MAX1778/ MAX1880–MAX1885 Quad-Output TFT LCD DC-DC Converters with Buffer General Description The MAX1778/MAX1880–MAX1885 multiple-output DC-DC converters provide the regulated voltages required by active matrix thin-film transistor (TFT) liquid crystal displays (LCD) in a low-profile TSSOP package. One high-power step-up converter and two low-power charge pumps convert the 2.7V to 5.5V input voltage into three independent output voltages.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer ABSOLUTE MAXIMUM RATINGS IN, SHDN, TGND, FLTSET to GND...........................-0.3V to +6V DRVN to GND .........................................-0.3V to (VSUPN + 0.3V) DRVP to GND..........................................-0.3V to (VSUPP + 0.3V) PGND to GND.....................................................................±0.3V RDY, SUPB to GND ................................................-0.3V to +14V LX, SUPP, SUPN to PGND ...
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer ELECTRICAL CHARACTERISTICS (continued) (VIN = +3.0V, SHDN = IN, VSUPP = VSUPN = VSUPB = VSUPL = 10V, LDOOUT = FBL, BUF- = BUFOUT, BUF+ = FLTSET = TGND = PGND = GND, CREF = 0.22µF, CBUF = 1µF, TA = 0°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer ELECTRICAL CHARACTERISTICS (continued) (VIN = +3.0V, SHDN = IN, VSUPP = VSUPN = VSUPB = VSUPL = 10V, LDOOUT = FBL, BUF- = BUFOUT, BUF+ = FLTSET = TGND = PGND = GND, CREF = 0.22µF, CBUF = 1µF, TA = 0°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer ELECTRICAL CHARACTERISTICS (continued) (VIN = +3.0V, SHDN = IN, VSUPP = VSUPN = VSUPB = VSUPL = 10V, LDOOUT = FBL, BUF- = BUFOUT, BUF+ = FLTSET = TGND = PGND = GND, CREF = 0.22µF, CBUF = 1µF, TA = 0°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.) PARAMETER Output Voltage Input Offset Voltage SYMBOL VBUFOUT VOS CONDITIONS BUF+ = GND VSUPB = 4.5V to 13V, VCM = 1.2V to (VSUPB - 1.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer ELECTRICAL CHARACTERISTICS (VIN = +3.0V, SHDN = IN, VSUPP = VSUPN = VSUPB = VSUPL = 10V, LDOOUT = FBL, BUF- = BUFOUT, BUF+ = FLTSET = TGND = PGND = GND, CREF = 0.22µF, CBUF = 1µF, TA = -40°C to +85°C, unless otherwise noted.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer ELECTRICAL CHARACTERISTICS (continued) (VIN = +3.0V, SHDN = IN, VSUPP = VSUPN = VSUPB = VSUPL = 10V, LDOOUT = FBL, BUF- = BUFOUT, BUF+ = FLTSET = TGND = PGND = GND, CREF = 0.22µF, CBUF = 1µF, TA = -40°C to +85°C, unless otherwise noted.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN MAX UNITS 2.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer ELECTRICAL CHARACTERISTICS (continued) (VIN = +3.0V, SHDN = IN, VSUPP = VSUPN = VSUPB = VSUPL = 10V, LDOOUT = FBL, BUF- = BUFOUT, BUF+ = FLTSET = TGND = PGND = GND, CREF = 0.22µF, CBUF = 1µF, TA = -40°C to +85°C, unless otherwise noted.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC-DC Converters with Buffer Typical Operating Characteristics (Circuit of Figure 1, V IN = +3.3V, SHDN = IN, V MAIN = V SUPP = V SUPN = V SUPB = V SUPL = 8V, BUF- = BUFOUT, BUF+ = FLTSET = TGND = PGND = GND, TA = +25°C.) MAIN 8V OUTPUT EFFICIENCY vs. LOAD CURRENT VIN = 5V 8.00 90 EFFICIENCY (%) 7.96 CINTG = 470pF RCOMP = 24kΩ CCOMP = 470pF 7.92 70 200 400 600 VOUT = 8V RCOMP = 24kΩ CCOMP = 470pF CINTG = 470pF VIN = 5V 11.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer Typical Operating Characteristics (continued) (Circuit of Figure 1, V IN = +3.3V, SHDN = IN, V MAIN = V SUPP = V SUPN = V SUPB = V SUPL = 8V, BUF- = BUFOUT, BUF+ = FLTSET = TGND = PGND = GND, TA = +25°C.) -4 VSUPN = 6V 1.26 -6 60 VNEG (V) VSUPN = 7V 70 INEG = 10mA -8 VREF (V) 80 INEG = 1mA VSUPN = 8V 1.25 -10 50 1.24 -12 40 30 1.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer Typical Operating Characteristics (continued) (Circuit of Figure 1, V IN = +3.3V, SHDN = IN, V MAIN = V SUPP = V SUPN = V SUPB = V SUPL = 8V, BUF- = BUFOUT, BUF+ = FLTSET = TGND = PGND = GND, TA = +25°C.) STEP-UP CONVERTER SOFT-START (LIGHT LOAD) RIPPLE VOLTAGE WAVEFORMS STEP-UP CONVERTER SOFT-START (HEAVY LOAD) MAX1778 toc17 MAX1778 toc16 MAX1778 toc18 2V A A 8V 20V A 0 0 8V 8V B 6V B -5V 2V B 6V 4V 4V 0.5A 1.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer Typical Operating Characteristics (continued) (Circuit of Figure 1, V IN = +3.3V, SHDN = IN, V MAIN = V SUPP = V SUPN = V SUPB = V SUPL = 8V, BUF- = BUFOUT, BUF+ = FLTSET = TGND = PGND = GND, TA = +25°C.) LDO OUTPUT VOLTAGE vs. LDO OUTPUT CURRENT (INTERNAL LINEAR REGULATOR) 5.00 5.10 MAX1778 toc23 ILDOOUT = 0 5.02 5.08 5.06 5.00 ILDOOUT = 40mA 4.90 4.85 ILDOOUT = 0 5.04 VLDO (V) 4.95 VLDOOUT (V) 4.98 4.96 5.02 5.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer Typical Operating Characteristics (continued) (Circuit of Figure 1, V IN = +3.3V, SHDN = IN, V MAIN = V SUPP = V SUPN = V SUPB = V SUPL = 8V, BUF- = BUFOUT, BUF+ = FLTSET = TGND = PGND = GND, TA = +25°C.) MAX1778 toc28 CLDOOUT = 1µF 4OmA 10 CLDOOUT ESR (Ω) PSRR (dB) 80 MAX1778 toc29 100 MAX1778 toc27 100 LOAD-TRANSIENT RESPONSE (INTERNAL LINEAR REGULATOR) REGION OF STABLE CLDOOUT ESR vs.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer Typical Operating Characteristics (continued) (Circuit of Figure 1, V IN = +3.3V, SHDN = IN, V MAIN = V SUPP = V SUPN = V SUPB = V SUPL = 8V, BUF- = BUFOUT, BUF+ = FLTSET = TGND = PGND = GND, TA = +25°C.) 2.53 ILDO = 0 2.51 ILDO = 750mA 2.49 FIGURE 7 2.53 VLDO (V) VLDO (V) 2.55 MAX1778 toc33 2.55 LINEAR-REGULATOR OUTPUT VOLTAGE vs.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer Typical Operating Characteristics (continued) (Circuit of Figure 1, V IN = +3.3V, SHDN = IN, V MAIN = V SUPP = V SUPN = V SUPB = V SUPL = 8V, BUF- = BUFOUT, BUF+ = FLTSET = TGND = PGND = GND, TA = +25°C.) VSUPB = 13V VCM = VSUPB/2 0.6 -0.2 -0.6 0 0.2 4 -0.6 2 10 35 60 85 0 -40 -15 TEMPERATURE (°C) 10 35 60 85 0 2 4 TEMPERATURE (°C) BUFFER INPUT BIAS CURRENT vs. TEMPERATURE BUFFER INPUT BIAS CURRENT vs.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer Typical Operating Characteristics (continued) (Circuit of Figure 1, V IN = +3.3V, SHDN = IN, V MAIN = V SUPP = V SUPN = V SUPB = V SUPL = 8V, BUF- = BUFOUT, BUF+ = FLTSET = TGND = PGND = GND, TA = +25°C.) VCOM BUFFER LARGE-SIGNAL RESPONSE VCOM BUFFER LOAD-TRANSIENT RESPONSE VCOM BUFFER LOAD-TRANSIENT RESPONSE MAX1778 toc48 MAX1778 toc50 MAX1778 toc49 4.50V 500mA 200mA 0 A 4.00V 3.50V 4.50V A -200mA -500mA 4.2V 4.5V 4.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC-DC Converters with Buffer Pin Description PIN MAX1778 MAX1881 MAX1880 MAX1882 MAX1883 MAX1884 MAX1885 NAME 1 1 1 1 FB 2 2 2 2 INTG 3 3 3 3 FUNCTION Main Step-Up Regulator Feedback Input. Regulates to 1.25V nominal. Connect a resistive divider from the output (VMAIN) to FB to analog ground (GND). Main Step-Up Integrator Output. When using the integrator, connect 1000pF to analog ground (GND). To disable the integrator, connect INTG to REF.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer Pin Description (continued) PIN MAX1778 MAX1881 MAX1880 MAX1882 MAX1883 MAX1884 MAX1885 NAME FUNCTION Linear Regulator Output. Sources up to 40mA. Bypass to GND with a ceramic capacitor determined by: 18 14 — 12 — LDOOUT 15 — 13 — FBL Voltage Setting Input. Connect a resistive divider from the linear regulator output (VLDOOUT) to FBL to analog ground (GND). ⎛ ILDOOUT(MAX) ⎞ CLDOOUT ≥ 0.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer L1 6.8µH INPUT VIN = 3.3V CIN 4.7µF RRDY 100kΩ C1 0.22µF MAIN (8V) R8 49.9kΩ LX SHDN FB RDY SUPL LDOOUT TO LOGIC LDO VLDOOUT = 5V CLDO 4.7µF IN R7 150kΩ SUPB SUPN SUPP MAX1778 MAIN VMAIN = 8V COUT (2) 4.7µF R2 274kΩ R2 49.9kΩ C4 0.1µF C5 1.0µF DRVP C2 0.1µF FBL C4 0.1µF C7 1.0µF DRVN POSITIVE VPOS = 20V R3 750kΩ NEGATIVE VNEG = -5V FBN C3 1.0µF FBP R5 200kΩ R6 49.9kΩ CREF 0.22µF R4 49.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer Main Step-up Controller Changes in the feedback voltage-error signal shift the switch-current trip level, consequently modulating the MOSFET duty cycle. Under very light loads, an inherent switchover to pulseskipping takes place (Figure 3). When this occurs, the controller skips most of the oscillator pulses in order to reduce the switching frequency and gate charge losses.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer Dual Charge-Pump Regulator (MAX1778/ MAX1880–MAX1882 Only) The switching waveforms appear noisy and asynchronous when light loading causes pulse-skipping operation; this is a normal operating condition that improves light-load efficiency. The MAX1778/MAX1880–MAX1882 controllers contain two independent low-power charge pumps (Figure 4). One charge pump inverts the input voltage and provides a regulated negative output voltage.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer Negative Charge Pump During the first half-cycle, the p-channel MOSFET turns on, and flying capacitor C X(NEG) charges to VSUPN minus a diode drop (Figure 4). During the second half-cycle, the p-channel MOSFET turns off, and the n-channel MOSFET turns on, level shifting CX(NEG). This connects CX(NEG) in parallel with reservoir capacitor COUT(NEG).
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer SUPB MAX1778 MAX1880 MAX1881 MAX1882 MAX1883 MAX1884 MAX1885 VSUPB 4.5V TO 13V VBUFOUT 1.2V TO (VSUPB - 1.2V) CBUF BUFOUT gm BUF- R R11 BUF+ R R12 125mV GND VBUFOUT = ( R11R12+ R12 )V SUPB Figure 6. VCOM Buffer Block Diagram times, the amplifier’s transconductance increases as the output current increases (see the Typical Operating Characteristics). The VCOM buffer’s positive feedback input features dual mode operation.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer (ILX(MAX)). If the output does not reach regulation within 1ms, soft-start enters phase II, and the current limit is increased by another 25%. This process is repeated for phase III. The maximum 1.5A (typ) current limit is reached within 3072 clock cycles or when the output reaches regulation, whichever occurs first (see the startup waveforms in the Typical Operating Characteristics).
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer where IMAIN includes the primary load current and the input supply currents for the charge pumps (see the Charge-Pump Input Power and Efficiency Considerations section), linear regulator, and VCOM buffer.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer where η is the efficiency, fOSC is the oscillator frequency (see the Electrical Characteristics ), and I MAIN includes the primary load current and the input supply currents for the charge pumps (see the Charge-Pump Input Power and Efficiency Considerations section), linear regulator, and VCOM buffer. Considering the typical application circuit, the maximum average DC load current (IMAIN(MAX)) is 300mA with an 8V output.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer Rectifier Diode Use a Schottky diode with an average current rating equal to or greater than the peak inductor current, and a voltage rating at least 1.5 times the main output voltage (VMAIN).
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer Table 2. MAX1881/MAX1882/MAX1884/MAX1885 Component Values (fOSC = 500kHz) CIRCUIT 6 CIRCUIT 7 CIRCUIT 8 CIRCUIT 9 3.3V 3.3V 3.3V 3.3V VIN VMAIN 9V 9V 9V 9V IMAIN(MAX) 100mA 100mA 200mA 200mA VNEG -5V -5V -5V -5V 5mA INEG 2mA 2mA 5mA VPOS 24V 24V 24V 24V IPOS 2mA 2mA 5mA 5mA 10µH L 4.7µH 10µH 10µH IPEAK >1A >1A >1A >1A COUT 4.7µF 10µF 10µF 20µF R1 309kΩ 309kΩ 309kΩ 309kΩ R2 49.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer at higher output currents (see the Typical Operating Characteristics). So the maximum efficiency can be approximated by: ηPOS ≅ for the negative charge pump, where N is the stage number in which the flying capacitor appears, and V SUPD is the positive charge pump’s diode supply (Figure 4).
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer Capacitor Selection and Regulator Stability Capacitors are required at the input and output of the MAX1778/MAX1881/MAX1883/MAX1884 for stable operation over the full temperature range and with load currents up to 40mA. Connect a 1µF input bypass capacitor (CSUPL) between SUPL and ground to lower the source impedance of the input supply.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer Input-to-Output (Dropout) Voltage and Startup A linear regulator’s minimum input-to-output voltage differential (dropout voltage) determines the lowest useable supply voltage. Because the MAX1778/ MAX1881/MAX1883/MAX1884 use an internal pnp transistor (or external npn transistor), their dropout voltage is a function of the transistor’s collector-to-emitter saturation voltage (see the Typical Operating Characteristics).
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer layer boards, the top layer should contain the boost regulator and charge-pump power ground plane, and the inner layer should contain the analog ground plane and power-ground plane/path for the VCOM buffer and LDO. Connect all three ground planes together at one place near the PGND pin. 3) Locate all feedback resistive-dividers as close as possible to their respective feedback pins.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer Applications Information Larger output capacitors with higher voltage ratings allow configurations with output voltages above 10V. Additionally, physically larger inductors with less series resistance and higher saturation ratings provide more output current and higher efficiency. Low-Profile Components Notebook applications generally require low-profile components, potentially limiting the circuit’s performance.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer INPUT VIN = 3.3V L1 6.8µH CIN 4.7µF STARTUP MAIN VMAIN(START) = 8V C1 0.22µF SHDN C8 3.3µF COUT (2) 3.3µF R1 274kΩ LX IN SYSTEM MAIN VMAIN(SYS) = 8V FB R2 49.9kΩ C10 0.1µF SUPP C4 0.1µF MAX1778 C5 1.0µF DRVP C6 0.1µF INTG R7 10kΩ C7 1.0µF REF CREF 0.22µF R3 750kΩ R9 30kΩ FBP FLTSET R4 49.9kΩ R10 100kΩ STARTUP POSITIVE VPOS(START) = 20V SYSTEM POSITIVE VPOS(SYS) = 20V Q3 Q2 INPUT VIN = 3.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer INPUT VIN = 3.3V L1 6.8µH CIN 4.7µF LX IN C1 0.22µF SHDN R2 49.9kΩ SUPB REF CREF 0.22µF R1 274kΩ FB MAX1778 INTG MAIN VMAIN = 8V COUT (2) 4.7µF BUF- R3 10kΩ CSUPB 1.0µF BUFFER OUTPUT VBUFOUT = VSUPB/2 BUFOUT BUF+ PGND GND R4 10kΩ CBUF 1.0µF [( VV R3 = R4 SUPB BUFOUT ) -1] Figure 11. VCOM Buffer Soft-Start the Typical Operating Characteristics.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer Typical Operating Circuit MAIN INPUT TO LOGIC LDO OUTPUT IN LX SHDN FB RDY SUPL LDOOUT SUPB SUPN SUPP FBL MAX1778 DRVP DRVN NEGATIVE FBP POSITIVE FBN BUFOUT REF BUFFER OUTPUT BUFBUF+ INTG PGND 36 FLTSET GND TGND Maxim Integrated
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer Pin Configurations TOP VIEW FB 1 + 24 RDY INTG 2 23 TGND IN 3 22 LX BUF+ 4 21 PGND MAX1778 MAX1881 BUF- 5 FB 1 + INTG 2 23 TGND IN 3 22 LX BUF+ 4 21 PGND MAX1880 MAX1882 20 DRVP BUF- 5 SUPB 6 19 SUPP SUPB 6 19 SUPP BUFOUT 7 18 DRVN BUFOUT 7 18 DRVN GND 8 17 SUPN GND 8 17 SUPN REF 9 16 FLTSET REF 9 16 FLTSET FBP 10 15 FBL FBP 10 15 N.C. FBN 11 14 LDOOUT FBN 11 14 N.C. SHDN 12 13 N.C.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer Package Information Chip Information TRANSISTOR COUNT: 3739 38 For the latest package outline information and land patterns (footprints), go to www.maximintegrated.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.
MAX1778/MAX1880–MAX1885 Quad-Output TFT LCD DC/DC Converters with Buffer Revision History REVISION NUMBER REVISION DATE 2 10/12 DESCRIPTION Added MAX1880EUG/V+ to Ordering Information PAGES CHANGED 1 Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time.
