 VIN = 2.4V to 5.5V 2.0 VCTL = 0 or VIN -1 V +1 µA GON rising, VMODE = 1.24V, VCTL = 0 to 3V step, no load on GON 100 GON falling, VMODE = 1.24V, VCTL = 3V to 0 step, no load on GON 100 SRC Input Voltage VDLP = 0, VIN = 3V 2500 SRC Input Current MODE = DLP = CTL = LDO 150 250 µA DRN Input Current MODE = DLP = LDO, VDRN = 8V, VCTL = 0 150 250 µA SRC-to-GON Switch On-Resistance DLP = CTL = LDO 15 30 Ω DRN-to-GON Switch On-Resistance DLP = LDO, VCTL = 0 65 130 Ω GON-to-PGND Switch On-Resistance VDLP = 0, VIN = 3V 2500 Ω MODE Switch On-Resistance VDLP = 0, VIN = 3V 1000 Ω MODE 1 Voltage Threshold MODE rising 0.9 x VLDO V MODE Capacitor Charge Current (MODE 2) VMODE = 1.5V 40 50 62 µA MODE 2 Switch Transition Voltage Threshold GON connected to DRN 2.3 2.5 2.7 V MODE Current-Source Stop Threshold MODE rising 3.3 3.5 3.7 V DLP Capacitor Charge Current During startup, VDLP = 1.0V 4 5 6 µA 2.375 2.500 2.625 V 9.7 10.0 10.3 V/V CTL-to-SRC Propagation Delay ns DLP Turn-On Threshold THR-to-GON Voltage Gain VGON = 12V, VTHR = 1.2V Ω OPERATIONAL AMPLIFIER SUPB Supply Range 13.0 V SUPB Supply Current Buffer configuration, VPOSB = 4V, no load 1.0 mA Input Offset Voltage VNEGB, VPOSB = VSUPB/2, TA = +25°C 12 mV Input Bias Current VNEGB, VPOSB = VSUPB/2 -50 +50 nA 0 VSUPB V Input Common-Mode Voltage Range 4.5 _______________________________________________________________________________________ 3 MAX8758 ELECTRICAL CHARACTERISTICS (continued) MAX8758 Step-Up Regulator with Switch Control and Operational Amplifier for TFT LCD ELECTRICAL CHARACTERISTICS (continued) (VIN = V SHDN = +3V, OUT = +10V, FREQ = GND, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS MIN IOUTB = 100µA VSUPB 15 IOUTB = 5mA VSUPB 150 TYP MAX Output Voltage Swing High Output Voltage Swing Low UNITS mV IOUTB = -100µA 15 IOUTB = -5mA 150 mV Slew Rate 7.5 V/µs -3dB Bandwidth 12 MHz Gain-Bandwidth Product 8 MHz Short-Circuit Current OUTB shorted to VSUPB/2, sourcing 75 150 OUTB shorted to VSUPB/2, sinking 75 150 mA CONTROL INPUTS FREQ Input Low Voltage VIN = 1.8V to 5.5V 0.6 VIN = 1.8V to 2.4V 1.4 VIN = 2.4V to 5.5V 2.0 FREQ Pulldown Current VFREQ = 1.0V 3.5 SHDN Input Low Voltage VIN = 1.8V to 5.5V FREQ Input High Voltage SHDN Input High Voltage VIN = 1.8V to 2.4V 1.4 VIN = 2.4V to 3.6V 2.0 VIN = 3.6V to 5.5V 2.9 SHDN Input Current V V 5.0 6.0 µA 0.6 V V 0.001 1.0 µA TYP MAX UNITS ELECTRICAL CHARACTERISTICS (VIN = V SHDN = +3V, OUT = +10V, FREQ = GND, TA = -40°C to +85°C, unless otherwise noted.) (Note 2) PARAMETER CONDITIONS IN Input Voltage Range MIN 1.8 5.5 V 30 µA 1.75 V 5.2 V IN Quiescent Current VIN = 3V, VFB = 1.5V IN Undervoltage Lockout IN rising, 200mV hysteresis, LX remains off below this level LDO Output Voltage 6V ≤ VOUT ≤ 13V, ILDO = 12.5mA, VFB = 1.5V (Note 1) LDO Undervoltage Lockout Voltage LDO rising, 200mV hysteresis 2.4 3.0 V OUT Supply Voltage Range (Note 1) 4.5 13.0 V OUT Supply Current 4.8 VFB = 1.5V, no load 2.0 VFB = 1.1V, no load 10.0 mA STEP-UP REGULATOR Operating Frequency 4 FREQ = GND 512 768 FREQ = IN 990 1380 _______________________________________________________________________________________ kHz Step-Up Regulator with Switch Control and Operational Amplifier for TFT LCD (VIN = V SHDN = +3V, OUT = +10V, FREQ = GND, TA = -40°C to +85°C, unless otherwise noted.) (Note 2) PARAMETER Oscillator Maximum Duty Cycle CONDITIONS MIN TYP MAX UNITS FREQ = GND 91 99 FREQ = IN 88 96 1.220 1.252 V 75 280 µS 200 mΩ 3.0 A 28 V FB Regulation Voltage FB Transconductance ΔI = 5µA at COMP LX On-Resistance ILX = 200mA LX Current Limit 65% duty cycle 2.0 % POSITIVE GATE DRIVER TIMING AND CONTROL SWITCHES SRC Input Voltage Range SRC Input Current MODE = DLP = CTL = LDO 250 µA DRN Input Current MODE = DLP = LDO, VDRN = 8V, VCTL = 0 250 µA SRC-to-GON Switch On-Resistance DLP = CTL = LDO 30 Ω DRN-to-GON Switch On-Resistance DLP = LDO, VCTL = 0 THR-to-GON Voltage Gain VGON = 12V, VTHR = 1.2V 130 Ω 9.7 10.3 V/V 4.5 OPERATIONAL AMPLIFIER SUPB Supply Range 13.0 V SUPB Supply Current Buffer configuration, VPOSB = 4V, no load 1.0 mA Input Offset Voltage VNEGB, VPOSB = VSUPB / 2 18 mV VSUPB V Input Common-Mode Voltage Range 0 IOUTB = 100µA VSUPB - 15 IOUTB = 5mA VSUPB - 150 Output Voltage Swing High Output Voltage Swing Low Short-Circuit Current mV IOUTB = -100µA 15 IOUTB = -5mA 150 OUTB shorted to VSUPB/2, sourcing 75 OUTB shorted to VSUPB/2, sinking 75 mV mA Note 1: OUT and SUP can operate down to 4.5V. LDO will be out of regulation, but IC will function correctly. Note 2: -40°C specs are guaranteed by design, not production tested. _______________________________________________________________________________________ 5 MAX8758 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (Circuit of Figure 1, VIN = 3.3V, VMAIN = 8.5V, FREQ = SHDN = IN, TA = +25°C, unless otherwise noted.) 80 75 70 VIN = 1.8V 65 90 85 EFFICIENCY (%) 60 80 75 VIN = 1.8V 70 VIN = 3.3V 65 8.5 8.4 8.3 8.2 8.1 60 VIN = 3.3V 55 50 50 1 10 1000 100 7.9 1 10 1000 100 10 100 LOAD CURRENT (mA) IN QUIESCENT CURRENT vs. SUPPLY VOLTAGE IN QUIESCENT CURRENT vs. TEMPERATURE SWITCHING FREQUENCY vs. INPUT VOLTAGE SUPPLY CURRENT (μA) 20 28 CURRENT INTO IN PIN 27 26 VIN = 3.3V NOT SWITCHING VFB - 1.5V 25 NOT SWITCHING VFB - 1.5V 0 3.0 3.5 4.0 4.5 5.0 5.5 FREQ = VIN 1000 800 FREQ = AGND 600 IMAIN = 200mA 24 2.5 MAX8758 toc06 29 1200 SWITCHING FREQUENCY (kHz) 30 MAX8758 toc04 CURRENT INTO IN PIN 30 10 400 -40 -15 VIN (V) 10 35 60 85 1.5 2.5 TEMPERATURE (°C) 3.5 5.5 STEP-UP REGULATOR LOAD TRANSIENT RESPONSE MAX8758 toc07 MAX8758 toc08 VIN 2V/div VMAIN 5V/div IL 500mAV/div L = 4.7μH RCOMP = 100kΩ CCOMP1 = 220pF CCOMP2 = 47pF VMAIN AC-COUPLED 200mV/div IMAIN 500mA/div 50mA IL 1AV/div 0 1ms 4.5 VIN (V) STEP-UP REGULATOR HEAVY-LOAD SOFT-START 6 1000 LOAD CURRENT (mA) 40 2.0 1 LOAD CURRENT (mA) 50 1.5 fOSC = 1.2Hz VIN = 3.3V 8.0 fOSC = 640kHz L = 10μH 55 MAX8758 toc05 EFFICIENCY (%) 85 VIN = 5.5V OUTPUT VOLTAGE (V) 90 8.6 MAX8758 toc02 VIN = 5.5V fOSC = 1.2MHz L = 4.7μH STEP-UP REGULATOR OUTPUT VOLTAGE vs. LOAD CURRENT (VMAIN = 8.5V) 95 MAX8758 toc01 95 STEP-UP REGULATOR EFFICIENCY vs. LOAD CURRENT (VMAIN = 8.5V) MAX8758 toc03 STEP-UP REGULATOR EFFICIENCY vs. LOAD CURRENT (VMAIN = 8.5V) SUPPLY CURRENT (μA) MAX8758 Step-Up Regulator with Switch Control and Operational Amplifier for TFT LCD 20μs/div _______________________________________________________________________________________ Step-Up Regulator with Switch Control and Operational Amplifier for TFT LCD (Circuit of Figure 1, VIN = 3.3V, VMAIN = 8.5V, FREQ = SHDN = IN, TA = +25°C, unless otherwise noted.) STEP-UP REGULATOR PULSED LOAD TRANSIENT RESPONSE TIMER-DELAY LATCH RESPONSE TO OVERLOAD MAX8758 toc09 L = 4.7μH RCOMP = 100kΩ CCOMP1 = 220pF CCOMP2 = 47pF MAX8758 toc10 IL 1AV/div VMAIN 5V/div 0V LX 5V/div 0V VMAIN AC-COUPLED 200mV/div IL 2A/div IMAIN 1A/div 0A 20μs/div 20ms/div NO LOAD BUFFER CONFIGURATION VPOSB = VSUPB / 2 VSUPB = 12V ISUPB (mA) 0.25 0.20 0.15 0.20 VSUPB = 8V 0.15 VSUPB = 5V 0 MAGNITUDE (dB) 0.25 10 MAX8758 toc12 0.30 MAX8758 toc11 NO LOAD BUFFER CONFIGURATION POS_ = VSUPB / 2 ISUPB (mA) OPERATIONAL AMPLIFIER FREQUENCY RESPONSE FOR VARIOUS CLOAD SUPB SUPPLY CURRENT vs. TEMPERATURE MAX8758 toc13 SUPB SUPPLY CURRENT vs. SUPB VOLTAGE 0.30 -10 1000pF -20 -30 VSUP = 8.5V AV = 1 RL = 10kΩ -40 0.10 0.10 4.5 6.0 7.5 9.0 10.5 VSUPB (V) 12.0 13.5 15.0 POWER-SUPPLY REJECTION RATIO vs. FREQUENCY -50 -40 -10 20 TEMPERATURE (°C) 50 100 70 1k 10k 100k FREQUENCY (Hz) OP-AMP LOAD TRANSIENT RESPONSE OP-AMP RAIL-TO-RAIL INPUT/OUTPUT MAX8758 toc16 MAX8758 toc14 100 VPOSB 5V/div 80 PSRR (dB) 56pF MAX8758 toc15 120 MAX8758 Typical Operating Characteristics (continued) 60 0 IOUTB 50mA/div VOUTB 5V/div 40 VOUTB 2V/div 20 VSUPB = 8.5V 0 1 10 100 1k 10k 100k 1M 100μs/div 1μs/div FREQUENCY (Hz) _______________________________________________________________________________________ 7 Typical Operating Characteristics (continued) (Circuit of Figure 1, VIN = 3.3V, VMAIN = 8.5V, FREQ = SHDN = IN, TA = +25°C, unless otherwise noted.) OP-AMP LARGE-SIGNAL STEP RESPONSE HIGH-VOLTAGE SWITCH CONTROL FUNCTION (MODE 1) OP-AMP SMALL-SIGNAL STEP RESPONSE MAX8758 toc17 MAX8758 toc18 MAX8758 toc19 VMODE VCTL VPOSB 100mV/div AC-COUPLED VOUTB 2V/div VOUTB 200mV/div AC-COUPLED 1μs/div MAX8758 toc20 200ns/div 400μs/div POSITIVE CHARGE-PUMP OUTPUT VOLTAGE vs. CHARGE-PUMP LOAD CURRENT NEGATIVE CHARGE-PUMP OUTPUT VOLTAGE vs. LOAD CURRENT VGON 24 23 22 -8 VIN = 3.3V fOSC = 1.2MHz VIN = 3.3V fOSC = 1.2MHz -10 20 0 5 10 15 CHARGE-PUMP LOAD CURRENT (mA) 8 -7 -9 21 400μs/div -6 OUTPUT VOLTAGE (V) VCTL -5 MAX8758 toc21 25 VMODE VGON MAX8758 toc22 HIGH-VOLTAGE SWITCH CONTROL FUNCTION (MODE 2) OUTPUT VOLTAGE (V) MAX8758 Step-Up Regulator with Switch Control and Operational Amplifier for TFT LCD 20 0 5 10 15 CHARGE-PUMP LOAD CURRENT (mA) _______________________________________________________________________________________ 20 Step-Up Regulator with Switch Control and Operational Amplifier for TFT LCD PIN NAME FUNCTION 1 GND Analog Ground 2 GON Internal High-Voltage-Switch Common Connection. GON is the output of the high-voltage-switchcontrol block. GON is internally pulled to PGND through a 1kΩ resistor in shutdown. See the HighVoltage Switch Control section for details. 3 CTL High-Voltage, Switch-Control Block Timing Pin. See the High-Voltage Switch Control section for details. 4 DLP High-Voltage, Switch-Control Block Delay Pin. Connect a capacitor from DLP to GND to set the delay time. A 5µA current source charges CDLP. DLP is internally pulled to GND by a resistor in shutdown. See the High-Voltage Switch Control section for details. 5 THR GON Falling Regulation Adjustment Pin. Connect THR to the center of a resistive voltage-divider between LDO or OUT and GND to adjust the VGON falling regulation level. The actual regulation level is 10 x VTHR. See the High-Voltage Switch Control section for details. 6 SUPB Operational Amplifier Supply Input. Bypass SUPB to GND with a 0.1µF capacitor. 7 OUTB Operational Amplifier Output 8 NEGB Operational Amplifier Inverting Input 9 POSB Operational Amplifier Noninverting Input 10 N.C. No Connection. Not internally connected. 11 LDO 5V Internal Linear Regulator Output. This regulator powers all internal circuitry except the operational amplifier. Bypass LDO to GND with a 0.22µF or greater ceramic capacitor. 12 OUT Internal Linear Regulator Supply Pin. OUT is the supply input of the internal 5V linear regulator. Connect OUT directly to the output of the step-up regulator. 13 I.C. Internally Connected. Make no connection to this pin. 14 SS Soft-Start Control Pin. Connect a capacitor between SS and GND to set the soft-start period of the step-up regulator. See the Bootstrapping and Soft-Start section for details. 15 COMP Error Amplifier Compensation Pin. See the Step-Up Regulator Loop Compensation section for details. 16 FREQ Frequency-Select Pin. Connect FREQ to GND for 600kHz operation, and connect FREQ to IN for 1.2MHz operation. 17 IN Supply Pin. Bypass IN to GND with a 1µF ceramic capacitor. Place the capacitor close to the IN pin. 18 LX Switching Node. LX is the drain of the internal power MOSFET. Connect the inductor and the Schottky diode to LX and minimize trace area for low EMI. 19 SHDN Shutdown Control Pin. Pull SHDN low to turn off the step-up regulator, the operational amplifier, and the switch control block. 20 FB Feedback Pin. The FB regulation point is 1.24V (typ). Connect FB to the center of a resistive voltagedivider between the step-up regulator output and GND to set the step-up regulator output voltage. Place the divider close to the FB pin. 21 PGND Power Ground 22 MODE High-Voltage, Switch-Control Block-Mode Selection Timing-Adjustment Pin. See the High-Voltage Switch Control section for details. MODE is high impedance when it is connected to LDO. MODE is internally pulled down by a 1kΩ resistor during UVLO, when VDLP < 0.5 x VLDO, or in shutdown. 23 DRN High-Voltage, Switch-Control Input. DRN is the drain of the internal high-voltage p-channel MOSFET connected to GON. 24 SRC High-Voltage Switch-Control Input. SRC is the source of the internal high-voltage p-channel MOSFET. _______________________________________________________________________________________ 9 MAX8758 Pin Description MAX8758 Step-Up Regulator with Switch Control and Operational Amplifier for TFT LCD Typical Operating Circuit driver supplies. The input voltage range for the IC is from +1.8V to +5.5V, but the Figure 1 circuit is designed to run from 2.7V to 3.6V. Table 1 lists some selected components and Table 2 lists the contact information of component suppliers. The typical operating circuit (Figure 1) of the MAX8758 is a power-supply solution for TFT LCD panels in notebook computers. The circuit generates a +8.5V source driver supply, and approximately +22V and -7V gate D4 C17 0.1μF D2 D3 C6 0.1μF VGOFF -8V/20mA C18 0.1μF C15 0.1μF C19 0.1μF VIN +1.8V TO +5.5V C1 3.3μF 6.3V L1 4.7μH C2 3.3μF 6.3V R4 10Ω R10 100kΩ VMAIN +8.5V/300mA D1 R1 200kΩ 1% LX C3 4.7μF 10V C4 4.7μF 10V FB IN C6 1μF R2 34.0kΩ 1% GND FREQ SHDN R3 100kΩ MAX8758 PGND COMP C7 220pF C8 33pF OUT LDO SUPB C12 0.1μF C9 0.22μF SS R5 100kΩ POSB C10 0.022μF R6 100kΩ NEGB MODE C11 150pF TO VCOM BACKPLANE OUTB R7 51.1kΩ 1% THR FROM TCON CTL R9 20kΩ DRN R8 20.0kΩ 1% DLP C13 0.033μF VGON +24V/20mA GON SRC C14 0.1μF Figure 1. Typical Operating Circuit 10 ______________________________________________________________________________________ C5 4.7μF 10V Step-Up Regulator with Switch Control and Operational Amplifier for TFT LCD MAX8758 VIN LX MAX8758 IN PGND LDO LINEAR REGULATOR AND BOOTSTRAP STEP-UP REGULATOR CONTROLLER FB COMP SHDN SS FREQ SRC SUPB GON DRN NEGB SWITCH CONTROL OUTB CTL THR POSB MODE DLP GND Figure 2. Functional Diagram Table 1. Component List DESIGNATION DESCRIPTION C1, C2 3.3µF ±10%, 6.3V X5R ceramic capacitors (0603) TDK C1608X5R0J335M C3, C4, C5 4.7µF ±20%, 10V X5R ceramic capacitors (1206) TDK C3216X5R1A475M D1 D2, D3, D4 L1 3A, 30V Schottky diode (M-flat) Toshiba CMS02 (top mark S2) 200mA, 100V dual diodes (SOT23) Fairchild MMBD4148SE (top mark D4) 4.2µH, 1.9A inductor Sumida CDRH6D12-4R2 Detailed Description The MAX8758 is designed primarily for TFT LCD panels used in notebook computers. It contains a high-performance step-up regulator, a high-speed operational amplifier, a logic-controlled, high-voltage switch-control block with programmable delay, and an internal linear regulator for bootstrapping operation. Figure 2 shows the MAX8758 functional block diagram. Step-Up Regulator The step-up regulator is designed to generate the LCD source driver supply. It employs a current-mode, fixedfrequency PWM architecture to maximize loop bandwidth and provide fast transient response to pulsed loads typical of TFT LCD panel source drivers. The internal oscillator offers two pin-selectable frequency options (640kHz/1.2MHz), allowing users to optimize their designs based on the specific application requirements. ______________________________________________________________________________________ 11 MAX8758 Step-Up Regulator with Switch Control and Operational Amplifier for TFT LCD Table 2. Component Suppliers PHONE FAX Fairchild Semiconductor SUPPLIER 408-822-2000 408-822-2102 www.fairchildsemi.com WEBSITE Sumida 847-545-6700 847-545-6720 www.sumida.com TDK 847-803-6100 847-390-4405 www.component.tdk.com Toshiba 949-455-2000 949-859-3963 www.toshiba.com/taec The internal n-channel power MOSFET reduces the number of external components. The supply rail of the internal gate driver is bootstrapped to the internal linear regulator output to improve the efficiency at low-input voltages. The external-capacitor, soft-start function effectively controls inrush currents. The output voltage can be set from VIN to 13V with an external resistive voltage-divider. PWM Control Block Figure 3 is the block diagram of the step-up regulator. 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 ≈ VOUT − VIN VOUT LX CLOCK LOGIC AND DRIVER PGND ILIM COMPARATOR SOFTSTART ILIMIT SLOPE COMP OSCILLATOR PWM COMPARATOR SS ∑ CURRENT SENSE FAULT COMPARATOR TO FAULT LOGIC ERROR AMP where VOUT is the output voltage of the step-up regulator. On the rising edge of the internal oscillator 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. A transconductance error amplifier compares the FB voltage with a 1.24V (typ) reference voltage. The error amplifier changes the COMP voltage by charging or discharging the COMP capacitor. The COMP voltage is compared with a ramp, which is the sum of the current-sense signal and a slope compensation signal. Once the ramp signal 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 Schottky diode (D1 in Figure 1). 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 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. 12 FB 1.0V 1.24V COMP FREQ Figure 3. Step-Up Regulator Block Diagram Bootstrapping and Soft-Start The MAX8758 features bootstrapping operation. In normal operation, the internal linear regulator supplies power to the internal circuitry. The input of the linear regulator (OUT) should be directly connected to the output of the step-up regulator. The step-up regulator is enabled when the input voltage at OUT is above 1.75V, SHDN is high, and the fault latch is not set. After being enabled, the regulator starts open-loop switching to generate the supply voltage for the linear regulator with a controlled duty cycle. The internal reference block turns on when the LDO voltage exceeds 2.7V (typ). When the reference voltage reaches regulation, the PWM controller and the current-limit circuit are enabled and the step-up regulator enters soft-start. ______________________________________________________________________________________ Step-Up Regulator with Switch Control and Operational Amplifier for TFT LCD Fault Protection During steady-state operation, the MAX8758 monitors the FB voltage. If the FB voltage is below 1V (typ), the MAX8758 activates an internal fault timer. If there is a continuous fault for the fault-timer duration, the MAX8758 sets the fault latch, shutting down all the outputs. Once the fault condition is removed, cycle the input voltage to clear the fault latch and reactivate the device. The faultdetection circuit is disabled during the soft-start time. The MAX8758 monitors the OUT voltage for undervoltage and overvoltage conditions. If the OUT voltage is below 1.4V (typ) or above 13.5V (typ), the MAX8758 disables the gate driver of the step-up regulator and prevents the internal MOSFET from switching. The OUT undervoltage and overvoltage conditions do not set the fault latch. Table 3. Frequency Selection FREQ SWITCHING FREQUENCY (kHz) GND 600 IN 1200 Operational Amplifier The MAX8758’s operational amplifier is typically used to drive the LCD backplane (VCOM) or the gamma-correction-divider string. The operational amplifier features ±150mA output short-circuit current, 7.5V/µs slew rate, and 12MHz bandwidth. The rail-to-rail input and output capability maximizes system flexibility. Short-Circuit Current Limit The operational amplifier limits short-circuit current to approximately ±150mA if the output is directly shorted to SUPB or to GND. If the short-circuit condition persists, the junction temperature of the IC rises until it reaches the thermal shutdown threshold (+160°C typ). Once the junction temperature reaches the thermal shutdown threshold, an internal thermal sensor immediately sets the thermal fault latch, shutting off all the IC’s outputs. The device remains inactive until the input voltage is cycled or SHDN is toggled. The thermal-overload protection prevents excessive power dissipation from overheating the MAX8758. When the junction temperature exceeds TJ = +160°C, a thermal sensor immediately activates the fault protection, which sets the fault latch and shuts down all the outputs, allowing the device to cool down. Once the device cools down by approximately 15°C, cycle the input voltage or toggle SHDN to clear the fault latch and restart 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 = +150°C. Driving Pure Capacitive Load The operational amplifier is 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 that can be easily driven by the operational amplifier. However, if the operational amplifier is 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’s bandwidth decreases and gain peaking increases. A 5Ω to 50Ω small resistor placed between OUTB and the capacitive load reduces peaking but also reduces the gain. An alternative method of reducing peaking is to place a series RC network (snubber) in parallel with the capacitive load. The RC network does not continuously load the output or reduce the gain. Typical values of the resistor are between 100Ω and 200Ω and the typical value of the capacitor is 10pF. Frequency Selection (FREQ) The FREQ pin selects the switching frequency. Table 3 shows the switching frequency based on the FREQ connection. High-frequency (1.2MHz) operation optimizes the application for the smallest component size, trading off efficiency due to higher switching losses. Low-frequency (600kHz) operation offers the best overall efficiency at the expense of component size and board space. The MAX8758’s high-voltage switch-control block (Figure 5) consists of two high-voltage, p-channel MOSFETs: Q1, between SRC and GON and Q2, between GON and DRN. The switch-control block is enabled when VDLP exceeds VLDO/2 and then Q1 and Q2 are controlled by CTL and MODE. There are two different modes of operation (see the Typical Operating Characteristics section.) Thermal-Overload Protection High-Voltage Switch Control ______________________________________________________________________________________ 13 MAX8758 The soft-start timing can be adjusted with an external capacitor connected between SS and GND. After the step-up regulator is enabled, the SS pin is immediately charged to 0.5V. Then the capacitor is charged at a constant current of 4µA (typ). During this time, the SS voltage directly controls the peak inductor current, allowing a linear ramp from zero up to the full current limit. The maximum load current is available after the voltage on SS exceeds 1.5V. The soft-start capacitor is discharged to ground when SHDN is low. The soft-start routine minimizes inrush current and voltage overshoot and ensures a well-defined startup behavior (see the Step-Up Regulator Heavy Load Soft-Start waveform in the Typical Operating Characteristics). MAX8758 Step-Up Regulator with Switch Control and Operational Amplifier for TFT LCD Activate the first mode by connecting MODE to LDO. When CTL is logic high, Q1 turns on and Q2 turns off, connecting GON to SRC. When CTL is logic low, Q1 turns off and Q2 turns on, connecting GON to DRN. GON can then be discharged through a resistor connected between DRN and PGND or AVDD. Q2 turns off and stops discharging GON when VGON reaches 10 times the voltage on THR. When VMODE is less than 0.9 x VLDO, the switch control block works in the second mode. The rising edge of VCTL turns on Q1 and turns off Q2, connecting GON to SRC. An internal n-channel MOSFET Q3 between MODE and GND is also turned on to discharge an external capacitor between MODE and GND. The falling edge of VCTL turns off Q3, and an internal 50µA current source starts charging the MODE capacitor. Once VMODE exceeds 0.5 x VREF, the switch control block turns off Q1 and turns on Q2, connecting GON to DRN. GON can then be discharged through a resistor connected between DRN and GND or AVDD. Q2 turns off and stops discharging GON when VGON reaches 10 times the voltage on THR. The timing of enabling the switch control block can be adjusted with an external capacitor connected between DLP and GND. An internal current source starts charging the DLP capacitor if the input voltage is above 1.75V (typ), SHDN is high, and the fault latch is not set. The voltage on DLP linearly rises because of the constant-charging current. When VDLP goes above 2.5V (typ), the switch control block is enabled. The switch control block is disabled and DLP is held low when the MAX8758 is shut down or in a fault state. Linear Regulator (LDO) The MAX8758 includes an internal 5V linear regulator. OUT is the input of the linear regulator and should be directly connected to the output of the step-up regulator. The input voltage range is between 4.5V and 13V. The output of the linear regulator (LDO) is set to 5V (typ). The regulator powers all the internal circuitry including the gate driver. This feature significantly improves the efficiency at low input voltages. Bypass the LDO pin to GND with a 0.22µF or greater ceramic capacitor. 14 Design Procedure Step-Up Regulator Step-Up Regulator Inductor Selection The 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. Physical size and cost are also important factors to be considered. 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 I2R losses in the entire power path. However, large inductor 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-load current. The best trade-off between inductor size and circuit efficiency for step-up regulators 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. ______________________________________________________________________________________ Step-Up Regulator with Switch Control and Operational Amplifier for TFT LCD MAX8758 REF 5μA DLP FAULT Q4 SHDN REF_OK SRC 0.5 x VREF Q1 GON 9R 1kΩ REF Q3 R Q2 R 50μA DRN THR 4R MODE 1kΩ 5R Q5 CTL Figure 4. Switch Control ______________________________________________________________________________________ 15 MAX8758 Step-Up Regulator with Switch Control and Operational Amplifier for TFT LCD In Figure 1’s Typical Operating Circuit, the LCD’s gateon and gate-off voltages are generated from two unregulated charge pumps driven by the step-up regulator’s LX node. The additional load on LX must therefore be considered in the inductance calculation. The effective maximum output current IMAIN(EFF) becomes the sum of the maximum load current on the step-up regulator’s output plus the contributions from the positive and negative charge pumps: IMAIN(EFF) = IMAIN(MAX) + nNEG x INEG + (nPOS + 1) x IPOS where IMAIN(MAX) is the maximum output current, nNEG is the number of negative charge-pump stages, nPOS is the number of positive charge-pump stages, INEG is the negative charge-pump output current, and IPOS is the positive charge-pump output current, assuming the pump source for IPOS is VMAIN. The required inductance can then be calculated as follows: ⎛ V ⎞ L = ⎜ IN ⎟ ⎝ VMAIN ⎠ 2 IIN(DCMAX , ) = IMAIN(EFF) × VMAIN VIN(MIN) × ηMIN Calculate the ripple current at that operating point and the peak current required for the inductor: ( VIN(MIN) × VMAIN − VIN(MIN) L × VMAIN × fOSC The inductor’s saturation current rating and the guaranteed minimum value of the MAX8758’s 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. 2 ⎛ 8.5V − 3.3V ⎞ ⎛ 0.85 ⎞ × ⎜ ⎟ × ⎜ ⎟ ≈ 4.2μH ⎝ 0.36A × 1.2MHz ⎠ ⎝ 0.4 ⎠ Using the circuit’s minimum input voltage (3V) and estimating efficiency of 80% at that operating point: IIN(DC,MAX) = 0.36A × 8.5V ≈ 1.28A 3V × 0.8 The ripple current and the peak current are: IRIPPLE = 3V × (8.5V − 3V) ≈ 0.4 A 4.2μH × 8.5V × 1.2MHz IPEAK = 1.28A + 0.4 A ≈ 1.48A 2 The peak-inductor current does not exceed the guaranteed minimum value of the LX current limit in the Electrical Characteristics table. Step-Up Regulator 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(C) + VARIPPLE(ESR) VRIPPLE(C) ≈ ) I IPEAK = IIN(DC,MAX) + RIPPLE 2 16 ⎛ 3.3V ⎞ L = ⎜ ⎟ ⎝ 8.5V ⎠ ⎛ ⎞ VMAIN − VIN ⎛ ηTYP ⎞ × ⎜ ⎟ ⎟ × ⎜⎝ LIR ⎠ ⎝ IMAIN(EFF) × fOSC ⎠ where VIN is the typical input voltage and ηTYP is the expected efficiency obtained from the appropriate curve in the Typical Operating Characteristics. 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 (ηMIN) taken from an appropriate curve in the Typical Operating Characteristics: IRIPPLE = Considering the Typical Operating Circuit, the maximum load current (IMAIN(MAX)) is 300mA for the stepup regulator, 20mA for the two-stage positive charge pump, and 20mA for the one-stage negative charge pump. Altogether, the effective maximum output current, IMAIN(EFF) is 360mA with an 8.5V output and a typical input voltage of 3.3V. The switching frequency is set to 1.2MHz. Choosing an LIR of 0.4 and estimating efficiency of 85% at this operating point: ⎛ V IMAIN − VIN ⎞ × ⎜ MAIN CMAIN V × fSW ⎟⎠ ⎝ MAIN and VRIPPLE(ESR) ≈ IPEAK x RESR where IPEAK is the peak inductor current (see the StepUp Regulator 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. ______________________________________________________________________________________ Step-Up Regulator with Switch Control and Operational Amplifier for TFT LCD Step-Up Regulator Rectifier Diode The MAX8758’s 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. Step-Up Regulator Output Voltage Selection The output voltage of the step-up regulator can be adjusted by connecting a resistive voltage-divider from the output (VOUT) to GND with the center tap connected to FB (see Figure 1). Select R2 in the 10kΩ to 50kΩ range. Calculate R1 with the following equation: Place CCOMP2 (C8 in Figure 1) from COMP to GND to add an additional high-frequency pole. UseCCOMP2 between 10pF and 47pF. Step-Up Regulator Soft-Start Capacitor The soft-start capacitor should be large enough that it does not reach final value before the output has reached regulation. Calculate the soft-start capacitor (CSS) value using: CSS = 21 × 10−6 × CMAIN ⎛ ⎞ V 2MAIN − VIN × VMAIN × ⎜ ⎟ ⎝ VIN × IINRUSH − IMAIN × VMAIN ⎠ where CMAIN is the total output capacitance, VMAIN is the maximum output voltage, and IINRUSH is the peak inrush current allowed, IMAIN is the maximum output current, and VIN is the minimum input voltage. The load must wait for the soft-start cycle to finish before drawing a significant amount of load current. The duration after which the load can begin to draw maximum load current is: tMAX = 6.77 x 105 x CSS Charge Pumps ⎛V ⎞ R1 = R2 × ⎜ MAIN − 1⎟ ⎝ VFB ⎠ where VFB, the step-up regulator’s feedback set point, is 1.25V. Place R1 and R2 close to the IC. Step-Up Regulator Loop Compensation Choose RCOMP (R3 in Figure 1) to set the high-frequency integrator gain for fast transient response. Choose CCOMP (C7 in Figure 1) 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 ≈ 315 × VIN × VMAIN × CMAIN L × IMAIN(MAX) VMAIN × CMAIN CCOMP ≈ 10 × IMAIN(MAX) × RCOMP To further optimize transient response, vary RCOMP in 20% steps and CCOMP in 50% steps while observing transient-response waveforms. Selecting the Number of Charge-Pump Stages For highest efficiency, always choose the lowest number of charge-pump stages that meet the output voltage requirement. The number of positive charge-pump stages is given by: nPOS = VGON − VMAIN VMAIN − 2 × VD where nPOS is the number of positive-charge-pump stages, V GON is the positive-charge-pump output, VMAIN is the main step-up regulator output, and VD is the forward voltage drop of the charge-pump diode. The number of negative charge-pump stages is given by: nNEG = − VGOFF VMAIN − 2 × VD where nNEG is the number of negative-charge-pump stages, VGOFF is the negative charge-pump output, VMAIN is the main step-up regulator output, and VD is the forward voltage drop of the charge-pump diode. ______________________________________________________________________________________ 17 MAX8758 Step-Up Regulator Input Capacitor Selection The input capacitor reduces the current peaks drawn from the input supply and reduces noise injection into the IC. Two 10µF ceramic capacitors are used in the Typical Applications Circuit (Figure 1) 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, the input capacitance can be reduced below the values used in the Typical Applications Circuit. MAX8758 Step-Up Regulator with Switch Control and Operational Amplifier for TFT LCD Charge-Pump Flying Capacitors Increasing the flying capacitor (C6, C17, C18) value lowers the effective source impedance and increases the output-current capability. Increasing the capacitance indefinitely has a negligible effect on output-current capability because the diode impedance places a lower limit on the source impedance. Ceramic capacitors of 0.1µF or greater work well in most applications that require output currents in the order of 10mA to 20mA. The flying capacitor’s voltage rating must exceed the following: VC > n x VMAIN 2) where n is the stage number in which the flying capacitor appears, and VMAIN is the output voltage of the main step-up regulator. Charge-Pump Output Capacitor Increasing the output capacitance or decreasing the ESR reduces the output voltage ripple and the peak-topeak voltage during load transients. With ceramic capacitors, the output voltage ripple is dominated by the capacitance value. Use the following equation to approximate the required capacitor value: CMAIN _ CP ≥ ILOAD _ CP 2 × fOSC × VRIPPLE _ CP where CMAIN_CP is the output capacitor of the charge pump, I LOAD_CP is the load current of the charge pump, and VRIPPLE_CP is the peak-to-peak value of the output ripple. The charge-pump output capacitor is typically also the input capacitor for a linear regulator. Often, its value must be increased to maintain the linear regulator’s stability. Charge-Pump Rectifier Diodes Use low-cost, silicon-switching diodes with a current rating equal to or greater than two times the average charge-pump input current. If it helps avoid an extra stage, some or all of the diodes can be replaced with Schottky diodes with equivalent current ratings. PC Board Layout and Grounding Careful PC board layout is important for proper operation. Use the following guidelines for good PC board layout: 1) Minimize the area of high-current loops by placing the step-up regulator’s inductor, diode, and output capacitors near its input capacitors, its LX, and PGND pin. The high-current input loop goes from 18 3) 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 highcurrent output loop is from the positive terminal of the input capacitor to the inductor, to the output diode (D1), 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. Create a power ground island (PGND) for the step-up regulator, consisting of the input and output capacitor grounds and the PGND pin. Maximizing the width of the power ground traces improves efficiency and reduces output voltage ripple and noise spikes. Create an analog ground plane (GND) consisting of the GND pin, the feedback-divider ground connection, the COMP and DLP capacitor ground connections, and the device’s exposed backside pad. Connect the PGND and GND islands by connecting the two ground pins directly to the exposed backside pad. Make no other connections between these separate ground planes. Place the feedback voltage-divider resistors as close to the feedback pin as possible. The divider’s center trace should be kept short. Placing the resistors far away causes the FB trace to become antennas that can pick up switching noise. Care should be taken to avoid running the feedback trace near LX. 4) Place the IN pin bypass capacitor as close to the device as possible. The ground connection of the IN bypass capacitor should be connected directly to the GND pin with a wide trace. 5) Minimize the length and maximize the width of the traces between the output capacitors and the load for best transient responses. 6) Minimize the size of the LX node while keeping it wide and short. Keep the LX node away from feedback node (FB) and analog ground. Use DC traces as shield if necessary. Refer to the MAX8758 evaluation kit for an example of proper board layout. ______________________________________________________________________________________ Step-Up Regulator with Switch Control and Operational Amplifier for TFT LCD TRANSISTOR COUNT: 3208 PROCESS: BiCMOS LX IN FREQ COMP SS I.C. TOP VIEW 18 17 16 15 14 13 SHDN 19 12 OUT FB 20 11 LDO PGND 21 10 N.C. MODE 22 9 POSB DRN 23 8 NEGB SRC 24 7 OUTB 4 5 6 THR SUPB GON 3 DLP 2 CTL 1 GND MAX8758 Chip Information THIN QFN 4mm x 4mm ______________________________________________________________________________________ 19 MAX8758 Pin Configuration 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.) QFN THIN.EPS MAX8758 Step-Up Regulator with Switch Control and Operational Amplifier for TFT LCD D2 D b C L 0.10 M C A B D2/2 D/2 k L MARKING XXXXX E/2 E2/2 C L (NE-1) X e E DETAIL A PIN # 1 I.D. E2 PIN # 1 I.D. 0.35x45° e/2 e (ND-1) X e DETAIL B e L1 L C L C L L L e e 0.10 C A C 0.08 C A1 A3 PACKAGE OUTLINE, 16, 20, 28, 32, 40L THIN QFN, 5x5x0.8mm 21-0140 -DRAWING NOT TO SCALE- COMMON DIMENSIONS A1 A3 b D E e k L L1 N ND NE JEDEC 0.70 0.75 0.80 0.70 0.75 0.80 0.70 0.75 0.80 0.70 0.75 0.80 0.70 0.75 0.80 0 0.02 0.05 0 0.02 0.05 0.20 REF. 0.20 REF. 0.25 0.30 0.35 0.25 0.30 0.35 4.90 5.00 5.10 4.90 5.00 5.10 4.90 5.00 5.10 4.90 5.00 5.10 0.80 BSC. 0.65 BSC. 0.25 - 0.25 - 0 0.02 0.05 0.02 0.05 0 0.20 REF. 0.20 REF. 0.20 0.25 0.30 0.20 0.25 0.30 4.90 5.00 5.10 4.90 5.00 5.10 4.90 5.00 5.10 4.90 5.00 5.10 0.50 BSC. 0.50 BSC. - 0.25 0.25 - 0 0.02 0.05 0.20 REF. 0.15 0.20 0.25 4.90 5.00 5.10 4.90 5.00 5.10 0.40 BSC. 0.25 0.35 0.45 0.30 0.40 0.50 0.45 0.55 0.65 0.45 0.55 0.65 0.30 0.40 0.50 0.40 0.50 0.60 - 0.30 0.40 0.50 16 4 4 20 5 5 WHHB WHHC 1 2 EXPOSED PAD VARIATIONS PKG. 16L 5x5 20L 5x5 28L 5x5 32L 5x5 40L 5x5 SYMBOL MIN. NOM. MAX. MIN. NOM. MAX. MIN. NOM. MAX. MIN. NOM. MAX. MIN. NOM. MAX. A H 28 7 7 WHHD-1 32 8 8 40 10 10 WHHD-2 ----- 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. D2 L E2 PKG. CODES MIN. NOM. MAX. T1655-1 T1655-2 T1655N-1 3.00 3.00 3.00 3.10 3.20 3.00 3.10 3.20 3.00 3.10 3.20 3.00 3.10 3.10 3.10 3.20 3.20 3.20 T2055-2 T2055-3 T2055-4 3.00 3.00 3.00 3.10 3.20 3.00 3.10 3.20 3.00 3.10 3.20 3.00 3.10 3.10 3.10 3.20 3.20 3.20 T2055-5 T2855-1 T2855-2 T2855-3 T2855-4 T2855-5 T2855-6 T2855-7 T2855-8 T2855N-1 T3255-2 T3255-3 T3255-4 T3255N-1 3.15 3.15 2.60 3.15 2.60 2.60 3.15 2.60 3.15 3.15 3.00 3.00 3.00 3.00 3.25 3.25 2.70 3.25 2.70 2.70 3.25 2.70 3.25 3.25 3.10 3.10 3.10 3.10 3.15 3.15 2.60 3.15 2.60 2.60 3.15 2.60 3.15 3.15 3.00 3.00 3.00 3.00 3.25 3.25 2.70 3.25 2.70 2.70 3.25 2.70 3.25 3.25 3.10 3.10 3.10 3.10 3.35 3.35 2.80 3.35 2.80 2.80 3.35 2.80 3.35 3.35 3.20 3.20 3.20 3.20 T4055-1 3.20 3.30 3.40 3.20 3.30 3.40 3.35 3.35 2.80 3.35 2.80 2.80 3.35 2.80 3.35 3.35 3.20 3.20 3.20 3.20 MIN. NOM. MAX. ±0.15 ** ** ** ** ** ** 0.40 DOWN BONDS ALLOWED NO YES NO NO YES NO YES ** NO NO YES YES NO ** ** 0.40 ** ** ** ** ** NO YES YES NO NO YES NO NO ** YES ** ** ** ** ** SEE COMMON DIMENSIONS TABLE 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, EXCEPT EXPOSED PAD DIMENSION FOR T2855-1, T2855-3, AND T2855-6. 10. WARPAGE SHALL NOT EXCEED 0.10 mm. 11. MARKING IS FOR PACKAGE ORIENTATION REFERENCE ONLY. 12. NUMBER OF LEADS SHOWN ARE FOR REFERENCE ONLY. 13. LEAD CENTERLINES TO BE AT TRUE POSITION AS DEFINED BY BASIC DIMENSION "e", ±0.05. PACKAGE OUTLINE, 16, 20, 28, 32, 40L THIN QFN, 5x5x0.8mm 21-0140 -DRAWING NOT TO SCALE- H 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 © 2005 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc.