MAX1839 查看數據表（PDF） - Maxim Integrated

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MAX1839

Wide Brightness Range CCFL Backlight Controllers

Maxim Integrated 

Wide Brightness Range

CCFL Backlight Controllers

a proven application that is useful for a wide range of

CCFL tubes and power ranges. Table 5 shows the rec-

ommended components for a 4.5W application.

MOSFETs

The MAX1739/MAX1839 require three external switches

to operate: N1, N2A, and N2B. N1 is the buck switch;

select a logic-level N-channel MOSFET with low RDSON

to minimize conduction losses (100mΩ, 30V typ). Also

select a comparable-power Schottky diode for D1.

N2A/N2B are the Royer oscillator switches that drive

the transformer primary; select a dual-logic-level N-

channel MOSFET with low RDSON to minimize conduc-

tion losses (100mΩ, 30V typ).

Sense Resistors

R4 and R5 sense the transformer’s primary voltage.

Figure 9 shows the relationship between the primary

and secondary voltage. To set the maximum average

secondary transformer voltage, set R5 = 10kΩ, and

select R5 according to the following formula:

R4

= R5

 1.5VS(RMS)

 N



− 1

where VS is the maximum RMS secondary transformer

voltage (above the strike voltage), and N is the turns

ratio of the transformer.

Table 4. CCFL Specifications

SPECIFICATION

CCFL Minimum Strike

Voltage

(Kick-Off Voltage)

CCFL Typical Operating

Voltage

(Lamp Voltage)

SYMBOL

VS

VL

UNITS

VRMS

VRMS

DESCRIPTION

Although CCFLs typically operate at <550VRMS, a higher voltage

(1000VRMS and up) is required initially to start the tube. The strike

voltage is typically higher at cold temperatures and at the tube’s end

of life. This voltage is set by the combination of the maximum primary

voltage (center-tap voltage limit corresponding to

VCTFB = 0.6V) and the transformer (T1) turns ratio.

Once a CCFL has been struck, the voltage required to maintain light

output falls to approximately 550VRMS. Short tubes may operate on as

little as 250VRMS. The CCFL operating voltage stays relatively

constant, even as the tube’s brightness is varied.

CCFL Maximum Operating

Current (Lamp Current)

IL

mARMS

The maximum RMS AC current through a CCFL is typically 5mARMS.

DC current is not allowed through CCFLs. The maximum lamp current

is set by the sense resistor (R13) at the maximum brightness setting.

CCFL Maximum Frequency

fL

(Lamp Frequency)

The maximum AC-lamp-current frequency. The MAX1739/ MAX1839

kHz

synchronize to the Royer oscillator frequency set by the external

components and are designed to operate between 32kHz and

100kHz.

Table 5. Components for the Standard Application Circuit

DESIGNATION

L1

N1

N2

T1

DESCRIPTION

47µH, 1.1A inductor

30V, 0.1Ω N-channel MOSFET

30V, 95mΩ dual N-channel MOSFET

8.7µH, 180:1 transformer

RECOMMENDED DEVICE

CR104-470

FDN361AN

FDC6561AN

5371-T001 (CIUH842 style)

D1

30V, 1A Schottky diode

D2

0.1A Schottky diode

D3

0.1A dual Schottky diode

C6

22pF, 3.1kV capacitor

C7

0.1µF, 63V, low-dissipation capacitor

CRS02

BAT54

MMBD4148SE

GHM1038-SL-220J-3K

SMD1812

MANUFACTURER

Sumida

Fairchild

Fairchild

Sumida

Toshiba

Fairchild

Fairchild

Murata

WIMA

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