參數(shù)資料
型號(hào)： MAX1839EEP
廠商： MAXIM INTEGRATED PRODUCTS INC
元件分類(lèi)： 穩(wěn)壓器
英文描述： Wide Brightness Range CCFL Backlight Controllers
中文描述： FLUORESCENT LIGHT CONTROLLER, 64 kHz SWITCHING FREQ-MAX, PDSO20
封裝： 0.150 INCH, 0.025 INCH PITCH, QSOP-20
文件頁(yè)數(shù)： 13/26頁(yè)
文件大小： 444K
代理商： MAX1839EEP
M
Wide Brightness Range
CCFL Backlight Controllers
______________________________________________________________________________________
13
allow the circuit to operate in dropout at extremely low
battery voltages where the backlight
’
s performance is
secondary. All backlight circuit designs can undergo a
transient overvoltage condition when the laptop is
plugged into the AC adapter and V
BATT
suddenly
increases. The MAX1739/MAX1839 contain a unique
clamp circuit on V
CCI
. Along with the feed-forward cir-
cuitry, it ensures that there is not a transient transformer
overvoltage when leaving dropout.
The PK_DET_CLAMP circuit limits V
CCI
to the peaks of
the buck-regulator
’
s PWM ramp generator. As the cir-
cuit reaches dropout, V
CCI
approaches the peaks of
the PWM ramp generator in order to reach maximum
duty cycle. If V
BATT
decreases further, the control loop
loses regulation and V
CCI
tries to reach its positive sup-
ply rail. The clamp circuit on V
CCI
keeps this from hap-
pening, and V
CCI
rides just above the peaks of the
PWM ramp. As V
BATT
decreases further, the feed-for-
ward PWM ramp generator loses amplitude and the
clamp drags V
CCI
down with it to a voltage below
where V
CCI
would have been if the circuit was not in
dropout. When VBATT is suddenly increased out of
dropout, V
CCI
is still low and maintains the drive on the
transformer at the old dropout level. The circuit then
slowly corrects and increases V
CCI
to bring the circuit
back into regulation.
Buck Regulator
The buck regulator uses the signals from the PWM
comparator, the current-limit detection on CS, and
DPWM signals to control the high-side MOSFET duty
cycle. The regulator uses voltage-mode PWM control
and is synchronized to the Royer oscillator. A falling
edge on SYNC turns on the high-side MOSFET after a
375ns minimum off-time delay. The PWM comparator or
the CS current limit ends the on-cycle.
Interface Selection
Table 1 lists the functionality of
SH
/SUS, CRF/SDA, and
CTL/SCL in each of the three interface modes of the
MAX1739/MAX1839. The MAX1739 features both an
SMBus digital interface and an analog interface, while
the MAX1839 features only the analog interface. Note
that MODE can also synchronize the DPWM frequency
(see
Synchronizing the DPWM Frequency
).
Dimming Range
Brightness is controlled by either the analog interface
(see
Analog Interface
) or the SMBus interface (see
SMBus Interface
). CCFL brightness is adjusted in three
ways:
1) Lamp current control, where the magnitude of the
average lamp current is adjusted.
2) DPWM control, where the average lamp current is
pulsed to the lamp with a variable duty cycle.
3) A combination of the first two methods.
In each of the three methods, a 5-bit brightness code is
generated from the selected interface and is used to
set the lamp current and/or DPWM duty cycle.
The 5-bit brightness code defines the lamp current
level with ob00000 representing minimum lamp current
and ob11111 representing maximum lamp current. The
average lamp current is measured across an external
sense resistor (see
Sense Resistors
). The voltage on
the sense resistor is measured at CSAV. The brightness
code adjusts the regulation voltage at CSAV (V
CSAV
).
The minimum average V
CSAV
is V
MINDAC
/10, and the
maximum average is set by the following formula:
V
CSAV
= V
REF
31 / 320 + V
MINDAC
/ 320
which is between 193.75mV and 200mV.
Note that if V
CSAV
does not exceed 100mV peak (which
is about 32mV average) for over 2 seconds, the
MAX1739/MAX1839 will assume a lamp-out condition
and shut down (see
Lamp-Out Detection
).
The equation relating brightness code to C
SAV
regula-
tion voltage is:
V
CSAV
= V
REF
n / 320 + V
MINDAC
(32 - n) / 320
where n is the brightness code.
To always use maximum average lamp current when
using DPWM control, set V
MINDAC
to V
REF
.
DPWM control works similar to lamp current control in
that it also responds to the 5-bit brightness code. A
DIGITAL
INTERFACE
ANALOG INTERFACE
PIN
MODE = VL
(MAX1739 only)
MODE = REF,
V
CTL
/SCL = 0 = maximum brightness
Logic-level shutdown control input
Reference input for minimum brightness
Analog control input to set brightness (range from 0 to CRF/SDA)
MODE = GND,
V
CTL
/SCL = 0 = minimum brightness
SH
/SUS
CRF/SDA
CTL/SCL
SMBus suspend
SMBus data I/O
SMBus clock input
Reference input for maximum brightness
Table 1. Interface Modes
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
MAX1839EEP+ 功能描述:顯示驅(qū)動(dòng)器和控制器 CCFL Backlight Controller 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
MAX1839EEP+T 功能描述:顯示驅(qū)動(dòng)器和控制器 CCFL Backlight Controller 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
MAX1839EEP-T 功能描述:顯示驅(qū)動(dòng)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
MAX183ACNG 功能描述:模數(shù)轉(zhuǎn)換器 - ADC RoHS:否 制造商:Texas Instruments 通道數(shù)量:2 結(jié)構(gòu):Sigma-Delta 轉(zhuǎn)換速率:125 SPs to 8 KSPs 分辨率:24 bit 輸入類(lèi)型:Differential 信噪比:107 dB 接口類(lèi)型:SPI 工作電源電壓:1.7 V to 3.6 V, 2.7 V to 5.25 V 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-32
MAX183ACNG+ 功能描述:模數(shù)轉(zhuǎn)換器 - ADC RoHS:否 制造商:Texas Instruments 通道數(shù)量:2 結(jié)構(gòu):Sigma-Delta 轉(zhuǎn)換速率:125 SPs to 8 KSPs 分辨率:24 bit 輸入類(lèi)型:Differential 信噪比:107 dB 接口類(lèi)型:SPI 工作電源電壓:1.7 V to 3.6 V, 2.7 V to 5.25 V 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-32
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