MAX1729EUB ,ECB and LCD Display Bias Supply with Accurate Output Voltage and Temperature CompensationELECTRICAL CHARACTERISTICS(V = +3V, CTLIN = IN, FB = GND, T = -40°C to +85°C, unless otherwise note ..
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The MAX172 uses a standard microprocessor interface
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MAX172ACWG ,Complete 10s CMOS 12-Bit ADCapplications, can be used with a
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..
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MAX1729EUB
ECB and LCD Display Bias Supply with Accurate Output Voltage and Temperature Compensation
ECB and LCD Display Bias Supply with Accurate
Output Voltage and Temperature Compensation
General DescriptionThe MAX1729 micropower step-up/step-down DC-DC
converter is ideally suited for electrically controlled bire-
fringence (ECB) and liquid-crystal-display (LCD) bias-
supply generation. It provides step-up/step-down
voltage conversion and reduces output ripple by using
a step-up DC-DC converter followed by a linear regula-
tor. This architecture permits a physically smaller induc-
tor than those used in competing SEPIC and flyback
topologies. This device features low quiescent current
(67µA typical). A logic-controlled shutdown mode fur-
ther reduces quiescent current to 0.4µA typical.
The MAX1729 features an input that dynamically
adjusts the output voltage to control display color or
contrast. It offers two feedback modes: internal and
external. Internal feedback mode allows output volt-
ages between 2.5V and 16V, and is specifically
designed to hold temperature drift to ±11ppm/°C.
External feedback mode allows the MAX1729 output
voltage range to be tailored for various displays.
An on-chip temperature sensor with a positive tempera-
ture coefficient provides compensation for LCD/ECB
display temperature characteristics. In internal feed-
back mode, the buffered temperature sensor output is
read and used to adjust the output voltage via a digital
control signal. External feedback mode features an
additional compensation method in which the tempera-
ture output is summed directly into the feedback net-
work to provide first-order negative temperature
compensation of the output voltage. The MAX1729 is
available in the space-saving 10-pin µMAX package.
ApplicationsECB Display Bias & Color Adjustment
LCD Display Bias & Contrast Adjustment
Cellular Phones
Personal Digital Assistants
FeaturesHigh-Accuracy Reference Voltage (±1%)±11ppm/°C Output Voltage DriftOn-Chip Temperature Sensor OutputAccurate Voltage and Temperature Provide:
Consistent ECBColors
Consistent LCD Gray-Scale Contrast+2.7V to +5.5V Input Voltage RangeOutput Voltage Range
+2.5V to +16V in Internal Feedback Mode
Programmable in External Feedback ModeDynamic Control of the Output Voltage67µA Supply Current 0.4µA Shutdown Current 10-Pin µMAX Package (1.09mm max height)Evaluation Kit Available (MAX1729EVKIT)
MAX1729
Typical Operating Circuit
Ordering Information
Pin Configuration
MAX1729
ECB and LCD Display Bias Supply with Accurate
Output Voltage and Temperature Compensation
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(VIN= +3V, CTLIN = IN, FB = GND, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.) (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.
IN to GND.................................................................-0.3V to +6V
LX, PS, OUT to GND...............................................-0.3V to +20V
CTLIN, FB, REF, COMP, TC to GND...........-0.3V to (VIN+ 0.3V)
LX to PS..................................................................-20V to +1.0V
LX, PS, OUT Current...........................................................60mA
Continuous Power Dissipation (TA= +70°C)
10-pin µMAX (derate 5.6mW/°C above +70°C)..........444mW
Operating Temperature Range...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +160°C
Lead Temperature (soldering, 10sec).............................+300°C
MAX1729
ECB and LCD Display Bias Supply with Accurate
Output Voltage and Temperature Compensation
Note 1:Specifications to -40°C are guaranteed by design, not production tested.
Note 2:When VINis below this level, the boost and LDO outputs are disabled.
Note 3:Guaranteed by design.
Note 4:Minimum time to hold CTLIN low to invoke shutdown. If CTLIN is held low for less than tOFF, device does not enter shutdown.
Note 5:Switching regulator regulates this voltage to keep LDO from dropping out.
ELECTRICAL CHARACTERISTICS(VIN= +3V, CTLIN = IN, FB = GND, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note 1)
MAX1729
ECB and LCD Display Bias Supply with Accurate
Output Voltage and Temperature Compensation
Typical Operating Characteristics(Circuit of Figure 2, TA = +25°C, unless otherwise noted.)
MAX1729
ECB and LCD Display Bias Supply with Accurate
Output Voltage and Temperature Compensation
Typical Operating Characteristics (continued)(Circuit of Figure 2, TA= +25°C, unless otherwise noted.)
MAX1729
Detailed DescriptionThe MAX1729 is designed to provide bias voltage for
ECB or LCD displays. It is composed of a step-up
DC-DC converter followed by a linear regulator
(Figure 1), a combination that provides step-up/step-
down voltage conversion while minimizing output rip-
ple. The device allows you to adjust a display’s color or
contrast by dynamically adjusting the MAX1729’s out-
put voltage using a PWM control signal. In internal
feedback mode, the output voltage is adjustable
between +2.5V and +16V. In external feedback mode,
the output voltage is adjustable, and its range is set by
a resistor network that is programmed to match the out-
put voltage range of LCD/ECB displays needing a max-
imum output up to +18V.
Boost ConverterThe MAX1729’s DC-DC boost converter is implemented
with an on-chip N-channel MOSFET, a diode, and an
error comparator. The IC’s unique PFM control system
varies the on-time and off-time of the switch based on the
boost converter’s input and output voltage values, as fol-
lows:
where K is typically 8V-µs. This timing maintains discon-
tinuous conduction and sets the peak inductor current
(IPEAK) to:
where L is the inductance of L1 (Figures 2, 3, and 4).
When the error comparator detects that the drop across
the linear regulator (VPS- VOUT) is less than approximate-
ly 0.6V, the internal switch is turned on (tONinitiates) and
current through the inductor ramps to IPEAK. At the end of
tON, the switch is turned off for at least tOFF, allowing the
ECB and LCD Display Bias Supply with Accurate
Output Voltage and Temperature Compensation
Pin Description
