19-1788; Rev 0; 10/00 KIT ATION EVALU LE B A IL A AV Triple Charge-Pump TFT LCD DC-DC Converter Features ♦ Adjustable Outputs The dual low-power charge pumps independently regulate one positive output (VPOS) and one negative output (VNEG). These additional outputs use external diode and capacitor multiplier stages (as many stages as required) to regulate output voltages up to +35V and -35V. The constant switching frequency and a proprietary regulation algorithm minimize output ripple and capacitor sizes for all three charge pumps. The MAX1747 is available in the ultra-thin TSSOP package (1.1mm max height). ♦ Fast Transient Response Up to +5.5V Main High-Power Output Up to +35V Positive Charge-Pump Output Down to -35V Negative Charge-Pump Output ♦ 200kHz to 2MHz Adjustable Switching Frequency ♦ +2.7V to +4.5V Input Supply ♦ Internal Power MOSFETs ♦ 0.1µA Shutdown Current ♦ Internal Soft-Start ♦ Power-Ready Output ♦ Internal Supply Sequencing ♦ Ultra-Thin Solution (No Inductors) ♦ Thin TSSOP Package (1.1mm max) Ordering Information PART MAX1747EUP PIN-PACKAGE -40°C to +85°C 20 TSSOP Typical Operating Circuit Applications TFT Active-Matrix LCDs Passive-Matrix Displays TEMP. RANGE INPUT SUPM CXP IN CXN Personal Digital Assistants (PDAs) MAIN OUTPUT Pin Configuration TO µC SHDN RDY OUT SUPP SUPN FB DRVN TOP VIEW TGND 1 20 OUT TGND 2 19 CXP RDY 3 18 SUPM FB 4 INTG 5 MAX1747 17 CXN MAX1747 16 PGND IN 6 15 SUPP GND 7 14 DRVP REF 8 13 SUPN FBP 9 12 DRVN FBN 10 11 SHDN NEGATIVE OUTPUT DRVP FBN REF TGND GND FBP INTG PGND POSITIVE OUTPUT TSSOP ________________________________________________________________ Maxim Integrated Products 1 For price, delivery, and to place orders, please contact Maxim Distribution at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. MAX1747 General Description The MAX1747 triple charge-pump DC-DC converter provides the regulated voltages required by active matrix thin-film transistor (TFT) liquid-crystal displays (LCDs) in a low-profile TSSOP package. One highpower and two low-power charge pumps convert the +2.7V to +4.5V input supply voltage into three independent output voltages. The primary high-power charge pump generates an output voltage (VOUT) between 4.5V and 5.5V that is regulated within ±1%. The low-power BiCMOS control circuitry and the low on-resistance (R ON ) power MOSFETs maximize efficiency. The adjustable switching frequency (200kHz to 2MHz) provides fast transient response and allows the use of small low-profile ceramic capacitors. MAX1747 Triple Charge-Pump TFT LCD DC-DC Converter ABSOLUTE MAXIMUM RATINGS IN, SUPM, OUT, TGND to GND................................-0.3V to +6V SHDN........................................................................-0.3V to +1V PGND to GND.....................................................................±0.3V SUPM to IN .........................................................................±0.3V CXN to PGND.........................................-0.3V to (VSUPM + 0.3V) CXP to PGND ............................(VSUPM - 0.3V) to (VOUT + 0.3V) DRVN to GND .........................................-0.3V to (VSUPN + 0.3V) DRVP to GND..........................................-0.3V to (VSUPP + 0.3V) RDY to GND ...........................................................-0.3V to +14V SUPP, SUPN to GND..............................................-0.3V to +14V INTG, REF, FB, FBN, FBP to GND ...............-0.3V to (VIN + 0.3V) Continuous Current into: SUPM, CXN, CXP, OUT ..............................................±800mA SUPP, SUPN, DRVN, DRVP........................................±200mA SHDN...........................................................................+100µA All Other Pins ....................................................................±10mA Continuous Power Dissipation (TA = +70°C) 20-Pin TSSOP (derate 10.9mW/°C above +70°C) .......879mW Operating Temperature Range............................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (VIN = VSUPM = +3.0V, VSUPP = VSUPN = +5V, TGND = PGND = GND, I SHDN = 22µA, COUT = 2 ✕ 4.7µF, CREF = 0.22µF, CINTG = 1500pF, VOUT = +5V, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER Input Supply Range Input Undervoltage Threshold Input Quiescent Supply Current Output Quiescent Supply Current SYMBOL VIN VUVLO IIN + ISUPM IQ(OUT) Shutdown Supply Current Operating Frequency CONDITIONS fOSC MIN TYP 2.7 MAX UNITS 4.5 V 2.4 2.6 V VFB = VFBP = 1.5V, VFBN = -0.2V, VOUT = 5V, no load on DRVN and DRVP; CXN and CXP open 0.9 1.0 mA VFB = VFBP = 1.5V, VFBN = -0.2V, VOUT = 5V, no load on DRVN and DRVP; CXN and CXP open 2.5 4.0 mA V SHDN = 0, VSUPM = 5V 0.1 20 µA 1 1.2 MHz 5.5 V VIN falling, 40mV hysteresis (typ) I SHDN = 22µA 2.2 0.65 MAIN CHARGE PUMP Output Voltage Range Maximum Output Current VOUT IOUT(MAX) FB Regulation Voltage VFB FB Input Bias Current IFB 4.5 CX = 0.47µF 200 1.237 VFB = 1.25V -50 FB Power-Ready Trip Level Rising edge 1.09 FB Fault Trip Level Falling edge Integrator Transconductance mA 1.248 1.263 V +50 nA µS 530 Main Soft-Start Period 1.125 1.16 V 1.100 V 4.096 / FOSC s NEGATIVE LOW-POWER CHARGE PUMP SUPN Input Supply Range VSUPN SUPN Quiescent Current ISUPN SUPN Shutdown Current FBN Regulation Voltage 2 VFBN 13 V VFBN = -0.2V, no load on DRVN 2.7 0.6 0.8 mA V SHDN = 0, VSUPN = 13V 0.1 10 µA 0 +50 mV -50 _______________________________________________________________________________________ Triple Charge-Pump TFT LCD DC-DC Converter (VIN = VSUPM = +3.0V, VSUPP = VSUPN = +5V, TGND = PGND = GND, I SHDN = 22µA, COUT = 2 ✕ 4.7µF, CREF = 0.22µF, CINTG = 1500pF, VOUT = +5V, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER FBN Input Bias Current SYMBOL IFBN CONDITIONS VFBN = -50mV MIN DRVN PCH On-Resistance VFBN = 50mV DRVN NCH On-Resistance TYP MAX UNITS +50 nA 3 6 Ω 1 5 -50 VFBN = -50mV 20 FBN Power-Ready Trip Level Falling edge 80 FBN Fault Trip Level Rising edge Negative Soft-Start Period Ω kΩ 125 165 mV 140 mV 2.048/ FOSC s POSITIVE LOW-POWER CHARGE PUMP SUPP Input Supply Range VSUPP SUPP Quiescent Current ISUPP SUPP Shutdown Current FBP Regulation Voltage VFBP FBP Input Bias Current IFBP 13 V VFBP = 1.5V, no load on DRVP 2.7 0.6 0.8 mA V SHDN = 0, VSUPP = 13V 0.1 10 µA 1.25 1.30 V +50 nA 3 6 Ω VFBP = 1.20V 1.5 5 VFBP = 1.30V 20 1.20 VFBP = 1.5V -50 DRVP PCH On-Resistance DRVP NCH On-Resistance FBP Power-Ready Trip Level Rising edge FBP Fault Trip Level Falling edge 1.090 Positive Soft-Start Period 1.125 Ω kΩ 1.160 V 1.100 V 2.048/ FOSC s REFERENCE Reference Voltage VREF Reference Undervoltage Threshold -2µA < IREF < 50µA 1.231 1.25 1.269 V VREF rising 0.95 1.05 1.18 V 0.4 V LOGIC SIGNALS SHDN Input Low Voltage SHDN Bias Voltage I SHDN = 22µA 580 SHDN Bias Voltage Tempco SHDN Input Current Range 724 830 2 I SHDN For 200kHz to 2MHz operation 3 mV mV/°C 65 µA RDY Output Low Voltage ISINK = 2mA 0.25 0.5 V RDY Output High Leakage V RDY = 13V 0.01 1 µA _______________________________________________________________________________________ 3 MAX1747 ELECTRICAL CHARACTERISTICS (continued) MAX1747 Triple Charge-Pump TFT LCD DC-DC Converter ELECTRICAL CHARACTERISTICS (VIN = VSUPM = +3.0V, VSUPP = VSUPN = +5V, TGND = PGND = GND, I SHDN = 22µA, COUT = 2 1500pF, VOUT = +5V, TA = -40°C to +85°C, unless otherwise noted.) (Note 1) PARAMETER Input Supply Range Input Undervoltage Threshold Input Quiescent Supply Current Output Quiescent Supply Current SYMBOL VUVLO IIN + ISUPM IQ(OUT) 4.7µF, CREF = 0.22µF, CINTG = MIN MAX UNITS 2.7 4.5 V 2.2 2.6 V VFB = VFBP = 1.5V, VFBN = -0.2V, VOUT = 5V, no load on DRVN and DRVP; CXN and CXP open 1.0 mA VFB = VFBP = 1.5V, VFBN = -0.2V, VOUT = 5V, no load on DRVN and DRVP; CXN and CXP open 4.0 mA VIN Input Shutdown Current Operating Frequency CONDITIONS ✕ VIN falling, 40mV hysteresis (typ) 20 µA I SHDN = 22µA 0.65 1.2 MHz 4.5 5.5 CX = 0.47µF 200 V SHDN = 0, VSUPM = 5V fOSC MAIN CHARGE PUMP Output Voltage Range Output Current VOUT IOUT(MAX) FB Regulation Voltage VFB FB Input Bias Current IFB FB Power-Ready Trip Level 1.222 V mA 1.271 V VFB = 1.25V -50 +50 nA Rising edge 1.09 1.16 V 2.7 13 V VFBN = -0.2V, no load on DRVN 0.8 mA V SHDN = 0, VSUPN = 13V 10 µA -50 +50 mV -50 +50 nA NEGATIVE LOW-POWER CHARGE PUMP SUPN Input Supply Range VSUPN SUPN Quiescent Current ISUPN SUPN Shutdown Current FBN Regulation Voltage VFBN FBN Input Bias Current IFBN VFBN = 0 DRVN PCH On-Resistance VFBN = 50mV DRVN NCH On-Resistance FBN Power-Ready Trip Level VFBN = -50mV 20 Falling edge 80 6 Ω 5 Ω 165 mV kΩ POSITIVE LOW-POWER CHARGE PUMP SUPP Input Supply Range VSUPP SUPP Quiescent Current ISUPP SUPP Shutdown Current FBP Regulation Voltage VFBP FBP Input Bias Current IFBP 13 V VFBP = 1.5V, no load on DRVP 2.7 0.8 mA V SHDN = 0, VSUPP = 13V 10 µA VFBP = 1.5V 1.20 1.30 V -50 +50 nA 6 Ω DRVP PCH On-Resistance DRVP NCH On-Resistance FBP Power-Ready Trip Level 4 VFBP = 1.20V 5 VFBP = 1.30V 20 Rising edge 1.09 _______________________________________________________________________________________ Ω kΩ 1.16 V Triple Charge-Pump TFT LCD DC-DC Converter (VIN = VSUPM = +3.0V, VSUPP = VSUPM = +5V, TGND = PGND = GND, I SHDN = 22µA, COUT = 2 1500pF, VOUT = +5V, TA = -40°C to +85°C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS ✕ 4.7µF, CREF = 0.22µF, CINTG = MIN MAX UNITS -2µA < IREF < 50µA 1.222 1.269 V VREF rising 0.95 1.18 V 0.4 V I SHDN = 22µA 580 900 mV 65 µA REFERENCE Reference Voltage VREF Reference Undervoltage Threshold LOGIC SIGNALS SHDN Input Low Voltage SHDN Bias Voltage SHDN Input Current Range RDY Output Low Voltage For 200kHz to 2MHz operation I SHDN RDY Output High Leakage 3 ISINK = 2mA 0.5 V V RDY = 13V 1 µA Note 1: Specifications from 0°C to -40°C are guaranteed by design, not production tested. Typical Operating Characteristics (Circuit of Figure 1, VIN = VSUPM = +3.3V, TA = +25°C, unless otherwise noted.) EFFICIENCY (%) VOUT (V) 90 5.00 VIN = 4.0V 4.99 4.98 80 VIN = 3.3V 70 VIN = 4.0V 60 4.97 200 IOUT (mA) 300 400 80 70 VIN = 3.3V 60 50 40 40 100 90 VNEG = -7V WITH INEG = 10mA VPOS = 12V WITH IPOS = 5mA VIN = 4.0V 50 0 VOUT = 5V VIN = 2.8V 5.01 VIN = 2.8V VIN = 2.8V 100 EFFICIENCY (%) VIN = 3.3V VOUT = 5V MAX1747 toc02 5.02 100 MAX1747 toc01 5.03 MAIN OUTPUT EFFICIENCY vs. LOAD CURRENT (MAIN CHARGE PUMP ONLY) MAIN OUTPUT EFFICIENCY vs. LOAD CURRENT (MAIN CHARGE PUMP ONLY) MAX1747 toc03 MAIN OUTPUT EFFICIENCY vs. LOAD CURRENT (MAIN CHARGE PUMP ONLY) 0 100 200 IOUT (mA) 300 400 0 100 200 300 400 IOUT (mA) _______________________________________________________________________________________ 5 MAX1747 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (continued) (Circuit of Figure 1, VIN = VSUPM = +3.3V, TA = +25°C, unless otherwise noted.) SWITCHING FREQUENCY vs. ISHDN 14 12.0 MAX1747 toc05 2.0 MAX1747 toc04 16 NO-LOAD SUPPLY CURRENT vs. TEMPERATURE 1.6 MAX1747 toc06 NO-LOAD SUPPLY CURRENT vs. SWITCHING FREQUENCY 11.5 10 8 6 4 IIN + ISUPM (mA) FREQUENCY (MHz) 1.2 0.8 0.4 9.5 0.5 1.0 1.5 0 2.0 10 20 30 40 -40 50 10 35 60 85 ISHDN (mA) TEMPERATURE (°C) SWITCHING FREQUENCY vs. TEMPERATURE NEGATIVE LOW-POWER CHARGE-PUMP EFFICIENCY vs. LOAD CURRENT NEGATIVE LOW-POWER CHARGE-PUMP OUTPUT VOLTAGE vs. LOAD CURRENT VNEG = -7V 90 -6.4 80 1.00 0.95 -6.5 VSUPN = 5V VSUPN = 5V 70 VSUPN = 6V VNEG (V) EFFICIENCY (%) 1.05 MAX1747 toc09 -6.3 MAX1747 toc08 100 MAX1747 toc07 1.10 FREQUENCY (MHz) -15 FREQUENCY (MHz) 1.15 60 50 -6.6 -6.7 VSUPN = 6V -6.8 40 -6.9 VSUPN = 7V 0.90 VON = 3.3V RFREQ = 120kΩ 0.85 -40 -15 10 35 60 30 -7.0 20 -7.1 0 85 10 20 30 40 VSUPN = 7V 0 10 20 30 40 TEMPERATURE (°C) INEG (mA) INEG (mA) MAXIMUM NEGATIVE CHARGE-PUMP OUTPUT VOLTAGE vs. SUPPLY VOLTAGE POSITIVE LOW-POWER CHARGE-PUMP EFFICIENCY vs. LOAD CURRENT POSITIVE LOW-POWER CHARGE-PUMP OUTPUT VOLTAGE vs. LOAD CURRENT -14 INEG = 1mA -18 80 12.0 70 11.9 VSUPP = 7V 60 VSUPP = 6V 50 40 11.6 30 11.5 5 7 9 VSUPN (V) 11 13 0 10 20 IPOS (mA) 30 VSUPP = 6V VSUPP = 5V 11.4 20 3 11.8 11.7 VSUPP = 7V VPOS = 12V -22 12.1 VPOS (V) INEG = 10mA VSUPP = 5V 90 EFFICIENCY (%) -6 12.2 MAX1747 toc11 VNEG(NOMINAL) = -20V -10 100 MAX1747 toc10 -2 6 VON = 3.3V RFREQ = 120kΩ 9.0 0 0 10.5 10.0 2 0 11.0 MAX1747 toc12 ICC + IIN (mA) 12 VNEG (V) MAX1747 Triple Charge-Pump TFT LCD DC-DC Converter 40 0 10 20 IPOS (mA) _______________________________________________________________________________________ 30 40 Triple Charge-Pump TFT LCD DC-DC Converter MAXIMUM POSITIVE CHARGE-PUMP OUTPUT VOLTAGE vs. SUPPLY VOLTAGE MAX1747 toc13 VPOS(NOMINAL) = 32V 28 VPOS (V) LOAD TRANSIENT MAX1747 toc14 34 IPOS = 1mA 200mA IOUT 100mA/div 100mA 0 22 IPOS = 10mA 16 5.05V VOUT 50mV/div 5V 10 4.95V 4 3 5 7 9 11 40µs/div VIN = 3.3V, VOUT = 5.0V ROUT = 500Ω TO 25Ω CINTG = 1500pF 13 VSUPP (V) RIPPLE WAVEFORM STARTUP WAVEFORM (NO LOAD) MAX1747 toc15 MAX1747 toc16 VOUT 20mV/div VON 2V/div 2V 0 VCXP 2V/div 4V VNEG 10mV/div VPOS 10mV/div 2V 4V VOUT 2V/div 2V 0 400ns/div VOUT = +5.0V,IOUT = 200mA VNEG = -7V, INEG = 10mA VPOS = +12V, IPOS = 5mA 1ms/div VOUT = 5V, NO LOAD ON CONNECTED TO SHDN THROUGH A 58kΩ RESISTOR STARTUP WAVEFORM (200mA LOAD) POWER-UP SEQUENCE MAX1747 toc17 MAX1747 toc18 VON 2V/div 2V 0 VON 2V/div 2V 0 VCXP 2V/div 4V 2V 0 4V -10V VOUT 2V/div 2V 0 VMAIN 5V/div 5V VNEG 10V/div VPOS 10V/div 10V 0 1ms/div VOUT = 5V, ROUT = 25Ω (200mA) ON CONNECTED TO SHDN THROUGH A 58kΩ RESISTOR 2ms/div VMAIN = 5V, VNEG = -7V, VPOS = 12V ON CONNECTED TO SHDN THROUGH A 58kΩ RESISTOR _______________________________________________________________________________________ 7 MAX1747 Typical Operating Characteristics (continued) (Circuit of Figure 1, VIN = VSUPM = +3.3V, TA = +25°C, unless otherwise noted.) Triple Charge-Pump TFT LCD DC-DC Converter MAX1747 Pin Description PIN 1, 2 NAME TGND FUNCTION 3 RDY 4 FB 5 INTG 6 IN 7 GND Analog Ground. Connect to power ground (PGND) underneath the IC. 8 REF Internal Reference Bypass Terminal. Connect a 0.22µF capacitor from this terminal to analog ground (GND). External load capability to 50µA. REF is disabled in shutdown. 9 FBP Positive Charge-Pump Feedback Input. Regulates to 1.25V nominal. Connect feedback resistive divider to analog ground (GND). 10 FBN Negative Charge-Pump Regulator Feedback Input. Regulates to 0V nominal. Connect feedback resistive divider to the reference (REF). Must be connected to ground. Active-Low Open-Drain Output. Indicates all outputs are ready. The RON is 125Ω (typ). Main Charge-Pump Feedback Input. Regulates to 1.25V nominal. Connect to the center of a feedback resistive divider between the main output (OUT) and analog ground (GND). Main Charge-Pump Integrator Output. If used, connect 1500pF to analog ground (GND). To disable the integrator, connect to GND. Supply Input. +2.7V to +4.5V input range. Powers only the logic and reference. Bypass to analog ground (GND) with a 0.1µF capacitor as close to the pin as possible. Shutdown Input. Drive SHDN through an external resistor. When SHDN is pulled low, the device turns off and draws only 0.1µA. OUT is also pulled low through an internal 10Ω resistor in shutdown mode. When current is sourced into SHDN through RFREQ, the device activates, and the SHDN input current sets the oscillator’s switching frequency: RFREQ (kΩ) = 45.5 (MHz / mA) ✕ (VON - 0.7V) / fOSC (MHz) 11 SHDN 12 DRVN Negative Charge-Pump Driver Output. Output high level is VSUPN, and low level is PGND. 13 SUPN Negative Charge-Pump Driver Supply Voltage. Bypass to power ground (PGND) with a 0.1µF capacitor. 14 DRVP Positive Charge-Pump Driver Output. Output high level is VSUPP and low level is PGND. 15 SUPP Positive Charge-Pump Driver Supply Voltage. Bypass to power ground (PGND) with a 0.1µF capacitor. 16 PGND 17 CXN 18 SUPM 19 CXP Positive Terminal of the Main Charge-Pump Flying Capacitor 20 OUT Main Charge-Pump Output. Bypass to power ground (PGND) with 10µF for a 1MHz application (see Output Capacitor Selection). An internal 10Ω resistor discharges the output when the device is shut down. Power Ground. Connect to analog ground (GND) underneath the IC. Negative Terminal of the Main Charge-Pump Flying Capacitor Main Charge-Pump Supply Voltage Input Detailed Description The MAX1747 is an efficient triple-output power supply for TFT LCD applications. The device contains one high-power charge pump and two low-power charge pumps. The MAX1747 charge pumps switch continuously at a constant frequency, so the output noise contains well-defined frequency components, and the circuit requires much smaller external capacitors for a 8 given output ripple. The adjustable switching frequency is set by the current into the shutdown pin (see Frequency Selection and Shutdown). The main charge pump uses internal MOSFETs with low RON to provide high output current. The adjustable output voltage of the main charge pump can be set up to 5.5V with external resistors. The dual low-power charge pumps independently regulate a positive output _______________________________________________________________________________________ Triple Charge-Pump TFT LCD DC-DC Converter CIN 10µF SUPM R7 100k RFREQ 100k C1 0.1µF CXN IN CX 0.47µF VOUT +5V, 200mA OUT COUT (2) 4.7µF SUPP RDY D3 R1 150k SUPN C11 0.1µF SHDN C12 0.1µF C5 0.1µF R2 49.9k DRVN D4 FB D7 C6 1.0µF C9 0.1µF D1 C3 0.1µF MAX1747 DRVP D8 D2 C10 1.0µF D5 C7 0.1µF FBN VNEG -7V, 10mA MAX1747 CXP VIN = 3.0V R5 280k D6 R6 49.9k CREF 0.22µF C4 1.0µF REF FBP TGND INTG GND PGND VPOS +12V, 5mA CINTG 1500pF R4 49.9k R3 432k C8 1.0µF Figure 1. Typical Application Circuit (VPOS) and a negative output (VNEG). These two outputs use external diode and capacitor stages (as many stages as required) to regulate output voltages above +35V and under -35V. A proprietary regulation algorithm minimizes output ripple as well as capacitor sizes for all three charge pumps. Also included in the MAX1747 are a precision 1.25V reference that sources up to 50µA, shutdown, power-up sequencing, fault detection, and an activelow open-drain ready output. Main Charge Pump During the first half-cycle, the MAX1747 charges the flying capacitor (CX) by connecting it between the supply voltage (VSUPM) and ground (Figure 2). This initial charge is controlled by the variable N-channel on-resistance. During the second half-cycle, the MAX1747 level shifts the flying capacitor by stacking the voltage across CX on top of the supply voltage. This transfers the sum of the two voltages to the output capacitor (COUT). Dual Charge-Pump Regulators The MAX1747 contains two individual low-power charge pumps. Using a single stage, the first charge pump inverts the supply voltage (VSUPN) and provides a regulated negative output voltage. The second charge pump doubles the supply voltage (VSUPP) and provides a regulated positive output voltage. The MAX1747 contains internal P-channel and N-channel MOSFETs to control the power transfer. The internal MOSFETs switch at a constant frequency set by the current into the shutdown pin (see Frequency Selection and Shutdown). _______________________________________________________________________________________ 9 MAX1747 Triple Charge-Pump TFT LCD DC-DC Converter SUPM MAX1747 C1 OSC MAX1747 VSUPM = VIN 2.7V TO 4.5V VOUT OUT OSC CX CXN D4 R1 CINTG INTG PGND VREF 1.25V REF GND VNEG C6 R6 REF R2 CREF R5 FBN VREF 1.25V FB gm D3 C5 DRVN COUT CXP VSUPP = 2.7V TO 13V SUPN GND PGND CREF VNEG = -(R5/R6) ✕ VREF VREF = 1.25V VOUT = [1+ (R1/R2)] ✕ VREF VREF = 1.25V Figure 2. Main Charge-Pump Block Diagram Figure 3. Negative Charge-Pump Block Diagram Negative Charge Pump During the first half-cycle, the P-channel MOSFET turns on, and flying capacitor C5 charges to VSUPN minus a diode drop (Figure 3). During the second half-cycle, the P-channel MOSFET turns off, and the N-channel MOSFET turns on, level shifting C5. This connects C5 in parallel with the reservoir capacitor, C6. If the voltage across C6 minus a diode drop is lower than the voltage across C5, current flows from C5 to C6 until the diode (D4) turns off. The amount of charge transferred to the output is controlled by the variable N-channel RON. Driving SHDN low forces all three MAX1747 converters into shutdown mode. When disabled, the supply current drops to 20µA (max) to maximize battery life, and OUT is pulled to ground through an internal 10Ω resistor. For the low-power charge pumps, the output capacitance and load current determine the rate at which each output voltage will decay. The device activates (see Power-up Sequencing) once SHDN is forward biased (minimum of 3µA of current). Do not leave SHDN floating. For a typical application where shutdown is used only to set the switching frequency, connect SHDN to the input (V IN = 3.3V) with a 120kΩ resistor for a 1MHz switching frequency. The bias current into SHDN, programmed with an external resistor, determines the oscillator frequency (see Typical Operating Characteristics). To select the frequency, calculate the external resistor value, RFREQ, using the following formula: RFREQ = 45.5 (MHz / mA) ✕ (VON – 0.7V) / fOSC where RFREQ is in kΩ and fOSC is in MHz. Program the frequency in the 200kHz to 2MHz range. This frequency range corresponds to SHDN input currents between 3µA to 65µA. Proper operation of the oscillator is not guaranteed beyond these limits. Forcing SHDN below 400mV disables the device. Positive Charge Pump During the first half-cycle, the N-channel MOSFET turns on and charges the flying capacitor, C3 (Figure 4). This initial charge is controlled by the variable N-channel R ON . During the second half-cycle, the N-channel MOSFET turns off, and the P-channel MOSFET turns on, level shifting C3 by VSUPP volts. This connects C3 in parallel with the reservoir capacitor, C4. If the voltage across C4 plus a diode drop (VPOS + VDIODE) is smaller than the level-shifted flying capacitor voltage (VC3 + VSUPP), charge flows from C3 to C4 until the diode (D2) turns off. Frequency Selection and Shutdown The shutdown pin (SHDN) on the MAX1747 performs a dual function: it shuts down the device and determines the oscillator frequency. The SHDN input looks like a diode to ground and should be driven through a resistor (Figure 5). 10 Soft-Start For the MAX1747, soft-start is achieved by controlling the rise rate of the output voltage, regardless of output capacitance or output load, and limited only by the output impedance of the regulator (see Startup Waveforms ______________________________________________________________________________________ Triple Charge-Pump TFT LCD DC-DC Converter VSUPP = 2.7V TO 13V SUPP OSC D2 R3 FBP GND CIN RFREQ OSC DRVP VREF 1.25V VON = VIN IN MAX1747 D1 C3 MAX1747 MAX1747 SHDN VPOS GND R4 C4 PGND VPOS = [1 + (R3/R4)] ✕ VREF VREF = 1.25V RFREQ = kFREQ ✕ (VON - 0.7V)/fOSC RFREQ IS IN kΩ, kFREQ IS 45.5MHz/mA, AND fOSC IS IN MHz. Figure 4. Positive Charge-Pump Block Diagram Figure 5. Frequency Adjustment in the Typical Operating Characteristics). The main output voltage is controlled to be in regulation within 4096 clock cycles (1/fOSC). The negative and positive lowpower charge pumps are controlled to be in regulation within 2048 clock cycles. active while the positive charge pump stops switching and its output voltage decays, depending on output capacitance and load. The positive charge-pump output will not power up until the negative charge-pump output voltage rises above its power-up threshold (see Power-Up Sequencing). Power-Up Sequencing Upon power-up or exiting shutdown, the MAX1747 starts a power-up sequence. First, the reference powers up. Then the primary charge pump powers up with soft-start enabled. Once the main charge pump reaches 90% of its nominal value (VFB > 1.125V), the negative charge pump turns on. When the negative output voltage reaches approximately 90% of its nominal value (VFBN < 125mV), the positive charge pump starts up. Finally, when the positive output voltage reaches 90% of its nominal value (VFBP > 1.125V), the active-low ready signal (RDY) goes low (see Power Ready). Fault Detection Once RDY is low, and if any output falls below its fault detection threshold, RDY goes high impedance. For the reference, the fault threshold is 1.05V. For the main charge pump, the fault threshold is 88% of its nominal value (VFB < 1.1V). For the negative charge pump, the fault threshold is approximately 88% of its nominal value (VFBN > 140mV). For the positive charge pump, the fault threshold is 88% of its nominal value (VFBP < 1.1V). Once an output faults, all outputs later in the power sequence shut down until the faulted output rises above its power-up threshold. For example, if the negative charge-pump output voltage falls below the faultdetection threshold, the main charge pump remains Power Ready Power ready is an open-drain output. When the powerup sequence is properly completed, the MOSFET turns on and pulls RDY low with a typical 125Ω RON. If a fault is detected, the internal open-drain MOSFET appears as a high impedance. Connect a 100kΩ pullup resistor between RDY and IN for a logic level output. Voltage Reference The voltage at REF is nominally 1.25V. The reference can source up to 50mA with excellent load regulation (see Typical Operating Characteristics). Connect a 0.22µF bypass capacitor between REF and GND. During shutdown, the reference is disabled. Design Procedure Efficiency Considerations The efficiency characteristics of the MAX1747 regulated charge pumps are similar to a linear regulator. They are dominated by quiescent current at low output currents and by the input voltage at higher output currents (see Typical Operating Characteristics). Therefore, the maximum efficiency may be approximated by: Efficiency ≅ VOUT / (2 ✕ VSUPM) for the main charge pump Efficiency ≅ - VNEG / (VSUPN ✕ N) for the negative low-power charge pump ______________________________________________________________________________________ 11 MAX1747 Triple Charge-Pump TFT LCD DC-DC Converter Efficiency ≅ VPOS / [VSUPP ✕ (N+1)] for the positive low-power charge pump where N is the number of charge-pump stages. Output Voltage Selection Adjust the main output voltage by connecting a voltage-divider from the output (VOUT) to FB and GND (see Typical Operating Circuit). Adjust the negative lowpower output voltage by connecting a voltage-divider from the output (VNEG) to FBN to REF. Adjust the positive low-power output voltage by connecting a voltagedivider from the output (VPOS) to FBP to GND. Select R2, R4, and R6 in the 10kΩ to 200kΩ range. Calculate the remaining resistors with the following equations: R1 = R2 [(VOUT / VREF) – 1] R3 = R4 [(VPOS / VREF) – 1] R5 = R6 |VNEG / VREF| where VREF = 1.25V. VOUT may range from 4.5V to 5.5V, VPOS may range from VSUPP to +35V, and VNEG may range from 0 to -35V. Flying Capacitors Increasing the flying capacitor’s value increases the output-current capability. Above a certain point, larger capacitor values lower the secondary pole formed by the transfer capacitor and switch RON, which destabilizes the output. For the main charge pump, use a ceramic capacitor based on the following equation: CX ≤ 0.47µF × MHz fOSC For the low-power charge pumps, a 0.1µF ceramic capacitor works well in most applications. Smaller values may be used for lower current applications. Component suppliers are listed in Table 1. For the low-power charge pumps, the output capacitor should be anywhere from 5-times to 20-times larger than the flying capacitor, depending on the ripple tolerance. Increasing the output capacitance or decreasing the ESR reduces the output ripple voltage and the peak-to-peak transient voltage. Input Capacitors Using an input capacitor with a value equal to or greater than the output capacitor is recommended. Place the capacitor as close to the IC as possible. If the source impedance or inductance of the input supply is large, additional input bypassing may be required. For the low-power charge-pump inputs (SUPN and SUPP), using bypass capacitors with values equal to or greater than the flying capacitors is recommended. Place these capacitors as close to the supply voltage inputs as possible. Rectifier Diodes Use Schottky diodes with a current rating greater than 4 times the average output current, and with a voltage rating of 1.5 times VSUPP for the positive charge pump and VSUPN for the negative charge pump. Integrator Capacitor The MAX1747 contains an internal current integrator that improves the DC load regulation but increases the peak-to-peak transient voltage (see Load-Transient Waveform in the Typical Operating Characteristics). Connect a ceramic capacitor between INTG and GND based on the following equation: CINTG ≥ Table 1. Component Suppliers Output Capacitors SUPPLIER For the main charge pump, use a ceramic capacitor based on the following equation: CAPACITORS 20 2µF × MHz COUT ≥ × CX × fOSC AND fOSC MHz For low-frequency applications (close to 200kHz), selection of the output capacitor is limited solely by the switching frequency. However, for high-frequency applications (close to 2MHz), selection of the output capacitor is limited by the secondary pole formed by the flying capacitor and switch on-resistance. 12 150Hz × COUT fOSC PHONE FAX AVX 803-946-0690 803-626-3123 Kemet 408-986-0424 408-986-1442 Sanyo 619-661-6835 619-661-1055 Taiyo Yuden 408-573-4150 408-573-4159 Central 516-435-1110 516-435-1824 International Rectifier 310-322-3331 310-322-3332 Motorola 602-303-5454 602-994-6430 Nihon 847-843-7500 847-843-2798 DIODES ______________________________________________________________________________________ Triple Charge-Pump TFT LCD DC-DC Converter PC board should feature separate analog and power ground areas connected at only one point under the IC. To maximize output power and efficiency, and minimize output power ripple voltage, use extra-wide power ground traces, and solder the IC’s power ground pin directly to it. Avoid having sensitive traces near the switching nodes and high-current lines. Refer to the MAX1747 evaluation kit for an example of proper board layout. Chip Information TRANSISTOR COUNT: 2534 TSSOP,NO PADS.EPS Package Information 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. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 13 © 2000 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products. MAX1747 PC Board Layout and Grounding Careful printed circuit layout is important to minimize ground bounce and noise. First, place the main chargepump flying capacitor less than 0.2in (5mm) from the CXP and CXN pins with wide traces and no vias. Then place 0.1µF ceramic bypass capacitors near the charge-pump input pins (SUPP and SUPN) to the PGND pin. Keep the charge-pump circuitry as close to the IC as possible, using wide traces and avoiding vias when possible. Locate all feedback resistive dividers as close to their respective feedback pins as possible. The