MAX8727ETB+-MAX8727ETB+T Fast Delivery |IC PHOENIX CO.,LIMITED

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MAX8727ETB+-MAX8727ETB+T
TFT-LCD Step-Up DC-DC Converter
General Description
The MAX8727 is a high-performance step-up DC-DC
converter that provides a regulated supply voltage for
active-matrix thin-film transistor (TFT) liquid-crystal dis-
plays (LCDs). The MAX8727 incorporates current-
mode, fixed-frequency, pulse-width modulation (PWM)
circuitry with a built-in n-channel power MOSFET to
achieve high efficiency and fast transient response.
Users can select 640kHz or 1.2MHz operation using a
logic input pin (FREQ). The high switching frequencies
allow the use of ultra-small inductors and low-ESR
ceramic capacitors. The current-mode architecture pro-
vides fast transient response to pulsed loads. A com-
pensation pin (COMP) gives users flexibility in adjusting
loop dynamics. The 30V internal MOSFET can generate
output voltages up to 24V from an input voltage
between 2.6V and 5.5V. Soft-start slowly ramps the input
current and is programmed with an external capacitor.
The MAX8727 is available in a 10-pin thin DFN package.
Applications
Notebook Computer Displays
LCD Monitor Panels
Features90% EfficiencyAdjustable Output from VINto 24V2.6V to 5.5V Input Supply RangeInput Supply Undervoltage LockoutPin-Programmable 640kHz/1.2MHz Switching
FrequencyProgrammable Soft-Start0.1µA Shutdown CurrentSmall 10-Pin Thin DFN Package
MAX8727
TFT-LCD Step-Up DC-DC Converter
Ordering Information
19-3480; Rev 1; 8/05
EVALUATION KIT
AVAILABLE
PARTTEMP RANGEPIN-PACKAGE
MAX8727ETB-40°C to +85°C10 Thin DFN 3mm x 3mm
MAX8727ETB+-40°C to +85°C10 Thin DFN 3mm x 3mm
COMP12
GND4
GND5
SHDN
FREQMAX8727
TOP VIEW
THIN DFN
3mm x 3mm
Pin ConfigurationLX
GND
GND
FREQ
COMPSS1
VOUTVIN
2.6V TO 5.5V
SHDN
MAX8727
Minimal Operating Circuit
+Denotes lead-free package.
MAX8727
TFT-LCD Step-Up DC-DC Converter
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VIN= VSHDN= 3V, FREQ = GND, TA= 0°C to +85°C. Typical values are at TA= +25°C, unless otherwise noted.) (Note 1)
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.
LX to GND..............................................................-0.3V to +26V
IN, SHDN, FREQ, FB to GND...................................-0.3V to +6V
COMP, SS to GND.........................................-0.3V to VIN+ 0.3V
LX Switch Maximum Continuous RMS Current.....................2.4A
Continuous Power Dissipation (TA= +70°C)
10-Pin Thin DFN (derate 24.4mW/°C above +70°C)....1951mW
Operating Temperature Range...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +160°C
Lead Temperature (soldering, 10s).................................+300°C
PARAMETERCONDITIONSMINTYPMAXUNITS
VOUT < 18V2.65.5Input Voltage Range18V < VOUT < 24V4.05.5V
Output Voltage Range24V
IN Undervoltage-Lockout
ThresholdVIN rising, typical hysteresis is 50mV2.202.382.57V
VFB = 1.3V, not switching0.2250.440IN Quiescent CurrentVFB = 1.0V, switching25mA
IN Shutdown CurrentSHDN = GND0.110.0µA
ERROR AMPLIFIER
FB Regulation VoltageLevel to produce VCOMP = 1.24V1.221.241.26V
FB Input Bias CurrentVFB = 1.24V50125250nA
FB Line RegulationLevel to produce VCOMP = 1.24V, VIN = 2.6V to 5.5V0.050.15%/V
Transconductance100200300µS
Voltage Gain700V/V
Shutdown FB Input VoltageSHDN = GND0.050.100.15V
OSCILLATOR
FREQ = GND540640740FrequencyFREQ = IN100012201500kHz
Maximum Duty Cycle879093%
n-CHANNEL MOSFET
Current LimitVFB = 1V, 75% duty cycle3.03.84.6A
On-Resistance125250Ω
Leakage CurrentVLX = 24V3045µA
Current-Sense Transresistance0.110.210.31V/A
SOFT-START
Reset Switch Resistance100Ω
Charge CurrentVSS = 1.2V2.54.57.5µA
MAX8727
TFT-LCD Step-Up DC-DC Converter
ELECTRICAL CHARACTERISTICS (continued)
(VIN= VSHDN= 3V, FREQ = GND, TA= 0°C to +85°C. Typical values are at TA= +25°C, unless otherwise noted.) (Note 1)
PARAMETERCONDITIONSMINTYPMAXUNITS
CONTROL INPUTS
SHDN, FREQ Input Low VoltageVIN = 2.6V to 5.5V0.3 ×
VINV
SHDN, FREQ Input High VoltageVIN = 2.6V to 5.5V0.7 ×
VINV
SHDN, FREQ Input HysteresisVIN = 2.6V to 5.5V0.1 ×
VINV
FREQ Pulldown Current2.36.09.5µA
SHDN Input CurrentSHDN = GND0.0011µA
ELECTRICAL CHARACTERISTICS
(VIN= VSHDN= 3V, FREQ = GND, TA= -40°C to +85°C, unless otherwise noted.) (Note 1)
PARAMETERCONDITIONSMINTYPMAXUNITS
VOUT < 18V2.65.5Input Voltage Range18V < VOUT < 24V4.05.5V
Output Voltage Range24V
IN Undervoltage-Lockout
ThresholdVIN rising, typical hysteresis is 50mV2.202.57V
VFB = 1.3V, not switching0.44IN Quiescent CurrentVFB = 1.0V, switching5mA
IN Shutdown CurrentSHDN = GND10µA
ERROR AMPLIFIER
FB Regulation VoltageLevel to produce VCOMP = 1.24V1.2151.260V
FB Input Bias CurrentVFB = 1.24V250nA
FB Line RegulationLevel to produce VCOMP = 1.24V, VIN = 2.6V to 5.5V0.15%/V
Transconductance100300µS
Shutdown FB Input VoltageSHDN = GND0.050.15V
OSCILLATOR
FREQ = GND490770FrequencyFREQ = IN9001600kHz
Maximum Duty Cycle8694%
n-CHANNEL MOSFET
Current LimitVFB = 1V, 75% duty cycle3.05.1A
On-Resistance250mΩ
Current-Sense Transresistance0.110.31V/A
SOFT-START
Reset Switch Resistance100Ω
Charge CurrentVSS = 1.2V2.57.5µA
MAX8727
TFT-LCD Step-Up DC-DC Converter
Note 1:Specifications to -40°C are guaranteed by design, not production tested.
ELECTRICAL CHARACTERISTICS (continued)
(VIN= VSHDN= 3V, FREQ = GND, TA= -40°C to +85°C, unless otherwise noted.) (Note 1)
PARAMETERCONDITIONSMINTYPMAXUNITS
CONTROL INPUTS
SHDN, FREQ Input Low VoltageVIN = 2.6V to 5.5V0.3 ×
VINV
SHDN, FREQ Input High VoltageVIN = 2.6V to 5.5V0.7 ×
VINV
EFFICIENCY vs. LOAD CURRENT
(1.2MHz OPERATION)
MAX8727 toc01
LOAD CURRENT (mA)
EFFICIENCY (%)
L = 3.6μH
VIN = 5.0V
VIN = 3.3V
EFFICIENCY vs. LOAD CURRENT
(640kHz OPERATION)
MAX8727 toc02
LOAD CURRENT (mA)
EFFICIENCY (%)
L = 6.8μH
VIN = 5.0V
VIN = 3.3V
LOAD REGULATION
MAX8727 toc03
LOAD CURRENT (mA)
LOAD REGULATION (%)
VIN = 5.0V
VIN = 3.3V
SWITCHING FREQUENCY
vs. INPUT VOLTAGE
MAX8727 toc04
INPUT VOLTAGE (V)
SWITCHING FREQUENCY (kHz)
FREQ = IN
FREQ = GND
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX8727 toc05
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
SWITCHING
NONSWITCHING
SUPPLY CURRENT vs. TEMPERATURE
(SWITCHING)
MAX8727 toc06
TEMPERATURE (°C)
SUPPLY CURRENT (mA)6040200-20
VIN = 5.0V
VIN = 3.3V
Typical Operating Characteristics
(Circuit of Figure1. VIN= 5V, VMAIN= 15V, TA= +25°C unless otherwise noted.)
MAX8727
TFT-LCD Step-Up DC-DC Converter
SOFT-START
(RLOAD = 30Ω)
MAX8727 toc07
1ms/div
INDUCTOR
CURRENT
1A/div
VOUT
5V/div
LOAD-TRANSIENT RESPONSE
(ILOAD = 50mA TO 550mA)
MAX8727 toc08
1μs/div
INDUCTOR
CURRENT
1A/div
50mA
15V
VOUT
5mV/div
AC-COUPLED
IOUT
500mA/div
PULSED LOAD-TRANSIENT RESPONSE
(ILOAD = 100mA TO 1.1A)
MAX8727 toc09
1μs/div
INDUCTOR
CURRENT
1A/div
0.1A
15V
VOUT
5mV/div
AC-COUPLED
IOUT
1A/div
SWITCHING WAVEFORMS
(ILOAD = 600mA)
MAX8727 toc10
1μs/div
INDUCTOR
CURRENT
1A/div
10V/div
Typical Operating Characteristics (continued)
(Circuit of Figure1. VIN= 5V, VMAIN= 15V, TA= +25°C unless otherwise noted.)
MAX8727
TFT-LCD Step-Up DC-DC Converter
PINNAMEFUNCTIONCOMPCompensation Pin for Error Amplifier. Connect a series RC from COMP to ground. See the Loop
Compensation section for component selection guidelines.
2FB
Feedback Pin. The FB regulation voltage is 1.24V nominal. Connect an external resistive voltage-divider
between the step-up regulator’s output (VOUT) and GND, with the center tap connected to FB. Place the
divider close to the IC and minimize the trace area to reduce noise coupling. Set VOUT according to the
Output Voltage Selection section.SHDNShutdown Control Input. Drive SHDN low to turn off the MAX8727.GNDGround. Connect pins 4 and 5 directly together.GNDGround. Connect pins 4 and 5 directly together.
6LXSwitch Pin. LX is the drain of the internal MOSFET. Connect the inductor/rectifier diode junction to LX and
minimize the trace area for lower EMI. Connect pins 6 and 7 directly together.
7LXSwitch Pin. LX is the drain of the internal MOSFET. Connect the inductor/rectifier diode junction to LX and
minimize the trace area for lower EMI. Connect pins 6 and 7 directly together.INSupply Pin. Bypass IN with a minimum 1µF ceramic capacitor directly to GND.FREQFrequency-Select Input. When FREQ is low, the oscillator frequency is set to 640kHz. When FREQ is high, the
frequency is 1.2MHz. This input has a 5µA pulldown current.SS
Soft-Start Control Pin. Connect a soft-start capacitor (CSS) to this pin. Leave open for no soft-start. The soft-
start capacitor is charged with a constant current of 4.5µA. Full current limit is reached after t = 2.5 × 105 CSS.
The soft-start capacitor is discharged to ground when SHDN is low. When SHDN goes high, the soft-start
capacitor is charged to 0.4V, after which soft-start begins.
Pin DescriptionLX
GND
GND
FREQ
COMPSS1
VOUT
15V/600mA
VIN
4.5V TO 5.5V
SHDN
MAX8727
10μF
6.3V
10Ω
1μF
33nF
330pF
39pF
3.6μHD1
28.0kΩ
100kΩ
309kΩ
4.7μF
25V
4.7μF
25V
4.7μF
25V
Figure 1 Typical Operating Circuit
Detailed Description
The MAX8727 is a highly efficient power supply that
employs a current-mode, fixed-frequency, pulse-width
modulation (PWM) architecture for fast transient
response and low-noise operation. The device regu-
lates the output voltage through a combination of an
error amplifier, two comparators, and several signal
generators (Figure 2). The error amplifier compares the
signal at FB to 1.24V and varies the COMP output. The
voltage at COMP determines the current trip point each
time the internal MOSFET turns on. As the load
changes, the error amplifier sources or sinks current to
the COMP output to command the inductor peak cur-
rent necessary to service the load. To maintain stability
at high duty cycles, a slope-compensation signal is
summed with the current-sense signal.
At light loads, this architecture allows the MAX8727 to
“skip” cycles to prevent overcharging the output voltage.
In this region of operation, the inductor ramps up to a
peak value of approximately 50mA, discharges to the
output, and waits until another pulse is needed again.
Output Current Capability
The output current capability of the MAX8727 is a func-
tion of current limit, input voltage, operating frequency,
and inductor value. Because of the slope compensa-
tion used to stabilize the feedback loop, the inductor
current limit depends on the duty cycle. The current
limit is determined by the following equation:
ILIM= (1.26 - 0.35 x D) x ILIM_EC
where ILIM_ECis the current limit specified at 75% duty
cycle (see the Electrical Characteristics) and D is the
duty cycle.
The output current capability depends on the current-
limit value and is governed by the following equation:
where ILIMis the current limit calculated above, ηis the
regulator efficiency (85% nominal), and D is the duty
cycle. The duty cycle when operating at the current
limit is:
where VDIODEis the rectifier diode forward voltage and
RONis the on-resistance of the internal MOSFET.VVVRV
OUTINDIODE
OUTLIMONDIODE =−+×+DVOUTMAXLIMIN
OSC
OUT . =−××⎢⎥××05η
MAX8727
TFT-LCD Step-Up DC-DC Converter
GND
FREQ
COMP
4μA
5μA
ERROR
COMPARATOR
ERROR
AMPLIFIER
SKIP
COMPARATOR
CLOCK
SKIP
BIAS
SHDN
MAX8727CURRENT
SENSE
CONTROL
AND DRIVER
LOGIC
SOFT-
START
SLOPE
COMPEN-
SATION
OSCILLATOR
1.24V
Figure 2. MAX8727 Functional Diagram

Partno	Mfg	Dc	Qty	Available	Descript
MAX8727ETB+ \|MAX8727ETB	MAXIM	N/a	391	avai	TFT-LCD Step-Up DC-DC Converter
MAX8727ETB+T \|MAX8727ETBT	MAX	N/a	2500	avai	TFT-LCD Step-Up DC-DC Converter