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

Table 1. Component List

DESIGNATION

DESCRIPTION

4.7µF ±20%, 25V X5R

ceramic capacitor (1210)

C1

Murata GRM32RR61E475K

Taiyo Yuden TMK325BJ475MN

TDK C3225X7R1E475M

1µF ±10%, 25V X7R

ceramic capacitor (1206)

C2

Murata GRM31MR71E105K

Taiyo Yuden TMK316BJ105KL

TDK C3216X7R1E105K

15pF ±1pF, 3kV high-voltage

C3

ceramic capacitor (1808)

Murata GRM42D1X3F150J

TDK C4520C0G3F150F

0.022µF ±10%, 16V X7R

ceramic capacitor (0402)

C4

Murata GRP155R71C223K

Taiyo Yuden EMK105BJ223KV

TDK C1005X7R1C223K

C5, C6, C8, C9

0.1µF ±10%, 25V X7R

ceramic capacitors (0603)

Murata GRM188R71E104K

Taiyo Yuden TMK107BJ104KA

TDK C1608X7R1E104K

Table 2. Component Suppliers

SUPPLIER

Central Semiconductor

Fairchild Semiconductor

Murata

Sumida

Taiyo Yuden

TDK

WEBSITE

www.centralsemi.com

www.fairchildsemi.com

www.murata.com

www.sumida.com

www.t-yuden.com

www.components.tdk.com

Typical Operating Circuit

The Typical Operating Circuit of the MAX8709B (Figure 1)

is a complete CCFL backlight inverter for notebook TFT

LCD panels. The circuit works over an input voltage

range of 7V to 24V with an RMS lamp current of 6mA.

The circuit’s maximum RMS open-lamp voltage is limit-

ed to 1600V. Table 1 lists recommended component

options, and Table 2 lists the component suppliers’

contact information.

DESIGNATION

DESCRIPTION

0.47µF ±10%, 10V X5R

ceramic capacitor (0603)

C7

Taiyo Yuden LMK107BJ474KA

TDK C1608X5R1A474K

Dual silicon switching diode,

D1

common anode (SOT-323)

Central Semiconductor CMSD2836

Diodes Incorporated BAW56W

NH1/2, NL1/2

30V, 0.095 dual n-channel MOSFETs

(6-pin SOT23)

Fairchild FDC6561AN

R1

150Ω ±1% resistor (0603)

R2

R3

R4, R5

T1

2kΩ ±5% resistor (0603)

39Ω ±1% resistor (0603)

100kΩ ±5% resistors (0603)

CCFL transformer, 1:93 turns ratio

Sumida 5371-400-W1423

TOKO T912MG-1018

Detailed Description

The MAX8709B controls a full-bridge resonant inverter to

convert an unregulated DC input into a near-sinusoidal

AC output for powering CCFLs. The lamp brightness is

adjusted by turning the lamp on and off with an internal

DPWM signal. The duty cycle of the DPWM signal is set

through an SMBus-compatible 2-wire serial interface.

Figure 2 shows the functional diagram of the MAX8709B.

Resonant Operation

The MAX8709B drives the four n-channel power

MOSFETs that make up the zero-voltage-switching

(ZVS) full-bridge inverter as shown in Figure 3. Assume

that NH1 and NL2 are turned on at the beginning of a

switching cycle as shown in Figure 3(a). The primary cur-

rent flows through MOSFET NH1, DC blocking cap C2,

the primary side of transformer T1, and MOSFET NL2.

During this interval, the primary current ramps up until the

controller turns off NH1. When NH1 turns off, the primary

current forward biases the body diode of NL1, which

clamps the LX1 voltage just below ground as shown in

Figure 3(b). When the controller turns on NL1, its drain-to-

source voltage is near zero because its forward-biased

body diode clamps the drain. Since NL2 is still on, the pri-

mary current flows through NL1, C2, the primary side of

T1, and NL2. Once the primary current drops to the mini-

mum current threshold (6mV / RDS(ON)), the controller

turns off NL2. The remaining energy in T1 charges up the

LX2 node until the body diode of NH2 is forward biased.

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