MAX1996AETI+ Maxim Integrated Products, MAX1996AETI+ Datasheet - Page 20

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

Specifications of MAX1996AETI+

• Lead Free Status / Rohs Status: Details

The secondary voltages of both transformers are moni-
tored through the two identical capacitive voltage-
dividers (C3/C4 and C13/C11). Dual-diode D6 rectifies
the two sensed voltages and passes the signal to the
VFB pin. A full-wave rectified sinusoidal waveform
appears at the VFB pin. The RMS value of this new VFB
signal is greater than the half-wave rectified signal in
the single-lamp application. To compensate for the
waveform change and the forward-voltage drop in the
diodes, the capacitive voltage-divider ratio must be
decreased. Choose C3 around 10pF to 22pF, and
select C4 according to C4 = V
V
voltage.
High-Efficiency, Wide Brightness
Range, CCFL Backlight Controller
Figure 12. Dual-Lamp Application Circuit
20
T, MAX
C9
______________________________________________________________________________________
C7
C8
is the maximum transformer secondary RMS
R4
D2-1
C5
R3
C10
LX1
BST1
GND
NH1
NL1
MAX1996A
T, MAX
NH2
NL2
/1.33V
✕
BST2
ILIM
LX2
C3, where
C1
C2
D2-2
C6
Careful PC board layout is critical to achieve low
switching losses and clean, stable operation. The high-
voltage and switching-power stages require particular
attention (Figure 13). The high-voltage sections of the
layout need to be well separated from the control cir-
cuit. Most layouts are constrained to long narrow PC
boards, so this separation occurs naturally.
Follow these guidelines for good PC board layout:
1) Keep the high-current paths short and wide, espe-
T1
T2
cially at the ground terminals. This is essential for
stable, jitter-free operation, and high efficiency.
R6
C3
C4
C11
C13
CCFL
CCFL2
R2
R6
VIN
5V TO 28V
ON/OFF
REFERENCE INPUT
CONTROL INPUT
D3
D4
D5
D1
D6
Layout Guidelines
C12
R7
N1
R1
R5