Rainbow Electronics MAX8709 - Manual (Page 8)

MAX8709
High-Efficiency CCFL Backlight
Controller with SMBus Interface
8 _______________________________________________________________________________________
Pin Description
PIN NAME FUNCTION
1 ILIM
Current-Limit Threshold Adjustment. Connect a resistive voltage-divider between REF or V CC and GND.
The current-limit threshold measured between LX_ and GND is 1/5th the voltage forced at ILIM. The ILIM
adjustment range is 0 to 3V. Connect ILIM to V
CC to select the default current-limit threshold of 0.2V.
2 REF
2V Reference Output. Bypass REF to GND with a 0.1µF ceramic capacitor. REF is discharged to GND
during shutdown.
3 LOT
Lamp-Out Threshold Adjustment. The lamp-out threshold is 30% of the voltage at LOT. The LOT
adjustment range is from 0.5V to V
REF .
4 GND
Analog Ground. The ground return for V CC , REF, and other analog circuitry. Connect GND to PGND
under the IC at the IC’s backside exposed metal pad.
5 ISEC
Secondary Current-Limit Sense Input. The secondary current limit controls the transformer secondary
current even if the IFB sense resistor is shorted. See the Secondary Current Limit (ISEC) section.
6 SDA SMBus Serial Data Input
7 SCL SMBus Serial Clock Input
8 SUS SMBus Suspend Input
9, 10, 11, 23 N.C. No Connection. Not internally connected.
12 V DD
Gate-Driver Supply Input. Connect V DD to V CC , the output of the linear regulator. Bypass V DD with a
0.1µF capacitor to PGND.
13 PGND Power Ground. Gate-driver current flows through this pin.
14 GL2 Low-Side MOSFET NL2 Gate-Driver Output
15 GL1 Low-Side MOSFET NL1 Gate-Driver Output
16 GH1 High-Side MOSFET NH1 Gate-Driver Output
17 LX1
Switching Node Connection. LX1 is the internal gate driver’s (GH1’s) source connection for the high-side
MOSFET NH1. LX1 is also the sense input to the current comparators.
18 BST1
Driver Bootstrap Input for High-Side MOSFET NH1. Connect BST1 through a diode to V
DD
and through a
0.1µF capacitor to LX1 (Figure 1).
19 BST2
Driver Bootstrap Input for High-Side MOSFET NH2. Connect BST2 through a diode to V DD and through a
0.1µF capacitor to LX2 (Figure 1).
20 LX2
Switching Node Connection. LX2 is the internal gate driver’s (GH2’s) source connection for the high-side
MOSFET NH2. LX2 is also the sense input to the current comparators.
21 GH2 High-Side MOSFET NH2 Gate-Driver Output
22 VFB
Lamp Output Feedback Sense Input. The average value on VFB is regulated during startup and open-
lamp conditions to 0.5V by controlling the on-time of high-side switches. A capacitive voltage-divider
between the CCFL lamp output and GND is sensed to set the maximum average lamp output voltage.
24 IFB
Lamp Current-Sense Input. The voltage on IFB is used to regulate the lamp current. If the IFB input falls
below 30% of the LOT voltage for 1.22s, then the MAX8709 activates the lamp-out fault latch.
25 CCI
Current-Loop Compensation Pin. CCI is the output of the current-loop transconductance amplifier (GMI)
that regulates the CCFL current. The CCI voltage controls the time interval during which the full bridge
applies the input voltage (BATT) to the transformer primary. Connect CCI to GND through a 0.1µF
capacitor. CCI is internally discharged to GND in shutdown.