Maxim DS3992Z-09N+ Two-channel, push-pull ccfl controller Datasheet

Rev 0; 9/06
Two-Channel, Push-Pull CCFL Controller
Features
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.
The DS3992 uses a push-pull drive scheme to convert a
DC voltage (5V to 24V) to the high voltage (300VRMS to
1400VRMS) AC waveform that is required to power the
CCFLs. The push-pull drive scheme uses a minimal
number of external components, which reduces component and assembly cost and makes the printed circuit
board (PC board) design easy to implement. The pushpull drive scheme also provides an efficient DC-to-AC
conversion and produces near-sinusoidal waveforms.
Two-Channel CCFL Controller for Backlighting
LCD Panels for PC Monitors and LCD-TVs
Minimal BOM Provides Low-Cost Inverter Solution
Per-Channel Lamp Fault Monitoring for LampOpen, Lamp Overcurrent, Failure to Strike, and
Overvoltage Conditions
Accurate (±10%) On-Board Oscillator for Lamp
Frequency (40kHz to 80kHz)
Accurate (±10%) On-Board Oscillator for DPWM
Burst-Dimming Frequency (90Hz to 220Hz or
180Hz to 440Hz)
Device Supply Undervoltage Lockout
Inverter Supply Undervoltage Lockout
Burst-Dimming Soft-Start Minimizes Audible
Transformer Noise
Strike Frequency Boost
100% to < 10% Dimming Range
4.5V to 5.5V Single-Supply Operation
-40°C to +85°C Temperature Range
16-Pin SO Package (150 mils)
Applications
LCD PC Monitors
LCD-TVs
Ordering Information
TEMP RANGE
DIMMING
FREQUENCY RANGE
DS3992Z-09P+
-40°C to +85°C
90Hz to 220Hz
Positive
16 SO-16 (150 mils)
DS3992Z-09N+
-40°C to +85°C
90Hz to 220Hz
Negative
16 SO-16 (150 mils)
DS3992Z-18P+
-40°C to +85°C
180Hz to 440Hz
Positive
16 SO-16 (150 mils)
DS3992Z-18N+
-40°C to +85°C
180Hz to 440Hz
Negative
16 SO-16 (150 mils)
DS3992Z-09P+T&R
-40°C to +85°C
90Hz to 220Hz
Positive
16 SO-16 (150 mils)
DS3992Z-09N+T&R
-40°C to +85°C
90Hz to 220Hz
Negative
16 SO-16 (150 mils)
DS3992Z-18P+T&R
-40°C to +85°C
180Hz to 440Hz
Positive
16 SO-16 (150 mils)
DS3992Z-18N+T&R
-40°C to +85°C
180Hz to 440Hz
Negative
16 SO-16 (150 mils)
PART
BRIGHT POLARITY
+Denotes lead-free package.
T&R denotes tape-and-reel package.
PIN-PACKAGE
Pin Configuration
TOP VIEW
LOSC 1
16 VCC
POSC 2
15 VCC
BRIGHT 3
Typical Operating Circuits appear at end of data sheet.
14 OVD2
13 LCM2
SVM 4
GA1 5
DS3992
12 GB2
GB1 6
11 GA2
LCM1 7
10 VCC
OVD1 8
9 GND
SO-150
______________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1
DS3992
General Description
DS3992
Two-Channel, Push-Pull CCFL Controller
ABSOLUTE MAXIMUM RATINGS
Voltage on VCC Relative to Ground.......................-0.5V to +6.0V
Voltage on Any Leads Other
Than VCC ..............0.5V to (VCC + 0.5V), not to exceed +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
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.
RECOMMENDED OPERATING CONDITIONS
(TA = -40°C to +85°C.)
PARAMETER
Supply Voltage
SVM Voltage Range
BRIGHT Voltage Range
SYMBOL
MAX
UNITS
4.5
5.5
V
VSVM
-0.3
VCC +
0.3
V
VBRIGHT
-0.3
VCC +
0.3
V
VCC
CONDITIONS
(Note 1)
MIN
TYP
LCM Voltage Range
VLCM
(Note 2)
-0.3
VCC +
0.3
V
OVD Voltage Range
VOVD
(Note 2)
-0.3
VCC +
0.3
V
20
nC
TYP
MAX
UNITS
8
16
mA
0.4
V
Gate-Driver Output Charge Loading
QG
ELECTRICAL CHARACTERISTICS
(VCC = +4.5V to +5.5V, TA = -40°C to +85°C.)
PARAMETER
SYMBOL
CONDITIONS
Supply Current
ICC
GA, GB loaded with 600pF, 2 channels
active
Low-Level Output Voltage (GA, GB)
VOL
IOL = 4mA
High-Level Output Voltage (GA, GB)
VOH1
UVLO Threshold: VCC Rising
VCC 0.4
V
VUVLOR
UVLO Threshold: VCC Falling
VUVLOF
UVLO Hysteresis
VUVLOH
SVM Falling-Edge Threshold
IOH1 = -1mA
MIN
4.3
3.7
V
100
VSVM
1.9
V
2.0
mV
2.1
V
SVM Hysteresis
VSVMH
150
LCM and OVD DC Bias Voltage
VDCB
1.35
mV
V
LCM and OVD Input Resistance
RDCB
50
kΩ
Lamp-Off Threshold
VLOT
(Note 3)
1.65
1.75
1.85
V
Lamp Over Current
VLOC
(Note 3)
3.15
3.35
3.55
V
Lamp Regulation Threshold
VLRT
(Note 3)
2.25
2.35
2.45
V
VOVDT
(Note 3)
2.25
2.35
2.45
V
80
kHz
OVD Threshold
Lamp Frequency Range
2
fLFS:OSC
_____________________________________________________________________
40
Two-Channel, Push-Pull CCFL Controller
DS3992
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +4.5V to +5.5V, TA = -40°C to +85°C.)
PARAMETER
SYMBOL
Lamp Frequency Tolerance
fLFS:TOL
DPWM Frequency Range
fDSR:OSC
DPWM Frequency Tolerance
fDSR:TOL
BRIGHT Voltage:
Minimum Brightness
VBMIN
BRIGHT Voltage:
Maximum Brightness
VBMAX
Gate-Driver Output Rise/Fall Time
tR / tF
MAX
UNITS
LOSC resistor ±2% over temperature
CONDITIONS
MIN
-10
TYP
+10
%
DS3992Z-09P/N
90
220
DS3992Z-18P/N
180
440
POSC resistor ±2% over temperature
-10
+10
DS3992Z-09P / DS3992Z-18P
0.5
DS3992Z-09N / DS3992Z-18N
2.0
DS3992Z-09P / DS3992Z-18P
2.0
DS3992Z-09N / DS3992Z-18N
0.5
CL = 600pF
50
100
GAn and GBn Duty Cycle
44
Strike Time
tSTRIKE
500
Hz
%
V
V
ns
%
ms
Note 1: 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 VDCB.
Typical Operating Characteristics
(VCC = 5.0V, TA = +25°C, unless otherwise noted.)
7.5
7.0
DPWM = 100%
DPWM = 50%
6.5
DPWM = 10%
5.5
SVM ≤ 2V
5.0
4.5
GATE QC = 3.5nC
fLFOSC = 64kHz
4.0
9.5
VCC = 5.0V
VCC = 4.5V
9.0
8.5
8.0
7.5
7.0
6.5
SUPPLY VOLTAGE (V)
-40.0
0.8
0.6
0.4
0.2
DPWM
FREQUENCY
0
-0.2
LAMP
FREQUENCY
-0.4
-0.6
GATE QC = 3.5nC
fLFOSC = 64kHz
DPWM = 100%
-0.8
6.0
4.5 4.6 4.7 4.8 4.9 5.0 5.1 5.2 5.3 5.4 5.5
1.0
DS3992 toc02
VCC = 5.5V
FREQUENCY CHANGE (%)
SUPPLY CURRENT (mA)
8.0
SUPPLY CURRENT (mA)
8.5
6.0
10.0
DS3992 toc01
9.0
INTERNAL FREQUENCY CHANGE
vs. TEMPERATURE
ACTIVE SUPPLY CURRENT
vs. TEMPERATURE
DS3992 toc03
ACTIVE SUPPLY CURRENT
vs. SUPPLY VOLTAGE
22.5
TEMPERATURE (°C)
85.0
-1.0
-40.0
22.5
85.0
TEMPERATURE (°C)
_____________________________________________________________________
3
Typical Operating Characteristics (continued)
(VCC = 5.0V, TA = +25°C, unless otherwise noted.)
1ms
5.0V GA
2ms
2.0V SVM
10μs
5.0V GB
1ms
5.0V GB
2ms
5.0V GB
10μs
2.0V LCM
1ms
2.0V LCM
2ms
2.0V LCM
10μs
2.0V OVD
1ms
2.0V OVD
2ms
2.0V OVD
1ms
5.0V GA
LAMP STRIKE—EXPANDED VIEW
SOFT-START AT VINV = 16V
DS3984 toc08
BURST DIMMING AT 150Hz AND 50%
50μs
5.0V GA
1ms
5.0V GA
1ms
5.0V GB
50μs
5.0V GB
1ms
5.0V GB
1ms
2.0V LCM
50μs
2.0V LCM
1ms
2.0V LCM
1ms
2.0V OVD
50μs
2.0V OVD
1ms
2.0V OVD
DS3992 toc10
LAMP OUT (LAMP OPENED),
AUTORETRY DISABLED
0.25
5.0V GA
0.25
5.0V GB
LAMP OPENED
0.25
2.00V LCM
0.25
2.00V OVD
4
DS3992 toc06
DS3992 toc05
DS3992 toc04
10μs
5.0V GA
TYPICAL STARTUP WITH SVM
BURST DIMMING AT 150Hz AND 10%
_____________________________________________________________________
DS3992 toc09
TYPICAL OPERATION AT 16V
DS3992 toc07
DS3992
Two-Channel, Push-Pull CCFL Controller
Two-Channel, Push-Pull CCFL Controller
PIN
NUMBER
NAME
I/O
1
LOSC
⎯
Lamp Oscillator Resistor Adjust. A resistor (RLOSC) to ground on this pin sets the frequency of
the lamp oscillator (fLFS:OSC). [RLOSC x fLFS:OSC = 1.6E9].
Burst Dimming DPWM Oscillator Resistor Adjust. A resistor (RPOSC) to ground on this lead
sets the frequency (fDSR:OSC) of the burst-dimming DPWM oscillator. [RPOSC x fDSR:OSC = 4.0E6
for DS3992Z-09P and DS3992Z-09N and RPOSC x fDSR:OSC = 8.0E6 for DS3992Z-18P and
DS3992Z-18N].
FUNCTION
2
POSC
⎯
3
BRIGHT
I
Lamp Brightness Control. An analog voltage at this input controls the lamp brightness. See
Table 1 for details.
4
SVM
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 VCC if not used.
5
GA1
O
MOSFET Gate Drive A for Channel 1. Connect directly to the gate of a logic-level mode
n-channel MOSFET.
6
GB1
O
MOSFET Gate Drive B for Channel 1. Connect directly to the gate of a logic-level mode
n-channel MOSFET.
7
LCM1
I
Lamp Current Monitor Input for Channel 1. Lamp current is monitored by a resistor placed in
series with the low-voltage side of the lamp.
8
OVD1
I
Over Voltage Detection for Channel 1. Lamp voltage is monitored by a capacitor divider
placed on the high-voltage side of the lamp.
9
GND
⎯
Signal Ground
10
VCC
⎯
Supply. 4.5V to 5.5V.
11
GA2
O
MOSFET Gate Drive A for Channel 2. Connect directly to the gate of a logic-level mode
n-channel MOSFET.
12
GB2
O
MOSFET Gate Drive B for Channel 2. Connect directly to the gate of a logic-level mode
n-channel MOSFET.
13
LCM2
I
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.
14
OVD2
I
Overvoltage Detection for Channel 2. Lamp voltage is monitored by a capacitor divider
placed on the high-voltage side of the lamp.
15
VCC
⎯
Supply. 4.5V to 5.5V.
16
VCC
⎯
Supply. 4.5V to 5.5V.
_____________________________________________________________________
5
DS3992
Pin Description
Two-Channel, Push-Pull CCFL Controller
DS3992
Functional Diagrams
UVLO
SYSTEM
ENABLE /
POR
VCC
[4.5V TO 5.5V]
VREF
DS3992
2.0V
SVM
SUPPLY VOLTAGE
MONITOR
FAULT
HANDLING
[40kHz TO 80kHz]
LOSC
EXTERNAL
RESISTOR LAMP
FREQUENCY SET
CHANNEL FAULT
CHANNEL ENABLE
LCMn
LAMP CURRENT
MONITOR
[20.48MHz TO 40.96MHz]
x512
PLL
TWO
INDEPENDENT
CCFL
CONTROLLERS
(SEE FIGURE 2)
40kHz TO 80kHz
OSCILLATOR (±10%)
ANALOG
BRIGHTNESS BRIGHT
CONTROL
POSC
EXTERNAL
RESISTOR DPWM
FREQUENCY SET
GAn MOSFET
GBn GATE DRIVERS
90Hz TO 220Hz OR
180Hz TO 440Hz
OSCILLATOR (±10%)
RAMP
GENERATOR
DPWM
SIGNAL
90Hz TO 220Hz OR
180Hz TO 440Hz
Figure 1. DS3992 Functional Diagram
6
OVDn
OVERVOLTAGE
DETECTION
_____________________________________________________________________
GND
Two-Channel, Push-Pull CCFL Controller
LAMP OUT
CHANNEL ENABLE
400mV
CHANNEL FAULT
LCMn
LAMP CURRENT MONITOR
LAMP OVERCURRENT
2.0V
DIGITAL
CCFL
CONTROLLER
DIMMING PWM SIGNAL
512 x LAMP FREQUENCY
[20.48MHz TO 40.96MHz]
LAMP STRIKE AND REGULATION
64 LAMP CYCLE
INTEGRATOR
OVERVOLTAGE
OVDn
OVERVOLTAGE DETECTOR
LAMP MAXIMUM VOLTAGE REGULATION
LAMP FREQUENCY
[40kHz TO 80kHz]
1.0V
1.0V
GATE
DRIVERS
GAn MOSFET
GATE
GBn DRIVERS
Figure 2. DS3992 Per Channel Logic Diagram
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 accurately control the CCFL current.
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 determine the duty cycle for the MOSFET gates.
The DS3992 supports a 1 lamp per channel configuration with fully independent lamp control and minimal
DPWM SIGNAL
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.
Block diagrams of the DS3992 are shown in Figures 1
and 2. More operating details of the DS3992 are discussed 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 pulsewidth-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
90Hz TO 220Hz
OR
180Hz TO 440Hz
LAMP CURRENT
Figure 3. Digital-PWM Dimming and Soft-Start
_____________________________________________________________________
7
DS3992
Functional Diagrams (continued)
DS3992
Two-Channel, Push-Pull CCFL Controller
Table 1. BRIGHT Analog Dimming Input Configuration
SLOPE
MINIMUM BRIGHTNESS
MAXIMUM BRIGHTNESS
DS3992Z-09P and DS3992Z-18P
DEVICE
Positive
BRIGHT < 0.5V
BRIGHT > 2.0V
DS3992Z-09N and DS3992Z-18N
Negative
BRIGHT > 2.0V
BRIGHT < 0.5V
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, there is a soft-start whereby the lamp current is slowly ramped to reduce the potential to create
audible transformer noise.
The slope of the BRIGHT dimming input is either positive 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 100%.
Lamp Strike
On lamp strike, the DS3992 boosts the normal operating lamp frequency by 33%. 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.
Setting the Lamp and DPWM Frequencies
Using External Resistors
Both the lamp and DPWM frequencies are set using
external resistors. The resistance required for either frequency can be determined using the following formula:
ROSC =
K
fOSC
where K = 1600kΩ x kHz for lamp frequency calculations. 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).
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 calculation, K = 4kΩ x kHz. For the lamp-frequency-resistor
(RLOSC) calculation, K = 1600kΩ x kHz, which is always
the lamp frequency K value regardless of the frequency.
8
The previous formula can now be used to calculate the
resistor values for RLOSC and RPOSC as follows:
1600kΩ x kHz
= 32kΩ
50kHz
4kΩ x kHz
RPOSC =
= 25kΩ
0.160kHz
RLOSC =
Supply Monitoring
The DS3992 has supply voltage monitors for both the
inverter’s DC supply (VINV) and its own VCC supply to
ensure that both voltage levels are adequate for proper
operation. The inverter supply is monitored for undervoltage conditions at the SVM pin. An external resistordivider 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 supply trip point (VTRIP) can be customized to shut off the
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.
⎛ R + R2 ⎞
VTRIP = 2.0 ⎜ 1
⎟
⎝
R1 ⎠
The VCC monitor is a 5V supply undervoltage lockout
(UVLO) that prevents operation when the DS3992 does
not have adequate voltage for its analog circuitry to
operate or to drive the external MOSFETs. The VCC
monitor features hysteresis to prevent VCC noise from
causing spurious operation when VCC is near the trip
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 overcurrent, 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:
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.
_____________________________________________________________________
Two-Channel, Push-Pull CCFL Controller
FAULT STATE
[MUST POWER CYCLE THE DS3992
OR TAKE SVM BELOW 2V TO RESET
THE CCFL CONTROLLER]
YES
LAMP OVERCURRENT
[INSTANTANEOUS]
DS3992
DEVICE AND
INVERTER SUPPLIES
AT PROPER LEVELS?
STRIKE LAMP
[RAMP AND REGULATE TO
OVD THRESHOLD]
LAMP STRIKE TIMEOUT
[65536 LAMP CYCLES]
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]
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 disable the MOSFET gate drivers and go into the faulthandling state.
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 current. 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.
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:
• VCC drops below the UVLO threshold.
•
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.
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
28% to 35% 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
DS3992
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.
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 nchannel MOSFET’s power dissipation, and a break-
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 QG, which is specified in the
Recommended Operating Conditions table. These
specifications are easily met by many of the dual nchannel MOSFETs now available in SO-8 packages.
Table 2. Transformer Specifications (as Used in the Typical Operating Circuit )
PARAMETER
Turns Ratio (Secondary/Primary)
CONDITIONS
MIN
(Notes 1, 2, 3)
Frequency
TYP
UNITS
80
kHz
6
W
40
40
Output Power
Output Current
Primary DCR
MAX
5
Center tap to one end
Secondary DCR
8
mA
200
mΩ
500
Ω
Primary Leakage
12
µH
Secondary Leakage
185
mH
Primary Inductance
70
µH
500
mH
Secondary Inductance
Secondary Output Voltage
1000ms minimum
2000
Continuous
1000
VRMS
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: 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.
10
____________________________________________________________________
Two-Channel, Push-Pull CCFL Controller
Single Per Channel Operating Circuit
INVERTER SUPPLY VOLTAGE
(5V ±10% TO 24V ±10%)
SVM
RLCM
1
ILAMP(RMS x 2
DUAL POWER MOSFET
DEVICE
SUPPLY VOLTAGE
(5V ±10%)
CCFL
LAMP
GA1
VCC
VCC
RLCM
VCC
TRANSFORMER
GB1
OVERVOLTAGE DETECTION
OVD1
LAMP CURRENT MONITOR
LCM1
ANALOG LAMP
BRIGHTNESS
CONTROL
BRIGHT
DS3992
DUAL POWER MOSFET
CCFL
LAMP
GA2
LOSC
RLCM
TRANSFORMER
RESISTOR SET
LAMP FREQUENCY
GB2
OVD2
POSC
RESISTOR SET
BURST DIMMING
FREQUENCY
LCM2
OVERVOLTAGE DETECTION
LAMP CURRENT MONITOR
GND
____________________________________________________________________
11
DS3992
Typical Operating Circuits
Two-Channel, Push-Pull CCFL Controller
DS3992
Typical Operating Circuits (continued)
Multi-Lamp Per Channel Operating Circuit
ON = OPEN
OFF/RESET = CLOSED
INVERTER SUPPLY VOLTAGE
(12V ±10% TO 24V ±10%)
SVM
DS3992
1 OF 2 CHANNELS
DUAL N-CHANNEL POWER MOSFET
DEVICE
SUPPLY VOLTAGE
(5V ±10%)
VCC
VCC
CCFL
LAMP
A
GA
VCC
GB
+5V
ANALOG LAMP
BRIGHTNESS
CONTROL
CCFL
LAMP
B
BRIGHT
LCM
2N3904
LOSC
+5V
RESISTOR SET
LAMP FREQUENCY
CCFL
LAMP
C
2N3904
POSC
RESISTOR SET
BURST DIMMING
FREQUENCY
+5V
2N3904
OVD
GND
12
____________________________________________________________________
Two-Channel, Push-Pull CCFL Controller
TRANSISTOR COUNT: 53,000
SUBSTRATE CONNECTED TO GROUND
Package Information
For the latest package outline information, go to
www.maxim-ic.com/DallasPackInfo.
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 ____________________ 13
© 2006 Maxim Integrated Products
is a registered trademark of Maxim Integrated Products, Inc.
is a registered trademark of Dallas Semiconductor Corporation.
Springer
DS3992
Chip Topology
Power-Supply Decoupling
To achieve best results, it is highly recommended that a
decoupling capacitor be used on pin 10, the IC powersupply pin. Pins 15 and 16, also VCC pins, do require
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
close as possible to the VCC and GND pins of the IC to
minimize lead inductance.
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