19-2157; Rev 1; 10/02
High-Efficiency, Wide Brightness
Range, CCFL Backlight Controllers
General Description
The MAX1895/MAX1995 integrated controllers are opti-
mized to drive cold-cathode fluorescent lamps (CCFL)
using a synchronized full-bridge inverter architecture.
Synchronized drive provides near sinusoidal wave-
forms over the entire input range to maximize the life of
CCFLs. The controllers also operate over a wide input
voltage range with high efficiency and broad dimming
range.
The MAX1895/MAX1995 include safety features that
limit the transformer secondary voltage and protect
against single-point fault conditions including lamp-out
and short-circuit faults.
The MAX1895/MAX1995 regulate the CCFL brightness
in three ways: linearly controlling the lamp current, digi-
tal pulse-width modulating (DPWM) the lamp current, or
using both methods simultaneously to achieve the
widest dimming range (>30:1). CCFL brightness can
be controlled with either an analog voltage (both
MAX1895 and MAX1995) or a two-wire SMBus™ com-
patible interface (MAX1895 only).
The MAX1895/MAX1995 directly drive the four external
N-channel power MOSFETs of the full-bridge inverter.
An internal 5.3V linear regulator powers the MOSFET
drivers, the synchronizable DPWM oscillator, and most
of the internal circuitry. The MAX1895/MAX1995 are
available in the space-saving 28-pin thin QFN package
and operate over the -40°C to +85°C temperature
range.
Features
o
Synchronized-to-Resonant Frequency
Good Crest Factor for Longer Lamp Life
Ensures Maximum Strike Capability
o
High Power to Light Efficiency
o
Wide Dimming Range (3 Methods)
Lamp Current Adjust: >3 to 1
Digital PWM (DPWM): >10 to 1
Combined: >30 to 1
o
Feed-Forward for Fast Response to Step Change
of Input Voltage
o
Wide Input Voltage Range (4.6V to 28V)
o
Transformer Secondary Voltage Limiting to
Reduce Transformer Stress
o
Lamp-Out Protection with 2s Timeout
o
Short-Circuit and Other Single-Point Fault
Protections
o
Synchronizable DPWM Frequency
o
Dual-Mode Brightness Control Interface
SMBus Serial Interface (MAX1895 Only)
Analog Interface (Both Devices)
o
High-Accuracy Analog Interface
Separate 100% Brightness Voltage Reference
Pin (CRFSDA)
Separate Minimum Lamp-Current Set-Point Pin
(MINDAC)
o
Small Footprint 28-Pin Thin QFN (5mm x 5mm)
Package
MAX1895/MAX1995
Applications
Notebook Computers
Car Navigation Displays
LCD Monitors
Point-of-Sale Terminals
Portable Display Electronics
Pin Configurations
N.C.
CCI
V
FB
IFB
BATT
28
27
26
CCV
V
CC
TOP VIEW
25
24
23
Ordering Information
PART
MAX1895ETI
MAX1895EGI*
MAX1995ETI
MAX1995EGI*
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
28 Thin QFN 5
✕
5
28 QFN 5
✕
5
28 Thin QFN 5
✕
5
28 QFN 5
✕
5
22
ILIM
REF
MINDAC
GND
MODE
CRF/SDA
CTL/SCL
1
2
3
4
5
6
7
10
11
12
13
14
8
9
21
20
19
GH2
LX2
BST2
BST1
LX1
GH1
GL1
MAX1895
18
17
16
15
*Contact
factory for availability.
Pin Configurations continued at end of data sheet.
SMBus is a trademark of Intel Corp.
N.C.
N.C.
PGND
N.C.
SH/SUS
THIN QFN
________________________________________________________________
Maxim Integrated Products
GL2
V
DD
1
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.
High-Efficiency, Wide Brightness
Range, CCFL Backlight Controllers
MAX1895/MAX1995
ABSOLUTE MAXIMUM RATINGS
BATT to GND..........................................................-0.3V to +30V
BST1, BST2 to GND ...............................................-0.3V to +36V
BST1 to LX1, BST2 to LX2 ........................................-0.3V to +6V
GH1 to LX1 ...............................................-0.3V to (BST1 + 0.3V)
GH2 to LX2 ...............................................-0.3V to (BST2 + 0.3V)
V
CC
, V
DD
to GND .....................................................-0.3V to +6V
REF, ILIM to GND .......................................-0.3V to (V
CC
+ 0.3V)
GL1, GL2 to GND .......................................-0.3V to (V
DD
+ 0.3V)
MINDAC, IFB, CCV, CCI to GND .............................-0.3V to +6V
MODE to GND ...........................................................-6V to +12V
V
FB
to GND..................................................................-6V to +6V
CRF/SDA, CTL/SCL,
SH/SUS
to GND ......................-0.3V to +6V
PGND to GND .......................................................-0.3V to +0.3V
Continuous Power Dissipation (T
A
= +70°C)
28-Pin QFN (derate 20.84mW/°C above +70°C) .......1667mW
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+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
(V
BATT
= 12V, MINDAC = GND, V
CC
= V
DD
, V
SH/SUS
= 5.3V,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at
T
A
= +25°C.) (Note1)
PARAMETER
V
BATT
Input Voltage Range
V
BATT
Quiescent Current
V
BATT
Quiescent Current, Shutdown
V
CC
Output Voltage, Normal Operation
V
CC
Output Voltage, Shutdown
V
CC
Undervoltage Lockout Threshold
V
CC
Undervoltage Lockout Hysteresis
V
CC
POR Threshold
V
CC
POR Hysteresis
REF Output Voltage, Normal Operation
GH1, GH2, GL1, GL2 On-Resistance
GH1, GH2, GL1, GL2 Maximum Output
Current
BST1, BST2 Leakage Current
Input Resonant Frequency
Minimum Off-Time
Maximum Off-Time
Maximum Current-Limit Threshold
LX1-GND, LX2-GND (Fixed)
Maximum Current-Limit Threshold
LX1-GND, LX2-GND (Adjustable)
ILIM = V
CC
V
ILIM
= 0.5V
V
ILIM
= 2.0V
BST_ = 12V, LX_ = 7V
Guaranteed by design
20
200
20
180
80
370
300
30
200
100
400
Rising edge
Falling edge
4.5V < V
CC
< 5.5V, I
LOAD
= 40µA
I
TEST
= 100mA, V
CC
= V
DD
= 5.3V
1.96
0.9
CONDITIONS
V
CC
= V
DD
= V
BATT
V
CC
= V
DD
= open
V
SH
/SUS
= 5.5V
SH
/SUS = 0
V
SH
/SUS
= 5.5V, 6V < V
BATT
< 28V
0 < I
LOAD
< 20mA
SH
/SUS = GND, no load
V
CC
rising (leaving lockout)
V
CC
falling (entering lockout)
4
200
1.75
50
2.00
2
1
5
300
400
40
220
120
430
2.04
6
2.7
5.0
3.5
V
BATT
= 28V
V
BATT
= V
CC
= 5V
6
5.35
4.6
MIN
4.6
5.5
3.2
TYP
MAX
5.5
28
6
6
20
5.5
5.5
4.5
UNITS
V
mA
µA
V
V
V
mV
V
mV
V
Ω
A
µA
kHz
ns
µs
mV
mV
2
_______________________________________________________________________________________
High-Efficiency, Wide Brightness
Range, CCFL Backlight Controllers
ELECTRICAL CHARACTERISTICS (continued)
(V
BATT
= 12V, MINDAC = GND, V
CC
= V
DD
, V
SH/SUS
= 5.3V,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at
T
A
= +25°C.) (Note1)
PARAMETER
Minimum Current-Crossing Threshold
LX1-GND, LX2-GND
Current-Limit Leading-Edge Blanking
D/A Converter Resolution
MINDAC Input Voltage Range
MINDAC Input Bias Current
MINDAC Digital PWM Disable Threshold
IFB Input Voltage Range
V
MINDAC
= 0, DAC code = 11111 binary
IFB Regulation Point
IFB Input Bias Current
IFB Lamp-Out Threshold
IFB to CCI Transconductance
CCI Output Impedance
V
FB
Input Voltage Range
V
FB
Input Bias Current
V
FB
Regulation Point
V
FB
to CCV Transconductance
V
FB
Zero-Voltage Crossing Threshold
CCV Output Impedance
No AC signal on MODE
Digital PWM Chop-Mode Frequency
MODE to DPWM Sync Ratio
Lamp-Out Detection Timeout Timer
(Note 2)
MODE Operating Voltage Range
MODE Input Current
Positive Analog Interface Mode
MODE = GND Threshold (V
CTL/SCL
= 0
sets minimum brightness)
Negative Analog Interface Mode
MODE = REF Threshold (V
CTL/SCL
= 0
sets maximum brightness = 0)
SMBus Interface Mode
MODE = V
CC
Threshold
MODE = GND or V
CC
Sync clock average value on MODE to sync
DPWM oscillator, not in shutdown. (Note 3)
32kHz AC signal on MODE
100kHz AC signal on MODE
f
MODE
/f
DPWM
NO AC signal on MODE
V
IFB
< 0.1V
32kHz AC signal on MODE
100kHz AC signal on MODE
-5.5
-1
2.10
205
1V < V
CCV
< 2.7V
-10
20
220
250
781
128
2.33
2.05
0.66
+11.0
+1
0.6
V
µA
V
2.60
s
235
Hz
V
FB
= 0
-2
-0.5
490
510
40
+10
1V < V
CCI
< 2.5V
V
MINDAC
= 0, DAC code = 00100 binary
V
MINDAC
= 1V, DAC code = 00000 binary
MINDAC = V
CC
Guaranteed monotonic
200
5
0
-2
2.4
0
368
30
180
-2
125
150
100
20
+2
0.5
530
388
50
200
3.5
2
+2
4.0
1.7
408
70
220
+2
175
µA
mV
µS
MΩ
V
µA
mV
µS
mV
MΩ
mV
CONDITIONS
MIN
TYP
6
300
400
MAX
UNITS
mV
ns
Bits
V
µA
V
V
MAX1895/MAX1995
Sync clock average value on MODE to sync
DPWM oscillator, not in shutdown. (Note 3)
Sync clock average value on MODE to sync
DPWM oscillator, not in shutdown. (Note 3)
1.4
V
CC
-
0.6
2.6
V
V
_______________________________________________________________________________________
3
High-Efficiency, Wide Brightness
Range, CCFL Backlight Controllers
MAX1895/MAX1995
ELECTRICAL CHARACTERISTICS (continued)
(V
BATT
= 12V, MINDAC = GND, V
CC
= V
DD
, V
SH/SUS
= 5.3V,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at
T
A
= +25°C.) (Note1)
PARAMETER
MODE AC Signal Amplitude
MODE AC Signal Synchronization Range
CRF/SDA Input Range
CRF/SDA Input Current
CTL/SCL Input Range
CTL/SCL Input Current
A/D Converter Resolution
A/D Converter Hysteresis
SH
/SUS Input Low Voltage
SH
/SUS Input High Voltage
SH
/SUS Input Hysteresis
SH
/SUS Input Bias Current
SDA, SCL Input Low Voltage
SDA, SCL Input High Voltage
SDA, SCL Input Hysteresis
SDA Output Low Sink Current
SCL Serial Clock High Period
SCL Serial Clock Low Period
Start Condition Setup-Time
Start Condition Hold-Time
SDA Valid to SCL Rising-Edge Setup
Time, Slave Clocking in Data
SCL Falling-Edge to SDA Transition
SCL Falling-Edge to SDA Valid, Reading
Out Data
V
CRF/SDA
= 0.4V
T
HIGH
T
LOW
t
SU:STA
t
HD:STA
t
SU:DAT
t
HD:DAT
T
DV
4
4
4.7
4.7
4
250
0
700
2.1
300
2.1
300
-1
+1
0.8
MODE = REF or GND
Guaranteed monotonic
V
CRF/SDA
= 5.5V,
SH
/SUS = V
CC
V
CRF/SDA
= 5.5V,
SH
/SUS = 0
-1
0
-1
5
1
0.8
CONDITIONS
Peak-to-peak (Note 4)
Chopping oscillator synchronized to MODE
MIN
2
32
2.7
TYP
MAX
5
100
5.5
20
+1
V
CRF
/
SDA
+1
UNITS
V
kHz
V
µA
V
µA
bits
LSB
V
V
mV
µA
V
V
mV
mA
µs
µs
µs
µs
ns
ns
ns
ELECTRICAL CHARACTERISTICS
(V
BATT
= 12V, MINDAC = GND, V
CC
= V
DD
, V
SH/SUS
= 5.3V,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note1)
PARAMETER
V
BATT
Input Voltage Range
V
BATT
Quiescent Current
V
BATT
Quiescent Current, Shutdown
CONDITIONS
V
CC
= V
DD
= V
BATT
V
CC
= V
DD
= open
V
SH/SUS
= 5.5V
V
SH/SUS
= 0
V
BATT
= 28V
V
BATT
= V
CC
= 5V
MIN
4.6
5.5
TYP
MAX
5.5
28.0
6
6
20
UNITS
V
mA
µA
4
_______________________________________________________________________________________
High-Efficiency, Wide Brightness
Range, CCFL Backlight Controllers
ELECTRICAL CHARACTERISTICS (continued)
(V
BATT
= 12V, MINDAC = GND, V
CC
= V
DD
, V
SH/SUS
= 5.3V,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note1)
PARAMETER
V
CC
Output Voltage, Normal Operation
V
CC
Output Voltage, Shutdown
V
CC
Undervoltage Lockout Threshold
V
CC
POR Threshold
REF Output Voltage, Normal Operation
GH1, GH2, GL1, GL2 On-Resistance
Maximum Current-Limit Threshold
LX1-GND, LX2-GND (Fixed)
Maximum Current-Limit Threshold
LX1-GND, LX2-GND (Adjustable)
IFB Input Voltage Range
IFB Regulation Point
IFB Input Bias Current
IFB Lamp-Out Threshold
VFB Input Voltage Range
VFB Input Bias Current
VFB Regulation Point
VFB Zero-Voltage Crossing Threshold
SHVSUS Input Low Voltage
SHVSUS Input High Voltage
SDA, SCL Input Low Voltage
SDA, SCL Input High Voltage
SDA Output Low Sink Current
V
CRF/SDA
= 0.4V
2.1
4
2.1
0.8
VFB = 0
V
MINDAC
= 0, DAC code = 11111 binary
CONDITIONS
V
SH/SUS
= 5.5V, 6V < V
BATT
< 28V
0 < I
LOAD
< 20mA
SH/SUS
= GND, no load
V
CC
rising (leaving lockout)
V
CC
rising (entering lockout)
Rising edge
4.5V < V
CC
< 5.5V, I
LOAD
= 40µA
I
TEST
= 100mA
I
LIM
= V
CC
V
ILIM
= 0.5V
V
ILIM
= 2.0V
180
80
360
0
335
-1
120
-2
-0.1
480
-20
4.0
0.9
1.96
2.7
2.04
10
220
120
440
1.7
440
+1
180
+2
+0.1
540
+20
0.8
MIN
5.0
3.5
TYP
MAX
5.5
5.5
4.5
UNITS
V
V
V
V
V
Ω
mV
mV
V
mV
µA
mV
V
µA
mV
mV
V
V
V
V
mA
MAX1895/MAX1995
Note 1:
Specifications to -40°C are guaranteed by design based on final test characterization results.
Note 2:
Corresponds to 512 DPWM cycles or 65536 MODE cycles.
Note 3:
The MODE pin thresholds are only valid while the part is operating. When in shutdown V
REF
= 0 and the part only differenti-
ates between SMB mode and ADC mode. When in shutdown and with ADC mode selected the CRF/SDA and CTL/SCL pins
are at high impedance and will not cause extra supply current when their voltages are not at GND or V
CC
.
Note 4:
The amplitude is measured with the following circuit:
V
AMPLITUDE
> 2V
500pF
MODE
10kΩ
_______________________________________________________________________________________
5
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