MAXIM MAX1610

19-1128; Rev 0; 9/96
KIT
ATION
EVALU
E
L
B
A
AVAIL
Digitally Controlled CCFL Backlight
Power Supplies
The MAX1610/MAX1611 are fully integrated, highefficiency drivers for cold-cathode fluorescent lamps
(CCFLs). They operate from a 4.5V to 26V power
source. An on-board, high-switching-frequency power
MOSFET reduces external component count and magnetics size. The MAX1610/MAX1611 protect against
open or shorted lamps. The CCFL can be driven from
an isolated transformer secondary winding to improve
efficiency and avoid flicker at dim tube settings.
Brightness is adjusted by scaling the lamp current, or
by operating with a fixed lamp current and chopping
the CCFL on and off at a rate faster than the eye can
detect.
The MAX1610’s digital inputs increment, decrement, or
clear an internal, 5-bit up/down counter, which sets
CCFL brightness. The MAX1611 uses a System
Management Bus (SMBus) 2-wire serial interface to
directly set CCFL brightness. Both devices include
micropower shutdown and a linear regulator that eliminates the need for a separate logic supply. The digital
interface remains active in shutdown, preserving the
brightness setting.
________________________Applications
Notebook/Laptop Computers
____________________________Features
® Direct Digital Control of CCFL Brightness
® Low Supply Current: 3mA Max Operating
20µA Max Shutdown
® Low-Voltage Operation, Down to 4.5V
® Internal 26V, 0.7W Power Switch
® Protection Against Open or Shorted Lamps
® Supports Isolated Transformer Secondary
Winding
® SMBus Serial Interface (MAX1611)
® No Flicker at Low Brightness (internal 280Hz
current chopping)
® High Power-to-Light Efficiency
® Selectable 290kHz/145kHz Switching Frequency
® Oscillator SYNC Input
® 16-Pin Narrow SO Package
______________Ordering Information
TEMP. RANGE
PART
PIN-PACKAGE
Point-of-Sale Terminals
MAX1610CSE
0°C to +70°C
16 Narrow SO
Portable Medical Equipment
MAX1611CSE
0°C to +70°C
16 Narrow SO
Instrument Displays
__________________________________________________________Pin Configurations
TOP VIEW
UP 1
16 BATT
SDA 1
16 BATT
DN 2
15 LX
SCL 2
15 LX
SHDN 3
SYNC 4
MAX1610
14 BST
SMBSUS 3
13 GND
SYNC 4
SS 5
12 VL
CC 6
11 CS
CSAV 7
10 OTP
MINDAC 8
9
SO
REF
14 BST
MAX1611
13 GND
SS 5
12 VL
CC 6
11 CS
CSAV 7
10 OTP
MINDAC 8
9
REF
SO
________________________________________________________________ Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
MAX1610/MAX1611
_______________General Description
MAX1610/MAX1611
Digitally Controlled CCFL Backlight
Power Supplies
ABSOLUTE MAXIMUM RATINGS
BATT to GND ............................................................-0.3V to 28V
BST to GND ..............................................................-0.3V to 30V
BST to LX ....................................................................-0.3V to 6V
LX to GND ................................................-0.6V to (BATT + 0.3V)
VL to GND...................................................................-0.3V to 6V
CS, CSAV, CC, SYNC, REF, MINDAC,
SS, OTP to GND............................................-0.3V to (VL + 0.3V)
SHDN, UP, DN to GND ...............................................-0.3V to 6V
SMBSUS, SDA, SCL to GND ......................................-0.3V to 6V
BATT, LX Current .....................................................................1A
SDA Current ........................................................................50mA
VL Current ...........................................................................50mA
Continuous Power Dissipation (TA = +70°C)
SO (derate 8.70mW/°C above +70°C) .........................696mW
Operating Temperature Range
MAX1610CSE/MAX1611CSE ..............................0°C to +70°C
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10sec) .............................+300°C
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.
ELECTRICAL CHARACTERISTICS
(TA = 0°C to +70°C, BATT = 8.2V, MINDAC = 0V, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
26
V
1.5
3
mA
10
20
µA
SUPPLY AND REFERENCE
BATT Input Voltage Range
BATT Quiescent Supply Current,
Operate Mode
4.75
BATT = 25V
BATT Quiescent Supply Current,
Shutdown Mode
VL Output Voltage, Operate Mode
4.75V < BATT < 26V
VL Output Voltage, Shutdown Mode
REF Output Voltage
No load
REF Load Regulation
ISOURCE = 100µA
4.25
4.5
4.75
V
3.0
3.6
4.75
V
1.92
2.0
2.08
V
6
20
mV
0.7
1.0
Ω
10
µA
SWITCHING REGULATOR
BATT-to-LX Switch On-Resistance
BST - LX = 4.1V
LX Switch Off-Leakage Current
Oscillator Frequency
SYNC = REF
250
290
330
SYNC = GND
125
145
165
Oscillator SYNC Pin Synchronization Range
240
SYNC High Pulse Width
200
ns
SYNC Low Pulse Width
200
ns
SYNC Input Current
SYNC = GND or VL
350
kHz
-1
SYNC Input Low Voltage
SYNC Input High Voltage
1
µA
0.5
V
4.0
V
Power-Switch Maximum Duty Cycle
SYNC = REF
89
91
SS Source Current
SS = GND
2.5
4.0
SS Sink Current
SS = 0.5V
2
2
kHz
_______________________________________________________________________________________
%
5.5
µA
mA
Digitally Controlled CCFL Backlight
Power Supplies
(TA = 0°C to +70°C, BATT = 8.2V, MINDAC = 0V, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
DAC AND ERROR AMPLIFIER
DAC Resolution
Guaranteed monotonic
5
Bits
MINDAC Input Voltage Range
0
1
V
MINDAC Input Bias Current
-1
1
µA
MINDAC Digital PWM Threshold
3
CSAV Input Voltage Range
CSAV Regulation Point
0
D/A at full scale
232
D/A at 1LSB
V
1.0
247
260
12
CSAV Input Bias Current
-5
5
V
mV
µA
CSAV to CC Voltage-to-Current Converter
Transconductance
CC = 2V, CSAV = 1V, D/A at 1LSB
85
µmho
CC Sink Current
CC = 2V, CSAV = 1V, D/A at 1LSB
80
µA
CC Source Current
CC = 2V, CSAV = 0V, D/A at full scale
20
µA
OPEN AND SHORTED TUBE PROTECTION
OTP Voltage Trip Point
Referred to REF
OTP Input Bias Current
GND < OTP < VL
OTP rising
-20
20
mV
-1
1
µA
CS Overcurrent Cutoff Threshold
500
mV
MAX1610 LOGIC LEVELS
SHDN, UP, DN Input Low Voltage
0.8
SHDN, UP, DN Input High Voltage
2.4
SHDN, UP, DN Input Bias Current
-1
V
V
1
µA
0.8
V
MAX1611 LOGIC LEVELS
SMBSUS, SDA, SCL Input Low Voltage
SMBSUS, SDA, SCL Input High Voltage
2.2
SMBSUS, SDA, SCL Input Bias Current
SDA Output Low Sink Current
-1
VSDA = 0.6V
6
V
1
µA
mA
_______________________________________________________________________________________
3
MAX1610/MAX1611
ELECTRICAL CHARACTERISTICS (continued)
MAX1610/MAX1611
Digitally Controlled CCFL Backlight
Power Supplies
TIMING CHARACTERISTICS—MAX1610
(Figure 1, TA = +25°C, unless otherwise noted.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
UP, DN Pulse Width High
t1
1
µs
UP, DN Pulse Width Low
t2
1
µs
UP, DN Pulse Separation
t3
1
µs
Counter Reset Time
t4
1
µs
TIMING CHARACTERISTICS—MAX1611
(Figures 2 and 3, TA = +25°C, unless otherwise noted.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
SCL Serial Clock High Period
tHIGH
4
µs
SCL Serial Clock Low Period
tLOW
4.7
µs
SCL, SCA Rise Time
tR
(Note 1)
1
µs
SCL, SDA Fall Time
tF
(Note 1)
0.3
µs
Start Condition Setup Time
tSU:STA
4.7
µs
Start Condition Hold Time
tHD:STA
4
µs
SDA Valid to SCL Rising Edge
Setup Time, Slave Clocking in Data
tSU:DAT
500
SCL Falling Edge to SDA
Transition
tHD:DAT
SCL Falling Edge to SDA Valid,
Reading Out Data
(Note 1)
0
tDV
Note 1: Guaranteed by design.
4
ns
_______________________________________________________________________________________
ns
1
µs
Digitally Controlled CCFL Backlight
Power Supplies
1.8
1.9
1.8
1.7
SHDN = VL, OTP = 3V
4.5
VL VOLTAGE (V)
2.0
SHDN = VL, OTP = 3V
BATT CURRENT (mA)
1.6
1.4
1.2
1.0
10
100
1000
3.0
2.0
0
4
8
12
16
20
24
28
0
10
20
30
40
BATT (V)
VL OUTPUT CURRENT (mA)
VL OUTPUT VOLTAGE
vs. VL LOAD CURRENT
BATT SUPPLY CURRENT
vs. BATT VOLTAGE (SHDN = OV)
VL OUTPUT VOLTAGE
vs. BATT VOLTAGE (SHDN = OV)
SHDN = OV
8
BATT = 12V
3.55
3.50
3.45
3.40
3.0
2.5
0
200
400
600
800
3.5
4
3.35
3.30
NO LOAD ON VL,
SHDN = OV
4.5
4.0
6
2
BATT = 5V
5.0
VL (V)
BATT CURRENT (µA)
3.65
3.60
10
MAX1610/1611-TOC4
SHDN = GND
2.0
0
1000
4
8
12
16
20
24
28
BATT (V)
VL LOAD CURRENT (µA)
0
4
8
12
16
20
24
28
BATT (V)
VL OUTPUT VOLTAGE
vs. BATT VOLTAGE (SHDN = VL)
MAX1610/1611-TOC7
5.0
4.5
4.0
VL (V)
0
3.5
REF OUTPUT CURRENT (µA)
3.70
VL VOLTAGE (V)
10000
MAX1610/1611-TOC5
1
BATT = 12V
2.5
1.6
1.5
BATT = 5V
4.0
MAX1610/1611-TOC6
REF OUTPUT VOLTAGE (V)
2.1
5.0
MAX1610/1611-TOC2
SHDN = VL, BATT = 5V
VL OUTPUT VOLTAGE
vs. VL OUTPUT CURRENT
2.0
MAX1610/1611-TOC1
2.2
BATT SUPPLY CURRENT
vs. BATT VOLTAGE (SHDN = VL)
MAX1610/1611-TOC3
REF OUTPUT VOLTAGE
vs. REF OUTPUT CURRENT
3.5
3.0
2.5
NO LOAD ON VL,
SHDN = VL
2.0
0
4
8
12
16
20
24
28
BATT (V)
_______________________________________________________________________________________
5
MAX1610/MAX1611
__________________________________________Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
MAX1610/MAX1611
Digitally Controlled CCFL Backlight
Power Supplies
______________________________________________________________Pin Description
PIN
6
NAME
FUNCTION
MAX1610
MAX1611
1
—
UP
—
1
SDA
System Management Bus Serial Data Input and Open-Drain Output
2
—
DN
Logic-Level Input. A rising edge on DN decrements the 5-bit counter for the 5-bit DAC.
UP = DN = 1 presets the counter to mid-scale.
—
2
SCL
System Management Bus Serial Clock Input
3
—
SHDN
—
3
SMBSUS
4
4
SYNC
5
5
SS
Soft-Start Pin. A 4µA current source feeds the capacitor placed on SS. The voltage on this
pin limits the peak current in the switch. When the lamp is turned off, SS pulls to GND.
6
6
CC
Output of the Voltage-to-Current Converter; Input to the PWM Comparator, which sets the
current limit. A capacitor placed at CC sets the current-regulator-loop bandwidth.
7
7
CSAV
Input to the Voltage-to-Current Converter, which averages the voltage on CSAV using the
capacitor on CC.
8
8
MINDAC
The voltage at MINDAC sets the DAC’s minimum-scale output voltage. Tying MINDAC to
VL enables the internal 280Hz current-chopping mode.
9
9
REF
2.0V Reference Output. Bypass with 0.1µF to GND.
10
10
OTP
Open-Tube Protection Comparator. As long as OTP exceeds the reference voltage, the
N-channel BATT-to-LX switch is forced off.
11
11
CS
Low-Side Current-Sense Input. The current-mode regulator terminates the switch cycle
when the voltage at CS exceeds REF - CC.
12
12
VL
Output of the Internal Linear Regulator. VL can be overdriven by a voltage greater than 4.75V
to operate the chip from +5V ± 5%, and to conserve power. Bypass with 0.1µF to GND.
13
13
GND
System Ground
14
14
BST
Power Input to the High-Side Gate Driver, which switches the internal N-channel MOSFET
on and off.
15
15
LX
Ground Connection for the Internal High-Side Gate Driver; source-connection point for the
internal N-channel MOSFET
16
16
BATT
Logic-Level Input. A rising edge on UP increments the 5-bit counter for the 5-bit DAC.
UP = DN = 1 presets the counter to mid-scale.
Logic-Level Shutdown Input Pin. Applying a logic low to SHDN places the chip in a lowsupply-current shutdown mode.
System Management Bus Suspend Mode Input. SMBSUS Selects one of two chipconfiguration settings, which are preprogrammed serially.
Oscillator Synchronization Input. Tying SYNC to REF sets the oscillator frequency to 290kHz.
Tying SYNC to GND or VL lowers the oscillator frequency to 145kHz.
4.5V to 25V Battery-Voltage Input Point. Connects to the internal N-channel power MOSFET’s
drain, and to the input of the internal linear regulator that powers the chip.
_______________________________________________________________________________________
Digitally Controlled CCFL Backlight
Power Supplies
t2
MAX1610/MAX1611
t1
t4
UP
t3
DN
Figure 1. MAX1610 UP and DN Signal Timing
START
CONDITION
MOST SIGNIFICANT
ADDRESS BIT (A6)
CLOCKED INTO SLAVE
A5 CLOCKED
INTO SLAVE
A4 CLOCKED
INTO SLAVE
A3 CLOCKED
INTO SLAVE
• • •
SCL
tHD:STA
tLOW
tHIGH
• • •
SDA
tSU:STA
tSU:DAT
tHD:DAT
tSU:DAT
tHD:DAT
Figure 2. MAX1611 SMB Serial-Interface Timing—Address
_______________________________________________________________________________________
7
MAX1610/MAX1611
Digitally Controlled CCFL Backlight
Power Supplies
RW BIT
CLOCKED
INTO SLAVE
SCL
ACKNOWLEDGED
BIT CLOCK
INTO MASTER
MOST SIGNIFICANT
BIT CLOCKED
• • •
SLAVE PULLING
SDA LOW
SDA
• • •
tDV
tDV
Figure 3. MAX1611 SMB Serial-Interface Timing—Acknowledge
_______________Detailed Description
Getting Started
A cold-cathode fluorescent lamp (CCFL) has two terminals. For the CCFL to emit light, the two lamp terminals
must be driven with a high-voltage (approximately
550V AC RMS) and high-frequency (approximately
45kHz) sine wave. The MAX1610/MAX1611 use a varying DC input voltage to create this high-voltage, highfrequency sine-wave drive. To select the correct
component values for the MAX1610/MAX1611 circuit,
several CCFL parameters and the minimum DC input
voltage must be specified; these are listed in Table 1.
Table 3 shows the recommended component values to
use with the circuit of Figure 4, depending on the particular CCFL parameters. The C2 values in Table 3
have been selected such that the normal operating
voltage on the secondary of T1 is as close as possible
to the CCFL strike voltage (where the strike voltage
(V S ) is assumed to be approximately 1.8 times the
CCFL operating voltage (VL)).
Components T1, C1, R2, Q1, and Q2 form a Royer
oscillator. A Royer oscillator is a resonant tank circuit
that oscillates at a frequency dependent on C1, the primary magnetizing inductance of T1 (LP ), and the
impedance seen by the T1 secondary. The
MAX1610/MAX1611 regulate the current fed into the
Royer oscillator by sensing the voltage on R1. For a
given current through the Royer oscillator (I R1), the
power delivered to the CCFL depends on the Royer
oscillator frequency. The R1 values in Table 3 have
been selected to ensure that the power into the CCFL
8
does not exceed its maximum rating, despite T1, C1, and
C2 component-value variations. The Royer oscillator
waveforms for the circuit of Figure 4 are shown in Figures
5 and 6.
Analog Circuitry
The MAX1610/MAX1611 maintain fixed CCFL brightness with varying input voltages on BATT by regulating
the current fed into the Royer oscillator. This current is
sensed via resistor R1 between CSAV and GND. An
internal switch from BATT-to-LX pulse-width modulates
at a fixed frequency to servo the CSAV pin to its regulation voltage. The CSAV regulation voltage can be
adjusted via the digital interface to set CCFL brightness. The MAX1610 and MAX1611 differ only in the
digital interface they use to adjust the internal 5-bit digital-to-analog converter (DAC) that sets the CSAV regulation voltage. The minimum-scale (min-scale) CSAV
regulation voltage is resistor adjustable using the MINDAC pin, setting the minimum CCFL brightness. The
D/A setting at MAX1610/MAX1611 power-up is preset
to mid-scale (10000 binary) (Figure 7).
MINDAC Sets the Minimum Scale
The MINDAC pin sets the lowest CCFL brightness
level. The voltage at MINDAC is divided by eight, and
sets the minimum CSAV regulation voltage. For example, in the circuit of Figure 4, R5 (150kΩ) and R6
(51kΩ) form a resistor divider from REF, which sets
MINDAC to 507mV (REF = 2.0V). This sets a minimum
CSAV regulation voltage of 63mV with a full-scale
CSAV regulation voltage of 247mV.
_______________________________________________________________________________________
Digitally Controlled CCFL Backlight
Power Supplies
16
VL
BATT
+
12
C2
D3
C9
MAX1610
MAX1611*
5
SS
C4
C6
CCFL
10
R7
BST
LX
14
15
T1
C7
CC
C3
1
2
3 4
5
R2
D1
C1
R3
OTP
6
L1
D2
6
MAX1610/MAX1611
VIN
10
C5
Q1
Q2
R4
4
9
SYNC
REF
CSAV
R5
8
C8
CS
MINDAC
GND
11
7
R1
13
R6
* DIGITAL INTERFACE NOT SHOWN
Figure 4. Typical Floating-Lamp Application Circuit
Table 1. Necessary CCFL Specifications
SPECIFICATION
UNITS
SYMBOL
DESCRIPTION
VRMS
VS
Although CCFLs typically operate at 550VRMS, a higher voltage
is required initially to light up the tube.
VRMS
VL
Once a CCFL has been struck, the voltage required to maintain
light output falls to approximately 550VRMS. Small tubes may
operate on as little as 250VRMS. The operating voltage of the
CCFL stays relatively constant, even as the tube’s brightness is
varied.
CCFL Maximum Operating
Current (“Lamp Current”)
mARMS
IL
The maximum root-mean-square AC current through a CCFL is
almost always 5mARMS. No DC current is allowed through any
CCFL.
CCFL Maximum Frequency
(“Lamp Frequency”)
kHz
fL
CCFL Minimum Strike Voltage
(“Kick-Off Voltage”)
CCFL Typical Operating Voltage
(“Lamp Voltage”)
DC Power Source Minimum
Input Voltage
V
VMIN
The maximum AC-lamp-current frequency.
The minimum DC input voltage to the MAX1610/MAX1611 circuit
determines the turns ratio required for the DC-AC conversion
transformer. Decreasing the minimum input voltage increases
the size of the transformer required for a given output power.
_______________________________________________________________________________________
9
MAX1610/MAX1611
Digitally Controlled CCFL Backlight
Power Supplies
Table 2. Typical Application Circuit Component Values
a) Resistors
b) Capacitors
TOLERANCE
POWER
RATING
SYMBOL
VALUE
TOLERANCE
WORKING
VOLTAGE
NOTES
(Note)
±1%
1/8W
C1
0.1µF
±20%
±25V
δF ≤ 0.001 @ 1kHz
510Ω
±10%
1/8W
51kΩ
±5%
1/16W
C2
(Note 1)
(pF)
±10%
±3kV
High voltage
R4
8.2kΩ
±5%
1/16W
C3, C5
27nF
±20%
25V
R5
150kΩ
±5%
1/16W
R6
51kΩ
±5%
1/16W
C4, C6,
C7, C8
0.1µF
-20%
25V
Ceramic, larger
values acceptable
R7
20Ω
±10%
1/16W
C9
10µF
-50%
35V
Tantalum, low ESR
SYMBOL
VALUE
R1
R2
R3
c) Other Components
SYMBOL
DESCRIPTION
GENERIC
PART
SURFACE-MOUNT
PART
MANUFACTURER
Q1, Q2
1A NPN switching transistor,
VCEO ≥ 50V
2N2222A
FMMT619, SOT23
Zetex
D1, D3
50mA silicon diode, VBR ≥ 40V
1N4148
CMPD4448, SOT23
Central
D2
1A Schottky diode, VBR ≥ 30V
1N5818
EC10QS04
Nihon
L1
100µH, 1A inductor
CDR125-101
Sumida
T1
6W Royer oscillator transformer, turns ratio 67:1,
secondary (pins 10 and 6) : primary (pins 1 and 3),
primary magnetizing inductance (LP) of 44µH ±20%
CTX110605
Coiltronics
Note: Component values depend on lamp characteristics. See Table 3 to select values.
Table 3. Selecting Circuit Values for Figure 4
fROY (kHz)
VL
(VRMS)
IL
(mARMS)
C2
R1
VCT
(VMAX)
MIN
TYP
MAX
250
3
22pF
1.21Ω
3.63V
50.3
58.6
71.8
250
5
43pF
0.715Ω
3.61V
43.3
49.7
60.3
300
3
18pF
1.18Ω
4.30V
52.1
61.0
75.1
300
5
36pF
0.681Ω
4.14V
45.6
52.8
64.7
450
5
20pF
0.732Ω
6.55V
51.1
59.7
73.3
500
5
18pF
0.715Ω
7.17V
52.1
61.0
75.1
7.29V
52.5
61.8
76.7
8.41V
53.6
63.1
78.1
550
5
18pF
0.665Ω
600
5
15pF
0.698Ω
Note: fROY = Royer oscillator damped resonant oscillation frequency. T1 primary magnetizing inductance (LP) = 44µH ±20%.
VCT = average voltage from the T1 center tap to the emitters of Q1 and Q2 (ignoring Q1, Q2 VCE,SAT).
C1 = 0.1µF ± 20%; C2 = ±10% tolerance; R1 = ±1% tolerance.
10
______________________________________________________________________________________
Digitally Controlled CCFL Backlight
Power Supplies
6V
T1
CENTER-TAP
VOLTAGE
BATT = 10V, IBATT = 0.20A,
MINDAC = 0.5V, D/A VALUE = 11111
FIGURE 4 CIRCUIT, C2 = 15pF,
R1 = 545Ω,
CCFL VL = 500VRMS, BATT = 15V,
MINDAC = 0.5V, D/A VALUE = 10000
0V
SS
VOLTAGE
0V
6V
1A
T1
CENTER-TAP
VOLTAGE
C1
CURRENT
-1A
0V
5µs/div
10ms/div
Figure 5. Royer Oscillator Typical Operating Waveforms for
Circuit of Figure 4
Figure 6. Start-Up Waveforms for Circuit of Figure 4
CSAV REGULATION VOLTAGE
REF / 8 = 250mV
FULL-SCALE
MID-SCALE
MIN-SCALE = MINDAC / 8
00000
00001
00010
00011
00100
00101
00110
00111
01000
01001
01010
01011
01100
01101
01110
01111
10000
10001
10010
10011
10100
10101
10110
10111
11000
11001
11010
11011
11100
11101
11110
11111
OmV
DAC CODE
NOTE: DAC CODE 00000 FORCES THE BATT-TO-LX SWITCH OFF REGARDLESS OF CSAV OR MINDAC VOLTAGE.
Figure 7. CSAV Regulation Voltage Range
______________________________________________________________________________________
11
MAX1610/MAX1611
3V
FIGURE 4 CIRCUIT, C2 = 15pF, IR1 = 462mA,
CCFL VL = 500VRMS
Open-Tube Protection (OTP)
Any real transformer used in a Royer oscillator will have a
maximum-allowed secondary voltage. If the maximumallowed secondary voltage is exceeded, the winding
insulation can break down, leading to permanent transformer damage. The maximum-allowed secondary voltage can be exceeded either when the CCFL drive circuit
is turned on without the CCFL being in place, or when
the CCFL becomes disconnected during normal operation due to a mechanical failure. To protect against these
fault conditions, use the OTP pin to sense the voltage on
the transformer center tap (pin 2 of Figure 4). Whenever
the voltage on OTP exceeds the REF reference voltage,
the BATT-to-LX power switch is forced off.
For example, in Figure 4, the CTX110605 transformer
has a maximum-allowed continuous secondary voltage
of 1340VRMS. D1 and C5 detect the peak voltage on
the center tap of T1. R3 and R4 determine the limit on
the center tap peak voltage. The relationship between
the voltage on the center tap of T1 and the secondary
voltage is diagrammed in Figure 8. Neglecting the
Q1/Q2 saturation voltage and the voltage on the R1
current-sense resistor yields Equation 1:
VCTPK =
VSEC 2
2N
where VSEC is the maximum root-mean-square voltage
allowed on the secondary, N is the secondary-to-primary turns ratio, and VCTPK is the peak voltage on the
transformer center tap.
Block Diagram of the Analog Section
Loop-Compensation Capacitor (CC)
The BATT-to-LX switch turns on at fixed frequency, and
turns off when the current-sense voltage on the CS pin
exceeds CC - REF. As the CC pin voltage rises, the CS
current limit rises as well. A transconductance amplifier
compares the voltage on CSAV to the desired regulation
voltage and outputs a current proportional to this error
to the CC pin. A capacitor from CC to GND sets the
bandwidth of this regulation loop, as shown in Equation 2:
BW =
πVCT
2
2π
ω
85
2πC3
where BW is the bandwidth of the CSAV regulation loop
in kHz, and C3 is the capacitance from CC to GND
in nF.
Soft Start (SS)
Soft start prevents the triggering of OTP upon powerup. Placing a capacitor from SS to GND soft starts the
Royer oscillator by slowly raising the CS current-limit
voltage. Internal circuitry pulls SS to GND during
power-on reset, or whenever the lamp is turned off (DAC
= 00000, shutdown mode, ON-1 = 0, or ON-0 = 0)
(Figures 10 and 11). When SS is not pulled to GND, an
internal 4µA current sources into the capacitor at the
SS pin. This pin is internally diode clamped to REF so
that it rises to a maximum voltage of about 2.7V.
Regardless of the voltage on CC, the CS current-sense
voltage is never allowed to exceed the voltage on SS
divided by 5.
Frequency Selection and Synchronization
The SYNC pin performs two functions: it sets the BATTto-LX switching frequency, and it allows the BATT-to-LX
switching frequency to be synchronized to an external
oscillator. SYNC tied to GND or VL sets a 145kHz
switching frequency; SYNC tied to REF sets a 290kHz
T1 SECONDARY
VOLTAGE (PIN 10–PIN 6)
Figure 9 shows a functional diagram of the analog circuitry in the MAX1610/MAX1611. The chips have identical analog circuitry, and differ only in their digital
interface.
T1 PRIMARY CENTER-TAP
VOLTAGE (PIN 2)
MAX1610/MAX1611
Digitally Controlled CCFL Backlight
Power Supplies
NπVCT
2
-NπVCT
2
2π
ω
NOTE: VCT = AVERAGE VOLTAGE FROM THE T1 CENTER TO THE EMITTERS OF Q1 AND Q2 (IGNORING Q1, Q2 VCE, SAT). ω = 2πfROY.
Figure 8. Transformer Primary/Secondary Voltage Relationship
12
______________________________________________________________________________________
Digitally Controlled CCFL Backlight
Power Supplies
MAX1610/MAX1611
BATT
BST
VL
DMOS
POWER
SWITCH
LEVEL
SHIFTER
4.5V
REG
GND
LX
CS
CSAV
Σ
GM
CC
5-BIT DAC
÷8
REF
MINDAC
(NOTE)
SYNC
+
2.0V
-
÷5
OSC
R
S
Q
4µA
SS
OTP
5
UP (SDA)
DN (SCL)
DIGITAL INTERFACE
SHDN (SMBSUS)
( ) ARE FOR MAX1611
NOTE: CIRCUITRY TO DETECT MINDAC = VL NOT SHOWN. SEE CHOPPING THE LAMP CURRENT SECTION.
Figure 9. Functional Diagram
______________________________________________________________________________________
13
MAX1610/MAX1611
Digitally Controlled CCFL Backlight
Power Supplies
MOST
SIGNIFICANT
ADDRESS BIT
START
CONDITION
LEAST
SIGNIFICANT
SLAVE
ADDRESS BIT ACKNOWLEDGE
MOST
SIGNIFICANT
R/W BIT
DATA BIT
SLAVE
ACKNOWLEDGE
LEAST
SIGNIFICANT
DATA BIT
SCL
SHDNB-0
REGSEL
SDA
D4-0
D3-0
D2-0
D1-0
STDBY-0
SLAVE PULLS
SDA LOW
D0-0
SLAVE PULLS
SDA LOW
Figure 10. MAX1611 Serial-Interface Single-Byte Write Example (REGSEL = 0)
MOST
SIGNIFICANT
ADDRESS BIT
START
CONDITION
LEAST
SIGNIFICANT
SLAVE
ADDRESS BIT ACKNOWLEDGE
MOST
SIGNIFICANT
R/W BIT
DATA BIT
SLAVE
ACKNOWLEDGE
LEAST
SIGNIFICANT
DATA BIT
SCL
REGSEL SHDNB-1
D4-1
SDA
D3-1
D2-1
D1-1
STDBY-1
SLAVE PULLS
SDA LOW
D0-1
SLAVE PULLS
SDA LOW
Figure 11. MAX1611 Serial-Interface Single-Byte Write Example (REGSEL = 1)
switching frequency. Any rising edge on SYNC restarts
a BATT-to-LX switch cycle by forcing the switch on.
________MAX1610 Digital Interface
The MAX1610 contains an internal 5-bit up/down counter
that sets the value of the internal 5-bit DAC. At power-on,
or when both the UP and DN pins are held high simultaneously, the 5-bit up/down counter is preset to 10000
binary, which corresponds to mid-scale. A rising edge
on UP increments the 5-bit up/down counter. A rising
edge on DN decrements the 5-bit up/down counter. The
counter will not roll over on either underflow or overflow.
For example, if the CCFL is at maximum intensity level,
rising edges on UP will not change the output.
The SHDN pin provides a way to lower the MAX1610
supply current to 10µA without resetting the 5-bit
up/down counter. With SHDN = 1, the MAX1610 operates normally with VL at 4.5V. When the BATT-to-LX
power switch operates, an additional 3mA of current
14
(other than the supply current) is consumed through
the BST pin, requiring VL to source at least 4.5mA of
current. With SHDN = 0, all analog circuitry turns off,
except for a coarse regulator that can source up to
500µA from VL. The coarse regulator preserves the
state of the internal logic and keeps the digital interface
active during shutdown (SHDN = 0).
________MAX1611 Digital Interface
A single byte of data written over the Intel System
Management Bus (SMBus™) controls the MAX1611.
Figures 10 and 11 show example single-byte writes. The
MAX1611 contains two 7-bit latches for storing configuration data. Only one of the 7-bit latches is active at a
time. The MAX1611 responds only to its own address,
0101101 binary. The SMBSUS pin selects which of the
two sets of configuration data is used. Figure 12 shows
a schematic diagram of the MAX1611’s digital circuitry.
Notice that the SMBSUS pin selects which one of the
______________________________________________________________________________________
Digitally Controlled CCFL Backlight
Power Supplies
MAX1610/MAX1611
OTPOK
CONTROL
LOGIC
8
SCL
8-BIT
SHIFT REGISTER
SDA
IN
DATA
LE
7
LE
LE
7-BIT LATCH-1
7-BIT LATCH-0
7
VL
7
CLR
SMBSUS
S
A
B
MULTIPLEXER
Y = A WHEN S IS LOW
Q
S
OTPOK
REF
Y
PRE
7
R
D_
OTP
OTP
COMPARATOR
SHDNB
STDBY
5
5-BIT DAC
SS
CIRCUITRY
BIAS
GENERATORS
Figure 12. MAX1611 Serial-Interface Circuitry Block Diagram
______________________________________________________________________________________
15
MAX1610/MAX1611
Digitally Controlled CCFL Backlight
Power Supplies
Table 4. MAX1611 Configuration Byte with REGSEL = 0
BIT
NAME
POR
STATE*
7
REGSEL
—
Register Select. A zero in this bit writes the remaining seven bits into the 7-bit latch-0
(Figure 13).
DESCRIPTION
6
SHDNB-0
0
Complete Shutdown. Pulling SMBSUS low with SHDNB-0 = 0 places the MAX1611 into a
low-quiescent-current shutdown mode, with the reference off and the VL linear-regulator
output switched to a low-current, coarse regulation mode. Pulling SMBSUS low with
SHDNB-0 = 1 puts the MAX1611 into its normal operational mode, with the reference and
internal VL linear regulator fully on. SHDNB-0 supersedes STDBY-0. As long as SHDNB-0 = 0
and SMBSUS = 0, it doesn't matter what STDBY-0 is; the MAX1611 still shuts down.
5
STDBY-0
0
Standby, disables CCFL supply only. As long as SMBSUS stays low and STDBY-0 = 0, the
internal power switch is kept off and SS is held shorted to GND; neither the internal reference nor the linear regulator is affected. With STDBY = 1 and SMBSUS low, the MAX1611
operates normally.
4
3
2
1
0
D4-0
D3-0
D2-0
D1-0
D0-0
1
0
0
0
0
DAC Input Data. With the SMBSUS pin low, bits D4-0 through D0-0 set the DAC.
* Initial register state after power-up.
Table 5. MAX1611 Configuration Byte with REGSEL = 1
BIT
NAME
POR
STATE*
7
REGSEL
—
Register Select. A one in this bit writes the remaining seven bits into the 7-bit latch-1
(Figure 13).
DESCRIPTION
6
SHDNB-1
1
Complete Shutdown. Pulling SMBSUS high with SHDNB-1 = 0 places the MAX1611 into a
low-quiescent-current shutdown mode, with the reference off and the VL linear regulator
output switched to a low-current coarse regulation mode. Pulling SMBSUS high with
SHDNB-1 = 1 puts the MAX1611 into its normal operational mode, with the reference and
internal VL linear regulator fully on. SHDNB-1 supersedes STDBY-1. As long as SHDNB-1 = 0
and SMBSUS = 0, it doesn’t matter what STDBY-1 is; the MAX1611 still shuts down.
5
STDBY-1
1
Standby, disables CCFL supply only. As long as SMBSUS stays high and STDBY-1 = 0,
the internal power switch is kept off and SS is held shorted to GND; neither the internal reference nor the linear regulator is affected. With STDBY-1 = 1 and SMBSUS high, the
MAX1611 operates normally.
4
3
2
1
0
D4-1
D3-1
D2-1
D1-1
D0-1
1
0
0
0
0
DAC Input Data. With the SMBSUS pin high, bits D4-1 through D0-1 set the DAC.
* Initial register state after power-up.
16
______________________________________________________________________________________
Digitally Controlled CCFL Backlight
Power Supplies
MAX1610/MAX1611
LEAST
SIGNIFICANT
SLAVE
ADDRESS BIT ACKNOWLEDGE
MOST
SIGNIFICANT
R/W BIT
DATA BIT
MOST
SIGNIFICANT
ADDRESS BIT
START
CONDITION
SCL
OTPOK
SDA
DA4
DA3
DA2
DA1
DA0
SLAVE PULLS
SDA LOW
MAX1611 DRIVES SDA
Figure 13. MAX1611 Serial-Interface Read Example
Table 6. MAX1611 Status Bits
BIT
NAME
POR
STATE*
FUNCTION
7
OTPOK
1
Latched Open-Tube Detection. OTPOK = 0 indicates that open-tube detection has been
triggered. As soon as the voltage on the OTP pin exceeds REF, the OTPOK bit is cleared.
Reset the OTPOK pin by entering shutdown or standby.
6
5
—
—
—
—
Unused. These bits always return a logic one.
4
3
2
1
0
DA4
DA3
DA2
DA1
DA0
Displays the DAC setting selected by SMBSUS.
* Initial register state after power-up.
two 7-bit registers is used. Tables 4 and 5 describe the
data format for the configuration data.
Status information can be read from the MAX1611
using the SMBus read-byte protocol. Figure 13 shows
an example status read. Table 6 describes the status
information data format.
During shutdown (SMBSUS = 0 and SHDNB-0 = 0, or
SMBSUS = 1 and SHDNB-1 = 0), the MAX1611 serial
interface remains fully functional and can be used to set
either the SHDNB-0 or SHDNB-1 bits in order to return
the MAX1611 to its normal operational state.
_______ Chopping the Lamp Current
Chopping the lamp current allows lower sustainable light
levels without lamp flicker. Intensity is varied by controlling the on-time duty cycle. Tying MINDAC to VL activates a special mode, which allows the CCFL intensity to
be varied by turning the lamp on and off at a frequency
faster than the eye can detect. The SS pin pulls to GND
during off time and rises to 2.7V during on time. During
on time, the CSAV pin regulates to REF / 8 (250mV).
During off time, the BATT-to-LX power switch is forced
off and the CC compensation node goes high impedance. Omit R5, R6, and C4 of the circuit in Figure 4.
In this mode, leave SS floating and increase the CC
capacitance to 0.1µF. Also, insert a 330Ω resistor in series
with D1 (Figure 4) to prevent the open-lamp detection circuit from being tripped by the repeated striking of the
lamp. The SS pin will oscillate at the switching frequency
divided by 1024 (283Hz with SYNC = REF). The intensity
can be varied with the duty cycle at the SS pin. The duty
cycle is set by the DAC in 3% increments. Duty cycle will
vary with intensity. Full-scale yields a 100% duty cycle.
DAC codes 00001, 00010, and 00011 all yield the
______________________________________________________________________________________
17
MAX1610/MAX1611
Digitally Controlled CCFL Backlight
Power Supplies
tance in the Royer resonant tank. Table 8 lists suppliers
for the high-voltage ballast capacitor, C2.
minimum 9% duty cycle. DAC code 00000 shuts off the
lamp entirely (0% duty cycle). Figure 14 shows the
chopped waveforms with the DAC set to mid-scale.
__________ Applications Information
Directly Regulating the Lamp Current
The MAX1610/MAX1611 can directly regulate the CCFL
current by tapping into the secondary of T1 (Figure 15).
This allows more precise setting of the maximum lamp
current (IL). The disadvantage of this approach is that
the secondary-to-ground voltage is twice that shown in
Figure 4, increasing the likelihood of the thermometer
effect, where one end of the lamp is brighter than the
other. Figure 15 uses the same component values as
Figure 4, except for R1, R40, D40, and D41. D40 and
D41 are the same type of diode as D1. R1 should be
0.68Ω ±10% to set a peak current limit of about 735mA.
Use a 107Ω ±1% resistor for R40 to set a lamp current
of 5mARMS. This circuit accepts a wide range of lamp
types without component adjustments.
4V
SS
VOLTAGE
0V
BATT = 15V, MINDAC = VL, SS = OPEN, CC = 0.1µF,
C2 = 15pF, MID-SCALE SETTING, D/A VALUE = 10000
15V
T1
CENTER-TAP
VOLTAGE
0V
500µs/div
Component Suppliers
Table 7 lists three different sources for C1. C1 requires
a low dissipation factor to prevent overheating as energy
is cycled between C1 and the T1 magnetizing induc-
Figure 14. Chopped Waveforms
VIN
C2
16
VL
BATT
+
12
CCFL
D3
C9
SS
C4
10
R7
BST
LX
14
15
CC
C3
2
1
L1
5
R2
D1
C1
R3
OTP
3 4
C7
D2
6
6
T1
MAX1610
MAX1611
5
C6
10
Q1
Q2
C5
R4
4
9
SYNC
REF
CSAV
R5
8
C8
CS
MINDAC
GND
D40
11
7
R1
13
R6
Figure 15. Directly Regulating the CCFL Current
18
D41
______________________________________________________________________________________
R40
Digitally Controlled CCFL Backlight
Power Supplies
MAX1610/MAX1611
Table 7. Capacitor C1 Supplier Information
PART
SUPPLIER
SMD7.3104
WIMA
LOCATION
PHONE
FAX
NOTES/CONTACT
Elmsford, NY
914-347-2474
914-347-7230
Germany
(0621) 8785-0
(0621) 8710457158
Hong Kong
5-70-11-51
58-06-84-74
Dissipation factor (tan δ)
at 1kHz and 20°C ≤ 0.008.
CHEV0025J104
PACCOM
Electronics
Redmond, WA
206-883-9200
206-881-6959
Dissipation factor (tan δ)
at 1kHz ≤ 0.002.
4040N104M250
NOVACAP
Valencia, CA
805-295-5920
805-295-5928
Dissipation factor (tan δ)
at 1kHz and 20°C ≤ 0.0015.
Table 8. Capacitor C2 Supplier Information
PART
SUPPLIER
1808HA330KATMA
GHM1040SL330J3K
AVX/Kyocera
Murata
LOCATION
PHONE
FAX
Olean, NY
716-372-6611
716-372-6316
Vancouver, WA
206-696-2840
206-695-5836
Germany
08131 9004-0
08131 9004-44
Hong Kong
852-363-3303
852-765-8185
Smyrna, GA
404-436-1300
404-436-3030
Germany
49-911-66870
49-911-6687193
Taiwan
886-2-562-4218
886-2-536-6721
302C1812A330K
Metuchen Capacitors, Inc.
Old Bridge, NJ
908-679-3366
908-679-3222
302R29N330K
Johanson Dielectrics
Sylmar, CA
818-364-9800
818-364-6100
___________________Chip Information
TRANSISTOR COUNT : 5457
______________________________________________________________________________________
19
MAX1610/MAX1611
Digitally Controlled CCFL Backlight
Power Supplies
________________________________________________________Package Information
DIM
D
0°-8°
A
0.101mm
0.004in.
e
B
A1
E
C
L
Narrow SO
SMALL-OUTLINE
PACKAGE
(0.150 in.)
H
A
A1
B
C
E
e
H
L
INCHES
MAX
MIN
0.069
0.053
0.010
0.004
0.019
0.014
0.010
0.007
0.157
0.150
0.050
0.244
0.228
0.050
0.016
DIM PINS
D
D
D
8
14
16
MILLIMETERS
MIN
MAX
1.35
1.75
0.10
0.25
0.35
0.49
0.19
0.25
3.80
4.00
1.27
5.80
6.20
0.40
1.27
INCHES
MILLIMETERS
MIN MAX
MIN
MAX
0.189 0.197 4.80
5.00
0.337 0.344 8.55
8.75
0.386 0.394 9.80 10.00
21-0041A
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.
20 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600
© 1996 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.