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參數(shù)資料
| 型號： | MAX8729EEI |
| 廠商： | MAXIM INTEGRATED PRODUCTS INC |
| 元件分類： | 模擬信號調(diào)理 |
| 英文描述： | Constant-Frequency, Half-Bridge CCFL Inverter Controller |
| 中文描述： | SPECIALTY ANALOG CIRCUIT, PDSO28 |
| 封裝： | 0.150 INCH, 0.025 INCH PITCH, MO-137AF, QSOP-28 |
| 文件頁數(shù)： | 17/26頁 |
| 文件大?。?/td> | 395K |
| 代理商： | MAX8729EEI |
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M
Constant-Frequency, Half-Bridge CCFL
Inverter Controller
______________________________________________________________________________________
17
Upon power-up, V
COMP
slowly rises, increasing the duty
cycle of the high-side MOSFET switches and providing a
measure of soft-start. In addition, the MAX8729 charges
V
FB
to the overvoltage threshold (2.3V, typ) immediately
after the device is enabled. The DC voltage on V
FB
is
gradually discharged through an internal resistor during
startup. This feature is equivalent to slowly raising the
overvoltage threshold during startup, so it further
improves the soft-start behavior. The MAX8729 automati-
cally switches over to the constant-frequency operation
after the lamp current reaches regulation.
Feed-Forward Control and Dropout
Operation
The MAX8729 is designed to maintain tight control of
the lamp current when a line transient occurs. The
feed-forward control instantaneously adjusts the on-
time for changes in input voltage (V
IN
). This feature pro-
vides immunity to input-voltage variations and simplifies
loop compensation over wide-input voltage ranges. The
feed-forward control also improves the line regulation
for short DPWM on-times and makes startup transients
less dependent on the input voltage.
Feed-forward control is implemented by increasing the
internal voltage ramp rate for higher V
IN
. This has the
effect of varying t
ON
as a function of the input voltage
while maintaining about the same signal levels at V
COMP
.
Since the required voltage change across the compen-
sation capacitor is minimal, the controller’s response to
input voltage changes is essentially instantaneous.
DPWM Dimming Control
The MAX8729 controls the brightness of the CCFL by
“chopping” the lamp current on and off using a low-fre-
quency (between 100Hz and 350Hz) DPWM signal
either from the internal oscillator or from an external sig-
nal source. In DPWM operation, COMP controls the
dynamics of the lamp-current envelope. At the begin-
ning of the DPWM ON cycle, the average value of the
lamp-current feedback signal is below the regulation
point, so the transconductance error amplifier sources
current into the COMP capacitor. The switch on-time
(t
ON
) gradually increases as V
COMP
rises, which pro-
vides soft-start. At the end of the DPWM ON cycle, the
MAX8729 turns on a 100μA internal current source. The
current source linearly discharges the COMP capacitor,
gradually decreasing t
ON
, and providing soft-stop.
Using the Internal Oscillator
When the SEL pin is connected to ground, the
MAX8729 uses the internal oscillator to generate the
DPWM signal. The frequency of the internal DPWM
oscillator is adjustable through a resistor connected
between LF and GND. The DPWM frequency is given
by the following equation:
The adjustable range of the DPWM frequency is
between 100Hz and 300Hz (R
LF
is between 217k
Ω
and
103k
Ω
).
The CCFL brightness is proportional to the DPWM duty
cycle, which can be adjusted from 10% to 100% through
the CNTL pin. CNTL is an analog input with a usable
input voltage range between 0 and 2V, which is digitized
to select one of 128 brightness levels. As shown in
Figure 5, the MAX8729 ignores the first 13 steps, so the
first 13 steps all represent the same brightness. When
V
CNTL
is between 0 and 203mV, the DPWM duty cycle is
always 10%. When V
CNTL
is above 203mV, a 15.625mV
change on CNTL results in a 0.78% change in the
DPWM duty cycle. When V
CNTL
is equal to or above 2V,
the DPWM duty cycle is always 100%.
Using the External PWM Signal
To use the external DPWM signal to control the bright-
ness, connect SEL to V
CC
and connect LSYNC to the
external signal source. The frequency range of the
external signal is between 100Hz and 300Hz with R
LF
=
150k
Ω
. In this mode, the brightness control input CNTL
is disabled, and the brightness is proportional to the
duty cycle of the external signal. When the duty cycle
of the external signal is 100%, the CCFL reaches full
brightness. If the duty cycle of the external signal is
less than 10%, the CCFL brightness is adjusted
accordingly.
f
Hz x
R
k
DPWM
LF
=
Ω
207
150
CNTL VOLTAGE (mV)
1600
1200
400
800
0
2000
B
10
20
30
40
50
60
70
80
90
100
0
Figure 5. Theoretical Brightness vs. Control Voltage
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MAX8729EEI+ | 功能描述:顯示驅(qū)動器和控制器 Const-f Half-Bridge CCFL Inverter Ctlr RoHS:否 制造商:Panasonic Electronic Components 工作電源電壓:2.7 V to 5.5 V 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-44 封裝:Reel |
| MAX8729EEI+T | 功能描述:顯示驅(qū)動器和控制器 Const-f Half-Bridge CCFL Inverter Ctlr RoHS:否 制造商:Panasonic Electronic Components 工作電源電壓:2.7 V to 5.5 V 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-44 封裝:Reel |
| MAX8729EEI-T | 功能描述:顯示驅(qū)動器和控制器 RoHS:否 制造商:Panasonic Electronic Components 工作電源電壓:2.7 V to 5.5 V 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-44 封裝:Reel |
| MAX8729EVKIT | 功能描述:電源管理IC開發(fā)工具 MAX8729 Eval Kit RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
| MAX872C/D | 功能描述:基準(zhǔn)電壓& 基準(zhǔn)電流 RoHS:否 制造商:STMicroelectronics 產(chǎn)品:Voltage References 拓?fù)浣Y(jié)構(gòu):Shunt References 參考類型:Programmable 輸出電壓:1.24 V to 18 V 初始準(zhǔn)確度:0.25 % 平均溫度系數(shù)（典型值）:100 PPM / C 串聯(lián) VREF - 輸入電壓（最大值）: 串聯(lián) VREF - 輸入電壓（最小值）: 分流電流（最大值）:60 mA 最大工作溫度:+ 125 C 封裝 / 箱體:SOT-23-3L 封裝:Reel |
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