19-5857; Rev 2; 1/12 EVALUATION KIT AVAILABLE MAX16929 Automotive TFT-LCD Power Supply with Boost Converter and Gate Voltage Regulators General Description The MAX16929 is a highly integrated power supply for automotive TFT-LCD applications. The device integrates one buck converter, one boost converter, one 1.8V/3.3V regulator controller, and two gate voltage regulators. The device comes in several versions to satisfy common automotive power-supply requirements (see the Ordering Information/Selector Guide table). Designed to operate from a single 4V to 28V supply or 5.5V to 28V supply, the device is ideal for automotive TFT-LCD applications. Both the buck and boost converters use spread-spectrum modulation to reduce peak interference and to optimize EMI performance. The sequencing input (SEQ) allows flexible sequencing of the positive-gate and negative-gate voltage regulators. The power-good indicator (PGOOD) indicates a failure on any of the converters or regulator outputs. Integrated thermal shutdown circuitry protects the device from overheating. The MAX16929 is available in a 28-pin TSSOP package with exposed pad, and operates over the -40NC to +105NC temperature range. Features SOperating Voltage Range of 4V to 28V (Buck) or 3V to 5.5V (Boost) SIndependent 28V Input Buck Converter Powers TFT Bias Supply Circuitry and External Circuitry SHigh-Power (Up to 6W) Boost Output Providing Up to 18V S1.8V or 3.3V Regulator Provides 500mA with External npn Transistor SOne Positive-Gate Voltage Regulator Capable of Delivering 20mA at 28V SOne Negative-Gate Voltage Regulator SHigh-Frequency Operation 2.1MHz (Buck Converter) 2.2MHz (Boost Converter) SFlexible Stand-Alone Sequencing STrue Shutdown™ Boost Converter S6µA Low-Current Shutdown Mode (Buck) SInternal Soft-Start SOvertemperature Shutdown S-40NC to +105NC Operation Applications Automotive Dashboards Ordering Information/Selector Guide appears at end of data sheet. Automotive Central Information Displays Automotive Navigation Systems Typical Application Circuit appears at end of data sheet. True Shutdown is a trademark of Maxim Integrated Products, Inc. For related parts and recommended products to use with this part, refer to: www.maxim-ic.com/MAX16929.related ����������������������������������������������������������������� Maxim Integrated Products 1 For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. MAX16929 Automotive TFT-LCD Power Supply with Boost Converter and Gate Voltage Regulators ABSOLUTE MAXIMUM RATINGS INB, ENB to GND...................................................-0.3V to +42V BST to GND............................................................-0.3V to +47V BST to LXB...............................................................-0.3V to +6V LXB to GND...............................................................-6V to +42V AVL, PGOOD to GND..............................................-0.3V to +6V FBB to GND............................................................-0.5V to +12V CP, GH to GND......................................................-0.3V to +31V CP, GH to GND (VINA = 3.3V)...............................-0.3V to +29V LXP to GND............................................................-0.3V to +20V DRVN to GND.........................................................-25V to +0.3V INA, COMPV, FBP to GND.......................................-0.3V to +6V ENP, DR, FB, GATE, COMPI, FBGH, FBGL, REF, SEQ to GND......................-0.3V to (VINA + 0.3V) GND to PGNDP.....................................................-0.3V to +0.3V Continuous Power Dissipation (TA = +70NC) TSSOP (derate 27mW/NC above +70NC)...................2162mW Operating Temperature Range......................... -40NC to +105NC Junction Temperature Range............................ -40NC to +150NC Storage Temperature Range............................. -65NC to +150NC Lead Temperature (soldering, 10s).................................+300NC Soldering Temperature (reflow).......................................+260NC 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. PACKAGE THERMAL CHARACTERISTICS (Note 1) TSSOP Junction-to-Ambient Thermal Resistance (BJA)...........37NC/W Junction-to-Case Thermal Resistance (BJC)..................2NC/W Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a fourlayer board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial. ELECTRICAL CHARACTERISTICS (VINB = 12V, VINA = 5V, VGND = VPGNDP = 0V, TA = TJ = -40NC to +105NC, typical values are at TA = +25NC, unless otherwise noted.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS BUCK CONVERTER VOUTB = 5V (Note 3) Supply Voltage Range VINB VOUTB = 3.3V (Note 3) 5.5 28 4 28 t < 500ms Supply Current IINB Undervoltage Lockout VINB,UVLO 42 VENB = 0V 6 VENB = VINB, no load, TA = +25NC AVL rising 70 3.1 Undervoltage Lockout Hysteresis fSWB Spread-Spectrum Range SSR 1.9 VOUTB 6V P VINB P 18V, 5V, skip mode ILOAD < full load 3.3V, continuous mode 3.3V, skip mode High-Side DMOS RDS_ON Skip-Current Threshold Current-Limit Threshold 3.5 2.3 5 +3% -3% 5 +6% -3% 3.3 +3% 3.3 +6% 180 400 -3% ISKIP V MHz % -3% RDS_ON(LXB) ILXB = 1A IMAX 2.1 FA V +6 5V, continuous mode Output-Voltage Accuracy 9 0.5 PWM Switching Frequency V 16 V mI %IMAX IOUTB = 1.2A option 1.6 2 2.4 IOUTB = 2.0A option 2.7 3.4 4.08 A ����������������������������������������������������������������� Maxim Integrated Products 2 MAX16929 Automotive TFT-LCD Power Supply with Boost Converter and Gate Voltage Regulators ELECTRICAL CHARACTERISTICS (continued) (VINB = 12V, VINA = 5V, VGND = VPGNDP = 0V, TA = TJ = -40NC to +105NC, typical values are at TA = +25NC, unless otherwise noted.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN Soft-Start Ramp Time TYP MAX UNITS 3.9 ms Maximum Duty Cycle Continuous mode 80 % Minimum Duty Cycle Continuous mode 20 % Maximum Duty Cycle in Dropout Dropout Thermal Shutdown Temperature Thermal Shutdown Hysteresis 95 % +175 NC 15 NC POWER GOOD (PGOOD) Rising PGOOD Threshold Falling 94 90 PGOOD Debounce Time 92 95 13 % Fs Output High-Leakage Current 0.2 FA Output Low Level 0.4 V 2.2 V LOGIC LEVELS ENB Threshold ENB rising 1.4 ENB Hysteresis 1.8 0.2 ENB Input Current 3 5 V 9 FA 5.5 V 1.5 2.0 mA 2.7 2.9 V BOOST, POSITIVE (GH), NEGATIVE (GL), 1.8V/3.3V CONVERTERS INA Input Supply Range VINA INA Supply Current IINA INA Undervoltage Lockout Threshold VINA,UVLO 3 VFBP = VFBGH = 1.3V, VFBGL = 0V, LXP not switching VINA rising, hysteresis = 200mV, TA = +25NC INA Shutdown Current ISHDN VENP = 0V, TA = +25NC Thermal Shutdown Temperature TSHDN Temperature rising Thermal Shutdown Hysteresis 2.5 TH VFBP, VFBGH, or VFBGL below its threshold Duration to Trigger Fault Condition Autoretry Time 0.5 FA +165 NC 15 NC 238 ms 1.9 s REFERENCE (REF) REF Output Voltage VREF No output current REF Load Regulation 0 < IREF < 80FA, REF sourcing REF Undervoltage Lockout Threshold Rising edge, hysteresis = 200mV 1.236 1.25 -2 1.264 V +2 % 1.165 V 4.84 MHz OSCILLATOR Internal Oscillator Frequency fOSC Spread-Spectrum Modulation Frequency fSS TA = +25NC 3.96 4.40 fOSC/2 MHz ����������������������������������������������������������������� Maxim Integrated Products 3 MAX16929 Automotive TFT-LCD Power Supply with Boost Converter and Gate Voltage Regulators ELECTRICAL CHARACTERISTICS (continued) (VINB = 12V, VINA = 5V, VGND = VPGNDP = 0V, TA = TJ = -40NC to +105NC, typical values are at TA = +25NC, unless otherwise noted.) (Note 2) PARAMETER Spread-Spectrum Factor SYMBOL CONDITIONS SSR As a percentage of switching frequency, fSW MIN TYP MAX UNITS % Q4 BOOST CONVERTER Switching Frequency fSW 1.98 Maximum Duty Cycle LXP Current Limit 82 ILIM Low boost currentDuty cycle = 70%, limit option CCOMPI = 220pF High boost current- LXP Leakage Current ILK_LXP Output Voltage Range FBP Regulation Voltage PGOOD Threshold VPG_FBP FBP Load Regulation FBP Input Bias Current 1.87 110 250 VLXP = 20V, TA =+25NC 8.5 20 (Note 4) 30 A VINA mI FA ms 18 VINA = +3V to +5.5V, TA = +25NC 0 < ILOAD < full load TA = -40NC to +105NC 0.985 1.0 1.015 0.98 1.0 1.02 Measured at FBP 0.74 0.85 0.96 -1 V V V % 0.1 VFBP = +1V, TA = +25NC DI = Q2.5FA at COMPV, TA = +25NC FBP to COMPV Transconductance % 1.56 0 < ILOAD < full load VINA = +3V to +5.5V FBP Line Regulation 93.5 1.25 VSH VFBP MHz 0.78 RDS_ON(LXP) ILXP = 200mA Soft-Start Time 2.42 0.625 limit option LXP On-Resistance 2.20 %/V Q1 400 FA FS POSITIVE-GATE VOLTAGE REGULATOR (GH) Output Voltage Range VGH CP Overvoltage Threshold FBGH Regulation Voltage PGOOD Threshold VFBGH VPG_FBGH With external charge pump, TA = +25NC (maximum VCP = 29.5V) 5 29 V TA = +25NC (Note 6) 29.5 30.5 IGH = 1mA 0.98 1.0 1.034 V V Measured at FBGH 0.83 0.85 0.87 V FBGH Load Regulation IGH = 0 to 20mA 2 % FBGH Line Regulation VCP = 12V to 20V at VGH = 10V, IGH = 10mA 2 % FBGH Input Bias Current GH Output Current GH Current Limit VFBGH = 1V, TA = +25NC IGH VCP - VGH = 2V ILIM_GH Q1 20 35 GH Soft-Start Time FA mA 56 mA 7.45 ms NEGATIVE-GATE VOLTAGE REGULATOR (GL) Output Voltage Range VDRVN FBGL Regulation Voltage VFBGL -24 IDRVN = 100FA 0.212 0.242 -2 V 0.271 V ����������������������������������������������������������������� Maxim Integrated Products 4 MAX16929 Automotive TFT-LCD Power Supply with Boost Converter and Gate Voltage Regulators ELECTRICAL CHARACTERISTICS (continued) (VINB = 12V, VINA = 5V, VGND = VPGNDP = 0V, TA = TJ = -40NC to +105NC, typical values are at TA = +25NC, unless otherwise noted.) (Note 2) PARAMETER PGOOD Threshold SYMBOL VPG_FBGL CONDITIONS Measured at FBGL FBGL Input Bias Current VFBGL = +0.25V DRVN Source Current VFBGL = +0.5V, VDRVN = -10V DRVN Source Current Limit MIN TYP MAX 0.38 0.4 0.42 V Q1 FA 2 2.5 GL Soft-Start Time UNITS mA 4 mA 7.45 ms 1.8V/3.3V REGULATOR CONTROLLER Output Voltage VFB FB PGOOD Threshold VPG_FB FB Input Bias Current DR Drive Current VDR = VFB Measured at FB (Notes 5, 7) 3.3V regulator option 3.18 3.3 3.38 1.8V regulator option 1.746 1.8 1.854 3.3V regulator option, FB rising 2.4 2.57 2.7 1.8V regulator option 1.364 1.38 1.396 VFB = 1.8V 2.5 VFB = 3.3V 4.5 VFB = 1.8V 4.5 6 p-Channel FET GATE Sink Current VGATE = 0.5V 33 55 GATE Voltage Threshold Measured at GATE; below this voltage, the external p-channel FET is considered on V V FA mA INPUT SERIES SWITCH CONTROL 75 FA 1.25 V 500 kI DIGITAL LOGIC ENP, SEQ Input Pulldown Resistor Value RPD ENP, SEQ Input-Voltage Low VIL ENP, SEQ Input-Voltage High VIH PGOOD Leakage Current PGOOD Output-Voltage Low ILK_IN VOL 0.3 x VINA 0.7 x VINA V V TA = +25NC Q1 FA 2mA sink current, TA = +25NC 0.4 V Note 2: Specifications over temperature are guaranteed by design and not production tested. Note 3: Operation in light-load conditions or at extreme duty cycles result in skipped cycles, resulting in lower operating frequency and possibly limited output accuracy and load response. Note 4: 50% of the soft-start voltage time is due to the soft-start ramp, and the other 50% is due to the settling of the output voltage. Note 5: Guaranteed by design; not production tested. Note 6: After the voltage at CP exceeds this overvoltage threshold, the entire circuit switches off and autoretry is started. Note 7: FB power good is indicated by PGOOD. The condition VFB < VPG_FB does not shutdown/restart the device. ����������������������������������������������������������������� Maxim Integrated Products 5 MAX16929 Automotive TFT-LCD Power Supply with Boost Converter and Gate Voltage Regulators Typical Operating Characteristics (VINA = 5V, VINB = 12V, measurements taken on “A” version, unless otherwise noted; VSH = 12V, VGH = 18V, VGL = -6V, VREG = 3.3V, VOUTB = 5V, TA = +25NC, unless otherwise noted.) SHUTDOWN SUPPLY CURRENT (BUCK) 16 MAX16929 toc02 18 90 80 14 EFFICIENCY (%) SUPPLY CURRENT (µA) EFFICIENCY vs. LOAD CURRENT (BUCK) 100 MAX16929 toc01 20 12 10 8 VINB = 28V 50 40 30 4 20 2 10 0 8 4 12 16 20 24 28 0 0.4 LINE REGULATION (BUCK) IOUTB = 0A 5 4 3 VINB = 12V 2 ERROR (%) IOUTB = 1A 0 -0.8 IOUTB = 2A -3.2 -4.0 6 1 0 -1 -2 VINB = 18V VINB = 28V -3 -4 -5 -6 -2.4 4 8 10 12 14 16 18 20 22 24 26 28 0 INPUT VOLTAGE (V) 0.4 0.8 1.2 1.6 2.0 LOAD CURRENT (A) STARTUP WAVEFORMS (BUCK) LOAD-TRANSIENT RESPONSE (BUCK) MAX16929 toc05 MAX16929 toc06 VENB 5V/div ILXB 2A/div 1.8A IOUTB 1A/div 0.2A VOUTB 2V/div 1ms/div 2.0 LOAD REGULATION (BUCK) 1.6 -1.6 1.6 MAX16929 toc04 3.2 0.8 1.2 6 MAX16929 toc03 4.0 2.4 0.8 LOAD CURRENT (A) SUPPLY VOLTAGE (V) ERROR (%) VINB =18V 60 6 0 VINB =12V 70 VOUTB (AC-COUPLED) 100mV/div 400µs/div ����������������������������������������������������������������� Maxim Integrated Products 6 MAX16929 Automotive TFT-LCD Power Supply with Boost Converter and Gate Voltage Regulators Typical Operating Characteristics (continued) (VINA = 5V, VINB = 12V, measurements taken on “A” version, unless otherwise noted; VSH = 12V, VGH = 18V, VGL = -6V, VREG = 3.3V, VOUTB = 5V, TA = +25NC, unless otherwise noted.) LINE-TRANSIENT RESPONSE (BUCK) SHORT-CIRCUIT BEHAVIOR (BUCK) MAX16929 toc07 MAX16929 toc08 VOUTB 5V/div 28V VINB 10V/div 12V ILXB 2A/div VOUTB (AC-COUPLED) 50mV/div VPGOOD 5V/div 100ms/div 1ms/div LOAD DUMP RESPONSE INA SHUTDOWN SUPPLY CURRENT MAX16929 toc09 MAX16929 toc10 10 9 42V 8 12V SUPPLY CURRENT (nA) VINB 20V/div ILXB 2A/div VOUTB 5V/div 7 6 5 4 3 2 1 0 100ms/div 3.0 3.5 4.0 4.5 5.0 5.5 INPUT VOLTAGE (V) 0.8 0.6 VINA = 5V 70 ERROR (%) 50 40 -0.2 -0.4 -0.6 10 -0.8 0 -1.0 200 300 LOAD CURRENT (mA) 400 500 VINA = 3.3V 0 20 100 0.4 0.2 30 0 0.6 0.4 VINA = 3.3V 60 ILOAD = 0mA 0.8 ERROR (%) 80 LINE REGULATION (BOOST) 1.0 MAX16929 toc12 90 EFFICIENCY (%) LOAD REGULATION (BOOST) 1.0 MAX16929 toc11 100 MAX16929 toc13 EFFICIENCY vs. LOAD CURRENT (BOOST) 0.2 0 -0.2 -0.4 VINA = 5V -0.6 -0.8 -1.0 0 100 200 300 LOAD CURRENT (mA) 400 500 3.0 3.5 4.0 4.5 5.0 5.5 INPUT VOLTAGE (V) ����������������������������������������������������������������� Maxim Integrated Products 7 MAX16929 Automotive TFT-LCD Power Supply with Boost Converter and Gate Voltage Regulators Typical Operating Characteristics (continued) (VINA = 5V, VINB = 12V, measurements taken on “A” version, unless otherwise noted; VSH = 12V, VGH = 18V, VGL = -6V, VREG = 3.3V, VOUTB = 5V, TA = +25NC, unless otherwise noted.) STARTUP WAVEFORMS (BOOST) LOAD-TRANSIENT RESPONSE (BOOST) MAX16929 toc14 MAX16929 toc15 VENP 5V/div VLXP 10V/div 450mA ISH 500mA/div 50mA ILXP 1A/div VSH 100mV/div VSH 10V/div 100µs/div 4ms/div SUPPLY SEQUENCING WAVEFORMS (VSEQ = 0V) MAX16929 toc16 SUPPLY SEQUENCING WAVEFORMS (VSEQ = VINA) MAX16929 toc17 VENP 5V/div VGH 5V/div VSH 5V/div VGH 5V/div VSH 5V/div VREG 5V/div VREG 5V/div VGL 5V/div VGL 5V/div 10ms/div 10ms/div LOAD REGULATION (GH REGULATOR) -0.8 0.8 0.6 0.4 -1.6 0.2 ERROR (%) -1.2 -2.0 -2.4 0 -0.4 -3.2 -0.6 -3.6 -0.8 0 2 4 6 8 10 12 14 16 18 20 LOAD CURRENT (mA) ILOAD = 10mA -0.2 -2.6 -4.0 MAX16929 toc19 -0.4 ERROR (%) LINE REGULATION (GH REGULATOR) 1.0 MAX16929 toc18 0 VENP 5V/div ILOAD = 20mA -1.0 18 19 20 21 22 23 24 25 26 27 28 29 30 VCP VOLTAGE (V) ����������������������������������������������������������������� Maxim Integrated Products 8 MAX16929 Automotive TFT-LCD Power Supply with Boost Converter and Gate Voltage Regulators Typical Operating Characteristics (continued) (VINA = 5V, VINB = 12V, measurements taken on “A” version, unless otherwise noted; VSH = 12V, VGH = 18V, VGL = -6V, VREG = 3.3V, VOUTB = 5V, TA = +25NC, unless otherwise noted.) LINE REGULATION (GL REGULATOR) LOAD REGULATION (GL REGULATOR) 0.8 0.6 2.1 0.4 1.8 0.2 ERROR (%) ERROR (%) 2.4 1.5 1.2 MAX16929 toc21 2.7 0 ILOAD = 20mA -0.2 0.9 -0.4 0.6 -0.6 0.3 -0.8 ILOAD = 10mA -1.0 0 0 2 4 6 8 -24 -22 -20 -18 -16 -14 -12 -10 10 12 14 16 18 20 -8 LOAD CURRENT (mA) VCN VOLTAGE (V) LOAD REGULATION (3.3V LINEAR REGULATOR) LOAD-TRANSIENT RESPONSE (3.3V LINEAR REGULATOR) -6 MAX16929 toc23 MAX16929 toc22 0 -0.02 -0.04 -0.06 ERROR (%) 1.0 MAX16929 toc20 3.0 450mA IOUTB 500mA/div 50mA -0.08 -0.10 -0.12 VREG (AC-COUPLED) 100mV/div -0.14 -0.16 -0.18 -0.20 0 50 100 150 200 250 300 350 400 450 500 100µs/div LOAD CURRENT (mA) ����������������������������������������������������������������� Maxim Integrated Products 9 MAX16929 Automotive TFT-LCD Power Supply with Boost Converter and Gate Voltage Regulators Pin Configuration TOP VIEW + ENP 1 28 SEQ DR 2 27 REF FB 3 26 FBGL GATE 4 25 FBGH PGNDP 5 24 COMPI LXP 6 23 GND INA 7 22 DRVN COMPV 8 21 GH FBP 9 20 CP FBB 10 19 PGOOD AVL 11 18 GND BST 12 17 ENB LXB 13 16 INB LXB 14 15 INB MAX16929 EP TSSOP Pin Description PIN NAME FUNCTION 1 ENP Boost Circuitry and 1.8V/3.3V Regulator Controller Enable Input. ENP has an internal 500kI pulldown resistor. Drive high for normal operation and drive low to place the device (except buck converter) in shutdown. 2 DR 1.8V or 3.3V Regulator Output. DR has a 4.5mA (min) drive capability. For greater output current capability, use an external npn bipolar transistor whose base is connected to DR. 3 FB 1.8V or 3.3V Regulator Feedback Input. FB is regulated to 1.8V or 3.3V. Connect FB to DR when powering loads demanding less than 4.5mA. For greater output current capability, use an external npn bipolar transistor whose emitter is connected to FB. 4 GATE External p-Channel FET Gate Drive. GATE is an open-drain driver connected to the gate of the external input series p-channel FET. Connect a pullup resistor between GATE and INA. During a fault condition, the gate driver turns off and the pullup resistor turns off the FET. 5 PGNDP 6 LXP Boost Converter Switching Node. Connect LXP to the inductor and catch diode of the boost converter. 7 INA Boost Circuitry and 1.8V/3.3V Regulator Controller Power Input. Connect INA to a 3V to 5.5V supply. 8 COMPV Boost Error Amplifier Compensation Connection. Connect a compensation network between COMPV to GND. 9 FBP Boost Converter Feedback Input. FBP is regulated to 1V. Connect FBP to the center of a resistive divider connected between the boost output and GND. Boost Converter Power Ground ���������������������������������������������������������������� Maxim Integrated Products 10 MAX16929 Automotive TFT-LCD Power Supply with Boost Converter and Gate Voltage Regulators Pin Description (continued) PIN NAME FUNCTION 10 FBB Buck Converter Feedback Input. FBB is regulated to either 3.3V or 5V. Connect FBB to the output-voltage node, OUTB, as shown in the Typical Application Circuit. 11 AVL Buck Converter Internal 5V Regulator. Connect a 1FF capacitor between AVL and the analog ground plane. Do not use AVL to power external circuitry. 12 BST Buck Converter Bootstrap Capacitor Connection. Connect a 0.1FF capacitor between BST and LXB. 13, 14 LXB Buck Converter Inductor Connection. Connect the inductor, boost capacitor, and catch diode at this node. 15, 16 INB Buck Converter Power Input. Connect to a 4V to 28V supply. Connect a 1FF or larger ceramic capacitor in parallel with a 47FF bulk capacitor from INB to the power ground plane. Connect both INB power inputs together. 17 ENB Buck Converter Enable Input. ENB is a high-voltage compatible input. Connect to INB for normal operation and connect to ground to disable the buck converter. 18, 23 GND Analog Ground 19 PGOOD 20 CP Positive-Gate Voltage Regulator Power Input. Connect CP to the positive output of the external charge pump. Ensure that VCP does not exceed the CP overvoltage threshold as given in the Electrical Characteristics table. 21 GH Positive-Gate Voltage Regulator Output 22 DRVN Negative-Gate Voltage Regulator Driver Output. DRVN is the open drain of an internal p-channel FET. Connect DRVN to the base of an external npn pass transistor. 24 COMPI Boost Slope Compensation Connection. Connect a capacitor between COMPI and GND to set the slope compensation. 25 FBGH Positive-Gate Voltage Regulator Feedback Input. FBGH is regulated to 1V. Connect FBGH to the center of a resistive divider connected between GH and GND. 26 FBGL Negative-Gate Voltage Regulator Feedback Input. FBGL is regulated to 0.25V. Connect FBGL to the center of a resistive divider connected between REF and the output of the negative-gate voltage regulator. 27 REF 1.25V Reference Output. Bypass REF to GND with a 0.1FF ceramic capacitor. 28 SEQ Sequencing Input. SEQ has an internal 500kI pulldown resistor. SEQ determines the sequence in which VGH and VGL power-up. See Table 1 for supply sequencing options. — EP Open-Drain Power-Good Output. Connect PGOOD to INA through an external pullup resistor. Exposed Pad. Connect to a large contiguous copper ground plane for optimal heat dissipation. Do not use EP as the only electrical ground connection. ���������������������������������������������������������������� Maxim Integrated Products 11 MAX16929 Automotive TFT-LCD Power Supply with Boost Converter and Gate Voltage Regulators Detailed Description The MAX16929 is a highly integrated power supply for automotive TFT-LCD applications. The device integrates one buck converter, one boost converter, one 1.8V/3.3V regulator controller, one positive-gate voltage regulator, and one negative-gate voltage regulator. The device achieves enhanced EMI performance through spread-spectrum modulation. Digital input control allows the device to be placed in a low-current shutdown mode and provides flexible sequencing of the gate voltage regulators. Internal thermal shutdown circuitry protects the device from overheating. The buck converter is designed to shut down when its die temperature reaches +175NC (typ), while the boost circuitry does so at +165NC (typ). Each resumes normal operation once its die temperature has fallen 15NC below its respective thermal shutdown temperature. The device is factory-trimmed to provide a variety of power options to meet the most common automotive TFT-LCD display power requirements, as outlined in the Ordering Information/Selector Guide table. Buck Converter The device features a current-mode buck converter with an integrated high-side FET, which requires no external compensation network. The buck converter regulates the output voltage to within Q3% in continuous mode over line and load conditions. The high 2.1MHz (typ) switching frequency allows for small external components, reduced output ripple, and guarantees no AM interference. A power-good (PGOOD) indicator is available to monitor output-voltage quality. The enable input allows the device to be placed in shutdown, reducing supply current to 70FA. The buck converter comes with a preset output voltage of either 3.3V or 5V, and can deliver either 1.2A or 2A to the output. Enable (ENB) Connect ENB to INB for always-on operation. ENB is also compatible with 3.3V logic systems and can be controlled through a microcontroller or by automotive KEY or CAN inhibit signals. Internal 5V Regulator (AVL) AVL is an internal 5V regulator that supplies power to the buck controller and charges the boost capacitor. After enabling the buck converter, VAVL begins to rise. Once VAVL exceeds the undervoltage lockout voltage of 3.5V (max), LXB starts switching. Bypass AVL to GND with a 1FF ceramic capacitor. Spread-Spectrum Modulation The buck converter features spread-spectrum operation that varies the internal operating frequency of the buck converter by +6% relative to the switching frequency of 2.1MHz (typ). Soft-Start The buck converter features an internal soft-start timer. The output voltage takes 3.9ms to ramp up to its set voltage. If a short circuit or undervoltage is encountered after the soft-start timer has expired, the device enters hiccup mode, during which soft-start is reattempted every 16ms. This process repeats until the short circuit has been removed. Overcurrent Protection The device enters hiccup mode in one of three ways. If eight consecutive current limits are detected and the output is below 77% of its nominal value, the buck converter enters hiccup mode. The converter enters hiccup mode immediately if the output is short circuited to ground (output below 1V). Additionally, the device enters hiccup mode if 256 consecutive overcurrent events are detected when the output is greater than 77% of its nominal value. In hiccup mode, the buck controller idles for 16ms before reattempting soft-start. Power Good (PGOOD) When an overcurrent condition causes the buck output to fall below 92% of its set voltage, the open-drain powergood indicator output (PGOOD) asserts low. PGOOD deasserts once the output voltage has risen above 95% of its set voltage. PGOOD serves as a general fault indicator for all the converters and regulators. Besides indicating an undervoltage on the buck output, it also indicates any of the faults listed in the Fault Conditions and PGOOD section. Boost Converter The boost converter 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 2.2MHz switching frequency allows the use of low-profile inductors and ceramic capacitors to minimize the thickness of LCD panel designs. The integrated low on-resistance MOSFET and ���������������������������������������������������������������� Maxim Integrated Products 12 MAX16929 Automotive TFT-LCD Power Supply with Boost Converter and Gate Voltage Regulators the device’s built-in digital soft-start functions reduce the number of external components required while controlling inrush currents. The output voltage can be set from VINA to 18V with an external resistive voltage-divider. The regulator controls the output voltage 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 =1 − ηVIN VO where VIN is the voltage at INA, VO = VSH (the boost output voltage), and E is the efficiency of the boost converter, as shown in the Typical Operating Characteristics. Figure 1 shows the functional diagram of the boost regulator. An error amplifier compares the signal at FBP to 1V and changes the COMPV output. The voltage at COMPV sets the peak inductor current. As the load varies, the error amplifier sources or sinks current to the COMPV output accordingly to produce the peak inductor current necessary to service the load. To maintain stability at high duty cycles, a slope-compensation signal (set by the capacitor at COMPI) is summed with the current-sense signal. On the rising edge of the internal clock, the controller turns on the n-channel MOSFET and applies the input voltage across the inductor. The current through the inductor ramps up linearly, storing energy in its magnetic field. Once the sum of the current feedback signal and the slope compensation exceeds the COMPV voltage, the controller turns off the MOSFET. The inductor current then flows through the diode to the output. The MOSFET remains off for the rest of the clock cycle. LXP CLOCK LOGIC AND DRIVER PGNDP ILIM COMPARATOR SOFTSTART PWM COMPARATOR Σ VLIMIT CURRENT SENSE 2.2MHz OSCILLATOR SLOPE COMP ERROR AMP TO FAULT LOGIC FAULT COMPARATOR MAX16929 COMPI FBP 0.85V 1V COMPV Figure 1. Boost Converter Functional Diagram ���������������������������������������������������������������� Maxim Integrated Products 13 MAX16929 Automotive TFT-LCD Power Supply with Boost Converter and Gate Voltage Regulators The external p-channel FET controlled by GATE protects the output during fault conditions and provides True Shutdown of the converter. Connect a pullup resistor between GATE and INA (see the Boost Converter section to select the value for the pullup resistor). Under normal operation, GATE turns on the p-channel FET, connecting the supply to the boost input. During a fault condition or in shutdown, GATE is off and the pullup resistor turns off the p-channel FET, disconnecting the supply from the boost input. Spread-Spectrum Modulation The high-frequency 2.2MHz operation of the boost converter keeps switching noise outside of the AM band. The device achieves enhanced EMI performance by modulating the switching frequency by Q4%. The modulating signal is pseudorandom and changes each switching period (i.e., fSS = 2.2MHz). Startup Immediately after power-up, coming out of shutdown, or going into autoretry, the boost converter performs a short-circuit detection test on the output by connecting the input (INA) to the switching node (LXP) through an internal 50I resistor. If the resulting voltage on LXP exceeds 1.2V, the device turns on the external pMOS switch by pulling GATE low. The boost output ramps to its final value in 15ms. An overloaded or shorted output is detected if the resulting voltage on LXP is below 1.2V. The external pMOS switch remains off and the converter does not switch. After the fault blanking period of 238ms, the device pulls PGOOD low and starts the autoretry timer. The short-circuit detection feature places a lower limit on the output load of approximately 46I when the input voltage is 3V. Fault Conditions and PGOOD PGOOD signals whether all the regulators and the boost converter are operating normally. PGOOD is an opendrain output that pulls low if any of the following faults occur: 1) The boost output voltage falls below 85% of its set value. 2) The positive-gate voltage regulator output (VGH) falls below 85% of its set value. 4) The LXP voltage is greater than 21V (typ). 5) The positive charge-pump voltage (VCP) is greater than 30.5V (typ). 6) The 1.8V/3.3V regulator output voltage falls below 85% of its nominal value. 7) The buck output voltage falls below 92% of its nominal value. If any of the first three fault conditions persists for longer than the 238ms fault blanking period, the device pulls PGOOD low, turns off all outputs, and starts the autoretry timer. If either condition 4 or 5 occurs, the device pulls PGOOD low and turns off all outputs immediately. The device initiates startup only after the fault has cleared. If condition 6 occurs, the device pulls PGOOD low, but does not turn off any of the outputs. During startup, PGOOD is masked and goes high as soon as the 1.8V/3.3V regulator controller turns on. This regulator turns on as soon as VINA exceeds the INA undervoltage lockout threshold. Autoretry When the autoretry counter finishes incrementing after 1.9s, the device attempts to turn on the boost converter and gate voltage regulators in the order shown in Table 1. The device continues to autoretry as long as the fault condition persists. A fault on the 1.8V/3.3V regulator output causes PGOOD to go low, but does not result in the device shutting down and going into autoretry. Current Limit The effective current limit of the boost converter is reduced by the internally injected slope compensation by an amount dependent on the duty cycle of the converter. The effective current limit is given by: ILIM(EFF) =192 × 10 -12 × ILIM_DC_0 × D C COMPI where ILIM(EFF) is the effective current limit, ILIM_DC_0 = 1.1A or 2.2A depending on the boost converter currentlimit option, D is the duty cycle of the boost converter, and CCOMPI is the value of the capacitor at the COMPI input. Estimate the duty cycle of the converter using the formulas shown in the Design Procedure section. 3) The negative-gate voltage regulator output (VGL) falls below 85% of its set value. ���������������������������������������������������������������� Maxim Integrated Products 14 MAX16929 Automotive TFT-LCD Power Supply with Boost Converter and Gate Voltage Regulators 1.8V/3.3V Regulator Controller The 1.8V/3.3V regulator controller delivers 4.5mA (min) to an external load. Connect FB to DR for a regulated 1.8V/3.3V output. For higher output capability, use an external npn transistor as shown in the Typical Application Circuit. The drive capability of the regulator is then increased by the current gain of the transistor (hFE). When using an external transistor, use DR as the base drive and connect FB to the transistor’s emitter. Bypass the base to ground with a 0.1FF ceramic capacitor. If the boost output current is greater than 300mA, connect a 30kI resistor between DR and GND. Positive-Gate Voltage Regulator (GH) The positive-gate voltage regulator includes a p-channel FET output stage to generate a regulated output between +5V and VCP - 2V. The regulator maintains accuracy over wide line and load conditions. It is capable of at least 20mA of output current and includes current-limit protection. VGH is typically used to provide the TFT-LCD gate drivers’ gate-on voltage. The regulator derives its positive supply voltage from a noninverting charge pump, a single-stage example of which is shown in the Typical Application Circuit. A higher voltage using a multistage charge pump is possible, as described in the Charge Pumps section. Negative-Gate Voltage Regulator (GL) The negative-gate voltage regulator is an analog gain block with an open-drain p-channel output. It drives an external npn pass transistor with a 6.8kI base-to-emitter resistor (see the Pass Transistor Selection section). Its guaranteed base drive source current is at least 2mA. VGL is typically used to provide the TFT-LCD gate drivers’ gate-off voltage. The output of the negative-gate voltage regulator (i.e., the collector of the external npn pass transistor) has load- dependent bypassing requirements. Connect a ceramic capacitor between the collector and ground with the value shown in Table 3. The regulator derives its negative supply voltage from an inverting charge pump, a single-stage example of which is shown in the Typical Application Circuit. A more negative voltage using a multistage charge pump is possible as described in the Charge Pumps section. The external npn transistor is not short-circuit protected. To maintain proper pulldown capability of external npn transistor and optimal regulation, a minimum load of at least 500µA is recommended on the output of the GL regulator. Enable (ENP) Use the enable input (ENP) to enable and disable the boost section of the device. Connect ENP to INA for normal operation and to GND to place the device in shutdown. In shutdown, the INA supply current is reduced to 0.5FA. Soft-Start and Supply Sequencing (SEQ) When enabled, the boost output ramps up from VINA to its set voltage. Once the boost output reaches 85% of the set voltage and the soft-start timer expires, the gate voltage regulators turn on in the order shown in Table 1. The 1.8V/3.3V regulator controller is enabled at the beginning of the boost converter’s soft-start. Both gate voltage regulators have a 7.45ms soft-start time. The second one turns on as soon as the output of the first reaches 85% of its set voltage. Thermal Shutdown Internal thermal shutdown circuitry shuts down the device immediately when the die temperature exceeds +165NC. A 15NC thermal shutdown hysteresis prevents the device from resuming normal operation until the die temperature falls below +150NC. Table 1. Supply Sequencing CONTROL INPUTS ENP SEQ 0 X SUPPLY SEQUENCING FIRST SECOND THIRD Device is in shutdown 1 0 VSH VGH VGL 1 1 VSH VGL VGH ���������������������������������������������������������������� Maxim Integrated Products 15 MAX16929 Automotive TFT-LCD Power Supply with Boost Converter and Gate Voltage Regulators Design Procedure Buck Converter Inductor Selection Three key inductor parameters must be specified for operation with the device: inductance value (L), inductor saturation current (ISAT), and DC resistance (RDC). To determine the inductance value, select the ratio of inductor peak-to-peak ripple current to average output current (LIR) first. For LIR values that are too high, the RMS currents are high, and therefore I2R losses are high. Use high-valued inductors to achieve low LIR values. Typically, inductance is proportional to resistance for a given package type, which again makes I2R losses high for very low LIR values. A good compromise between size and loss is to select a 30%-to-60% peak-to-peak ripple current to average-current ratio. If extremely thin high-resistance inductors are used, as is common for LCD-panel applications, the best LIR can increase between 0.5 and 1.0. The size of the inductor is determined as follows: (V -V ) × D L = INB O and LIR × I O × fSWB D= VO η × VINB where VINB is the input voltage, VO is the output voltage, IO is the output current, E is the efficiency of the buck converter, D is the duty cycle, and fSWB is 2.1MHz (the switching frequency of the buck converter). The efficiency of the buck converter can be estimated from the Typical Operating Characteristics and accounts for losses in the internal switch, catch diode, inductor RDC, and capacitor ESR. To ensure the buck converter does not shut down during load dump input-voltage transients to 42V, an inductor value larger than calculated above should be used. Table 2 lists the minimum inductance that should be used for proper operation during load dump. The saturation current rating (ISAT) must be high enough to ensure that saturation can occur only above the maximum current-limit value. Find a low-loss inductor having the lowest possible DC resistance that fits in the allotted dimensions. Table 2. Minimum Buck Inductor Value Required for Normal Operation During Load Dump BUCK VOUTB (V) BUCK IOUTB (A) LMIN (µH) 3.3 1.2 3.3 3.3 2 6.8 5 1.2 3.3 5 2 4.7 Capacitor Selection The input and output filter capacitors should be of a lowESR type (tantalum, ceramic, or low-ESR electrolytic) and should have IRMS ratings greater than: IINB(RMS) = I O D × (1-D + I OUTB(RMS) = LIR × I O 12 LIR 2 ) for the input capacitor 12 for the output capacitor where D is the duty cycle given above. The output voltage contains a ripple component whose peak-to-peak value depends on the value of the ESR and capacitance of the output capacitor, and is approximately given by: DVRIPPLE = DVESR + DVCAP DVESR = LIR x IO x RESR LIR × I O ∆VCAP = 8 × C × fSWB Diode Selection The catch diode should be a Schottky type to minimize its voltage drop and maximize efficiency. The diode must be capable of withstanding a reverse voltage of at least the maximum input voltage in the application. The diode should have an average forward current rating greater than: ID = IO × (1-D) where D is the duty cycle given above. In addition, ensure that the peak current rating of the diode is greater than: LIR I OUTB × 1 + 2 ���������������������������������������������������������������� Maxim Integrated Products 16 MAX16929 Automotive TFT-LCD Power Supply with Boost Converter and Gate Voltage Regulators Boost Converter Inductor Selection Three key inductor parameters must be specified for operation with the device: inductance value (L), inductor saturation current (ISAT), and DC resistance (RDC). To determine the inductance value, select the ratio of inductor peak-to-peak ripple current to average input current (LIR) first. For LIR values that are too high, the RMS currents are high, and therefore I2R losses are high. Use high-valued inductors to achieve low LIR values. Typically, inductance is proportional to resistance for a given package type, which again makes I2R losses high for very low LIR values. A good compromise between size and loss is to select a 30%-to-60% peak-to-peak ripple current to average-current ratio. If extremely thin high-resistance inductors are used, as is common for LCD-panel applications, the best LIR can increase between 0.5 and 1.0. The size of the inductor is determined as follows: L= V ×I VINA × D and IINP = O O LIR × IINP × fSW ηVINA D =1 − ηVINA VO where VINA is the input voltage, VO is the output voltage, IO is the output current, IINP is the average boost input current, E is the efficiency of the boost converter, D is the duty cycle, and fSW is 2.2MHz (the switching frequency of the boost converter). The efficiency of the boost converter can be estimated from the Typical Operating Characteristics and accounts for losses in the internal switch, catch diode, inductor RDC, and capacitor ESR. Capacitor Selection The input and output filter capacitors should be of a lowESR type (tantalum, ceramic, or low-ESR electrolytic) and should have IRMS ratings greater than: IRMS = IRMS =I O LIR × IINP 12 for the input capacitor LIR 2 12 for the output capacitor 1− D D+ where IINP and D are the input current and duty cycle given above. The output voltage contains a ripple component whose peak-to-peak value depends on the value of the ESR and capacitance of the output capacitor and is approximately given by: DVRIPPLE = DVESR + DVCAP ∆VESR =IINP × (1+ ∆VCAP = LIR ) × R ESR 2 IO × D C OUT ×fSW where IINP and D are the input current and duty cycle given above. Rectifier Diode The catch diode should be a Schottky type to minimize its voltage drop and maximize efficiency. The diode must be capable of withstanding a reverse voltage of at least VSH. The diode should have an average forward current rating greater than: ID = IINP × (1-D) where IINP and D are the input current and duty cycle given above. In addition ensure that the peak current rating of the diode is greater than: LIR IINP × 1+ 2 Output-Voltage Selection The output voltage of the boost converter can be adjusted by using a resistive voltage-divider formed by RTOP and RBOTTOM. Connect RTOP between the output and FBP and connect RBOTTOM between FBP and GND. Select RBOTTOM in the 10kI to 50kI range. Calculate RTOP with the following equation: R TOP = R BOTTOM × ( VO − 1) VFBP where VFBP, the boost converter’s feedback set point, is 1V. Place both resistors as close as possible to the device and connect RBOTTOM to the analog ground plane. Loop Compensation Choose RCOMPV to set the high-frequency integrator gain for fast transient response. Choose CCOMPV to set the integrator zero to maintain loop stability. For low-ESR output capacitors, use Table 3 to select the initial values for RCOMPV and CCOMPV. Use a 22pF capacitor in parallel with RCOMPV + CCOMPV. ���������������������������������������������������������������� Maxim Integrated Products 17 MAX16929 Automotive TFT-LCD Power Supply with Boost Converter and Gate Voltage Regulators Table 3. Compensation Component Values VSH (V) 8 18 ISH (mA) 200 200 VINA (V) 3.3 5 PIN (W) 1.75 3.75 L (µH) 5 5 RCOMPV (kI) 33 39 CCOMPV (pF) 220 180 CCOMPI (pF) 820 330 VSH 55FA and the resulting gate source voltage (VGS) turns on the FET. When the gate drive is removed under a fault condition or in shutdown, RSG bleeds off charge to turn off the FET. Size RSG to produce the VGS needed to turn on the FET. 1.8V/3.3V Regulator Controller VCP npn Bipolar Transistor Selection There are two important considerations in selecting the pass npn bipolar transistor: current gain (hFE) and power dissipation. Select a transistor with an hFE high enough to ensure adequate drive capability. This condition is satisfied when IDR x (hFE + 1) is greater than the maximum load current. The regulator can source IDR= 4.5mA (min). The transistor should be capable of dissipating: PNPN_REG = (VINA - VREG_OUT) × ILOAD(MAX) where VREG_OUT = 1.8V or 3.3V. Bypass DR to ground with a 0.1FF ceramic capacitor. For applications in which the boost output current exceeds 300mA, connect a 30kI resistor from DR to ground. LXP Figure 2. Multistage Charge Pump for Positive Output Voltage Supply Considerations INA needs to be at least 4.5V for the 3.3V regulator to operate properly. VCN Charge Pumps LXP Selecting the Number of Charge-Pump Stages For most applications, a single charge-pump stage is sufficient, as shown in the Typical Application Circuit. Connect the flying capacitors to LXP. The output voltages generated on the storage capacitors are given by: Figure 3. Multistage Charge Pump for Negative Output Voltage To further optimize transient response, vary RCOMPV in 20% steps and CCOMPV in 50% steps while observing transient-response waveforms. The ideal transient response is achieved when the output settles quickly with little or no overshoot. Connect the compensation network to the analog ground plane. Use the following formula to calculate the value for CCOMPI: CCOMPI ≤ 950 × 10-6 × L/(VSH + VSCHOTTKY - VINA) p-Channel FET Selection The p-channel FET used to gate the boost converter’s input should have low on-resistance. Connect a resistor (RSG) between the source and gate of the FET. Under normal operation, RSG carries a gate drive current of VCP = 2 x VSH + VSCHOTTKY - 2 x VD VCN = -(VSH + VSCHOTTKY - 2 x VD) where VCP is the positive supply for the positive-gate voltage regulator, and VCN is the negative supply for the negative-gate voltage regulator. Where larger output voltages are needed, use multistage charge pumps (however, the maximum charge-pump voltage is limited by the absolute maximum ratings of CP and DRVN). Figure 2 and Figure 3 show the configuration of a multistage charge pump for both positive and negative output voltages. For mutistage charge pumps the output voltages are: VCP = VSH + n × (VSH + VSCHOTTKY - 2 x VD) VCN = -n × (VSH + VSCHOTTKY - 2 x VD) For highest efficiency, choose the lowest number of charge-pump stages that meets the output requirement. ���������������������������������������������������������������� Maxim Integrated Products 18 MAX16929 Automotive TFT-LCD Power Supply with Boost Converter and Gate Voltage Regulators The number of positive charge-pump stages needed is given by: n CP = VGH+VDROPOUT − VSH VSH+VSCHOTTKY − 2 × VD and the number of negative charge-pump stages is given by: |VGL |+VDROPOUT n CN = VSH + VSCHOTTKY − 2 × VD where nCP is the number of positive charge-pump stages, nCN is the number of negative charge-pump stages, VGH is the positive-gate voltage regulator output voltage, VGL is the negative-gate voltage regulator output voltage, VSH is the boost converter’s output voltage, VD is the forward-voltage drop of the charge-pump diode, VSCHOTTKY is the forward drop of the Schottky diode of the boost converter, and VDROPOUT is the dropout margin for the regulator. Use VDROPOUT = 0.3V for the negative voltage regulator and VDROPOUT = 2V at 20mA for the positive-gate voltage regulator. Flying Capacitors Increasing the flying capacitor (CX) 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 internal switch resistance and the diode impedance place a lower limit on the source impedance. A 0.1FF ceramic capacitor works well in most low-current applications. The voltage rating of the flying capacitors for the positive charge pump should exceed VCP, and that for the negative charge pump should exceed the magnitude of VCN. Charge-Pump Output Capacitor Increasing the output capacitance or decreasing the ESR reduces the output-ripple voltage and the peak-to-peak transient voltage. With ceramic capacitors, the outputvoltage ripple is dominated by the capacitance value. Use the following equation to approximate the required output capacitance for the noninverting charge pump connected to CP: C OUT_CP ≥ D × ILOAD_CP fSW × VRIPPLE_CP where COUT_CP is the output capacitor of the charge pump, D is the duty cycle of the boost converter, ILOAD_ CP is the load current of the charge pump, fSW is the switching frequency of the boost converter, and VRIPPLE_ CP is the peak-to-peak value of the output ripple. For the inverting charge pump connected to CN, use the following equation to approximate the required output capacitance: C OUT_CN ≥ (1-D) × ILOAD_CN fSW × VRIPPLE_CN where COUT_CN is the output capacitor of the charge pump, D is the duty cycle of the boost converter, ILOAD_CN is the load current of the charge pump, fSW is the switching frequency of the boost converter, and VRIPPLE_CN is the peak-to-peak value of the output ripple. Charge-Pump Rectifier Diodes Use high-speed 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 an equivalent current rating. Positive-Gate Voltage Regulator Output-Voltage Selection The output voltage of the positive-gate voltage regulator can be adjusted by using a resistive voltage-divider formed by RTOP and RBOTTOM. Connect RTOP between the output and FBGH, and connect RBOTTOM between FBGH and GND. Select RBOTTOM in the 10kI to 50kI range. Calculate RTOP with the following equation: R TOP = R BOTTOM × ( VGH − 1) VFBGH where VGH is the desired output voltage and VFBGH = 1V (the regulated feedback voltage for the regulator). Place both resistors as close as possible to the device. Avoid excessive power dissipation within the internal pMOS device of the regulator by paying attention to the voltage drop across the drain and source. The amount of power dissipation is given by: PGL = (VCP - VGH) × ILOAD(MAX) where VCP is the noninverting charge-pump output voltage applied to the drain, VGH is the regulated output voltage, and ILOAD(MAX) is the maximum load current. Stability Requirements The positive-gate voltage regulator (GH) requires a minimum output capacitance for stability. For an output ���������������������������������������������������������������� Maxim Integrated Products 19 MAX16929 Automotive TFT-LCD Power Supply with Boost Converter and Gate Voltage Regulators voltage of 5V to (VCP - 2V) and an output current of 10mA to 15mA, use a minimum capacitance of 0.47FF. Negative-Gate Voltage Regulator Output-Voltage Selection The output voltage of the negative-gate voltage regulator can be adjusted by using a resistive voltage-divider formed by RTOP and RBOTTOM. Connect RTOP between REF and FBGL, and connect RBOTTOM between FBGL and the collector of the external npn transistor. Select RTOP greater than 20kI to avoid loading down the reference output. Calculate RBOTTOM with the following equation: V − VGL R BOTTOM = R TOP × FBGL VREF − VFBGL where VGL is the desired output voltage, VREF = 1.25V, and VFBGL = 0.25V (the regulated feedback voltage of the regulator). Pass Transistor Selection The pass transistor must meet specifications for current gain (hFE), input capacitance, collector-emitter saturation voltage, and power dissipation. The transistor’s current gain limits the guaranteed maximum output current to: V ILOAD(MAX) = (IDRVN − BE ) × h FE(MIN) R BE where IDRVN is the minimum guaranteed base-drive current, VBE is the transistor’s base-to-emitter forward voltage drop, and RBE is the pulldown resistor connected between the transistor’s base and emitter. Furthermore, the transistor’s current gain increases the regulator’s DC loop gain (see the Stability Requirements section), so excessive gain destabilizes the output. The transistor’s saturation voltage at the maximum output current determines the minimum input-to-output voltage differential that the regulator can support. Also, the package’s power dissipation limits the usable maximum input-to-output voltage differential. The maximum powerdissipation capability of the transistor’s package and mounting must exceed the actual power dissipated in the device. The power dissipated equals the maximum load current (ILOAD(MAX)_GL) multiplied by the maximum input-to-output voltage differential: PNPN_GL = (VGL - VCN) × ILOAD(MAX)_GL where VGL is the regulated output voltage on the collector of the transistor, VCN is the inverting charge-pump output voltage applied to the emitter of the transistor, and ILOAD(MAX)_GL is the maximum load current. Note that the external transistor is not short-circuit protected. Stability Requirements The device’s negative-gate voltage regulator uses an internal transconductance amplifier to drive an external pass transistor. The transconductance amplifier, the pass transistor, the base-emitter resistor, and the output capacitor determine the loop stability. The transconductance amplifier regulates the output voltage by controlling the pass transistor’s base current. The total DC loop gain is approximately: A V_GL ≅ ( I × h FE 4 ) × (1 + BIAS ) × VREF VT ILOAD where VT is 26mV at room temperature, and IBIAS is the current through the base-to-emitter resistor (RBE). For the device, the bias current for the negative-gate voltage regulator is 0.1mA. Therefore, the base-to-emitter resistor should be chosen to set 0.1mA bias current: R BE = VBE 0.7V = = 7kΩ 0.1mA 0.1mA Use the closest standard resistor value of 6.8kI. The output capacitor and the load resistance create the dominant pole in the system. However, the internal amplifier delay, pass transistor’s input capacitance, and the stray capacitance at the feedback node create additional poles in the system, and the output capacitor’s ESR generates a zero. For proper operation, use the following equations to verify that the regulator is properly compensated: 1) First, determine the dominant pole set by the regulator’s output capacitor and the load resistor: fPOLE_GL = ILOAD(MAX)_GL 2π × C OUT_GL × VOUT_GL The unity-gain crossover frequency of the regulator is: fCROSSOVER = AV_GL × fPOLE_GL 2) The pole created by the internal amplifier delay is approximately 1MHz: fPOLE_AMP = 1MHz 3) Next, calculate the pole set by the transistor’s input capacitance, the transistor’s input resistance, and the base-to-emitter pullup resistor: ���������������������������������������������������������������� Maxim Integrated Products 20 MAX16929 Automotive TFT-LCD Power Supply with Boost Converter and Gate Voltage Regulators 1 2π × CIN × (R BE /RIN ) fPOLE_IN = where: CIN = gm h , RIN = FE 2πfT gm gm is the transconductance of the pass transistor, and fT is the transition frequency. Both parameters can be found in the transistor’s data sheet. Because RBE is much greater than RIN, the above equation can be simplified: fPOLE_IN = 1 2π × CIN × RIN Substituting for CIN and RIN yields: fPOLE = fT h FE 4) Next, calculate the pole set by the regulator’s feedback resistance and the capacitance between FBGL and GND (including stray capacitance): fPOLE_FBGL = 1 2π × C FBGL × (R TOP /R BOTTOM ) where CFBGL is the capacitance between FBGL and GND and is equal to 30pF, RTOP is the upper resistor of the regulator’s feedback divider, and RBOTTOM is the lower resistor of the divider. 5) Next, calculate the zero caused by the output capacitor’s ESR: fZERO_ESR = 1 2π × C OUT_LR × R ESR where RESR is the equivalent series resistance of COUT_LR. To ensure stability, make COUT_LR large enough so the crossover occurs well before the poles and zero calculated in steps 2 to 5. The poles in steps 3 and 4 generally occur at several MHz and using ceramic capacitors ensures the ESR zero also occurs at several MHz. Placing the crossover frequency below 500kHz is sufficient to avoid the amplifier delay pole and generally works well, unless unusual component choices or extra capacitances move one of the other poles or the zero below 1MHz. Table 4. Minimum Output Capacitance vs. Output Voltage Range for Negative-Gate Voltage Regulator (IOUT = 10mA to 15mA) OUTPUT VOLTAGE RANGE MINIMUM OUTPUT CAPACITANCE (µF) -2V R VGL R -4V 2.2 -5V R VGL R -7V -8V R VGL R -13V 1.5 1 Applications Information Power Dissipation An IC’s maximum power dissipation depends on the thermal resistance from the die to the ambient environment and the ambient temperature. The thermal resistance depends on the IC package, PCB copper area, other thermal mass, and airflow. More PCB 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 buck converter, boost converter, positive-gate voltage regulator, negative-gate voltage regulator, and the 1.8V/3.3V regulator controller. Buck Converter In the buck converter, conduction and switching losses in the internal MOSFET are dominant. Estimate these losses using the following formula: PLXB ≈ [(IOUTB × √D)2 × RDS_ON(LXB)] + [0.5 × VINB × IOUTB × (tR + tF) × fSWB] where IOUTB is the output current, D is the duty cycle of the buck converter, RDS_ON(LXB) is the on-resistance of the internal high-side FET, VINB is the input voltage, (tR + tF) is the time is takes for the switch current and voltage to settle to their final values during the rising and falling transitions, and fSWB is the switching frequency of the buck converter. RDS_ON(LXB) is 180mI (typ) and (tR + tF) is 4.4ns + 4.6ns = 9ns at VINB = 12V. Table 4 is a list of recommended minimum output capacitance for the negative-gate voltage regulator and are applicable for output currents in the 10mA to 15mA range. ���������������������������������������������������������������� Maxim Integrated Products 21 MAX16929 Automotive TFT-LCD Power Supply with Boost Converter and Gate Voltage Regulators Boost Converter Power dissipation in the boost converter is primarily due to conduction and switching losses in the low-side FET. Conduction loss is produced by the inductor current flowing through the on-resistance of the FET during the on-time. Switching loss occurs during switching transitions and is a result of the finite time needed to fully turn on and off the FET. Power dissipation in the boost converter can be estimated with the following formula: PLXP ≈ [(IIN(DC,MAX) × √D)2 × RDS_ON(LXP)] + VSH × IIN(DC,MAX) × fSW × [(tR-V + tF-I) + (tR-I + tF-V)] where IIN(DC,MAX) is the maximum expected average input (i.e., inductor) current, D is the duty cycle of the boost converter, RDS_ON(LXP) is the on-resistance of the internal low-side FET, VSH is the output voltage, and fSW is the switching frequency of the boost converter. RDS_ON(LXP) is 110mI (typ) and fSW is 2.2MHz. The voltage and current rise and fall times at the LXP node are equal to tR-V (voltage rise time), tF-V (voltage fall time), tR-I (current rise time), and tF-I (current fall time), and are determined as follows: Ensure that the voltage on CP does not exceed the CP overvoltage threshold as given in the Electrical Characteristics table. Negative-Gate Voltage Regulator Use the lowest number of charge-pump stages possible to provide the negative voltage to the negative-gate voltage regulator. Estimate the power dissipated in the negative-gate voltage regulator using the following: PGL = (VINA + |VCN| - VBE) × IDRVN where VBE is the base-emitter voltage of the external npn bipolar transistor, and IDRVN is the current sourced from DRVN to the RBE bias resistor and to the base of the transistor, which is given by: 1.8V/3.3V Regulator Controller The power dissipated in the 1.8V/3.3V regulator controller is given by: V + VSCHOTTKY t F-V = SH K F-V t F-I = PGH = (VCP - VGH) × ILOAD(MAX)_GH I V IDRVN = BE + GL RBE h FE +1 V + VSCHOTTKY t R-V = SH K R-V t R-I = Positive-Gate Voltage Regulator Use the lowest number of charge-pump stages possible in supplying power to the positive-gate voltage regulator. Doing so minimizes the drain-source voltage of the integrated pMOS switch and power dissipation. The power dissipated in the switch is given as: IIN(DC,MAX) K R-I IIN(DC,MAX) K F-I KR-V, KF-V, KR-I, and KF-I are the voltage and current slew rates of the LXP node and are supply dependent. Use Table 5 to determine their values. PREG = (VINA - VOUT_REG - VBE) × IDR where VOUT_REG = 1.8V or 3.3V, VBE is the base-emitter voltage of the external npn bipolar transistor, and IDR is the current sourced from DR to the base of the transistor. IDR is given by: I IDR = LOAD h FE + 1 where ILOAD is load current of the 1.8V/3.3V regulator controller, and hFE is the current gain of the transistor. Table 5. LXP Voltage and Current Slew Rates vs. Supply Voltage LXP VOLTAGE AND CURRENT SLEW RATES RISING VOLTAGE SLEW RATE KR-V (V/ns) FALLING VOLTAGE SLEW RATE KF-V (V/ns) RISING CURRENT SLEW RATE KR-I (A/ns) FALLING CURRENT SLEW RATE KF-I (A/ns) 3.3 0.52 1.7 0.13 0.38 5 1.35 2 0.3 0.44 VINA (V) ���������������������������������������������������������������� Maxim Integrated Products 22 MAX16929 Automotive TFT-LCD Power Supply with Boost Converter and Gate Voltage Regulators Total Power Dissipation The total power dissipated in the package is the sum of the losses previously calculated. Therefore, total power dissipation can be estimated as follows: PT = PLXB + PLXP + PGH + PGL + PREG Achieve maximum heat transfer by connecting the exposed pad to a thermal landing pad and connecting the thermal landing pad to a large ground plane through thermal vias. Layout Considerations 2) Connect input and output capacitors to the power ground planes; connect all other capacitors to the analog ground plane. 3) Keep the high-current paths as short and wide as possible. Keep the path of switching currents short. 4) Place the feedback resistors as close to the IC as possible. Connect the negative end of the resistive divider and the compensation network to the analog ground plane. Careful PCB layout is critical in achieving stable and optimized performance. Follow the following guidelines for good PCB layout: 5) Route the high-speed switching node LXB and LXP away from sensitive analog nodes (FB, FBP, FBGH, FBGL, FBB, and REF). 1) Place decoupling capacitors as close as possible to the device. Connect the power ground planes and the analog ground plane together at one point close to the device. Refer to the MAX16929 Evaluation Kit data sheet for a recommended PCB layout. Ordering Information/Selector Guide REGULATOR VREG (V) BUCK VOUTB (V) BUCK IOUTB (A) BOOST ILIM (A) PIN-PACKAGE MAX16929AGUI/V+ 3.3 5 2 1.5 28 TSSOP-EP* MAX16929BGUI/V+ 1.8 5 2 1.5 28 TSSOP-EP* MAX16929CGUI/V+ 1.8 3.3 2 1.5 28 TSSOP-EP* MAX16929DGUI/V+ 3.3 5 2 0.75 28 TSSOP-EP* MAX16929EGUI/V+ 3.3 5 1.2 0.75 28 TSSOP-EP* MAX16929FGUI/V+ 1.8 5 2 0.75 28 TSSOP-EP* MAX16929GGUI/V+ 1.8 5 1.2 0.75 28 TSSOP-EP* MAX16929HGUI/V+ 1.8 3.3 2 0.75 28 TSSOP-EP* MAX16929IGUI/V+ 1.8 3.3 1.2 0.75 28 TSSOP-EP* PART Note: All devices are specified over the -40°C to +105°C operating temperature range. /V denotes an automotive qualified part. +Denotes a lead(Pb)-free/RoHS-compliant package. *EP = Exposed pad. Chip Information PROCESS: BiCMOS Package Information For the latest package outline information and land patterns (footprints), go to www.maxim-ic.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO. 28 TSSOP-EP U28ME+1 21-0108 90-0147 ���������������������������������������������������������������� Maxim Integrated Products 23 MAX16929 Automotive TFT-LCD Power Supply with Boost Converter and Gate Voltage Regulators Typical Application Circuit OUTB RCOMPV CCOMPI INA CCOMPV COMPI COMPV GATE LP OPTIONAL LXP DR LXP VREG 1.8V/3.3V FB 1.8V/3.3V REGULATOR CONTROLLER VSH VINA TO 18V BOOST PGNDP FBP VCN OSCILLATOR VCN CP DRVN VSH VGH GH POSITIVE GATE VOLTAGE REGULATOR NEGATIVE GATE VOLTAGE REGULATOR FBGH VGL FBGL BST 4V TO 28V OUTB INB REF LXB 3.3V/5V BUCK BANDGAP REFERENCE GND ENP FBB CONTROL INA SEQ ENB AVL PGOOD GND MAX16929 ���������������������������������������������������������������� Maxim Integrated Products 24 MAX16929 Automotive TFT-LCD Power Supply with Boost Converter and Gate Voltage Regulators Revision History REVISION NUMBER REVISION DATE 0 5/11 Initial release 1 9/11 Removed ENB from the FBB to GND range in the Absolute Maximum Ratings 2 2 1/12 Corrected the CCOMPI formula in the Loop Compensation section 18 DESCRIPTION PAGES CHANGED — 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. The parametric values (min and max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2012 Maxim Integrated Products 25 Maxim is a registered trademark of Maxim Integrated Products, Inc.