MAX1996AETI+ Maxim Integrated Products, MAX1996AETI+ Datasheet - Page 15

• Manufacturer Part Number: MAX1996AETI+
• Description: Display Drivers CCFL Backlight Controller
• Manufacturer: Maxim Integrated Products

Specifications of MAX1996AETI+

• Lead Free Status / Rohs Status: Details

The analog interface’s internal ADC uses 1-bit hystere-
sis to keep the lamp from flickering between two codes.
V
required to transition the brightness code as V
increases and can be calculated as follows:
V
transition the brightness code as V
can be calculated as follows:
where n is the brightness code. See Figure 7 for a
graphical representation of the thresholds.
Figure 7. Brightness Code
CTL
CTL
V
mode, MODE = GND)
V
mode, MODE = REF)
V
MODE = GND)
V
mode, MODE = REF)
CTL(TH)
CTL(TH)
CTL(TH)
CTL(TH)
’s negative threshold is the voltage required to
’s positive threshold (V
31
30
29
3
2
1
0
1
= (n + 2) / 33 V
= (33 - n) / 33 V
= n / 33 V
= (31 - n) / 33 V
33
32
33
1
33
31
33
2
______________________________________________________________________________________
CRF
33
30
33
3
V
V
V
V
CTL
CRF
CTL
CRF
(Positive-Scale ADC mode,
CRF
33
29
33
CRF
CRF
4
(MODE = REF)
CTL(TH)
(MODE = GND)
(Positive-Scale ADC
(Negative-Scale ADC
(Negative-Scale ADC
30
33
33
Range, CCFL Backlight Controller
3
CTL
High-Efficiency, Wide Brightness
) is the voltage
31
33
33
2
decreases and
32
33
33
1
1
0
CTL
See the Digital Interface section for instructions on
using the SMBus interface.
Unlike conventional dimming control circuits that have
separate supplies and require additional minimum
brightness circuitry, the MAX1996A provides dedicated
pins for dimming control. The advantages of the
MAX1996A’s analog interface are illustrated in Figure 8.
The analog interface is very simple in that the output
voltage range of the dimming control circuit matches
the input voltage range of the inverter control IC. With
this method, it is possible to guarantee the maximum
dimming range (Figure 9). For the conventional inter-
face, the control voltage and the input voltage have dif-
ferent ranges. To avoid nonuniform lighting across the
CCFL tube, or the thermometer effect, the lower limits of
maximum and minimum control voltages have to be
above the upper limits of the maximum and minimum
input voltages, respectively. Therefore, the useful dim-
ming range is reduced. For the MAX1996A’s analog
interface, the control voltage has the same range as the
input voltage, so the useful dimming range is maxi-
mized.
MODE has two functions: one is to select the interface
mode as described in the Interface Selection section
and the other is to synchronize the DPWM chopping
frequency to an external signal to prevent unwanted
artifacts in the display screen.
To synchronize the DPWM frequency, connect MODE to
V
Figure 8. Analog Interface for Dimming
CC
CONVENTIONAL
, REF, or GND through a 10kΩ resistor. Then connect
INTERFACE
INTERFACE
MAX1996A
Synchronizing the DPWM Frequency
DIMMING
CONTROL
DIMMING
CONTROL
CIRCUIT
CIRCUIT
VCCA
VCCA
REF
0 TO V
CIRCUIT
MIN
DIM
MAX
MINDAC
V
V
V
CRF
CTL
CTL
CONTROLLER
MAX1996A
INVERTER
VCCB
VCCB
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