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| 型号： | MAX8798ETX+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 22/31页 |
| 文件大小： | 0K |
| 描述： | IC INTERNAL-SW BOOST REG 36-TQFN |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 50 |
| 应用： | LCD 监视器，笔记本电脑显示器 |
| 电流 - 电源： | 400µA |
| 电源电压： | 1.8 V ~ 6 V |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 36-WFQFN 裸露焊盘 |
| 供应商设备封装： | 36-TQFN 裸露焊盘（6x6） |
| 包装： | 管件 |
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Internal-Switch Boost Regulator with
Integrated 3-Channel Scan Driver for TFT LCDs
? V IN ? ?
? ? η TYP ?
V MAIN ? V IN
? V MAIN ? ? I MAIN ( EFF ) × f OSC ? ? ? LIR ?
Design Procedure
Main Step-Up Regulator
Inductor Selection
The minimum inductance value, peak current rating, and
series resistance are factors to consider when selecting
the inductor. These factors influence the converter’s effi-
ciency, maximum output-load capability, transient
response time, and output-voltage ripple. Physical size
and cost are also important factors to be considered.
The maximum output current, input voltage, output volt-
age, and switching frequency determine the inductor
value. Very high inductance values minimize the cur-
rent ripple, and therefore, reduce the peak current that
decreases core losses in the inductor and I 2 R losses in
the entire power path. However, large inductor values
also require more energy storage and more turns of
wire that increase physical size and can increase I 2 R
losses in the inductor. Low inductance values decrease
the physical size, but increase the current ripple and
peak current. Finding the best inductor involves choos-
ing the best compromise between circuit efficiency,
inductor size, and cost.
The equations used here include a constant called LIR
that is the ratio of the inductor peak-to-peak ripple cur-
rent to the average DC inductor current at the full-load
I MAIN ( EFF ) = I MAIN ( MAX ) + n NEG × I NEG + ( n POS + 1 ) × I POS
where I MAIN(MAX) is the maximum step-up output cur-
rent, n NEG is the number of negative charge-pump
stages, n POS is the number of positive charge-pump
stages, I NEG is the negative charge-pump output cur-
rent, and I POS is the positive charge-pump output cur-
rent, assuming the initial pump source for I POS is
V MAIN .
Calculate the approximate inductor value using the typ-
ical input voltage (V IN ), the maximum output current
(I MAIN(EFF) ), the expected efficiency ( η TYP ) taken from
an appropriate curve in the Typical Operating Char-
acteristics, and an estimate of LIR based on the above
discussion:
2
L = ? ? ? ? ?
Choose an available inductor value from an appropriate
inductor family. Calculate the maximum DC input cur-
rent at the minimum input voltage V IN(MIN) using con-
servation of energy and the expected efficiency at that
operating point ( η MIN ) taken from an appropriate curve
in the Typical Operating Characteristics:
current. The best trade-off between inductor size and
circuit efficiency for step-up regulators generally has an
LIR between 0.3 and 0.5. However, depending on the
,
I IN ( DCMAX ) =
I MAIN(EFF) × V MAIN
V IN ( MIN ) × η MIN
AC characteristics of the inductor core material and
ratio of inductor resistance to other power-path resis-
tances, the best LIR can shift up or down. If the induc-
Calculate the ripple current at that operating point and
the peak current required for the inductor:
tor resistance is relatively high, more ripple can be
accepted to reduce the number of turns required and
increase the wire diameter. If the inductor resistance is
relatively low, increasing inductance to lower the peak
current can decrease losses throughout the power
I RIPPLE =
V IN(MIN) × ( V MAIN ? V IN(MIN) )
L × V MAIN × f OSC
I PEAK IN ( DCMAX ) + RIPPLE
= I
path. If extremely thin high-resistance inductors are
used, as is common for LCD panel applications, the
best LIR can increase to between 0.5 and 1.0.
Once a physical inductor is chosen, higher and lower
values of the inductor should be evaluated for efficien-
cy improvements in typical operating regions.
In Figure 2, the LCD’s gate-on and gate-off supply volt-
ages are generated from two unregulated charge
pumps driven by the step-up regulator’s LX node. The
additional load on LX must therefore be considered in
the inductance and current calculations. The effective
maximum output current, I MAIN(EFF) becomes the sum
of the maximum load current of the step-up regulator’s
output plus the contributions from the positive and neg-
ative charge pumps:
I
,
2
The inductor ’s saturation current rating and the
MAX8798’s LX current limit (I LIM ) should exceed I PEAK
and the inductor’s DC current rating should exceed
I IN(DC,MAX) . For good efficiency, choose an inductor
with less than 0.1 Ω series resistance.
Considering Figure 2, the maximum load current
(I MAIN(MAX) ) is 300mA, with an 8V output and a typical
input voltage of 3.3V. The effective full-load step-up
current is:
I MAIN ( EFF ) = 300 mA + 2 × 20 mA + ( 2 + 1 ) × 20 mA = 400 mA
22
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|---|---|
| MAX8798ETX+ | 功能描述:显示驱动器和控制器 Internal-Switch Boost Regulator RoHS:否 制造商:Panasonic Electronic Components 工作电源电压:2.7 V to 5.5 V 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:QFN-44 封装:Reel |
| MAX8798ETX+T | 功能描述:显示驱动器和控制器 Internal-Switch Boost Regulator RoHS:否 制造商:Panasonic Electronic Components 工作电源电压:2.7 V to 5.5 V 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:QFN-44 封装:Reel |
| MAX8798EVCMAXQU+ | 功能描述:显示开发工具 MAX8798 Eval Kit RoHS:否 制造商:4D Systems 产品:4Display Shields 工具用于评估:?OLED-160-G1, ?OLED-160-G2 接口类型:Serial 工作电源电压:5 V |
| MAX8798EVKIT+ | 功能描述:显示开发工具 MAX8798 Eval Kit RoHS:否 制造商:4D Systems 产品:4Display Shields 工具用于评估:?OLED-160-G1, ?OLED-160-G2 接口类型:Serial 工作电源电压:5 V |
| MAX8799EVKIT+ | 制造商:Maxim Integrated Products 功能描述:SINGLE-PHASE AMD CPU - Boxed Product (Development Kits) |
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