Rainbow-electronics MAX8709 Manual do Utilizador descarregar pdf (Página 11)

MAX8709

High-Efficiency CCFL Backlight

Controller with SMBus Interface

______________________________________________________________________________________ 11

Typical Operating Circuit

The Typical Operating Circuit of the MAX8709 (Figure

1) is a complete CCFL backlight inverter for notebook

TFT LCD panels. The circuit works over an input volt-

age range of 7V to 24V with an RMS lamp current of

6mA. The circuit’s maximum RMS open-lamp voltage is

limited to 1600V. Table 1 lists recommended compo-

nent options, and Table 2 lists the component suppli-

ers’ contact information.

Detailed Description

The MAX8709 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 inter-

face. Figure 2 shows the functional diagram of the

MAX8709.

Resonant Operation

The MAX8709 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 current 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 volt-

age 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 primary current flows

through NL1, C2, the primary side of T1, and NL2. Once

the primary current drops to the minimum current thresh-

old (6mV / R

DS(ON)

), the controller turns off NL2. The

remaining energy in T1 charges up the LX2 node until the

Table 1. Component List

DESIGNATION

DESCRIPTION

4.7µF ±20%, 25V X5R

ceramic capacitor (1210)

Murata GRM32RR61E475K

Taiyo Yuden TMK325BJ475MN

TDK C3225X7R1E475M

1µF ±10%, 25V X7R

ceramic capacitor (1206)

Murata GRM31MR71E105K

Taiyo Yuden TMK316BJ105KL

TDK C3216X7R1E105K

15pF ±1pF, 3kVhigh-voltage

ceramic capacitor (1808)

Murata GRM42D1X3F150J

TDK C4520C0G3F150F

0.022µF ±10%, 16V X7R

ceramic capacitor (0402)

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

DESIGNATION DESCRIPTION

0.47µF ±10%, 10V X5R

ceramic capacitor (0603)

Taiyo Yuden LMK107BJ474KA

TDK C1608X5R1A474K

Dual silicon switching diode,

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 2kΩ ±5% resistor (0603)

R3 39Ω ±1% (resistor (0603)

R4, R5 100kΩ ±5% resistors (0603)

CCFL transformer, 1:93 turns ratio

Sumida 5371-400-W1423

TOKO T912MG-1018

Table 2. Component Suppliers

SUPPLIER WEBSITE

Central Semiconductor www.centralsemi.com

Fairchild Semiconductor www.fairchildsemi.com

Murata www.murata.com

Sumida www.sumida.com

Taiyo Yuden www.t-yuden.com

TDK www.components.tdk.com

1 2 ... 6 7 8 9 10 11 12 13 14 15 16 ... 22 23

Comentários a estes Manuais

Sem comentários

Rainbow-electronics MAX8709 Manual do Utilizador Página 11

Comentários a estes Manuais

Manuais e produtos relacionados com Sensores Rainbow-electronics MAX8709