MAX8709B Просмотр технического описания (PDF) - Maxim Integrated

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MAX8709B

High-Efficiency CCFL Backlight Controller with SMBus Interface

Maxim Integrated 

High-Efficiency CCFL Backlight

Controller with SMBus Interface

PIN

1

2

3

4

5

6

7

8

9, 10, 11, 23

12

13

14

15

16

17

18

19

20

21

22

24

25

NAME

ILIM

REF

LOT

GND

ISEC

SDA

SCL

SUS

N.C.

VDD

PGND

GL2

GL1

GH1

LX1

BST1

BST2

LX2

GH2

VFB

IFB

CCI

Pin Description

FUNCTION

Current-Limit Threshold Adjustment. Connect a resistive voltage-divider between REF or VCC and GND.

The current-limit threshold measured between LX_ and GND is 1/5 the voltage forced at ILIM. The ILIM

adjustment range is 0 to 3V. Connect ILIM to VCC to select the default current-limit threshold of 0.2V.

2V Reference Output. Bypass REF to GND with a 0.1µF ceramic capacitor. REF is discharged to GND

during shutdown.

Lamp-Out Threshold Adjustment. The lamp-out threshold is 30% of the voltage at LOT. The LOT

adjustment range is from 0.5V to VREF.

Analog Ground. The ground return for VCC, REF, and other analog circuitry. Connect GND to PGND

under the IC at the IC’s backside exposed metal pad.

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.

SMBus Serial Data Input

SMBus Serial Clock Input

SMBus Suspend Input

No Connection. Not internally connected.

Gate-Driver Supply Input. Connect VDD to VCC, the output of the linear regulator. Bypass VDD with a

0.1µF capacitor to PGND.

Power Ground. Gate-driver current flows through this pin.

Low-Side MOSFET NL2 Gate-Driver Output

Low-Side MOSFET NL1 Gate-Driver Output

High-Side MOSFET NH1 Gate-Driver Output

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.

Driver Bootstrap Input for High-Side MOSFET NH1. Connect BST1 through a diode to VDD and through a

0.1µF capacitor to LX1 (Figure 1).

Driver Bootstrap Input for High-Side MOSFET NH2. Connect BST2 through a diode to VDD and through a

0.1µF capacitor to LX2 (Figure 1).

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.

High-Side MOSFET NH2 Gate-Driver Output

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.

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 MAX8709B activates the lamp-out fault latch.

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.

8 _______________________________________________________________________________________

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