Rainbow Electronics MAX8759 - Manual (Page 10)

MAX8759
Low-Cost, SMBus, CCFL Backlight Controller
10 ______________________________________________________________________________________
Pin Description
PIN NAME FUNCTION
1 BATT
Supply Input. BATT is the input to the internal 5.35V linear regulator that powers the device. Bypass BATT
to GND with a 0.1µF ceramic capacitor.
2 SDA SMBus Serial Data Input
3 SCL SMBus Serial Clock Input
4 TFLT
Fault-Timer Adjustment Pin. Connect a capacitor from TFLT to GND to set the time-out periods for open-
lamp and secondary overcurrent faults.
5 VALS Ambient-Light-Sensor Supply Pin. Bypass VALS to GND with a 0.1µF capacitor.
6 ALS Ambient-Light-Sensor Input
7 PWMI DPST Control Input
8 PWMO
DPST Buffer Output. Connect a capacitor between PWMO and GND. The capacitor forms a lowpass filter
with an internal 40k
Ω (typ) resistor for filtering the DPST signal.
9 FREQ
Chopping-Frequency Adjustment Pin. Connect a resistor from FREQ to GND to set the DPWM frequency:
f
DPWM = 210Hz × 169kΩ / R
FREQ .
10 COMP
Transconductance Error Amplifier Output. A compensation capacitor connected between COMP and GND
sets the rise and fall time of the lamp-current envelope in DPWM operation.
11 DEL
Adaptive Zero-Crossing-Delay Adjustment Pin. Connect a resistor between DEL and GND to adjust the
range of the zero-crossing delay. Connecting DEL to V
CC disables the zero-crossing delay function.
12 IFB1
Lamp-Current-Feedback Input. The IFB1 sense signal is internally full-wave rectified. IFB1 is compared
with IFB2 and the larger is used for lamp-current regulation. The average value of the rectified signal is
regulated to 785mV (typ) by controlling the on-time of high-side switch. An open-lamp fault is generated if
the peak voltage of IFB1 is below 600mV for a fault delay period set by TFLT.
13 IFB2
Lamp-Current-Feedback Input. The IFB2 sense signal is internally full-wave rectified. IFB1 is compared
with IFB2 and the larger is used for lamp-current regulation. The average value of the rectified signal is
regulated to 800mV (typ) by controlling the on-time of high-side switch. An open-lamp fault is generated if
the peak voltage of IFB2 is below 600mV for a fault-delay period set by TFLT. IFB2 input can be disabled
by connecting IFB2 to V
CC .
14 VFB
Transformer Secondary Voltage-Feedback Input. A capacitive voltage-divider between the high-voltage
terminal of the CCFL tube and GND sets the maximum average lamp voltage during striking and lamp-out
fault. When the peak voltage on VFB exceeds the internal overvoltage threshold, the controller turns on an
internal current sink, discharging the COMP capacitor to limit the switch on-time. The VFB pin is also used
to detect a secondary undervoltage condition. If the peak voltage on VFB is below 230mV continuously for
250µs during the DPWM ON period, the MAX8759 shuts down.
15 ISEC
Transformer Secondary Current-Feedback Input. A current-sense resistor connected between the low-
voltage end of the transformer secondary and the ground sets the maximum secondary current during
short-circuit fault. When the peak voltage on ISEC exceeds the internal overcurrent threshold, the
controller turns on an internal current sink discharging the COMP capacitor.
16 LX1
GH1 Gate-Driver Return. LX1 is the input to the current-limit and zero-crossing comparators. The device
senses the voltage across the low-side MOSFET NL1 to detect primary current zero crossing and primary
overcurrent.
17 GH1 High-Side MOSFET NH1 Gate Driver Output