MAX1739EEP+ Maxim Integrated Products, MAX1739EEP+ Datasheet - Page 15

• Manufacturer Part Number: MAX1739EEP+
• Description: Display Drivers Wide Brightness Rang e CCFL Backlight Con
• Manufacturer: Maxim Integrated Products

Specifications of MAX1739EEP+

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

See Digital Interface for instructions on using the
SMBus interface.
MODE has two functions: one is to select the interface
mode as described in Interface Selection, and the other
is to synchronize the DPWM “chopping” frequency to
an external signal to prevent unwanted effects in the
display screen.
To synchronize the DPWM frequency, connect MODE
to VL, REF, or GND through a 10kΩ resistor. Then con-
nect a 500pF capacitor from an AC signal source to
MODE as shown in Figure 6. The synchronization range
is from 32kHz to 100kHz, which corresponds to a
DPWM frequency range of 250Hz to 781Hz (128 MODE
pulses per DPWM cycle). High DPWM frequencies limit
the dimming range. See Loop Compensation for more
information concerning high DPWM frequencies.
The MAX1739/MAX1839 directly drive the two external
MOSFETs used in the Royer oscillator. This has many
advantages over the traditional method that uses bipo-
lar switching and an extra winding on the transformer.
Directly driving the MOSFET eliminates the need for an
extra winding on the transformer, which reduces cost
and minimizes the size of the transformer. Also, driving
the switches directly improves commutation efficiency
and commutation timing. Using MOSFETs for the
switches typically improves overall inverter efficiency
due to lower switch drops.
The Royer topology works as a zero voltage crossing
(ZVC) detector and switches currents between the two
sections of the transformer primary windings. The two
windings work alternately, each generating a half wave
that is transferred to the secondary to produce the full-
Table 3. Brightness Adjustment Ranges (for 33:1 Dimming)
Note: The current-level range is solely determined by the MINDAC-to-REF ratio and is externally set.
BRIGHTNESS
Maximum
Brightness
Minimum
Brightness
Synchronizing the DPWM Frequency
Royer Oscillator MOSFET Drivers
MODE = GND,
V
V
MODE = GND,
V
V
V REF / 3
SCALE ADC
CTL/SCL
CRF/SDA
CTL/SCL
MINDAC
______________________________________________________________________________________
POSITIVE-
=
=
= 0,
MODE = REF,
V
MODE = REF,
V
V
CTL/SCL
CTL/SCL
MINDAC
SCALE ADC
NEGATIVE-
= V
= V REF / 3
= 0
CRF/SDA
CCFL Backlight Controllers
,
Bright [4:0] =
ob11111
Bright [4:0] =
ob00000,
V
V REF / 3
MINDAC
SMBus
Wide Brightness Range
wave sinusoidal lamp voltage and current. The
MAX1739/MAX1839 detect the zero crossing through
the SYNC pin; the threshold is set at 500mV referred to
CS and has a typical delay of 50ns. The active switch-
ing forces commutation very close to the ZVC point and
has better performance than the traditional winding-
based ZVC switchover. Commutation can be further
Figure 5. Brightness Code
=
31
30
29
3
2
1
0
1
Full-scale
DAC OUTPUT =
195.83mV
Zero-scale
DAC OUTPUT =
V
MINDAC
33
32
33
OUTPUT
1
DAC
33
31
33
2
/ 10
33
30
33
3
V
V
V
V
CTL
CRF
CTL
CRF
33
29
33
4
DPWM DUTY
(MODE = REF)
CYCLE
(MODE = GND)
100
(%)
9
30
33
33
3
31
33
33
2
32
33
33
1
COMBINED
LEVEL (%)
POWER
100
1
0
3
15