DS3992Z-09P [MAXIM]
Two-Channel, Push-Pull CCFL Controller; 双通道，推挽式CCFL控制器
| 型号： | DS3992Z-09P |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Two-Channel, Push-Pull CCFL Controller |
| 文件： | 总13页 (文件大小：226K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
Rev 0; 9/06
Two-Channel, Push-Pull CCFL Controller
DS392
General Description
Features
ꢀ Two-Channel CCFL Controller for Backlighting
The DS3992 is a low-cost, two-channel controller for
cold-cathode fluorescent lamps (CCFLs) that are used
to backlight liquid crystal displays (LCDs). The DS3992
can drive multiple CCFLs per channel, making it ideal
for 4- and 6-lamp LCD PC monitor and TV applications.
LCD Panels for PC Monitors and LCD-TVs
ꢀ Minimal BOM Provides Low-Cost Inverter Solution
ꢀ Per-Channel Lamp Fault Monitoring for Lamp-
Open, Lamp Overcurrent, Failure to Strike, and
Overvoltage Conditions
The DS3992 uses a push-pull drive scheme to convert a
ꢀ Accurate (±±10% On-Board Oscillator for Lamp
DC voltage (5V to 24V) to the high voltage (300V
to
RMS
Frequency (41kHz to 81kHz%
1400V
) AC waveform that is required to power the
RMS
CCFLs. The push-pull drive scheme uses a minimal
number of external components, which reduces compo-
nent and assembly cost and makes the printed circuit
board (PC board) design easy to implement. The push-
pull drive scheme also provides an efficient DC-to-AC
conversion and produces near-sinusoidal waveforms.
ꢀ Accurate (±±10% On-Board Oscillator for DPꢀM
Burst-Dimming Frequency (91Hz to 221Hz or
±81Hz to 441Hz%
ꢀ Device Supply Undervoltage Lockout
ꢀ Inverter Supply Undervoltage Lockout
ꢀ Burst-Dimming Soft-Start Minimizes Audible
Transformer Noise
ꢀ Strike Frequency Boost
Applications
ꢀ ±110 to < ±10 Dimming Range
ꢀ 4.5V to 5.5V Single-Supply Operation
ꢀ -41°C to +85°C Temperature Range
ꢀ ±6-Pin SO Package (±51 mils%
LCD PC Monitors
LCD-TVs
Ordering Information
DIMMING
FREQUENCY RANGE
PART
TEMP RANGE
BRIGHT POLARITY
PIN-PACKAGE
DS3992Z-09P+
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
90Hz to 220Hz
90Hz to 220Hz
180Hz to 440Hz
180Hz to 440Hz
90Hz to 220Hz
90Hz to 220Hz
180Hz to 440Hz
180Hz to 440Hz
Positive
Negative
Positive
Negative
Positive
Negative
Positive
Negative
16 SO-16 (150 mils)
16 SO-16 (150 mils)
16 SO-16 (150 mils)
16 SO-16 (150 mils)
16 SO-16 (150 mils)
16 SO-16 (150 mils)
16 SO-16 (150 mils)
16 SO-16 (150 mils)
DS3992Z-09N+
DS3992Z-18P+
DS3992Z-18N+
DS3992Z-09P+T&R
DS3992Z-09N+T&R
DS3992Z-18P+T&R
DS3992Z-18N+T&R
+Denotes lead-free package.
T&R denotes tape-and-reel package.
Pin Configuration
TOP VIEW
1
2
3
4
5
6
7
8
16
15
V
V
LOSC
POSC
BRIGHT
SVM
CC
CC
14 OVD2
13
LCM2
12 GB2
Typical Operating Circuits appear at end of data sheet.
DS3992
GA1
GA2
GB1
11
10
9
V
CC
LCM1
OVD1
GND
SO-±51
______________________________________________ Maxim Integrated Products
±
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
±-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Two-Channel, Push-Pull CCFL Controller
ABSOLUTE MAXIMUM RATINGS
Voltage on V
Relative to Ground.......................-0.5V to +6.0V
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range.............................-55°C to +125°C
Soldering Temperature...................See J-STD-020 Specification
CC
Voltage on Any Leads Other
Than V ..............0.5V to (V
+ 0.5V), not to exceed +6.0V
CC
CC
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.
DS392
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
SVM Voltage Range
V
-0.3
-0.3
-0.3
-0.3
V
V
V
SVM
V
V
V
+
+
+
CC
0.3
BRIGHT Voltage Range
LCM Voltage Range
V
BRIGHT
CC
V
V
(Note 2)
(Note 2)
LCM
OVD
0.3
CC
OVD Voltage Range
V
0.3
Gate-Driver Output Charge Loading
Q
20
nC
G
ELECTRICAL CHARACTERISTICS
(V
= +4.5V to +5.5V, T = -40°C to +85°C.)
A
CC
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
16
UNITS
G , G loaded with 600pF, 2 channels
A
B
Supply Current
I
8
mA
V
CC
active
Low-Level Output Voltage (GA, GB)
High-Level Output Voltage (GA, GB)
V
I
= 4mA
0.4
OL
OL
V
-
CC
V
I
= -1mA
V
OH1
OH1
0.4
UVLO Threshold: V
UVLO Threshold: V
UVLO Hysteresis
Rising
Falling
V
4.3
2.1
V
V
CC
CC
UVLOR
UVLOF
UVLOH
V
3.7
1.9
V
100
2.0
mV
V
SVM Falling-Edge Threshold
SVM Hysteresis
V
SVM
V
150
1.35
50
mV
V
SVMH
LCM and OVD DC Bias Voltage
LCM and OVD Input Resistance
Lamp-Off Threshold
V
DCB
R
kΩ
V
DCB
V
LOT
LOC
(Note 3)
(Note 3)
(Note 3)
(Note 3)
1.65
3.15
2.25
2.25
40
1.75
3.35
2.35
2.35
1.85
3.55
2.45
2.45
80
Lamp Over Current
V
V
Lamp Regulation Threshold
OVD Threshold
V
V
LRT
V
V
OVDT
Lamp Frequency Range
f
kHz
LFS:OSC
2
_____________________________________________________________________
Two-Channel, Push-Pull CCFL Controller
DS392
ELECTRICAL CHARACTERISTICS (continued%
(V
= +4.5V to +5.5V, T = -40°C to +85°C.)
CC
A
PARAMETER
SYMBOL
CONDITIONS
LOSC resistor 2ꢀ over temperature
DS3992Z-09P/N
MIN
-10
90
TYP
MAX
+10
220
440
+10
0.5
UNITS
Lamp Frequency Tolerance
DPWM Frequency Range
DPWM Frequency Tolerance
f
ꢀ
LFS:TOL
f
Hz
ꢀ
V
DSR:OSC
DS3992Z-18P/N
180
-10
f
POSC resistor 2ꢀ over temperature
DS3992Z-09P / DS3992Z-18P
DS3992Z-09N / DS3992Z-18N
DS3992Z-09P / DS3992Z-18P
DS3992Z-09N / DS3992Z-18N
DSR:TOL
BRIGHT Voltage:
Minimum Brightness
V
BMIN
2.0
2.0
BRIGHT Voltage:
Maximum Brightness
V
V
BMAX
0.5
100
44
Gate-Driver Output Rise/Fall Time
GAn and GBn Duty Cycle
Strike Time
t
/ t
F
C = 600pF
L
50
ns
ꢀ
R
t
500
ms
STRIKE
Note ±: All voltages are referenced to ground unless otherwise noted. Currents into the I.C. are positive, out of the I.C. negative.
Note 2: During fault conditions, the AC-coupled feedback values are allowed to be below the Absolute Maximum Rating of the LCM or
OVD pin for up to 1s.
Note 3: Voltage with respect to V
DCB.
Typical Operating Characteristics
(V
= 5.0V, T = +25°C, unless otherwise noted.)
CC
A
ACTIVE SUPPLY CURRENT
vs. SUPPLY VOLTAGE
ACTIVE SUPPLY CURRENT
vs. TEMPERATURE
INTERNAL FREQUENCY CHANGE
vs. TEMPERATURE
9.0
8.5
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
1.0
10.0
9.5
9.0
8.5
8.0
7.5
7.0
6.5
6.0
V
= 5.5V
CC
0.8
0.6
V
= 5.0V
CC
V
= 4.5V
CC
0.4
DPWM
FREQUENCY
0.2
DPWM = 100%
DPWM = 50%
0
-0.2
-0.4
-0.6
-0.8
-1.0
LAMP
FREQUENCY
DPWM = 10%
SVM ≤ 2V
GATE Q = 3.5nC
C
GATE Q = 3.5nC
C
f
= 64kHz
LFOSC
f
= 64kHz
LFOSC
DPWM = 100%
4.5 4.6 4.7 4.8 4.9 5.0 5.1 5.2 5.3 5.4 5.5
SUPPLY VOLTAGE (V)
-40.0
22.5
85.0
-40.0
22.5
TEMPERATURE (°C)
85.0
TEMPERATURE (°C)
_____________________________________________________________________
3
Two-Channel, Push-Pull CCFL Controller
Typical Operating Characteristics (continued)
(V
= 5.0V, T = +25°C, unless otherwise noted.)
A
CC
TYPICAL OPERATION AT 16V
BURST DIMMING AT 150Hz AND 10%
TYPICAL STARTUP WITH SVM
DS392
2ms
2.0V SVM
1ms
5.0V G
10μs
5.0V G
A
A
1ms
10μs
2ms
5.0V G
5.0V G
5.0V G
B
B
B
1ms
2.0V LCM
2ms
2.0V LCM
10μs
2.0V LCM
1ms
2ms
10μs
2.0V OVD
2.0V OVD
2.0V OVD
BURST DIMMING AT 150Hz AND 50%
SOFT-START AT V = 16V
INV
LAMP STRIKE—EXPANDED VIEW
1ms
1ms
50μs
5.0V G
5.0V G
5.0V G
A
A
A
50μs
1ms
1ms
5.0V G
5.0V G
5.0V G
B
B
B
1ms
2.0V LCM
50μs
2.0V LCM
1ms
2.0V LCM
1ms
2.0V OVD
1ms
2.0V OVD
50μs
2.0V OVD
LAMP OUT (LAMP OPENED),
AUTORETRY DISABLED
0.25
5.0V
G
A
0.25
5.0V
G
B
LAMP OPENED
0.25
2.00V LCM
0.25
2.00V OVD
4
_____________________________________________________________________
Two-Channel, Push-Pull CCFL Controller
DS392
Pin Description
PIN
NUMBER
NAME
I/O
FUNCTION
Lamp Oscillator Resistor Adjust. A resistor (R ) to ground on this pin sets the frequency of
LOSC
1
2
3
4
LOSC
⎯
the lamp oscillator (f
). [R
x f
= 1.6E9].
LFS:OSC
LFS:OSC
LOSC
Burst Dimming DPꢀM Oscillator Resistor Adjust. A resistor (RPOSC) to ground on this lead
sets the frequency (f ) of the burst-dimming DPWM oscillator. [R x f = 4.0E6
DSR:OSC
POSC
DSR:OSC
POSC
BRIGHT
SVM
⎯
for DS3992Z-09P and DS3992Z-09N and R
DS3992Z-18N].
x f
= 8.0E6 for DS3992Z-18P and
DSR:OSC
POSC
Lamp Brightness Control. An analog voltage at this input controls the lamp brightness. See
Table 1 for details.
I
I
Supply Voltage Monitor. 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 will turn the lamps off and
reset the controller. Connect to V
if not used.
CC
MOSFET Gate Drive A for Channel ±. Connect directly to the gate of a logic-level mode
n-channel MOSFET.
5
6
7
8
GA1
GB1
O
O
I
MOSFET Gate Drive B for Channel ±. Connect directly to the gate of a logic-level mode
n-channel MOSFET.
Lamp Current Monitor Input for Channel ±. Lamp current is monitored by a resistor placed in
series with the low-voltage side of the lamp.
LCM1
Over Voltage Detection for Channel ±. Lamp voltage is monitored by a capacitor divider
placed on the high-voltage side of the lamp.
OVD1
GND
I
9
⎯
⎯
Signal Ground
10
V
Supply. 4.5V to 5.5V.
CC
MOSFET Gate Drive A for Channel 2. Connect directly to the gate of a logic-level mode
n-channel MOSFET.
11
12
13
14
GA2
GB2
O
O
I
MOSFET Gate Drive B for Channel 2. Connect directly to the gate of a logic-level mode
n-channel MOSFET.
Lamp Current Monitor Input for Channel 2. Lamp current is monitored by a resistor placed in
series with the low-voltage side of the lamp.
LCM2
OVD2
Overvoltage Detection for Channel 2. Lamp voltage is monitored by a capacitor divider
placed on the high-voltage side of the lamp.
I
15
16
V
V
⎯
⎯
Supply. 4.5V to 5.5V.
Supply. 4.5V to 5.5V.
CC
CC
_____________________________________________________________________
5
Two-Channel, Push-Pull CCFL Controller
Functional Diagrams
V
CC
UVLO
VREF
[4.5V TO 5.5V]
SYSTEM
ENABLE /
POR
DS392
DS3992
2.0V
SVM
SUPPLY VOLTAGE
MONITOR
CHANNEL FAULT
CHANNEL ENABLE
FAULT
HANDLING
LCMn
LAMP CURRENT
MONITOR
[20.48MHz TO 40.96MHz]
[40kHz TO 80kHz]
x512
PLL
TWO
LOSC
INDEPENDENT
CCFL
40kHz TO 80kHz
OSCILLATOR (±10%)
OVDn
OVERVOLTAGE
DETECTION
EXTERNAL
RESISTOR LAMP
FREQUENCY SET
CONTROLLERS
(SEE FIGURE 2)
ANALOG
BRIGHTNESS
GAn
BRIGHT
MOSFET
GATE DRIVERS
CONTROL
GBn
DPWM
SIGNAL
90Hz TO 220Hz OR
180Hz TO 440Hz
OSCILLATOR (±10%)
POSC
RAMP
GENERATOR
EXTERNAL
RESISTOR DPWM
FREQUENCY SET
90Hz TO 220Hz OR
180Hz TO 440Hz
GND
Figure 1. DS3992 Functional Diagram
6
_____________________________________________________________________
Two-Channel, Push-Pull CCFL Controller
DS392
Functional Diagrams (continued)
LAMP OUT
CHANNEL ENABLE
400mV
2.0V
LCMn
CHANNEL FAULT
LAMP OVERCURRENT
LAMP CURRENT MONITOR
DIGITAL
CCFL
CONTROLLER
LAMP STRIKE AND REGULATION
OVERVOLTAGE
DIMMING PWM SIGNAL
1.0V
64 LAMP CYCLE
INTEGRATOR
OVDn
512 x LAMP FREQUENCY
[20.48MHz TO 40.96MHz]
OVERVOLTAGE DETECTOR
LAMP MAXIMUM VOLTAGE REGULATION
1.0V
LAMP FREQUENCY
[40kHz TO 80kHz]
GAn
GBn
MOSFET
GATE
DRIVERS
GATE
DRIVERS
Figure 2. DS3992 Per Channel Logic Diagram
external components. The DS3992 is also capable of
controlling more than 1 lamp per channel using a
wired-OR feedback circuit. See the Typical Operating
Circuits section for more information.
Detailed Description
Each DS3992 channel drives two logic-level n-channel
MOSFETs that are connected between the ends of
a step-up transformer and ground (See the Typical
Operating Circuits). The transformer has a center tap
on the primary side that is connected to the DC inverter
voltage supply. The DS3992 alternately turns on the two
MOSFETs to create the high-voltage AC waveform on
the secondary side. By varying the duration of the
MOSFET turn-on times, the DS3992 is able to accurate-
ly control the CCFL current.
Block diagrams of the DS3992 are shown in Figures 1
and 2. More operating details of the DS3992 are dis-
cussed on the following pages of this data sheet.
Dimming Control
The DS3992 uses “burst” dimming to control the lamp
brightness. An analog voltage applied at the BRIGHT
input pin determines the duty cycle of a digital pulse-
width-modulated (DPWM) signal (90Hz to 220Hz for
DS3992Z-09P/DS3992Z-09N and 180Hz to 440Hz for
DS3992Z-18P/DS3992Z-18N). During the high period of
the DPWM cycle, the lamp is driven at the selected
lamp frequency (40kHz to 80kHz) as shown in Figure 3.
This part of the cycle is also called the “burst” period
because of the lamp frequency burst that occurs
A resistor in series with the CCFL’s ground connection
enables current monitoring. The voltage across this
resistor is fed to the lamp current monitor (LCM) input
and compared to an internal reference voltage to deter-
mine the duty cycle for the MOSFET gates.
The DS3992 supports a 1 lamp per channel configura-
tion with fully independent lamp control and minimal
90Hz TO 220Hz
DPWM SIGNAL
OR
180Hz TO 440Hz
LAMP CURRENT
Figure 3. Digital-PWM Dimming and Soft-Start
_____________________________________________________________________
7
Two-Channel, Push-Pull CCFL Controller
Table ±. BRIGHT Analog Dimming Input Configuration
DEVICE
SLOPE
Positive
Negative
MINIMUM BRIGHTNESS
BRIGHT < 0.5V
MAXIMUM BRIGHTNESS
BRIGHT > 2.0V
DS3992Z-09P and DS3992Z-18P
DS3992Z-09N and DS3992Z-18N
BRIGHT > 2.0V
BRIGHT < 0.5V
DS392
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 dim-
ming cycle, there is a soft-start whereby the lamp cur-
rent is slowly ramped to reduce the potential to create
audible transformer noise.
The previous formula can now be used to calculate the
resistor values for R
and R
as follows:
LOSC
POSC
1600kΩ x kHz
R
LOSC
=
= 32kΩ
50kHz
4kΩ x kHz
0.160kHz
R
POSC
=
= 25kΩ
Supply Monitoring
The DS3992 has supply voltage monitors for both the
inverter’s DC supply (V ) and its own V supply to
The slope of the BRIGHT dimming input is either posi-
tive or negative as shown in Table 1. For voltages
between 0.5V and 2.0V, the duty cycle will vary linearly
between the minimum and 100ꢀ.
INV
CC
ensure that both voltage levels are adequate for proper
operation. The inverter supply is monitored for under-
voltage conditions at the SVM pin. An external resistor-
divider at the SVM input feeds into a comparator (see
Figure 1) having a 2V threshold. Using the equation
below to determine the resistor values, the inverter sup-
Lamp Strike
On lamp strike, the DS3992 boosts the normal operat-
ing lamp frequency by 33ꢀ. This is done to increase
the voltage created and help insure that the lamp
strikes. In addition, the maximum strike voltage will be
applied to the lamp for over 500ms. Once the controller
detects that the lamp has struck, the frequency is
returned to the normal lamp frequency.
ply trip point (V
) can be customized to shut off the
TRIP
inverter when the inverter supply voltage drops below
the specified value.
Operating with the inverter voltage at too high of a level
can be damaging to the inverter components. Proper
use of the SVM can prevent this problem. If desired, SVM
can be disabled by connecting the SVM pin to GND.
Setting the Lamp and DPꢀM Frequencies
Using External Resistors
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:
R + R
⎛
⎞
1
2
V
TRIP
= 2.0
⎜
⎝
⎟
⎠
R
1
The V
monitor is a 5V supply undervoltage lockout
CC
K
(UVLO) that prevents operation when the DS3992 does
not have adequate voltage for its analog circuitry to
R
=
OSC
f
OSC
operate or to drive the external MOSFETs. The V
CC
where K = 1600kΩ x kHz for lamp frequency calcula-
tions. When calculating the resistor value for the DPWM
frequency, K will be one of two values depending on
the DS3992 version. If using the -09N/P version (90Hz
to 220Hz) then K = 4kΩ x kHz. K = 8kΩ x kHz for the
-18N/P version (180Hz to 440Hz).
monitor features hysteresis to prevent V
causing spurious operation when V
noise from
CC
is near the trip
CC
point. This monitor cannot be disabled by any means.
Fault Monitoring
The DS3992 provides extensive fault monitoring for
each channel. It can detect open-lamp, lamp overcur-
rent, failure to strike, and overvoltage conditions. Figure
4 shows a flowchart of how the DS3992 controls and
monitors each channel. The steps are as follows:
Example: Selecting the resistor values to configure the
-09P version to have a 50kHz lamp frequency and a
160Hz DPWM frequency: For the DPWM resistor calcula-
tion, K = 4kΩ x kHz. For the lamp-frequency-resistor
) calculation, K = 1600kΩ x kHz, which is always
the lamp frequency K value regardless of the frequency.
The lamps will not turn on unless the DS3992 supply
voltage is > 4.5V and the voltage at the supply voltage
monitor (SVM) input is > 2V.
(R
LOSC
8
_____________________________________________________________________
Two-Channel, Push-Pull CCFL Controller
DS392
DEVICE AND
INVERTER SUPPLIES
AT PROPER LEVELS?
FAULT STATE
[MUST POWER CYCLE THE DS3992
OR TAKE SVM BELOW 2V TO RESET
THE CCFL CONTROLLER]
YES
STRIKE LAMP
LAMP STRIKE TIMEOUT
[RAMP AND REGULATE TO
[65536 LAMP CYCLES]
OVD THRESHOLD]
IF LINE REGULATION
THRESHOLD IS MET
OVERVOLTAGE
[64 LAMP CYCLES]
RUN LAMP
[REGULATE LAMP
CURRENT BOUNDED BY
LAMP VOLTAGE]
LAMP-OUT TIMEOUT
[65,536 LAMP CYCLES]
LAMP OVERCURRENT
[INSTANTANEOUS]
MOSFET GATE DRIVERS ENABLED
RUN LAMP STAGE
Figure 4. Fault-Handling Flowchart
When both the DS3992 and the DC inverter supplies
are at acceptable levels, the DS3992 will attempt to
strike the lamps. The DS3992 slowly ramps up the
MOSFET gate duty cycle until the lamp strikes. The
controller detects 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
will stop increasing the MOSFET gate duty cycle to
keep from overstressing the system. The DS3992 will
go 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 DS3992 will dis-
able the MOSFET gate drivers and go into the fault-
handling state.
In the case of a lamp overcurrent condition, the
DS3992 will instantaneously declare the controller to be
in a fault state. If either channel on the DS3992 goes
into the fault state, only the faulty channel will be shut
down. Once a fault state is entered, the controller will
remain in that state until one of the following occurs:
•
•
V
drops below the UVLO threshold.
CC
The SVM input drops below 2.0V.
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 n-channel MOSFETs.
Once the lamp is struck, the DS3992 moves to the run
lamp stage. In the run lamp stage, the DS3992 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 65536 lamp cycles, then
the lamp is considered extinguished. In this case the
MOSFET gate drivers are disabled and the device
moves to the fault handling stage.
The transformer should be able to operate in the 40kHz
to 80kHz frequency range of the DS3992, and the turns
ratio should be selected so the MOSFET drivers run at
28ꢀ to 35ꢀ duty cycle during steady-state operation.
The transformer must be able to withstand the high
open-circuit voltage that will be used to strike the lamp.
Additionally, its primary/secondary resistance and
inductance characteristics must be considered
because they contribute significantly to determining the
_____________________________________________________________________
9
Two-Channel, Push-Pull CCFL Controller
efficiency and transient response of the system. Table 2
shows a transformer specification that has been utilized
for a 12V inverter supply, 438mm x 2.2mm lamp design.
down voltage high enough to handle the transient. The
breakdown voltage should be a minimum of 3x the
inverter voltage supply. Additionally, the total gate
charge must be less than Q , which is specified in the
G
The n-channel MOSFET must have a threshold voltage
that is low enough to work with logic-level signals, a low
on-resistance to maximize efficiency and limit the n-
channel MOSFET’s power dissipation, and a break-
Recommended Operating Conditions table. These
specifications are easily met by many of the dual n-
channel MOSFETs now available in SO-8 packages.
DS392
Table 2. Transformer Specifications (as Used in the Typical Operating Circuit%
PARAMETER
Turns Ratio (Secondary/Primary)
Frequency
CONDITIONS
(Notes 1, 2, 3)
MIN
TYP
MAX
UNITS
40
40
80
6
kHz
W
Output Power
Output Current
5
8
mA
mΩ
Ω
Primary DCR
Center tap to one end
200
500
12
Secondary DCR
Primary Leakage
µH
mH
µH
mH
Secondary Leakage
Primary Inductance
Secondary Inductance
185
70
500
1000ms minimum
Continuous
2000
1000
Secondary Output Voltage
V
RMS
Note ±: 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: 40:1 is the nominal turns ratio for driving a 438mm x 2.2mm lamp with a 12V supply. Refer to AN3375 for more information.
±1
____________________________________________________________________
Two-Channel, Push-Pull CCFL Controller
DS392
Typical Operating Circuits
Single Per Channel Operating Circuit
INVERTER SUPPLY VOLTAGE
(5V ±10% TO 24V ±10%)
SVM
1
R
LCM
I
x
2
LAMP(RMS
DUAL POWER MOSFET
DEVICE
SUPPLY VOLTAGE
(5V ±10%)
CCFL
LAMP
GA1
GB1
V
V
CC
CC
R
LCM
V
CC
TRANSFORMER
OVERVOLTAGE DETECTION
LAMP CURRENT MONITOR
OVD1
LCM1
ANALOG LAMP
BRIGHTNESS
CONTROL
DUAL POWER MOSFET
DS3992
BRIGHT
LOSC
CCFL
LAMP
GA2
GB2
R
LCM
TRANSFORMER
RESISTOR SET
LAMP FREQUENCY
OVERVOLTAGE DETECTION
LAMP CURRENT MONITOR
OVD2
LCM2
POSC
RESISTOR SET
BURST DIMMING
FREQUENCY
GND
____________________________________________________________________ ±±
Two-Channel, Push-Pull CCFL Controller
Typical Operating Circuits (continued)
Multi-Lamp Per Channel Operating Circuit
ON = OPEN
OFF/RESET = CLOSED
INVERTER SUPPLY VOLTAGE
DS392
(12V ±10% TO 24V ±10%)
SVM
DS3992
1 OF 2 CHANNELS
DUAL N-CHANNEL POWER MOSFET
DEVICE
SUPPLY VOLTAGE
(5V ±10%)
CCFL
LAMP
A
GA
GB
V
V
CC
CC
V
CC
+5V
CCFL
LAMP
B
ANALOG LAMP
BRIGHTNESS
CONTROL
BRIGHT
LOSC
LCM
2N3904
+5V
RESISTOR SET
CCFL
LAMP
C
LAMP FREQUENCY
2N3904
POSC
RESISTOR SET
BURST DIMMING
FREQUENCY
+5V
2N3904
OVD
GND
±2
____________________________________________________________________
Two-Channel, Push-Pull CCFL Controller
DS392
Power-Supply Decoupling
Chip Topology
To achieve best results, it is highly recommended that a
TRANSISTOR COUNT: 53,000
decoupling capacitor be used on pin 10, the IC power-
supply pin. Pins 15 and 16, also V pins, do require
SUBSTRATE CONNECTED TO GROUND
CC
connection to supply voltage, but do not require any
additional decoupling. Typical values of decoupling
capacitors are 0.01µF or 0.1µF. Use a high-quality,
ceramic, surface-mount capacitor, and mount it as
Package Information
For the latest package outline information, go to
close as possible to the V
minimize lead inductance.
and GND pins of the IC to
www.maxim-ic.com/DallasPackInfo.
CC
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ ±3
© 2006 Maxim Integrated Products
is a registered trademark of Maxim Integrated Products, Inc.
is a registered trademark of Dallas Semiconductor Corporation.
Springer
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