DS3991Z+T&R/PPV [MAXIM]
Fluorescent Light Controller;
| 型号： | DS3991Z+T&R/PPV |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Fluorescent Light Controller 控制器 |
| 文件： | 总16页 (文件大小：468K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
Rev 0; 1/08
Low-Cost CCFL Controller
DS391
General Description
Features
♦ CCFL Controller for Backlighting LCD Panels
The DS3991 is a controller for cold-cathode fluorescent
lamps (CCFLs) that are used to backlight liquid-crystal
displays (LCDs). The DS3991 is available for both
push-pull and half-bridge drive topologies.
♦ Minimal External Components Required
♦ Lamp Fault Monitoring for Lamp-Open, Lamp-
Overcurrent, Failure-to-Strike, and Overvoltage
Conditions
The DS3991 converts a DC voltage (5V to 24V) to the
high-voltage (300V
to 1400V
) AC waveform that
RMS
RMS
♦ Accurate (±±5% On-Board Oscillator for Lamp
is required to power the CCFLs. The push-pull and half-
bridge drive schemes use a minimal number of external
components, which reduces component and assembly
cost and makes the printed circuit board (PCB) design
easy to implement. Both drive schemes provide an effi-
cient DC to AC conversion and produce near-sinu-
soidal waveforms.
Frequency (40kHz to 80kHz%
♦ Accurate (±±5% On-Board Oscillator for DPꢀM
Burst-Dimming Frequency (80Hz to 300Hz%
♦ Device Supply Undervoltage Lockout
♦ Inverter Supply Undervoltage and Overvoltage
Lockouts
♦ Soft-Start on Burst-Dimming Minimizes Audible
Transformer Noise
Applications
♦ Strike Frequency Boost
LCD PC Monitors
LCD TVs
♦ 1005 to < 105 Dimming Range
♦ Low Cost
♦ Single-Supply Operation Range: 4.±V to ±.±V
♦ Temperature Range: -40°C to +8±°C
♦ 16-Pin SO Package (1±0 mils%
Ordering Information
PART
CONFIGURATION
Push-Pull
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
DIMMING FREQUENCY RANGE (Hz) PIN-PACKAGE
DS3991V+C
80 to 300
80 to 300
80 to 300
80 to 300
16 SO (150 mils)
16 SO (150 mils)
16 SO (150 mils)
16 SO (150 mils)
DS3991V+T&R/C
Push-Pull
DS3991V+
Half-Bridge
Half-Bridge
DS3991V+T&R
+Denotes a lead-free package.
T&R = Tape and reel.
Pin Configuration
TOP VIEW
SVML
SVMH
SLOPE
1
2
3
4
5
6
7
8
16
15
VCC
VCC
14 VCC
13 GND
12 OVD
11 LCM
Typical Operating Circuits appear at end of data sheet.
VCC
DS3991
LOSC
POSC/PWM
BRIGHT
PWM_EN
GB
GA
10
9
SO
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
Low-Cost CCFL Controller
ABSOLUTE MAXIMUM RATINGS
Voltage Range on VCC Relative to Ground ..........-0.5V to +6.0V
Voltage Range on Any Lead
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range.............................-55°C to +125°C
Soldering Temperature...................See J-STD-020 Specification
Other than VCC
-0.5V to (V
+ 0.5V),
..............................................
CC
not to exceed +6.0V
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.
DS391
RECOMMENDED OPERATING CONDITIONS
(T = -40°C to +85°C)
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Supply Voltage
V
(Note 1)
4.5
5.5
V
CC
V
+
CC
0.3
Input Logic 1
V
2.2
-0.3
-0.3
V
V
V
IH
Input Logic 0
V
+0.8
IL
BRIGHT, SVML, SVMH Voltage
Range
V
+
CC
V
V
RA
0.3
V
+
CC
0.3
LCM and OVD Voltage Range
(Note 2)
-0.3
V
RC
Gate-Driver Output Charge
Loading
Q
20
20
nC
pF
G
LOSC and POSC Loading
C
OSC
ELECTRICAL CHARACTERISTICS
(V
CC
= +4.5V to 5.5V, T = -40°C to +85°C.)
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Supply Current
I
GA, GB loaded with 300pF
5
10
mA
CC
Low-Level Output Voltage
(GA, GB)
V
I
I
= 4mA
= -1mA
0.4
V
V
OL
OL
High-Level Output Voltage
(GA, GB)
V
2.4
3.7
OH
OH
UVLO Threshold: V Rising
V
4.3
V
V
CC
UVLOR
UVLO Threshold: V Falling
CC
V
UVLOF
UVLOH
UVLO Hysteresis
V
100
2.00
2.00
150
1.35
50
mV
V
SVML Falling Threshold
SVMH Rising Threshold
SVML and SVMH Hysteresis
LCM and OVD DC Bias Voltage
LCM and OVD Input Resistance
Lamp-Off Threshold
V
1.94
1.94
2.06
2.06
SVMLT
V
V
SVMHT
V
mV
V
SVMH
V
DCB
R
DCB
kꢀ
V
V
LOT
(Note 3)
(Note 3)
1.65
3.25
1.75
3.35
1.85
3.45
Lamp Overcurrent Threshold
V
LOCT
V
2
_______________________________________________________________________________________
Low-Cost CCFL Controller
DS391
ELECTRICAL CHARACTERISTICS (continued%
(V
CC
= +4.5V to 5.5V, T = -40°C to +85°C.)
A
PARAMETER
SYMBOL
CONDITIONS
MIN
2.29
2.25
40
TYP
2.35
2.35
MAX
2.41
2.45
80
UNITS
Lamp Regulation Threshold
OVD Threshold
V
LRT
(Note 3)
(Note 3)
V
V
V
OVDT
Lamp Frequency
LF
kHz
OSCI
LOSC resistor 0.1% over temperature;
measured from 0°C to +85°C
Lamp Frequency Tolerance
LF
-5
80
-5
+5
300
+5
0
%
Hz
%
TOL
Burst-Dimming PWM Frequency
PF
OSCI
Burst-Dimming PWM Frequency
Tolerance
PF
POSC resistor 0.1% over temperature
TOL
BMIN
BMAX
SLOPE = 0
SLOPE = 1
SLOPE = 0
SLOPE = 1
V
V
BRIGHT Voltage: Minimum
Brightness
V
3.3
3.3
V
BRIGHT Voltage: Maximum
Brightness
V
0
V
Gate-Driver Output Rise/Fall
t /t
R F
C = 600pF
L
100
ns
Note 1: All voltages are referenced to ground unless otherwise noted. Currents into the IC are positive; currents out of the IC are
negative.
Note 2: During fault conditions, if AC-coupled, LCM and OVD can go below ground by up to 1V for up to 1s.
Note 3: Threshold voltage includes the DC bias-voltage offset.
Typical Operating Characteristics
(V
CC
= 5.0V, T = +25°C, unless otherwise noted.)
A
ACTIVE SUPPLY CURRENT
vs. SUPPLY VOLTAGE
ACTIVE SUPPLY CURRENT
vs. TEMPERATURE
INTERNAL FREQUENCY CHANGE
vs. TEMPERATURE
6.0
6.0
5.5
5.0
4.5
4.0
1.0
0.8
5.5
5.0
4.5
4.0
3.5
3.0
DPWM = 100%
0.6
DPWM FREQUENCY
0.4
DPWM = 50%
0.2
V
CC
= 5.5V
0
LAMP FREQUENCY
-0.2
-0.4
-0.6
-0.8
-1.0
V
= 5.0V
= 4.5V
CC
DPWM = 10%
GATE Q = 4.5nC
V
CC
GATE Q = 4.5nC
C
f
= 49.6kHz
LOSC
C
DPWM = 100%
SVM TRIPPED
f
= 49.6kHz
LOSC
4.5
4.7
4.9
5.1
5.3
5.5
-40.0
22.5
TEMPERATURE (°C)
85.0
-40.0
22.5
85.0
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
_______________________________________________________________________________________
3
Low-Cost CCFL Controller
Typical Operating Characteristics (continued)
(V
CC
= 5.0V, T = +25°C, multilamp configuration, unless otherwise noted.)
A
PUSH-PULL TYPICAL OPERATION
PUSH-PULL TYPICAL STARTUP
WITH SVM
AT V = 12.5V
INV
DS3991 toc04
DS3991 toc05
DS391
20μs
50ms
2.0V
5.0V
GA
GB
SVM
GB
20μs
5.0V
50ms
5.0V
20μs
50ms
2.0V
2.0V
LCM
OVD
LCM
OVD
20μs
2.0V
50ms
2.0V
PUSH-PULL SOFT-START
PUSH-PULL LAMP STRIKE,
EXPANDED VIEW
AT V = 12.5V
INV
DS3991 toc06
DS3991 toc07
0.1ms
5.0V
50ms
5.0V
GA
GB
GA
GB
0.1ms
5.0V
50ms
5.0V
0.1ms
2.0V
50ms
2.0V
LCM
OVD
LCM
OVD
0.1ms
2.0V
50ms
2.0V
PUSH-PULL BURST DIMMING
AT 133Hz, 10%
PUSH-PULL BURST DIMMING
AT 133Hz, 50%
DS3991 toc08
DS3991 toc09
1ms
5.0V
1ms
5.0V
GA
GB
GA
GB
1ms
5.0V
1ms
5.0V
1ms
2.0V
1ms
2.0V
LCM
OVD
LCM
OVD
1ms
2.0V
1ms
2.0V
4
_______________________________________________________________________________________
Low-Cost CCFL Controller
DS391
Typical Operating Characteristics (continued)
(V
CC
= 5.0V, T = +25°C, single-lamp configuration, unless otherwise noted.)
A
HALF-BRIDGE NORMAL OPERATION,
HALF-BRIDGE SOFT-START
AT V = 12.5V
20μs
INV
DS3991 toc10
DS3991 toc11
20μs
50μs
5.0V
5.0V
GA
GB
GA
GB
20μs
5.0V
50μs
5.0V
20μs
50μs
2.0V
2.0V
LCM
OVD
LCM
OVD
20μs
2.0V
50μs
2.0V
HALF-BRIDGE LAMP STRIKE,
HALF-BRIDGE BURST DIMMING
AT 166Hz, 10%
EXPANDED VIEW
DS3991 toc12
DS3991 toc13
0.5ms
5.0V
1ms
5.0V
GA
GB
GA
GB
0.5ms
5.0V
1ms
5.0V
0.5ms
2.0V
1ms
2.0V
LCM
OVD
LCM
OVD
0.5ms
2.0V
1ms
2.0V
HALF-BRIDGE BURST DIMMING
AT 166Hz, 50%
DS3991 toc14
1ms
5.0V
GA
1ms
5.0V
GB
1ms
2.0V
LCM
1ms
2.0V
OVD
_______________________________________________________________________________________
±
Low-Cost CCFL Controller
Pin Description
PIN
NAME
I/O
FUNCTION
BRIGHT Slope Select. This digital input determines the slope of the BRIGHT input when
an analog DC voltage is used to control lamp brightness (PWM_EN = 0).
SLOPE = 0: positive slope (0V = minimum brightness, 3.3V = 100% brightness)
SLOPE = 1: negative slope (0V = 100% brightness, 3.3V = minimum brightness)
1
SLOPE
I
DS391
2, 3, 4
5
VCC
ꢀ
Connect to Voltage Supply. These pins should be connected to the voltage supply pin, VCC.
Lamp Oscillator Resistor Adjust. A resistor (R ) to ground on this pin sets the frequency
LOSC
LOSC
O
of the lamp oscillator (F
). (R
x F
= 4.0E9).
LOSC
LOSC
LOSC
Burst-Dimming PWM Oscillator Resistor Adjust/PWM Digital Input. If PWM_EN = 0, a resistor
(R ) to ground on this pin sets the frequency (F ) of the burst-dimming PWM
POSC/
PWM
POSC
POSC
6
7
8
O/I
oscillator (R
x F
= 4.0E6). If PWM_EN =1, a digital 80Hz to 300Hz PWM signal at
POSC
POSC
this input controls the lamp brightness.
Lamp-Brightness Control. If PWM_EN = 0, a 0V to 3.3V analog DC voltage at this input
controls the brightness of the lamp.
BRIGHT
I
I
PWM Lamp-Brightness Control Enable. This digital input determines whether the BRIGHT or
POSC/PWM input is used to control lamp brightness.
PWM_EN = 0 = PWM disabled (analog DC voltage applied at the BRIGHT input)
PWM_EN = 1 = PWM enabled (digital PWM signal applied at the POSC/PWM input)
PWM_EN
9
GA
GB
O
O
MOSFET Gate Drive A. Drives a logic-level power MOSFET.
MOSFET Gate Drive B. Drives a logic-level power MOSFET.
10
Lamp Current Monitor Input. Lamp current is monitored by a resistor placed in series with
the low-voltage side of the lamp.
11
12
LCM
OVD
I
I
Overvoltage Detection Input. Lamp voltage is monitored by a capacitor divider placed on
the high-voltage side of the lamp.
13
14
GND
VCC
ꢀ
ꢀ
Signal Ground
Voltage Supply, 4.5V to 5.5V
Supply Voltage Monitor High. The DC inverter-supply voltage is monitored by an external
resistor divider. The resistor-divider should be set such that it provides 2V at this pin for the
maximum allowable range of the DC inverter supply. Pulling this input above 2V turns the
lamps off and resets the controller. Connect to GND if not used.
15
16
SVMH
SVML
I
I
Supply Voltage Monitor Low. The DC inverter-supply voltage is monitored by an external
resistor divider. The resistor-divider should be set such that it provides 2V at this pin for the
minimum allowable range of the DC inverter supply. Pulling this input below 2V turns the
lamps off and resets the controller. Connect to VCC if not used.
6
_______________________________________________________________________________________
Low-Cost CCFL Controller
DS391
Main System Block Diagram
UVLO
VREF
VCC (4.5V TO 5.5V)
SYSTEM
ENABLE/
POR
2.0V
2.0V
SVML
SUPPLY VOLTAGE
MONITOR LOW
DS3991
SVMH
SUPPLY VOLTAGE
MONITOR HIGH
CHANNEL FAULT
CHANNEL ENABLE
FAULT
HANDLING
40kHz TO 80kHz
OSCILLATOR ( 5%)
LCM
LAMP CURRENT
MONITOR
LOSC
EXTERNAL RESISTOR
LAMP FREQUENCY SET
CCFL
CONTROLLER
OVD
OVERVOLTAGE
DETECTION
(SEE THE
CCFL CHANNEL
BLOCK
PWM_EN
BRIGHT
ANALOG LAMP
BRIGHTNESS CONTROL
(PWM_EN = 0)
DIAGRAM)
POSITIVE OR
NEGATIVE SLOPE
SELECT
MUX
GA
GB
MOSFET
GATE DRIVERS
SLOPE
POSC
DPWM
SIGNAL
PWM LAMP
BRIGHTNESS CONTROL
(PWM_EN = 1)
80Hz TO 300Hz
OSCILLATOR ( 5%)
RAMP
GENERATOR
GND
EXTERNAL RESISTOR
BURST-DIMMING
FREQUENCY SET
80Hz TO 300Hz
_______________________________________________________________________________________
7
Low-Cost CCFL Controller
CCFL Channel Block Diagram
DS3991
LAMP OUT
CHANNEL ENABLE
CHANNEL FAULT
DS391
400mV
LCM
LAMP OVERCURRENT
LAMP CURRENT MONITOR
2.0V
1.0V
DIGITAL
CCFL
CONTROLLER
LAMP STRIKE AND REGULATION
OVERVOLTAGE
BURST-DIMMING
PWM SIGNAL
64 LAMP CYCLE
INTEGRATOR
OVD
OVERVOLTAGE DETECTOR
LAMP MAXIMUM VOLTAGE REGULATION
1.0V
LAMP FREQUENCY
(40kHz TO 80kHz)
GA
GATE
MOSFET
DRIVERS
GATE DRIVERS
GB
Dimming Control
Detailed Description
The DS3991 uses burst dimming to control the lamp
brightness. During the high period of the DPWM cycle,
the lamp is driven at the selected lamp frequency
(40kHz to 80kHz) as shown in Figure 1. This part of the
cycle is also called the burst period because of the
lamp-frequency burst that occurs during this time.
During the low period of the DPWM cycle, the controller
disables the MOSFET gate drivers so the lamp is not
driven. This causes the current to stop flowing in the
lamp, but the time is short enough to keep the lamp
from de-ionizing. Dimming is increased/decreased by
adjusting (i.e., modulating) the burst-period duty cycle.
At the beginning of each burst-dimming cycle, soft-start
slowly ramps the lamp current to reduce the potential to
create audible transformer noise.
The DS3991 is available for both push-pull and half-
bridge drive topologies. In both drive topologies, the
DS3991 drives two logic-level MOSFETs. The DS3991
alternately turns on the two MOSFETs to create the high-
voltage AC waveform on the secondary. By varying the
duration of the MOSFET turn-on times, the controller is
able to accurately control the amount of current flowing
through the CCFL lamp. See the Typical Push-Pull
Application and Typical Half-Bridge Application figures.
The DS3991 can also drive more than one CCFL lamp
per channel. The Typical Push-Pull Application, Multiple
Lamp Per Channel and Typical Half-Bridge Application,
Multiple Lamp Per Channel figures show an application
driving three lamps.
A series resistor on the low-voltage side of the CCFL
lamp enables current monitoring. The voltage developed
across this resistor is fed to the lamp current monitor
(LCM) input on the DS3991. The DS3991 compares the
resistor voltage against an internal reference voltage to
determine the duty cycle for the MOSFET gates. See the
Main System Block Diagram and the CCFL Channel
Block Diagram for more information.
There are two methods to control the duty cycle and
frequency of the burst-dimming DPWM. If the PWM_EN
pin is tied low, then the analog-control method is
enabled; a 0V to 3.3V analog voltage at the BRIGHT
input pin determines the duty cycle of a digital pulse-
width modulated (DPWM) signal. The frequency of the
DPWM signal is determined by the value of the resistor
tied from the POSC pin to ground. The slope of the
BRIGHT dimming input is either positive or negative
based on whether the SLOPE pin is tied low or high,
respectively.
8
_______________________________________________________________________________________
Low-Cost CCFL Controller
DS391
BURST-DIMMING PWM SIGNAL
(EITHER CREATED INSIDE THE DS3991 OR
SOURCED AT THE POSC/PWM PIN)
80Hz TO 300Hz
LAMP CURRENT
SOFT-START
Figure 1. Digital PWM Dimming and Soft-Start
If the PWM_EN pin is tied high, the digital control
method is enabled and an external PWM signal
between 80Hz and 300Hz is applied at the POSC/PWM
pin to set the brightness of the lamp. In the digital con-
trol method, the SLOPE and BRIGHT pins are not used.
Supply Monitoring
The DS3991 has supply-voltage monitors (SVML and
SVMH) for the inverter’s DC supply (V
) and an
INV
undervoltage lockout for the V
supply to ensure that
CC
voltage levels are adequate for proper operation. The
inverter supply is monitored for overvoltage conditions
at the SVMH pin and undervoltage conditions at the
SVML pin. External resistor-dividers at each SVM input
feed into two comparators, both having 2V thresholds
(see Figure 2). Using the equation below to determine
the resistor values, the SVMH and SVML trip points
Lamp Strike
On lamp strike, the DS3991 boosts the normal operating
lamp frequency by 33%. This is done to increase the
voltage created and help ensure that the lamp strikes.
Once the controller detects that the lamp has struck, the
frequency is returned to the normal lamp frequency.
(V
) can be customized to shut off the inverter when
TRIP
the inverter supply voltage rises above or drops below
specified values.
Setting the Lamp and DPꢀM Frequencies Using
External Resistors
Operating with the inverter supply at too low of a level can
prevent the transformer from reaching the strike voltage
and could potentially cause numerous other problems.
Operating with the inverter voltage at too high of a level
can be damaging to the inverter components. Proper use
of the SVMs can prevent these problems. If desired, the
high and/or low SVMs can be disabled by connecting the
SVMH pin to GND and the SVML pin to VCC.
Both the lamp and DPWM frequencies are set using
external resistors. The resistance required for either fre-
quency can be determined using the following formula:
K
R
=
OSC
f
OSC
where K = 4000kΩ x kHz for lamp frequency calcula-
tions, K = 4kΩ x kHz for DPWM frequency calculations.
Example: Select the resistor values to configure the
DS3991 to have a 50kHz lamp frequency and a 160Hz
DPWM frequency. For the DPWM resistor calculation, K
ꢁ
ꢄ
R
+ R
2
1
V
= 2.0 ꢀ
TRIP
ꢃ
ꢂ
ꢆ
ꢅ
R
1
= 4 kΩ x kHz. For the lamp frequency resistor (R
)
LOSC
The SVMH and SVML are high-impedance inputs and
noise on the inverter supply can cause the monitors to
inadvertently trigger even though the inputs contain hys-
teresis. The user may wish to add a lowpass filter to
reduce the noise present at the SVMH and SVML inputs.
calculation, K = 4000 kΩ x kHz. The formula above can
now be used to calculate the resistor values for R
LOSC
and R
as follows:
POSC
4000kꢀ ꢁ kHz
R
=
= 80kꢀ
The V
monitor is a 5V supply undervoltage lockout
CC
LOSC
50kHz
(UVLO) that prevents operation when the DS3991 does
not have adequate voltage for its analog circuitry to
4kꢀ ꢁ kHz
0.160kHz
operate or to drive the external MOSFETs. The V
CC
R
=
= 25kꢀ
POSC
monitor features hysteresis to prevent V
noise from
CC
_______________________________________________________________________________________
9
Low-Cost CCFL Controller
V
INV
V
INV
R
R
V
R
2
2
SVML
2.0V
SVMH
2.0V
DS3991
V
TRIP
TRIP
1
R
1
DS391
Figure 2. Setting the SVML and SVMH Threshold Voltages
DEVICE AND
INVERTER SUPPLIES
AT PROPER LEVELS?
FAULT STATE
(MUST POWER CYCLE THE DS3991
OR TAKE SVML BELOW 2V OR SVMH
ABOVE 2V TO RESET
YES
THE CCFL CONTROLLER)
STRIKE LAMP
(RAMP AND REGULATE TO
OVD THRESHOLD)
LAMP STRIKE TIMEOUT
(65,536 LAMP CYCLES)
IF LAMP REGULATION
THRESHOLD IS MET
OVERVOLTAGE
(64 LAMP CYCLES)
RUN LAMP
LAMP OVERCURRENT
(INSTANTANEOUS)
(REGULATE LAMP
CURRENT BOUNDED BY
LAMP VOLTAGE)
LAMP-OUT TIMEOUT
(65,536 LAMP CYCLES)
MOSFET GATE DRIVERS ENABLED
Figure 3. Fault-Handling Flowchart
causing spurious operation when V
is near the trip
The lamps do not turn on unless the DS3991 supply
voltage is > 4.5V and the voltage at the supply-voltage
monitor low (SVML) input is > 2V and the supply-volt-
age monitor high (SVMH) input is < 2V.
CC
point. This monitor cannot be disabled by any means.
Fault Monitoring
The DS3991 provides extensive fault monitoring. It can
detect open-lamp, lamp overcurrent, failure to strike,
and overvoltage conditions. Figure 3 shows a flowchart
of how the DS3991 controls and monitors each lamp.
The steps are as follows:
When both the DS3991 and the DC inverter supplies are
at acceptable levels, the DS3991 attempts to strike the
lamps. The DS3991 slowly ramps up the MOSFET gate
duty cycle until the lamp strikes. The controller detects
10 ______________________________________________________________________________________
Low-Cost CCFL Controller
DS391
that the lamp has struck by detecting current flow in the
lamp. If during the strike ramp, the maximum allowable
voltage is reached, the controller stops increasing the
MOSFET gate duty cycle to keep from overstressing the
system. The DS3991 goes into a fault-handling state if
the lamp has not struck after 65,536 lamp cycles. If an
overvoltage event is detected during the strike attempt,
the DS3991 disables the MOSFET gate drivers and
goes into the fault handling state.
Applications Information
Component Selection
External component selection has a large impact on the
overall system performance and cost. The two most
important external components are the transformers
and MOSFETs.
The transformer should be able to operate in the 40kHz
to 80kHz frequency range of the DS3991, and the turns
ratio should be selected so the MOSFET drivers run at
28% to 35% duty cycle during steady-state operation.
The transformer must be able to withstand the high
open-circuit voltage that is used to strike the lamp.
Additionally, its primary/secondary resistance and
inductance characteristics must be considered
because they contribute significantly to determining the
efficiency and transient response of the system. Table 1
shows a transformer specification that has been utilized
for a 12V inverter supply, 438mm x 2.2mm lamp design.
Once the lamp is struck, the DS3991 moves to the run-
lamp stage. In the run-lamp stage, the DS3991 adjusts
the MOSFET gate duty cycle to optimize the lamp cur-
rent. The gate duty cycle is always constrained to keep
the system from exceeding the maximum allowable
lamp voltage. If lamp current ever drops below the
lamp-out reference point for 65,536 lamp cycles, the
lamp is considered extinguished. In this case the MOS-
FET gate drivers are disabled and the device moves to
the fault-handling stage.
The MOSFETs must have a threshold voltage that is low
enough to work with logic-level signals, a low on-resis-
tance to maximize efficiency and limit the MOSFET’s
power dissipation, and a breakdown voltage high
enough to handle the transient. For push-pull topolo-
gies, the breakdown voltage of the MOSFETs should be
a minimum of 3x the inverter voltage supply.
Additionally, the total gate charge must be less than
In the case of a lamp overcurrent, the DS3991 instanta-
neously declares the controller to be in a fault state. If
the DS3991 goes into the fault state, the DS3991 shuts
down. Once a fault state is entered, the controller
remains in that state until one of the following occurs:
• V drops below the UVLO threshold
CC
• SVML input drops below 2.0V
• SVMH input goes above 2.0V
Q , which is specified in the Recommended Operating
G
Conditions table.
Table 1. Transformer Specifications (as used in the Typical Operating Circuits%
PARAMETER
CONDITIONS
(Notes 1, 2, 3)
MIN
TYP
40
MAX
UNITS
Turns Ratio (Secondary/Primary) Push-Pull Type
Turns Ratio (Secondary/Primary) Half-Bridge Type (Note 3)
80
Frequency
40
80
6
kHz
W
Output Power
Output Current
5
8
mA
mꢀ
ꢀ
Primary DCR
Center tap to one end
200
500
12
Secondary DCR
Primary Leakage
Secondary Leakage
Primary Inductance
Secondary Inductance
μH
mH
μH
mH
185
70
500
1000ms (min)
Continuous
2000
1000
Secondary Output Voltage
V
RMS
Note 1: Primary should be bifilar wound with center-tap connection.
Note 2: Turns ratio is defined as secondary winding divided by the sum of both primary windings.
Note 3: This is the nominal turns ratio for driving a 438mm x 2.2mm lamp with a 12V supply. Refer to Application Note 3375 for more
information on push-pull type applications.
______________________________________________________________________________________ 11
Low-Cost CCFL Controller
Typical Operating Circuits
Typical Push-Pull Application
DS391
ON = OPEN
OFF/RESET = CLOSED
INVERTER SUPPLY VOLTAGE
(5V 10% TO 24V 10%)
DEVICE
SUPPLY VOLTAGE
(5V 10%)
VCC
VCC
SVML
SVMH
VCC
VCC
DS3991
ANALOG LAMP
BRIGHTNESS CONTROL
BRIGHT
DUAL POWER MOSFET
PWM_EN
SLOPE
CCFL
LAMP
GA
GB
LOSC
TRANSFORMER
RESISTOR SET
LAMP FREQUENCY
OVERVOLTAGE DETECTION
LAMP CURRENT MONITOR
PWM LAMP BRIGHTNESS
CONTROL (OPTIONAL)
POSC/PWM
OVD
LCM
RESISTOR SET
BURST-DIMMING FREQUENCY
GND
12 ______________________________________________________________________________________
Low-Cost CCFL Controller
DS391
Typical Operating Circuits (continued)
Typical Half-Bridge Application
ON = OPEN
OFF/RESET = CLOSED
INVERTER SUPPLY VOLTAGE
(5V 10% TO 24V 10%)
DEVICE
SUPPLY VOLTAGE
(5V 10%)
VCC
VCC
SVML
SVMH
VCC
VCC
DS3991
ANALOG LAMP
BRIGHTNESS CONTROL
BRIGHT
PWM_EN
SLOPE
GA
GB
CCFL
LAMP
LOSC
TRANSFORMER
RESISTOR SET
LAMP FREQUENCY
DUAL POWER MOSFET
OVERVOLTAGE DETECTION
LAMP CURRENT MONITOR
PWM LAMP BRIGHTNESS
CONTROL (OPTIONAL)
POSC/PWM
OVD
LCM
RESISTOR SET
BURST-DIMMING FREQUENCY
GND
______________________________________________________________________________________ 13
Low-Cost CCFL Controller
Typical Operating Circuits (continued)
Typical Push-Pull Application, Multiple Lamps Per Channel
ON = OPEN
OFF/RESET = CLOSED
INVERTER SUPPLY VOLTAGE
(5V 10% TO 24V 10%)
DEVICE
SUPPLY VOLTAGE
(5V 10%)
DS391
VCC
VCC
SVML
SVMH
VCC
VCC
DUAL POWER MOSFET
DS3991
CCFL
LAMP
A
GA
GB
ANALOG LAMP
BRIGHTNESS
CONTROL
BRIGHT
+5V
CCFL
LAMP
B
PWM_EN
SLOPE
LCM
2N3904
+5V
CCFL
LAMP
C
LOSC
RESISTOR SET
LAMP FREQUENCY
2N3904
+5V
POSC/PWM
RESISTOR SET
BURST-DIMMING
FREQUENCY
2N3904
GND
OVD
14 ______________________________________________________________________________________
Low-Cost CCFL Controller
DS391
Typical Operating Circuits (continued)
Typical Half-Bridge Application, Multiple Lamps Per Channel
ON = OPEN
OFF/RESET = CLOSED
INVERTER SUPPLY VOLTAGE
(5V 10% TO 24V 10%)
DEVICE
SUPPLY VOLTAGE
(5V 10%)
VCC
VCC
SVML
SVMH
VCC
VCC
DS3991
CCFL
LAMP
A
GA
GB
ANALOG LAMP
BRIGHTNESS
CONTROL
BRIGHT
DUAL POWER MOSFET
+5V
CCFL
LAMP
B
PWM_EN
SLOPE
LCM
2N3904
+5V
CCFL
LAMP
C
LOSC
RESISTOR SET
LAMP FREQUENCY
2N3904
+5V
POSC/PWM
RESISTOR SET
BURST-DIMMING
FREQUENCY
2N3904
GND
OVD
______________________________________________________________________________________ 1±
Low-Cost CCFL Controller
Power-Supply Decoupling
Package Information
To achieve best results, it is highly recommended that
a decoupling capacitor be used on pin 14, the IC
power-supply pin. Typical values of decoupling capaci-
tors are 0.01µF or 0.1µF. Use a high-quality, ceramic,
surface-mount capacitor, and mount it as close as pos-
sible to the VCC and GND pins of the IC to minimize
lead inductance. Pins 2, 3, and 4 require connection to
supply voltage (VCC) but do not require any additional
decoupling.
For the latest package outline information, go to
www.maxim-ic.com/DallasPackInfo.
PACKAGE TYPE
DOCUMENT NO.
±6-G2008-001
16 SO (150 mils)
DS391
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2008 Maxim Integrated Products
is a registered trademark of Maxim Integrated Products, Inc.
相关型号：
DS3992Z-09P+T&R
Fluorescent Light Controller, 80kHz Switching Freq-Max, PDSO16, 0.150 INCH, LEAD FREE, SOP-16
MAXIM
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