MAX1839EEP ,Wide Brightness Range CCFL Backlight ControllersApplicationsNotebook/Laptop ComputersTOP VIEWCar Navigation DisplaysREF 1 20 BATTLCD MonitorsMINDAC ..
MAX183BCNG ,High-Speed 12-Bit A/D Converters With External Refernce inputGeneral Description
The MAX183/184/185 are 12-bit, high-speed,
BiCMOS, analog-to-digital conver ..
MAX183BCNG+ ,3µs, 12-Bit ADCFeatures
. 12-Blt Resolutlon and Accuracy
. Fast Conversion Tlmes:
MAX183 - 3ps
MAX184 - 5 ..
MAX183BCNG+ ,3µs, 12-Bit ADCGeneral Description
The MAX183/184/185 are 12-bit, high-speed,
BiCMOS, analog-to-digital conver ..
MAX183BCWG ,High-Speed 12-Bit A/D Converters With External Refernce inputFeatures
. 12-Blt Resolutlon and Accuracy
. Fast Conversion Tlmes:
MAX183 - 3ps
MAX184 - 5 ..
MAX1840EUB ,Low-Voltage SIM/Smart Card Level Translators in MAXApplicationsOrdering InformationSIM Interface in GSM Cellular TelephonesPART TEMP. RANGE PIN-PACKAG ..
MAX472CSA+ ,Precision, High-Side Current-Sense AmplifiersFeaturesThe MAX471/MAX472 are complete, bidirectional, high-♦ Complete High-Side Current Sensingsid ..
MAX472ESA ,Precision, High-Side Current-Sense AmplifiersFeaturesThe MAX471/MAX472 are complete, bidirectional, high-' Complete High-Side Current Sensingsid ..
MAX472ESA-T ,Precision, High-Side Current-Sense AmplifiersApplicationsMAX471CSA 0°C to +70°C 8 SOPortable PCs:MAX471EPA -40°C to +85°C 8 Plastic DIPNotebooks ..
MAX4731EUA+ ,50 Ohm, Dual SPST Analog Switches in UCSPApplications RANGE PACKAGE MARKMAX4731EUA -40°C to +85°C 8 µMAX —Battery-Powered SystemsMAX4731ETA ..
MAX4731EUA+T ,50 Ohm, Dual SPST Analog Switches in UCSPapplications.♦ Guaranteed < 0.1nA Leakage Current at When powered from a +3V supply, these switches ..
MAX4733EUA+ ,50 Ohm, Dual SPST Analog Switches in UCSPELECTRICAL CHARACTERISTICS—Single +3V Supply(V+ = +3V ±10%, V = +2.0V, V = +0.8V, T = T to T , unle ..
MAX1739EEP-MAX1839EEP
Wide Brightness Range CCFL Backlight Controllers
General DescriptionThe MAX1739/MAX1839 fully integrated controllers are
optimized to drive cold-cathode fluorescent lamps
(CCFLs) using the industry-proven Royer oscillator
inverter architecture. The Royer architecture provides
near sinusoidal drive waveforms over the entire input
range to maximize the life of CCFLs. The MAX1739/
MAX1839 optimize this architecture to work over a wide
input voltage range, achieve high efficiency, and maxi-
mize the dimming range.
The MAX1739/MAX1839 monitor and limit the trans-
former center-tap voltage when required. This ensures
minimal voltage stress on the transformer, which
increases the operating life of the transformer and
eases its design requirements. These controllers also
provide protection against many other fault conditions,
including lamp-out and buck short faults.
These controllers achieve 50:1 dimming range by
simultaneously adjusting lamp current and “chopping”
the CCFL on and off using a digitally adjusted pulse-
width modulated (DPWM) method. CCFL brightness is
controlled by an analog voltage or is set with an
SMBusTM-compatible two-wire interface (MAX1739).
The MAX1739/MAX1839 drive an external high-side
N-channel power MOSFET and two low-side N-channel
power MOSFETs, all synchronized to the Royer oscilla-
tor. An internal 5.3V linear regulator powers the MOS-
FET drivers and most of the internal circuitry. The
MAX1739/MAX1839 are available in space-saving
20-pin QSOP packages and operate over the -40°C to
+85°C temperature range.
________________________ApplicationsNotebook/Laptop Computers
Car Navigation Displays
LCD Monitors
Point-of-Sale Terminals
Portable Display Electronics
FeaturesFast Response to Input ChangeWide Input Voltage Range (4.6V to 28V)High Power-to-Light EfficiencyMinimizes Transformer Voltage StressLamp-Out Protection with 2s Timeout Buck Switch Short and Other Single-Point Fault
ProtectionIntegrated Royer MOSFET Drivers Reduce
Transformer Pin CountBuck Operation Synchronized to Royer OscillatorSynchronizable DPWM Frequency Pin-Selectable Brightness Control InterfaceSMBus Serial Interface (MAX1739)Analog Interface (MAX1739/MAX1839)
MAX1739/MAX1839
Wide Brightness Range
CCFL Backlight Controllers
Pin Configuration19-1755; Rev 1; 3/01
†Patent pending
SMBus is a trademark of Intel Corp.
Ordering Information
MAX1739/MAX1839
Wide Brightness Range
CCFL Backlight Controllers
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.
VBATTto GND...........................................................-0.3V to 30V
VBST, VSYNCto GND.................................................-0.3V to 34V
VBSTto VLX.................................................................-0.3V to 6V
VDHto VLX.................................................-0.3V to (VBST+ 0.3V)
VLXto GND...................................................-6V to (VBST+ 0.3V)
VL to GND...................................................................-0.3V to 6V
VCCV, VCCI, VREF, VDL1, VDL2to GND.........-0.3V to (VL + 0.3V)
VMINDAC, VCTFB, VCSAVto GND................................-0.3V to 6V
VCSto GND...................................................-0.6V to (VL + 0.3V)
VMODEto GND.............................................................-6V to 12V
VCRF/SDA, VCRF, VCTL/SCL, VCTL, VSH/SUS,
VSHto GND............................................................-0.3V to 6V
Continuous Power Dissipation (TA= +70°C)
20-Pin QSOP (derate 9.1mW/°C above +70°C)...........727mW
Operating Temperature.......................................-40°C to +85°C
Storage Temperature.........................................-65°C to +150°C
Lead Temperature (soldering, 10s).................................+300°C
MAX1739/MAX1839
Wide Brightness Range
CCFL Backlight Controllers
ELECTRICAL CHARACTERISTICS (continued)
MAX1739/MAX1839
Wide Brightness Range
CCFL Backlight Controllers
ELECTRICAL CHARACTERISTICS (continued)(V+ = 8.2V, VSH/SUS = VSH= 5.5V, MINDAC = GND, TA
= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)
MAX1739/MAX1839
Wide Brightness Range
CCFL Backlight Controllers
ELECTRICAL CHARACTERISTICS
Note 1:Corresponds to 512 DPWM cycles or 65536 MODE
cycles.
Note 2:When the buck switch is shorted, VCTFBgoes high
causing VCCVto go below the fault detection threshold.
Note 3:Corresponds to 64 DPWM cycles or 8192 MODE cycles.
Note 4:The MODE pin thresholds are only valid while the part is
operating. In shutdown, VREF= 0 and the part only
differentiates between SMB mode and ADC mode. In
shutdown with ADC mode selected, the CRF/SDA and
CTL/SCL pins are at high impedance and will not cause
extra supply current when their voltages are not at
GND or VL.
Note 5:The amplitude is measured with the following circuit:
Note 6:Specifications from -40°C to +85°C are guaranteed by
design, not production tested.
MAX1739/MAX1839
Wide Brightness Range
CCFL Backlight Controllers
Typical Operating Characteristics(VIN= 12V, VCTL= VCRF, VMINDAC= 1V, MODE = GND, Circuit of Figure 8.)
MAX1739/MAX1839
Wide Brightness Range
CCFL Backlight Controllers
Typical Operating Characteristics (continued)(VIN= 12V, VCTL= VCRF, VMINDAC= 1V, MODE = GND, Circuit of Figure 8.)
MAX1739/MAX1839
Wide Brightness Range
CCFL Backlight ControllersVL vs. IVL
MAX1739/1839 toc13
IVL (mA)
VL (V)
SHUTDOWN VL (V)
VL vs. BATT VOLTAGE
MAX1739/1839 toc14
VBATT (V)
VL (V)
VL vs. TEMPERATURE
MAX1739/1839 toc15
TEMPERATURE (°C)
VL (V)
SHUTDOWN VL (V)
Typical Operating Characteristics (continued)(VIN= 12V, VCTL= VCRF, VMINDAC= 1V, MODE = GND, Circuit of Figure 8.)
MAX1739/MAX1839
Wide Brightness Range
CCFL Backlight Controllers
MAX1739/MAX1839
Wide Brightness Range
CCFL Backlight Controllers
Detailed DescriptionThe MAX1739/MAX1839 regulate the brightness of a
CCFL in three ways:
1) Linearly controlling the lamp current.
2) Digitally pulse-width modulating (or chopping) the
lamp current (DPWM).
3) Using both methods simultaneously for widest dim-
ming range.
DPWM is implemented by pulse-width modulating the
lamp current at a rate faster than the human eye can
detect. Figure 1 shows the current and voltage wave-
forms for the three operating modes with the brightness
control set to 50% of full scale.
The MAX1739/MAX1839 include a 5.3V linear regulator
to power most of the internal circuitry, drivers for the
buck and Royer switches, and the synchronizable
DPWM oscillator. The MAX1739/MAX1839 are very flex-
ible and include a variety of operating modes, an ana-
log interface, an SMBus interface (MAX1739 only), a
shutdown mode, lamp-out detection, and buck-switch
short detection.
Figure 1. Brightness Control Methods
MAX1739/MAX1839
Wide Brightness Range
CCFL Backlight Controllers
Voltage and Current Control LoopsThe MAX1739/MAX1839 use two control loops. The cur-
rent control loop regulates the average lamp current. The
voltage control loop limits the maximum average primary-
side transformer voltage. The voltage control loop is
active during the beginning of DPWM on-cycles and in
some fault conditions. Limiting the transformer primary
voltage allows for a lower transformer secondary voltage
rating that can increase reliability and decrease cost of
the transformer. The voltage control loop acts to limit the
transformer voltage any time the current control loop
attempts to steer the transformer voltage above its limit as
set by VCTFB(see Sense Resistors).
The voltage control loop uses a transconductance
amplifier to create an error current based on the volt-
age between CTFB and the internal reference level
(600mV typ) (Figure 2). The error current is then used
to charge and discharge CCCVto create an error volt-
age VCCV. The current control loop produces a similar
signal based on the voltage between CSAV and its
internal reference level (see the Dimming Rangesec-
tion). This error voltage is called VCCI. The lower of
VCCVand VCCIis used with the buck regulator’s PWM
ramp generator to set the buck regulator’s duty cycle.
During DPWM, the two control loops work together to
limit the transformer voltage and to allow wide dimming
range with good line rejection. During the DPWM off-
cycle, VCCVis set to 1.2V and CCI is set to high imped-
ance. VCCVis set to 1.2V to create soft-start at the
beginning of each DPWM on-cycle in order to avoid
overshoot on the transformer primary. VCCIis set to
high impedance to keep VCCIfrom changing during the
off-cycles. This allows the current control loop to regu-
late the average lamp current only during DPWM on-
cycles and not the overall average lamp current.
Upon power-up, VCCIslowly rises, increasing the duty
cycle, which provides soft-start. During this time, VCCV,
which is the faster control loop, is limited to 150mV
above VCCI by the CCV-CLAMP. Once the secondary
voltage reaches the strike voltage, the lamp current
begins to increase. When the lamp current reaches the
regulation point, VCCIreaches steady state. With MIN-
DAC = VL (DPWM disabled), the current control loop
remains in control and regulates the lamp current.
With MINDAC between REF and GND, DPWM is
enabled and the MAX1739/MAX1839 begin pulsing the
lamp current. During the on-cycle, VCCVis at 150mV
above VCCI. After the on-cycle, VCCVis forced down to
1.2V to provide soft-start at the beginning of the next
on-cycle. Also, VCCI retains its value until the beginning
of the next on-cycle. When VCCVincreases, it causes
the buck regulator duty cycle to increase and provides
soft-start. When VCCVcrosses over VCCI, the current
control loop regains control and regulates the lamp cur-
rent. VCCVis limited to 150mV above VCCIfor the
remainder of the on-cycle.
In a lamp-out condition, VCCIincreases the primary
voltage in an attempt to maintain lamp current regula-
tion. As VCCIrises, VCCVrises with it until the primary
voltage reaches its set limit point. At this point, VCCV
stops rising and limits the primary voltage by limiting
the duty cycle. Because VCCVis limited to 150mV
above VCCI, the voltage control loop is quickly able to
limit the primary voltage. Without this clamping feature,
the transformer voltage would overshoot to dangerous
levels because VCCVwould take more time to slew
down from its supply rail. Once the MAX1739/MAX1839
sense less than 1/6 the full-scale current through the
lamp for 2 seconds, it shuts down the Royer oscillator
(see Lamp-Out Detection).
See the Sense Resistorssection for information about
setting the voltage and current control loop thresholds.
Feed-Forward ControlBoth control loops are influenced by the input voltage
feed-forward (VBATT) control circuitry of the MAX1739/
MAX1839. Feed-forward control instantly adjusts the
buck regulator’s duty cycle when it detects a change in
input voltage. This provides immunity to changes in
input voltage at all brightness levels. This feature
makes compensation over wide input ranges easier,
makes startup transients less dependent on input volt-
age, and improves line regulation for short DPWM on-
times.
The MAX1739/MAX1839 feed-forward control is imple-
mented by varying the amplitude of the buck-switch’s
PWM ramp amplitude. This has the effect of varying the
duty cycle as a function of input voltage while maintain-
ing the same VCCIand VCCV. In other words, VBATTfeed
forward has the effect of not requiring changes in error-
signal voltage (VCCIand VCCV) to respond to changes in
VBATT. Since the capacitors only need to change their
voltage minimally to respond to changes in VBATT, the
controller’s response is essentially instantaneous.
Transient Overvoltage Protection
from DropoutThe MAX1739/MAX1839 are designed to maintain tight
control of the transformer primary under all transient
conditions. This includes transients from dropout,
where VBATTis so low that the controller loses regula-
tion and reaches maximum duty cycle. Backlight
designs will want to choose circuit component values to
minimize the transformer turns ratio in order to minimize
primary-side currents and I2R losses. To achieve this,
MAX1739/MAX1839
Wide Brightness Range
CCFL Backlight ControllersFigure 2. Functional Diagram
MAX1739/MAX1839
Wide Brightness Range
CCFL Backlight Controllersallow the circuit to operate in dropout at extremely low
battery voltages where the backlight’s performance is
secondary. All backlight circuit designs can undergo a
transient overvoltage condition when the laptop is
plugged into the AC adapter and VBATTsuddenly
increases. The MAX1739/MAX1839 contain a unique
clamp circuit on VCCI. Along with the feed-forward cir-
cuitry, it ensures that there is not a transient transformer
overvoltage when leaving dropout.
The PK_DET_CLAMP circuit limits VCCIto the peaks of
the buck-regulator’s PWM ramp generator. As the cir-
cuit reaches dropout, VCCIapproaches the peaks of
the PWM ramp generator in order to reach maximum
duty cycle. If VBATTdecreases further, the control loop
loses regulation and VCCItries to reach its positive sup-
ply rail. The clamp circuit on VCCIkeeps this from hap-
pening, and VCCIrides just above the peaks of the
PWM ramp. As VBATTdecreases further, the feed-for-
ward PWM ramp generator loses amplitude and the
clamp drags VCCI down with it to a voltage below
where VCCIwould have been if the circuit was not in
dropout. When VBATT is suddenly increased out of
dropout, VCCIis still low and maintains the drive on the
transformer at the old dropout level. The circuit then
slowly corrects and increases VCCIto bring the circuit
back into regulation.
Buck Regulator The buck regulator uses the signals from the PWM
comparator, the current-limit detection on CS, and
DPWM signals to control the high-side MOSFET duty
cycle. The regulator uses voltage-mode PWM control
and is synchronized to the Royer oscillator. A falling
edge on SYNC turns on the high-side MOSFET after a
375ns minimum off-time delay. The PWM comparator or
the CS current limit ends the on-cycle.
Interface SelectionTable 1 lists the functionality of SH/SUS, CRF/SDA, and
CTL/SCL in each of the three interface modes of the
MAX1739/MAX1839. The MAX1739 features both an
SMBus digital interface and an analog interface, while
the MAX1839 features only the analog interface. Note
that MODE can also synchronize the DPWM frequency
(see Synchronizing the DPWM Frequency).
Dimming RangeBrightness is controlled by either the analog interface
(see Analog Interface) or the SMBus interface (see
SMBus Interface). CCFL brightness is adjusted in three
ways:
1) Lamp current control, where the magnitude of the
average lamp current is adjusted.
2) DPWM control, where the average lamp current is
pulsed to the lamp with a variable duty cycle.
3) A combination of the first two methods.
In each of the three methods, a 5-bit brightness code is
generated from the selected interface and is used to
set the lamp current and/or DPWM duty cycle.
The 5-bit brightness code defines the lamp current
level with ob00000 representing minimum lamp current
and ob11111 representing maximum lamp current. The
average lamp current is measured across an external
sense resistor (see Sense Resistors). The voltage on
the sense resistor is measured at CSAV. The brightness
code adjusts the regulation voltage at CSAV (VCSAV).
The minimum average VCSAVis VMINDAC/10, and the
maximum average is set by the following formula:
VCSAV= VREF✕31 / 320 + VMINDAC/ 320
which is between 193.75mV and 200mV.
Note that if VCSAVdoes not exceed 100mV peak (which
is about 32mV average) for over 2 seconds, the
MAX1739/MAX1839 will assume a lamp-out condition
and shut down (see Lamp-Out Detection).
The equation relating brightness code to CSAVregula-
tion voltage is:
VCSAV= VREF✕n / 320 + VMINDAC✕(32 - n) / 320
where n is the brightness code.
To always use maximum average lamp current when
using DPWM control, set VMINDACto VREF.
DPWM control works similar to lamp current control in
that it also responds to the 5-bit brightness code. A
