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MAX1748EUE+ |MAX1748EUEMAXIMN/a19avaiTriple-Output TFT-LCD DC-DC Converters
MAX1748EUE+ |MAX1748EUEMAXN/a380avaiTriple-Output TFT-LCD DC-DC Converters
MAX1748EUE+T |MAX1748EUETMAXIMN/a11335avaiTriple-Output TFT-LCD DC-DC Converters


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MAX4581ESE+ ,Low-Voltage, CMOS Analog Multiplexers/SwitchesELECTRICAL CHARACTERISTICS—Dual Supplies(V = 4.5V to 5.5V, V = -4.5V to -5.5V, V = 2.4V, V = 0.8V, ..
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MAX4582ASE ,Low-Voltage, CMOS Analog Multiplexers/SwitchesELECTRICAL CHARACTERISTICS—Dual Supplies(V = 4.5V to 5.5V, V = -4.5V to -5.5V, V = 2.4V, V = 0.8V, ..


MAX1748EUE+-MAX1748EUE+T
Triple-Output TFT-LCD DC-DC Converters
General Description
The MAX1748/MAX8726 triple-output DC-DC converters
in a low-profile TSSOP package provide the regulated
voltages required by active-matrix, thin-film transistor
(TFT) liquid-crystal displays (LCDs). One high-power
DC-DC converter and two low-power charge pumps
convert the +3.3V to +5V input supply voltage into three
independent output voltages.
The primary 1MHz DC-DC converter generates a boost-
ed output voltage (VMAIN) up to 13V using ultra-small
inductors and ceramic capacitors. The low-power
BiCMOS control circuitry and the low on-resistance
(0.35Ω) of the integrated power MOSFET allows effi-
ciency up to 93%.
The dual charge pumps independently regulate one
positive output (VPOS) and one negative output (VNEG).
These low-power outputs use external diode and
capacitor stages (as many stages as required) to regu-
late output voltages up to +40V and down to -40V. A
proprietary regulation algorithm minimizes output rip-
ple, as well as capacitor sizes for both charge pumps.
For both the MAX1748 and MAX8726, the supply
sequence is VMAINfirst, VNEGnext, and finally VPOS.
The MAX1748 soft-starts each supply as soon as the
previous supply finishes. The MAX8726 adds a delay
between the startups of VMAINand VNEGand also
between VNEGand VPOS.
The MAX1748/MAX8726 are available in the ultra-thin
TSSOP package (1.1mm max height).
Applications

TFT Active-Matrix LCD Displays
Passive-Matrix LCD Displays
PDAs
Digital Still Cameras
Camcorders
Features
Three Integrated DC-DC Converters1MHz Current-Mode PWM Boost Regulator
Up to +13V Main High-Power Output
±1% Accuracy
High Efficiency (93%)
Dual Charge-Pump Outputs
Up to +40V Positive Charge-Pump Output
Down to -40V Negative Charge-Pump Output
Internal Supply SequencingInternal Power MOSFETs+2.7V to +5.5V Input Supply0.1µA Shutdown Current0.6mA Quiescent CurrentInternal Soft-StartPower-Ready OutputUltra-Small External ComponentsThin TSSOP Package (1.1mm max)
MAX1748/MAX8726riple-Output TFT-LCD
DC-DC Converters

RDYTGND
PGND
SUPP
DRVP
SUPN
DRVN
SHDN
TOP VIEW
MAX1748
MAX8726
TSSOP

INTG
REF
GND
FBP
FBN
A "+" SIGN WILL REPLACE THE FIRST PIN INDICATOR ON LEAD-FREE PACKAGES.
Pin Configuration

19-3430; Rev 0; 10/04
EVALUATION KIT
AVAILABLE
Ordering Information
Typical Operating Circuit appears at end of data sheet.
PARTTEMP RANGEPIN-PACKAGE
MAX1748EUE
-40°C to +85°C16 TSSOP
MAX8726EUE
-40°C to +85°C16 TSSOP
MAX1748/MAX8726riple-Output TFT-LCD
DC-DC Converters
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS

(VIN= +3.0V, SHDN= IN, VSUPP= VSUPN= 10V, TGND = PGND = GND, CREF= 0.22µF, CINTG= 470pF, TA= 0°C to +85°C, unless
otherwise noted. Typical values are at TA= +25°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.
IN, SHDN, TGND 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
RDYto GND...........................................................-0.3V to +14V
LX, SUPP, SUPN to PGND.....................................-0.3V to +14V
INTG, REF, FB, FBN, FBP to GND...............-0.3V to (VIN+ 0.3V)
Continuous Power Dissipation (TA= +70°C)
16-Pin TSSOP (derate 9.4mW/°C above +70°C)..........755mW
Operating Temperature Range
MAX1748EUE/MAX8726EUE..........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s).................................+300°C
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS

Input Supply RangeVIN2.75.5V
Input Undervoltage ThresholdVUVLOVIN rising, 40mV hysteresis (typ)2.22.42.6V
IN Quiescent Supply CurrentIINVFB = VFBP = 1.5V, VFBN = -0.2V0.61mA
SUPP Quiescent CurrentISUPPVFBP = 1.5V0.40.8mA
SUPN Quiescent CurrentISUPNVFBN = -0.1V0.40.8mA
IN Shutdown CurrentV SHDN = 0, VIN = 5V0.110µA
SUPP Shutdown CurrentV SHDN = 0, VSUPP = 13V0.110µA
SUPN Shutdown CurrentV SHDN = 0, VSUPN = 13V0.110µA
MAIN BOOST CONVERTER

Output Voltage RangeVMAINVIN13V
FB Regulation VoltageVFBTA = 0°C to +85°C1.2351.2481.261V
FB Input Bias CurrentIFBVFB = 1.25V, INTG = GND-50+50nA
Operating FrequencyfOSC0.8511.15MHz
Oscillator Maximum Duty Cycle788590%
Load RegulationIMAIN = 0 to 200mA, VMAIN = 10V0.2%
Line Regulation0.1% / V
Integrator Gm320µmho
LX Switch On-ResistanceRLX(ON)ILX = 100mA0.350.7Ω
LX Leakage CurrentILXVLX = 13V0.0120µA
Phase I = soft-start (1.0ms)0.2750.3800.500
Phase II = soft-start (1.0ms)0.75
Phase III = soft-start (1.0ms)1.12LX Current LimitILX(MAX)
Phase IV = fully on (after 3.0ms)1.11.52.0
Maximum RMS LX Current1A
Soft-Start PeriodtSSPower-up to the end of phase III3072 /
fOSCs
FB Fault Trip Level1.071.11.14V
POSITIVE CHARGE PUMP

VSUPP Input Supply RangeVSUPP2.713.0V
MAX1748/MAX8726riple-Output TFT-LCD
DC-DC Converters
ELECTRICAL CHARACTERISTICS (continued)

(VIN= +3.0V, SHDN= IN, VSUPP= VSUPN= 10V, TGND = PGND = GND, CREF= 0.22µF, CINTG= 470pF, TA= 0°C to +85°C, unless
otherwise noted. Typical values are at TA= +25°C.)
PARAMETER SYMBOLCONDITIONSMINTYPMAXUNITS

Operating Frequency0.5 x
fOSCHz
FBP Regulation VoltageVFBP1.201.251.30V
FBP Input Bias CurrentIFBPVFBP = 1.5V-50+50nA
DRVP PCH On-Resistance310Ω
VFBP = 1.213V1.54ΩDRVP NCH On-ResistanceVFBP = 1.275V20kΩ
FBP Power-Ready Trip LevelRising edge1.0911.1251.159V
FBP Fault Trip LevelFalling edge1.11V
Maximum RMS DRVP Current0.1A
NEGATIVE CHARGE PUMP

VSUPN Input Supply RangeVSUPN2.713.0V
Operating Frequency0.5 x
fOSCHz
FBN Regulation VoltageVFBN-500+50mV
FBN Input Bias CurrentIFBNVFBN = -0.05V-50+50nA
DRVN PCH On-Resistance310Ω
VFBN = 0.035V1.54ΩDRVN NCH On-ResistanceVFBN = -0.025V20kΩ
FBN Power-Ready Trip LevelRising edge80110165mV
FBN Fault Trip LevelFalling edge130mV
Maximum RMS DRVN Current0.1A
REFERENCE

Reference VoltageVREF-2µA < IREF < +50µA1.2311.251.269V
Reference Undervoltage
ThresholdVREF rising0.91.051.2V
LOGIC SIGNALS

SHDN Input Low Voltage0.4V hysteresis (typ)0.9V
SHDN Input High Voltage2.1V
SHDN Input CurrentI SHDN0.011µA
RDY Output Low VoltageISINK = 2mA0.250.5V
RDY Output High VoltageV RDY = 13V0.011µA
MAX1748/MAX8726riple-Output TFT-LCD
DC-DC Converters
PARAMETERSYMBOLCONDITIONSMINMAXUNITS

Input Supply RangeVIN2.75.5V
Input Undervoltage ThresholdVUVLOVIN rising, 40mV hysteresis (typ)2.22.6V
IN Quiescent Supply CurrentIINVFB = VFBP = 1.5V, VFBN = -0.2V1mA
SUPP Quiescent CurrentISUPPVFBP = 1.5V0.8mA
SUPN Quiescent CurrentISUPNVFBN = -0.1V0.8mA
IN Shutdown CurrentV SHDN = 0, VIN = 5V10µA
SUPP Shutdown CurrentV SHDN = 0, VSUPP = 13V10µA
SUPN Shutdown CurrentV SHDN = 0, VSUPN = 13V10µA
MAIN BOOST CONVERTER

Output Voltage RangeVMAINVIN13.0V
FB Regulation VoltageVFB1.2221.271V
FB Input Bias CurrentIFBVFB = 1.25V, INTG = GND-50+50nA
Operating FrequencyFOSC0.751.25MHz
Oscillator Maximum Duty Cycle7890%
LX Switch On-ResistanceRLX(ON)ILX = 100mA0.7Ω
LX Leakage CurrentILXVLX = 13V20µA
Phase I = soft-start (1.0ms)0.2750.500LX Current LimitILX(MAX)Phase IV = fully on (after 3.0ms)1.12.0A
FB Fault Trip Level1.071.14V
POSITIVE CHARGE PUMP

SUPP Input Supply RangeVSUPP2.713.0V
FBP Regulation VoltageVFBP1.201.30V
FBP Input Bias CurrentIFBPVFBP = 1.5V-50+50nA
DRVP PCH On-Resistance10Ω
VFBP = 1.213V4ΩDRVP NCH On-ResistanceVFBP = 1.275V20kΩ
FBP Power-Ready Trip LevelRising edge1.0911.159V
NEGATIVE CHARGE PUMP

SUPN Input Supply RangeVSUPN2.713.0V
FBN Regulation VoltageVFBN-50+50mV
FBN Input Bias CurrentIFBNVFBN = -0.05V-50+50nA
DRVN PCH On-Resistance10Ω
VFBN = 0.035V4ΩDRVN NCH On-ResistanceVFBN = -0.025V20kΩ
FBN Power-Ready Trip LevelRising edge80165mV
REFERENCE

Reference VoltageVREF-2µA < IREF < +50µA1.2231.269V
Reference UndervoltageVREF rising0.91.2V
ELECTRICAL CHARACTERISTICS (continued)

(VIN= +3.0V, SHDN= IN, VSUPP= VSUPN= 10V, TGND = PGND = GND, CREF= 0.22µF, CINTG= 470pF, TA= -40°C to +85°C,
unless otherwise noted.) (Note 1)
MAX1748/MAX8726riple-Output TFT-LCD
DC-DC Converters

MAIN OUTPUT VOLTAGE
vs. LOAD CURRENT
MAX1748/8726 toc01
IMAIN (mA)
MAIN
(V)
VIN = 3.3VVIN = 5.0V
MAIN STEP-UP CONVERTER
EFFICIENCY vs. LOAD CURRENT
(BOOST ONLY)
MAX1748/8726 toc02
IMAIN (mA)
EFFICIENCY (%)
VIN = 3.3V
VMAIN = 10V
VIN = 5.0V
MAIN STEP-UP CONVERTER
EFFICIENCY vs. LOAD CURRENT
(BOOST ONLY)
MAX1748/8726 toc03
IMAIN (mA)
EFFICIENCY (%)
VIN = 3.3V
VMAIN = 8V
VIN = 5.0V10050150200250400300350
EFFICIENCY vs. LOAD CURRENT
(BOOST CONVERTER AND CHARGE PUMPS)

MAX1748/8726 toc04
IMAIN (mA)
EFFICIENCY (%)
VMAIN = 8V
VIN = 3.3V
VNEG = -5V WITH INEG = 10mA
VPOS = 15V WITH IPOS = 5mA
VMAIN = 10V
NEGATIVE CHARGE-PUMP OUTPUT
VOLTAGE vs. LOAD CURRENT
MAX1748/8726 toc05
INEG (mA)
NEG
(V)
VSUPN = 6V
VNEG = -5V
VSUPN = 8V
VSUPN = 10V
NEGATIVE CHARGE-PUMP EFFICIENCY
vs. LOAD CURRENT
MAX1748/8726 toc06
INEG (mA)
EFFICIENCY (%)
VSUPN = 6V
VNEG = -5V
VSUPN = 8V
VSUPN = 10V
Typical Operating Characteristics

(Circuit of Figure 5, VIN= 3.3V, TA= +25°C, unless otherwise noted.)
ELECTRICAL CHARACTERISTICS (continued)

(VIN= +3.0V, SHDN= IN, VSUPP= VSUPN= 10V, TGND = PGND = GND, CREF= 0.22µF, CINTG= 470pF, TA= -40°C to +85°C,
unless otherwise noted.) (Note 1)
PARAMETERSYMBOLCONDITIONSMINMAXUNITS
LOGIC SIGNALS

SHDN Input Low Voltage0.45V hysteresis (typ)0.9V
SHDN Input High Voltage2.1V
SHDN Input CurrentI SHDN1µA
RDY Output Low VoltageISINK = 2mA0.5V
RDY Output High LeakageV RDY = 13V1µA
Note 1:
Specifications from 0°C to -40°C are guaranteed by design, not production tested.
MAX1748/MAX8726riple-Output TFT-LCD
DC-DC Converters
Typical Operating Characteristics (continued)

(Circuit of Figure 5, VIN= 3.3V, TA= +25°C, unless otherwise noted.)796101112
MAXIMUM POSITIVE CHARGE-PUMP OUTPUT
VOLTAGE vs. SUPPLY VOLTAGE

MAX1748/8726 toc10
VSUPP (V)
POS
(V)
IPOS = 10mA
VPOS = 22V
IPOS = 1mA
IPOS = 20mA
SWITCHING FREQUENCY
vs. INPUT VOLTAGE
MAX1748/8726 toc11
INPUT VOLTAGE (V)
SWITCHING FREQUENCY (MHz)
MEASURED FROM THE
FALLING EDGE OF LX
VMAIN = 10V
IMAIN = 100mA
REFERENCE VOLTAGE
vs. REFERENCE LOAD CURRENT
MAX1748/8726 toc12
IREF (μA)
REF
(V)
VIN = 3.3V
VMAIN
10mV/div
VNEG
10mV/div
VPOS
10mV/div
RIPPLE WAVEFORMS

MAX1748/8726 toc13
1μs/div
VMAIN = 10V, IMAIN = 200mA,
VNEG = -5V, INEG = 10mA,
IMAIN
200mA/div
ILX
500mA/div
VMAIN
200mV/div
LOAD-TRANSIENT RESPONSE

MAX1748/8726 toc14
100μs/div
VIN = 3.3V, VMAIN = 10V,
RMAIN = 500Ω TO 50Ω (20mA TO 200mA)
IMAIN
200mA/div
ILX
500mA/div
VMAIN
200mV/div
LOAD-TRANSIENT RESPONSE
WITHOUT INTEGRATOR

MAX1748/8726 toc15
100μs/div
VIN = 3.3V, VMAIN = 10V, INTG = REF,
RMAIN = 500Ω TO 50Ω (20mA TO 200mA)
MAXIMUM NEGATIVE CHARGE-PUMP
OUTPUT VOLTAGE vs. SUPPLY VOLTAGE
MAX1748/8726 toc07
VSUPN (V)
NEG
(V)
INEG = 20mA
INEG = 1mA
INEG = 10mA
VNEG = -10mA14.4
POSITIVE CHARGE-PUMP OUTPUT
VOLTAGE vs. LOAD CURRENT
MAX1748/8726 toc08
IPOS (mA)
POS
(V)
VSUPN = 12V
VSUPN = 8V
VSUPN = 10V
POSITIVE CHARGE-PUMP EFFICIENCY
vs. LOAD CURRENT
MAX1748/8726 toc09
IPOS (mA)
EFFICIENCY (%)VSUPP = 12V
VSUPP = 8V
VSUPP = 10V
MAX1748/MAX8726riple-Output TFT-LCD
DC-DC Converters
Typical Operating Characteristics (continued)

(Circuit of Figure 5, VIN= 3.3V, TA= +25°C, unless otherwise noted.)
Pin Description

VMAIN
5V/div
10V
ILX
500mA/div
MAIN BOOST STARTUP WAVEFORM

MAX1748/8726 toc16
1ms/div
RMAIN = 1kΩ, VMAIN = 10V
VSHDN
2V/div
VMAIN
5V/div
10V
ILX
500mA/div
MAIN BOOST STARTUP
WAVEFORM WITH LOAD

MAX1748/8726 toc17
1ms/div
VMAIN = 10V, RMAIN = 50Ω (200mA)
VSHDN
2V/div
VMAIN
5V/div
VNEG
5V/div
VPOS
10V/div
MAX1748 POWER-UP SEQUENCING

MAX1748/8726 toc18
2ms/div
VMAIN = 10V, VNEG = -5V, VPOS = 15V
VSHDN
2V/div
PINNAMEFUNCTION
RDYActive-Low, Open-Drain Output. Indicates all outputs are ready. The on-resistance is 125Ω (typ).
2FBMain Boost Regulator Feedback Input. Regulates to 1.248V nominal. Connect feedback resistive
divider to analog ground (GND).INTGMain Boost Integrator Output. If used, connect 470pF to analog ground (GND). To disable integrator,
connect to REF.
4INSupply Input. +2.7V to +5.5V input range. Bypass with a 0.1µF capacitor between IN and GND, as
close to the pins as possible.GNDAnalog Ground. Connect to power ground (PGND) underneath the IC.REFInternal Reference Bypass Terminal. Connect a 0.22µF capacitor from this terminal to analog ground
(GND). External load capability to 50µA.FBPPositive Charge-Pump Regulator Feedback Input. Regulates to 1.25V nominal. Connect feedback
resistive divider to analog ground (GND).
VMAIN
5V/div
VNEG
5V/div
VPOS
10V/div
MAX8726 POWER-UP SEQUENCING

MAX1748/8726 toc19
4ms/div
VMAIN = 10V, VNEG = -5V, VPOS = 15V
VSHDN
5V/div
MAX1748/MAX8726riple-Output TFT-LCD
DC-DC Converters
Detailed Description

The MAX1748/MAX8726 are highly efficient triple-output
power supplies for TFT-LCD applications. These devices
contain one high-power step-up converter and two low-
power charge pumps. The primary boost converter uses
an internal n-channel MOSFET to provide maximum
efficiency and to minimize the number of external compo-
nents. The output voltage of the main boost converter
(VMAIN) can be set from VINto 13V with external resistors.
The dual charge pumps independently regulate a posi-
tive output (VPOS) and a negative output (VNEG). These
low-power outputs use external diode and capacitor
stages (as many stages as required) to regulate output
voltages up to +40V and down to -40V. A proprietary
regulation algorithm minimizes output ripple as well as
capacitor sizes for both charge pumps.
Also included in the MAX1748/MAX8726 is a precision
1.25V reference that sources up to 50µA, logic shut-
down, soft-start, power-up sequencing, fault detection,
and an active-low open-drain ready output.
Main Boost Converter

The MAX1748/MAX8726 main step-up converter
switches at a constant 1MHz internal oscillator frequen-
cy to allow the use of small inductors and output
capacitors. The MOSFET switch pulse width is modulat-
ed to control the power transferred on each switching
cycle and to regulate the output voltage.
During PWM operation, the internal clock’s rising edge
sets a flip-flop, which turns on the n-channel MOSFET
(Figure 1). The switch turns off when the sum of the
voltage-error, slope-compensation, and current-feed-
back signals trips the multi-input comparator and
resets the flip-flop. The switch remains off for the rest of
the clock cycle. Changes in the output-voltage error
signal shift the switch current trip level, consequently
modulating the MOSFET duty cycle.
Dual Charge-Pump Regulator

The MAX1748/MAX8726 contain two individual low-
power charge pumps. One charge pump inverts the
supply voltage (SUPN) and provides a regulated nega-
tive output voltage. The second charge pump doubles
the supply voltage (SUPP) and provides a regulated
positive output voltage. The MAX1748/MAX8726 con-
tain internal p-channel and n-channel MOSFETs to con-
trol the power transfer. The internal MOSFETs switch at
a constant 500kHz (0.5 xfOSC).
Negative Charge Pump

During the first half-cycle, the p-channel MOSFET turns
on and the flying capacitor C5 charges to VSUPNminus a
diode drop (Figure 2). 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,
charge flows from C5 to C6 until the diode (D5) turns off.
The amount of charge transferred to the output is
controlled by the variable n-channel on-resistance.
Positive Charge Pump

During the first half-cycle, the n-channel MOSFET turns
on and charges the flying capacitor C3 (Figure 3). This
initial charge is controlled by the variable n-channel on-
resistance. During the second half-cycle, the n-channel
MOSFET turns off and the p-channel MOSFET turns on,
level shifting C3 by VSUPPvolts. This connects C3 in par-
allel 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 (D3) turns off.
Pin Description (continued)
PINNAMEFUNCTION
FBNNegative Charge-Pump Regulator Feedback Input. Regulates to 0V nominal.SHDNActive-Low Logic-Level Shutdown Input. Connect SHDN to IN for normal operation.DRVNNegative Charge-Pump Driver Output. Output high level is VSUPN, and low level is PGND.SUPNNegative Charge-Pump Driver Supply Voltage. Bypass to PGND with a 0.1µF capacitor.DRVPPositive Charge-Pump Driver Output. Output high level is VSUPP, and low level is PGND.SUPPPositive Charge-Pump Driver Supply Voltage. Bypass to PGND with a 0.1µF capacitor.PGNDPower Ground. Connect to GND underneath the IC.LXMain Boost Regulator Power MOSFET n-Channel Drain. Connect output diode and output capacitor
as close to PGND as possible.TGNDMust be connected to ground.
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