MAX1739EEP+ Maxim Integrated Products, MAX1739EEP+ Datasheet - Page 19

• 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

The MAX1739/MAX1839 regulate the average current
through the CCFL. The current is sensed through the
sense resistor (R13) at CSAV. The voltage at CSAV is
the half-wave rectified representation of the current
through the lamp (Figure 10). The MAX1739/MAX1839
regulate the average voltage at CSAV (I
and are controlled by either the analog interface or the
SMBus interface. To set the maximum lamp current,
determine R13 as follows:
where I
MINDAC and the wave shape influence the actual max-
imum RMS lamp current. Use an RMS current meter to
make final adjustments to R13.
C
used during startup, maintaining lamp current regula-
tion, and during transients caused by changing the
lamp current setting. The standard C
0.01µF. Larger values limit lamp current overshoot.
Smaller values speed up its response to changes in the
lamp current setting, but can lead to instability for
extremely small values. Very large values of C
Figure 9. Transformer Primary/Secondary Voltage Relationship
CCI
sets the speed of the current control loop that is
CTFB
L,RMS,MAX
TO
πV
2
CT
R4
R5
V
R13 = 0.4304 / I
V
L1
CT
2π
ω
CT
is the average DC voltage at center top
______________________________________________________________________________________
is the maximum RMS lamp current.
T1
V
S
= V
N2A
S(RMS)
N
P
= N
N
Loop Compensation
S
L,RMS,MAX
✕
-NπV
NπV
1.1
N
2
2
P
N2B
CT
✕
CT
VCT
2π
ω
R13, AVG
N = N
CCI
S
/N
P
value is
✕
CCFL Backlight Controllers
R13)
CCI
Wide Brightness Range
increase the delay to strike voltage in DPWM and can
cause loss of regulation in the extreme case. Note that
very large C
C
the waveform shape, overall efficiency, and the maxi-
mum necessary secondary transformer voltage. Low val-
ues of C
using a CCFL with a large difference between its restrike
voltage and its operating voltage (characteristic of long
narrow CCFLs) during DPWM. A low value of C
improves stability when the lamp’s operating voltage
drops with an increase in lamp current. However, low
values of C
former voltage. C
Royer frequency, Royer Q value, and overall efficiency.
C
affects DPWM transients and operation in fault condi-
tions. If DPWM is not used, the voltage control loop
should only be active during fault conditions. The stan-
dard value of C
of C
response and not cause excessive ringing at the begin-
ning of a DPWM pulse. Note that the worst-case fault
Figure 10. Current-Sense Waveforms
6
CCV
not only affects loop compensation, but it also affects
I
CCV
R13, AVG
I
L,PK
sets the speed of the voltage control loop that
6
necessary to set an acceptable fault transient
T1
improve loop stability, especially in systems
6
CCV
2π
ω
I
L, RMS, MAX
increase the maximum necessary trans-
C6
CCV
can do the same thing.
7
interacts with C
is 3300pF. Use the smallest value
= 0.04304
R13
CCFL
-I
I
L,PK
L,PK
6
D5A
2π
ω
and affects the
D5B
R13
CSAV
I
6
L,RMS
also
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