MAX1996AETI+ Maxim Integrated Products, MAX1996AETI+ Datasheet - Page 12

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

Specifications of MAX1996AETI+

• Lead Free Status / Rohs Status: Details

The MAX1996A is designed to maintain tight control of
the transformer secondary under all transient conditions
including dropout. To maximize run time, it is desirable
to allow the circuit to operate in dropout at extremely
low battery voltages where the backlight’s performance
is not critical. When V
can lose regulation and run at maximum duty cycle.
Under these circumstances, a transient overvoltage
condition can occur when the AC adapter is suddenly
applied to power the circuit. The feed-forward circuitry
minimizes variations in lamp voltage due to such input
voltage steps. The regulator also clamps the voltage on
V
High-Efficiency, Wide Brightness
Range, CCFL Backlight Controller
12
Figure 4. Functional Diagram
CCI
REFERENCE
CONTROL
. Both features ensure that overvoltage transients
______________________________________________________________________________________
INPUT
INPUT
REF
Transient Overvoltage Protection
CRF/SDA
CTL/SCL
MODE
CCV
V
CCI
IFB
LX2
LX1
GND
ILMIT
FB
0.5V
BATT
GMV
GMI
is very low, the controller
0.15V
CLAMP
CCV
PK_DET
CLAMP
from Dropout
MUX
4mV
GENERATOR
DETECTOR
RAMP
PEAK
IMAX COMP
IMIN COMP
PWM COMP
DPWM
OSC
SMBus
LAMP CURRENT AND
DPWM CONTROL
DPWM
COMP
MAX1996A
CONTROL
LOGIC
do not appear on the transformer when leaving
dropout.
The V
the voltage-ramp generator. As the circuit reaches
dropout, V
ator in order to reach maximum t
further, the control loop loses regulation and V
reach its positive supply rail. The clamp on V
vents this from happening and V
peaks of the PWM ramp. If V
the feed-forward PWM ramp generator loses amplitude
and the clamp drags V
below where V
in dropout. When V
V
on the transformer at the old dropout level. The control
CCI
MINDAC = V
Y = 1, N =0
is still low and the MAX1996A maintains the drive
CCI
CC
SUPPLY
clamp is unique in that it limits at the peaks of
CCI
approaches the peaks of the ramp gener-
CCI
MINDAC
SH/SUS
PGND
BATT
BST1
BST2
GND
GH1
GH2
V
REF
LX1
LX2
GL1
V
GL2
CC
DD
would have been if the circuit were not
BATT
CCI
suddenly steps out of dropout,
BATT
down with it to a voltage
CCI
ON
continues to decrease,
. If V
rides just above the
BATT
CCI
decreases
CCI
tries to
VOLTAGE
INPUT
pre-