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參數(shù)資料
| 型號： | MAX1885EUP |
| 廠商： | MAXIM INTEGRATED PRODUCTS INC |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Fixed-Point Digital Signal Processor 256-BGA |
| 中文描述： | 2.05 A SWITCHING REGULATOR, 625 kHz SWITCHING FREQ-MAX, PDSO20 |
| 封裝： | 4.40 MM, 1.10 MM HEIGHT, MO-153AC, TSSOP-20 |
| 文件頁數(shù)： | 26/38頁 |
| 文件大?。?/td> | 1051K |
| 代理商： | MAX1885EUP |
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M
Quad-Output TFT LCD DC-DC
Converters with Buffer
26
______________________________________________________________________________________
where
η
is the efficiency, f
OSC
is the oscillator frequen-
cy (see
Electrical Characteristics
), and I
MAIN
includes
the primary load current and the input supply currents
for the charge pumps (see
Charge-Pump Input Power
and Efficiency Considerations
), linear regulator, and
VCOM buffer. Considering the typical application cir-
cuit, the maximum average DC load current
(I
MAIN(MAX)
) is 300mA with an 8V output. Based on the
above equations and assuming 85% efficiency, the
inductance value is then chosen to be 4.7μH.
The inductor
’
s saturation current rating should exceed
the peak inductor current throughout the normal operat-
ing range. The peak inductor current is then given by:
Under fault conditions, the inductor current may reach
up to 1.85A (I
LIM(MAX)
), see Electrical Characteristics).
However, the controller
’
s fast current-limit circuitry
allows the use of soft-saturation inductors while still pro-
tecting the IC.
The inductor
’
s DC resistance may significantly affect
efficiency due to the power loss in the inductor. The
power loss due to the inductor
’
s series resistance (P
LR
)
may be approximated by the following equation:
where R
L
is the inductor
’
s series resistance. For best per-
formance, select inductors with resistance less than the
internal N-channel MOSFET on-resistance (0.35
typ).
Use inductors with a ferrite core or equivalent. To mini-
mize radiated noise in sensitive applications, use a
shielded inductor.
Output Capacitor
Output capacitor selection depends on circuit stability
and output voltage ripple. A 10μF ceramic capacitor
works well in most applications (Tables 1 and 2).
Additional feedback compensation is required (see
Feedback Compensation
) to increase the margin for
stability by reducing the bandwidth further. In cases
where the output capacitance is sufficiently large, addi-
tional feedback compensation will not be necessary.
Output voltage ripple has two components: variations in
the charge stored in the output capacitor with each LX
pulse, and the voltage drop across the capacitor
’
s
equivalent series resistance (ESR) caused by the cur-
rent into and out of the capacitor:
where I
PEAK
is the peak inductor current (see Inductor
Selection). For ceramic capacitors, the output voltage
ripple is typically dominated by V
RIPPLE(C)
. The voltage
rating and temperature characteristics of the output
capacitor must also be considered.
Feedback Compensation
For stability, add a pole-zero pair from FB to GND in the
form of a compensation resistor (R
COMP
) in series with
a compensation capacitor (C
COMP
) as shown in Figure
2. Select R
COMP
to be half the value of R2, the low-side
feedback resistor.
Integrator Capacitor
The MAX1778/MAX1880
–
MAX1885 contain an internal
current integrator that improves the DC load regulation
but increases the peak-to-peak transient voltage (see
the load-transient waveforms in the
Typical Operating
Characteristics
). For highly accurate DC load regula-
tion, enable the current integrator by connecting a
470pF (
OSC
= 1MHz)/1000pF (
OSC
= 500kHz)
capacitor to INTG. To minimize the peak-to-peak tran-
sient voltage at the expense of DC regulation, disable
the integrator by connecting INTG to REF. When using
the MAX1883/MAX1884/MAX1885, connect a 100k
resistor to GND when disabling the integrator.
Input Capacitor
The input capacitor (C
IN
) in step-up designs reduces
the current peaks drawn from the input supply and
reduces noise injection. The value of C
IN
is largely
determined by the source impedance of the input sup-
ply. High source impedance requires high input capac-
itance, particularly as the input voltage falls. Since
step-up DC-DC converters act as
“
constant-power
”
loads to their input supply, input current rises as input
voltage falls. A good starting point is to use the same
capacitance value for C
IN
as for C
OUT
.
V
V
V
V
I
AND
V
V
V
V
I
C
RIPPLE
RIPPL( )
≈
RIPPLE ESR
RIPPLE ESR
PEAK ESR COUT
RIPPLE( )
MAIN
IN
MAIN
MAIN
OUT OSC
+
,
(
)
(
)
(
)
=
≈
P
R
I
X V
V
IN
LR
L
MAIN
MAIN
2
I
I
V
V
LIR
2
PEAK
MAIN MAX
MAIN
IN MIN
(
+
(
)
)
=
1
1
η
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MAX1885EUP-T | 功能描述:LCD 驅(qū)動器 Quad-Output TFT LCD DC-DC Converter with Buffer RoHS:否 制造商:Maxim Integrated 數(shù)位數(shù)量:4.5 片段數(shù)量:30 最大時鐘頻率:19 KHz 工作電源電壓:3 V to 3.6 V 最大工作溫度:+ 85 C 最小工作溫度:- 20 C 封裝 / 箱體:PDIP-40 封裝:Tube |
| MAX1886ESA+ | 制造商:Maxim Integrated Products 功能描述:HIGH-CURRENT VCOM DRIVE BUFFER - Rail/Tube |
| MAX1886EUK | 制造商:Maxim Integrated Products 功能描述:HIGH-CURRENT VCOM DRIVE BUFFER - Rail/Tube |
| MAX1886EUK+T | 功能描述:運算放大器 - 運放 RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-16 轉(zhuǎn)換速度:0.89 V/us 關(guān)閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
| MAX1886EUK-T | 功能描述:運算放大器 - 運放 RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-16 轉(zhuǎn)換速度:0.89 V/us 關(guān)閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
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