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PDF MAX1839 Data sheet ( Hoja de datos )
| Número de pieza | MAX1839 | |
| Descripción | Wide Brightness Range CCFL Backlight Controllers | |
| Fabricantes | Maxim Integrated | |
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19-1755; Rev 1; 3/01
Wide Brightness Range
CCFL Backlight Controllers
General Description
The 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.
________________________Applications
Notebook/Laptop Computers
Car Navigation Displays
LCD Monitors
Point-of-Sale Terminals
Portable Display Electronics
†Patent pending
SMBus is a trademark of Intel Corp.
Features
o Fast Response to Input Change
o Wide Input Voltage Range (4.6V to 28V)
o High Power-to-Light Efficiency
o Minimizes Transformer Voltage Stress
o Lamp-Out Protection with 2s Timeout
o Buck Switch Short and Other Single-Point Fault
Protection
o Integrated Royer MOSFET Drivers Reduce
Transformer Pin Count
o Buck Operation Synchronized to Royer Oscillator
o Synchronizable DPWM Frequency
o Pin-Selectable Brightness Control Interface
o SMBus Serial Interface (MAX1739)
o Analog Interface (MAX1739/MAX1839)
PART
MAX1739EEP
MAX1839EEP
Ordering Information
TEMP. RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
20 QSOP
20 QSOP
Pin Configuration
TOP VIEW
REF 1
MINDAC 2
CCI 3
CCV 4
SH/SUS 5
CRF/SDA 6
CTL/SCL 7
MODE 8
CSAV 9
CTFB 10
MAX1739
20 BATT
19 DH
18 LX
17 BST
16 VL
15 GND
14 CS
13 DL1
12 DL2
11 SYNC
QSOP
Pin Configurations continued at end of data sheet.
________________________________________________________________ Maxim Integrated Products 1
For price, delivery, and to place orders, please contact Maxim Distribution at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
1 page  
Wide Brightness Range
CCFL Backlight Controllers
ELECTRICAL CHARACTERISTICS
(V+ = 8.2V, VSH/SUS = VSH = 5.5V, MINDAC = GND, TA = -40°C to +85°C, unless otherwise noted.) (Note 6)
PARAMETER
CONDITIONS
MIN TYP
SUPPLY AND REFERENCE
VBATT Input Voltage Range
VBATT Quiescent Current, Shutdown
VL Output Voltage, Normal Operation
VL Undervoltage Lockout Threshold
VL = VBATT
VL = open
SH/SUS = SH = GND
6V < VBATT < 28V,
0 < ILOAD < 15mA
VL rising (leaving lockout)
VL falling (entering lockout)
4.6
6
5.0
4.0
REF Output Voltage, Normal
Operation
4.5V < VL < 5.5V, IREF = 40µA
1.95
VL POR Threshold
0.9
SWITCHING REGULATOR
DH Driver On-Resistance
DL1, DL2 Driver On-Resistance
SYNC Synchronization Range
Detect falling edges on SYNC
64
CS Overcurrent Threshold
408
DAC AND ERROR AMPLIFIER
CSAV Regulation Point
VMINDAC = 0, DAC code = 11111 binary
186
CTFB Regulation Point
560
CTFB to CCV Transconductance
1V < VCCV < 2.7V
30
ANALOG INTERFACE BRIGHTNESS CONTROL (MODE connected to REF or MODE connected to GND)
SH Input Low Voltage
SH Input High Voltage
2.1
SYSTEM MANAGEMENT BUS BRIGHTNESS CONTROL (MODE connected to VL)
CRF/SDA, CTL/SCL, SH/SUS Input
Low Voltage
CRF/SDA, CTL/SCL, SH/SUS Input
High Voltage
2.1
MAX UNITS
5.5
28
20
5.6
4.6
2.05
2.7
V
µA
V
V
V
V
18 Ω
18 Ω
200 kHz
492 mV
202 mV
640 mV
50 µmho
0.8 V
V
0.8 V
V
CRF/SDA Output Low Sink Current
VCRF/SDA = 0.4V
Note 1: Corresponds to 512 DPWM cycles or 65536 MODE
cycles.
Note 2: When the buck switch is shorted, VCTFB goes high
causing VCCV to 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.
4 mA
Note 5: The amplitude is measured with the following circuit:
VAMPLITUDE > 2V
500pF
MODE
10k
Note 6: Specifications from -40°C to +85°C are guaranteed by
design, not production tested.
_______________________________________________________________________________________ 5
5 Page 
Wide Brightness Range
CCFL Backlight Controllers
Voltage and Current Control Loops
The 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 CCCV to 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 Range sec-
tion). This error voltage is called VCCI. The lower of
VCCV and VCCI is 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, VCCV is set to 1.2V and CCI is set to high imped-
ance. VCCV is 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. VCCI is set to
high impedance to keep VCCI from 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, VCCI slowly 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, VCCI reaches 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, VCCV is at 150mV
above VCCI. After the on-cycle, VCCV is 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 VCCV increases, it causes
the buck regulator duty cycle to increase and provides
soft-start. When VCCV crosses over VCCI, the current
control loop regains control and regulates the lamp cur-
rent. VCCV is limited to 150mV above VCCI for the
remainder of the on-cycle.
In a lamp-out condition, VCCI increases the primary
voltage in an attempt to maintain lamp current regula-
tion. As VCCI rises, VCCV rises 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 VCCV is 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 VCCV would 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 Resistors section for information about
setting the voltage and current control loop thresholds.
Feed-Forward Control
Both 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 VCCI and VCCV. In other words, VBATT feed
forward has the effect of not requiring changes in error-
signal voltage (VCCI and 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 Dropout
The MAX1739/MAX1839 are designed to maintain tight
control of the transformer primary under all transient
conditions. This includes transients from dropout,
where VBATT is 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,
_______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 26 Páginas | |
| PDF Descargar | [ Datasheet MAX1839.PDF ] | |
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