MAX1889ETE ,Triple-Output TFT LCD Power Supply with Fault ProtectionFeaturesThe MAX1889 provides the three regulated output volt- High-Performance Step-Up Regulatora ..
MAX1889ETE+ ,Triple-Output TFT LCD Power Supply with Fault ProtectionApplicationsNotebook Computer DisplaysTOP VIEWLCD Monitors 16 15 14 13Car Navigation DisplaysSHDN 1 ..
MAX1889ETE+T ,Triple-Output TFT LCD Power Supply with Fault ProtectionFeaturesThe MAX1889 provides the three regulated output volt- ♦ High-Performance Step-Up Regulatora ..
MAX188ACPP ,Low-Power, 8-Channel, Serial 12-Bit ADCsGeneral Description ________
MAX188ACPP+ ,Low-Power, 8-Channel, Serial 12-Bit ADCsApplicationsCH1 2 19 SCLKPortable Data LoggingCSCH2 3 18Data-Acquisition CH3 417 DINMAX186High-Accu ..
MAX188ACPP+ ,Low-Power, 8-Channel, Serial 12-Bit ADCsFeatures♦ 8-Channel Single-Ended or 4-Channel The MAX186/MAX188 are 12-bit data-acquisition sys-Dif ..
MAX483CSA+ ,Low-Power, Slew-Rate-Limited RS-485/RS-422 TransceiversFeaturesThe MAX481, MAX483, MAX485, MAX487–MAX491, and♦ For Fault-Tolerant
MAX483CSA+ ,Low-Power, Slew-Rate-Limited RS-485/RS-422 TransceiversApplicationsguarantees a logic-high output if the input is open circuit.MAX3030E–MAX3033E: ±15kV E ..
MAX483CSA+T ,Low-Power, Slew-Rate-Limited RS-485/RS-422 TransceiversFeaturesThe MAX481, MAX483, MAX485, MAX487–MAX491, and♦ For Fault-Tolerant
MAX483CUA ,Low-Power / Slew-Rate-Limited RS-485/RS-422 TransceiversGeneral Description ________
MAX483CUA ,Low-Power / Slew-Rate-Limited RS-485/RS-422 TransceiversELECTRICAL CHARACTERISTICS(V = 5V ±5%, T = T to T , unless otherwise noted.) (Notes 1, 2)CC A MIN M ..
MAX483CUA ,Low-Power / Slew-Rate-Limited RS-485/RS-422 TransceiversMAX481/MAX483/MAX485/MAX487–MAX491/MAX148719-0122; Rev 5; 2/96Low-Power, Slew-Rate-LimitedRS-485/RS ..
MAX1889ETE
Triple-Output TFT LCD Power Supply with Fault Protection
General DescriptionThe MAX1889 provides the three regulated output volt-
ages required for active matrix, thin-film transistor liquid
crystal displays (TFT LCDs). It combines a high-perfor-
mance step-up regulator with two linear-regulator con-
trollers and multiple levels of protection circuitry for a
complete power-supply system.
The main DC-DC converter is a high-frequency
(500kHz/1MHz), current-mode step-up regulator with
an integrated N-channel power MOSFET that allows the
use of ultra-small inductors and ceramic capacitors.
With its high closed-loop bandwidth performance, the
MAX1889 provides fast transient response to pulsed
loads while operating with efficiencies over 85%. The
positive and negative linear-regulator controllers post-
regulate charge-pump outputs for TFT gate-on and
gate-off supplies.
The MAX1889 has a unique input switch control that
can replace the typical input fuse by disconnecting the
load from the input supply when a fault is detected.
The fault detector monitors all three regulated output
voltages and can monitor current from the input supply
as well. Additionally, the MAX1889 enters thermal shut-
down when its overtemperature threshold is reached.
The MAX1889 undervoltage lockout is set at 2.5V (max)
to allow the input supply to droop under pulsed load
conditions while avoiding any unexpected behavior
when its input voltage dips momentarily. Also, the built-
in soft-start and cycle-by-cycle current limiting prevent
input surge currents during power-up.
The MAX1889 is available in a 16-pin thin QFN pack-
age with a maximum thickness of 0.8mm for ultra-thin
LCD panel design.
ApplicationsNotebook Computer Displays
LCD Monitors
Car Navigation Displays
FeaturesHigh-Performance Step-Up Regulator
Fast Transient Response
Current-Mode Control Architecture
Built-In High-Efficiency N-Channel Power
MOSFET
Current-Limit Comparator
>85% Efficiency
Selectable Switching Frequency
(500kHz/1MHz)
Internal Soft-StartPositive Linear-Regulator ControllerNegative Linear-Regulator ControllerTriple-Level Protection Against Smoke or Fire
Input Switch Replaces Input Fuse
Output Overload Detection with Timer Latch
Thermal Shutdown2.7V to 5.5V Input Operating RangeUltra-Small External Components 1µA Shutdown Current (max)1mA Quiescent Current (max)Ultra-Thin 16-Pin QFN Package
(0.8mm Maximum Thickness)
MAX1889
Triple-Output TFT LCD Power Supply
with Fault Protection
Ordering Information
Pin Configuration19-2485; Rev 1; 10/02
* Future product—Contact factory for availability.
MAX1889riple-Output TFT LCD Power Supply
with Fault Protection
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICSStresses 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, OCN, OCP,
FB, FBP, FBN, FREQ to GND...............................-0.3V to +6V
PGND to GND.....................................................................±0.3V
LX to PGND............................................................-0.3V to +14V
DRVP to GND.........................................................-0.3V to +30V
REF, GATE, TGND to GND..........................-0.3V to (VIN+ 0.3V)
DRVN to GND.....................................(VIN- 28V) to (VIN+ 0.3V)
Continuous Power Dissipation (TA= +70°C)
16-Pin QFN (derate 19.2mW/°C above +70°C).........1538mW
Operating Temperature Range
MAX1889EGE..................................................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s).................................+300°C
MAX1889
Triple-Output TFT LCD Power Supply
with Fault Protection
ELECTRICAL CHARACTERISTICS (continued)(VIN= 3V, SHDN= IN, CREF= 0.22µF, PGND = GND, TA
= 0°C to +85°C. Typical values are at TA= +25°C, unless otherwise noted.)
MAX1889riple-Output TFT LCD Power Supply
with Fault Protection
ELECTRICAL CHARACTERISTICS(VIN= 3V, SHDN= IN, CREF= 0.22µF, PGND = GND, TA
= -40°C to +85°C.) (Note 4)
MAX1889
Triple-Output TFT LCD Power Supply
with Fault Protection
ELECTRICAL CHARACTERISTICS (continued)
(VIN= 3V, SHDN= IN, CREF= 0.22µF, PGND = GND, TA= -40°C to +85°C.) (Note 4)
Note 2:FB regulation voltage is tested with no slope compensation ramp. Slope compensation needs to be included when selecting
resisitors for setting the output voltage (see Main Step-Up Regulatorand Output Voltage Selection sections).
Note 3:Guaranteed by design. Not production tested.
Note 4:Specifications to -40°C are guaranteed by design, not production tested.
Typical Operating Characteristics
(Circuit of Figure 1, VIN= +3.3V, VMAIN= +9V, VPL= +20V, VNL= -7V, SHDN= FREQ = IN, PGND = GND, TA= +25°C, unless
otherwise noted.)
MAX1889riple-Output TFT LCD Power Supply
with Fault Protection
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN= +3.3V, VMAIN= +9V, VPL= +20V, VNL= -7V, SHDN= FREQ = IN, PGND = GND, TA= +25°C, unless
otherwise noted.)
MAX1889
Triple-Output TFT LCD Power Supply
with Fault Protection
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN= +3.3V, VMAIN= +9V, VPL= +20V, VNL= -7V, SHDN= FREQ = IN, PGND = GND, TA= +25°C, unless
otherwise noted.)
MAX1889riple-Output TFT LCD Power Supply
with Fault Protection
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN= +3.3V, VMAIN= +9V, VPL= +20V, VNL= -7V, SHDN= FREQ = IN, PGND = GND, TA= +25°C, unless
otherwise noted.)
MAX1889
Triple-Output TFT LCD Power Supply
with Fault Protection
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN= +3.3V, VMAIN= +9V, VPL= +20V, VNL= -7V, SHDN= FREQ = IN, PGND = GND, TA= +25°C, unless
otherwise noted.)
MAX1889riple-Output TFT LCD Power Supply
with Fault Protection
MAX1889
Triple-Output TFT LCD Power Supply
with Fault Protection
Figure 1. Standard Application Circuit
MAX1889riple-Output TFT LCD Power Supply
with Fault Protection
Figure 2. MAX1889 System Functional Diagram
MAX1889
Triple-Output TFT LCD Power Supply
with Fault Protection
Standard Application Circuit
The standard application circuit (Figure 1) of the
MAX1889 generates +9V, +20V, and -7V outputs for
TFT LCD displays. The input voltage is from 2.7V to
5.5V. Table 1 lists the recommended component
options and Table 2 lists the component suppliers.
Detailed Description
The MAX1889 contains a high-performance, step-up
switching regulator, two low-cost linear-regulator con-
trollers, and multiple levels of protection circuitry. Figure
2 shows the system functional diagram of the device.
The output voltage of the main step-up converter (VMAIN)
can be set from VINto 13V with an external resistive volt-
age-divider. The high switching frequency (500kH/1MHz)
of the main step-up converter and current-mode control
provide fast transient response and allow the use of low-
profile inductors and ceramic capacitors. The internal
power MOSFET minimizes the external component count
while achieving high efficiency by incorporating a loss-
less current-sensing technology.
The switching node (LX) can generate both positive
and negative voltage supplies by driving charge-pump
stages of capacitors and diodes. The user can use as
many charge-pump stages as needed to generate sup-
ply voltages of more than +30V and -15V. The positive
and negative linear-regulator controllers postregulate
the charge-pump supply voltages and allow users to
program power-up sequencing as well.
The unique input switch control of the MAX1889 senses
the current drawn from the input power supply by moni-
toring the voltage drop across the input P-channel
MOSFET and latches off if an overcurrent condition
lasts for more than the fault timer period. In addition, all
three outputs are monitored for fault conditions that last
longer than the fault latch timer. If the junction tempera-
ture of the IC exceeds +160°C, the device goes into a
latched shutdown state.
Main Step-Up Regulator
The main step-up regulator switches at 1MHz (or 500kHz)
and employs a current-mode control architecture to
maximize loop bandwidth to provide fast-transient
response to pulsed loads found in source drivers for TFT
LCD panels. Also, the high switching frequency allows
the use of low-profile inductors and capacitors to
minimize the thickness of LCD panel designs. The
integrated high-efficiency MOSFET and the IC’s built-in
soft-start function reduce the number of external com-
ponents required while controlling inrush current.
Table 1. Component List
Table 2. Component Suppliers
MAX1889riple-Output TFT LCD Power Supply
with Fault Protection
Depending on the input-to-output voltage ratio, the reg-
ulator controls the output voltage and the power deliv-
ered to the output by modulating the duty cycle (D) of
the power MOSFET in each switching cycle. The duty
cycle of the MOSFET is approximated by:
On the rising edge of the internal clock, the controller
sets a flip-flop, which turns on the N-channel MOSFET
(Figure 3). The input voltage is applied across the
inductor. The inductor current ramps up linearly, storing
energy in a magnetic field. Once the sum of the feed-
back voltage error-amplifier output, slope-compensa-
tion, and current-feedback signals trip the multi-input
PWM comparator, the MOSFET turns off, and the flip-
flop resets. Since the inductor current is continuous, a
transverse potential develops across the inductor that
turns on the diode (D1). The voltage across the inductor
becomes the difference between the output voltage and
the input voltage. This discharge condition forces the
current through the inductor to ramp back down, trans-
ferring the energy to the output capacitor and the load.
The MOSFET remains off for the rest of the clock cycle.
MAX1889
Triple-Output TFT LCD Power Supply
with Fault Protection
Positive Linear-Regulator Controller
The positive linear regulator provides the positive high
voltage for the TFT LCD gate drivers. The high voltage
can be produced using a charge-pump circuit as shown
in Figure 1. Use as many stages as necessary to obtain
the required output voltage (see the Selecting the
Number of Charge-Pump Stagessection). The positive
linear-regulator controller is an analog gain block with an
open-drain N-channel output. It drives an external PNP
pass transistor with a 3kΩbase-to-emitter resistor to
post-regulate the charge-pump output (Figure 1). The
regulator controller is designed to be stable with an out-
put capacitor of 0.1µF or more.
To enable the regulator using an external control signal,
apply the logic-control input in series with a signal
diode (Figure 1). Additional delay can be added with
external circuitry.
Note that the voltage rating of the DRVP output is 28V.
If higher voltages are present, an external cascode
NPN transistor should be used with the emitter con-
nected to DRVP, the base to VMAIN, and the collector to
the base of the PNP.
Negative Linear-Regulator Controller
The negative linear regulator provides the negative volt-
age required to supply gate drivers in TFT LCD panels.
The negative voltage can be produced using a charge
pump circuit as shown in Figure 1. Use as many stages
as necessary to obtain the required output voltage (see
the Selecting the Number of Charge-Pump Stagessec-
tion). The negative linear-regulator controller is an ana-
log gain block with an open-drain P-channel output. It
drives an external NPN pass transistor with a 3kΩbase-
to-emitter resistor to postregulate the charge-pump out-
put (Figure 1). The regulator controller is designed to
be stable with an output capacitor of 0.1µF or more.
The negative linear regulator is enabled as soon as the
main step-up regulator is enabled. To enable the regula-
tor using an external control signal, apply the logic-control
input through an open-drain output or an N-channel MOS-
FET (Figure 1). Additional delay can be added with exter-
nal circuitry (see the Applications Informationsection).
Note that the voltage rating of the DRVN output is
VIN- 28V. If higher voltages are present, an external
cascode PNP transistor should be used with the emitter
connected to DRVN, the base to GND, and the collec-
tor to the base of the NPN.
Undervoltage Lockout (UVLO)
The UVLO comparator of the MAX1889 compares the
input voltage at the IN pin with the UVLO threshold (2.7V
rising, 2.35V falling, typ) to ensure that the input voltage is
high enough for reliable operation. The 350mV (typ) hys-
teresis prevents supply transients from causing a restart.
Once the input voltage exceeds the UVLO threshold, the
controller enables the reference block. Once the refer-
ence is above 1.05V, an internal 12µA current source
pulls the GATE pin low and turns on an external P-chan-
nel MOSFET switch (P1, Figure 1) that connects the input
supply to the regulator. When the input voltage falls below
the UVLO threshold, the controller sets the fault latch and
pulls GATE high with an internal 100Ωswitch to turn off
P1 quickly (Figure 4).
Reference Voltage (REF)
The reference output is nominally 1.25V, and can
source at least 50µA (see the Typical Operating
Characteristics). Bypass REF with a 0.22µF ceramic
capacitor connected between REF and GND.
Oscillator Frequency (FREQ)
The internal oscillator frequency is pin programmable.
Connect FREQ to ground for 500kHz operation and to VIN
for 1MHz operation. Note that the soft-start period scales
with the oscillator frequency (see the Soft-Startsection).
Shutdown (SHDN)
A logic-low signal on the SHDNpin disables all device
functions including the reference. When shut down, the
supply current drops to 0.1µA (typ) to maximize battery
life. The output capacitance, feedback resistors, and load
current determine the rate at which each output voltage
decays. A logic-high signal on the SHDNpin activates the
MAX1889 (see the Power-Up Sequencingsection). Do not
leave the pin floating. If unused, connect SHDNto IN.
Toggling SHDNor cycling IN clears the fault latch.
Figure 4. External Input P-Channel MOSFET Switch Control
MAX1889riple-Output TFT LCD Power Supply
with Fault Protection
Power-Up Sequencing and
Inrush Current Control
Once SHDNis high, the MAX1889 enables the UVLO
circuitry and compares the input voltage with the UVLO
rising threshold (2.7V, typ). If the input voltage exceeds
the UVLO rising threshold, the reference is enabled.
When the reference voltage ramps up above 1.05V
(typ), the MAX1889 enables the oscillator and turns on
the external P-channel MOSFET P1 (Figure 1) by
pulling GATE low. GATE is pulled down with a 12µA
current source. Add a capacitor from the gate of P1 to
its drain to slow down the turn-on rate of the MOSFET,
and reduce inrush current. Once GATE reaches around
0.6V, an internal N-channel MOSFET turns on and pulls
GATE to ground in order to maximize the enhancement
of the external P-channel MOSFET. As P1 fully turns on,
the main step-up regulator powers up with soft-start
(see the Soft-Startsection). The negative linear regula-
tor is enabled at the same time as the main step-up
regulator. The positive linear regulator is enabled after
the soft-start routine is completed. The fault detection
timer begins after the main step-up regulator has fin-
ished its soft-start period.
Soft-Start
The soft-start of the main step-up regulator (Figure 3) is
achieved by ramping up the reference voltage of the
multi-input PWM comparator in 4096 oscillator clock
cycles. The 4096 clock cycles correspond to 4.096ms
for 1MHz operation and 8.192ms for 500kHz operation.
The reference of the PWM comparator comes from a
5-bit DAC that generates 32 steps when the reference
ramps up from 0V to its final value. This soft-start
method allows a gradual increase of the output voltage
to reduce the input surge current (see the startup
waveforms in the Typical Operating Characteristics).
The average input current is given as:
where VMAINis the main step-up regulator output volt-
age, VINis the input voltage, COUTis the main step-up
regulator output capacitor, ηis the efficiency of the
step-up regulator, and tSSis the soft-start period
(4.096ms for 1MHz operation and 8.192ms for 500kHz
operation).
Input Overcurrent Protection
The high-side overcurrent comparator of the MAX1889
provides input overcurrent protection when it is used
together with the external P-channel MOSFET switch P1
(Figure 1). Connect resistive voltage-dividers from the
source and drain of P1 to GND to set the overcurrent
threshold. The center taps of the dividers are connected
to the overcurrent comparator inputs (OCN and OCP)
See the Setting the Input Overcurrent Thresholdsection
for information on calculating resistor values.An overcur-
rent event activates the fault-protection circuitry.
Fault Protection
Once the soft-start routine is completed, if the output of
the main regulator or either linear regulator is below its
respective fault-detection threshold, or the input overcur-
rent comparator pulls high, the MAX1889 activates the
fault timer. If the fault condition still exists after the 64ms
fault-timer duration, the MAX1889 sets the fault latch,
which shuts down all the outputs except the reference,
which remains active. After removing the fault condition,
toggle SHDN(below 0.4V) or cycle the input voltage
(below 2.2V) to clear the fault latch and reactivate the
device.
Thermal Shutdown
The thermal shutdown feature limits total power dissipa-
tion in the MAX1889. When the junction temperature
(TJ) exceeds +160°C, a thermal sensor sets the fault
latch (Figure 2), which shuts down all the outputs
except the reference, allowing the device to cool down.
Once the device cools down by 15°C, toggle SHDN
(below 0.4V) or cycle the input voltage (below 2.2V) to
clear the fault latch and reactivate the device.
Design Procedure
Main Step-Up Regulator
Output Voltage Selection
Adjust the output voltage by connecting a resistive volt-
age-divider from the output (VMAIN) to GND with the
center tap connected to FB (Figure 1). Select R7 in the
10kΩto 50kΩrange. Calculate R6 with the following
equations:
where
For example, at VIN= 3V, VMAIN= 9V, D ≈0.66, and VFB
= 1.229V.
VMAINcan range from VINto 13V.
