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参数资料
| 型号： | MAX1621EEE+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 17/20页 |
| 文件大小： | 0K |
| 描述： | IC TEMP SENSOR W/ALARM 16QSOP |
| 标准包装： | 2,500 |
| 应用： | LCD 显示器 |
| 电流 - 电源： | 150µA |
| 电源电压： | 3 V ~ 5.5 V |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 16-SSOP（0.154"，3.90mm 宽） |
| 供应商设备封装： | 16-QSOP |
| 包装： | 带卷 (TR) |
Digitally Adjustable LCD Bias Supplies
LCDON typically drives an external PNP transistor,
switching a positive V OUT to the LCD. R7 limits the base
current in the PNP; R6 turns off the PNP when LCDON is
floating. R6 and R7 can be the same value. Choose R7
such that the minimum base current is greater than 1/50
of the collector current. For example, assume V OUT,MIN
= 12.5V and I LCD = 10mA, then determine R7 as follows:
coil inductance; however, for most inductor types, the
coil’s specified current can be exceeded by 20% with
no impact on efficiency.
The peak current is set by the coil inductance as follows:
I PK = k-factor / L
and
R7 ≤ 50 x (12.5 - 0.7) / 10mA = 59k ?
I OUT,MIN =
1
2
× I PK × V BATT,MIN /V OUT,MAX
Remember that LCD voltage is the regulated output volt-
age minus the drop across the PNP switch. The drop
across the external transistor (typically 300mV) must be
accounted for.
If a PFET is preferred for the LCDON switch, R6 and R7
in Figure 4 may both be raised to 1M ? or more to reduce
operating current. Be sure to choose a P FET with ade-
quate breakdown voltage. Since load current is typically
on the order of 10mA, an on-resistance of 10 ? or less is
usually adequate.
Choosing an Inductor
Practical inductor values range from 33μH to 1mH;
however, 100μH is a good choice for a wide range of
applications. Inductors with a ferrite core or equivalent
are recommended. The inductor’s current rating should
exceed the peak current as set by the k-factor and the
If we assume that V BATT,MIN = 5.3V, V OUT,MAX =
25V, I OUT,MIN = 15mA, and a minimum k-factor of
16μs-V, then the required I PK is:
I PK = 2 x 15mA x 25 / 5.3 = 142mA
and
L ≤ = 16μs-V / 142mA = 113μH
The next-lowest practical inductor value is 100μH. Its
current rating must be:
24μs-V (maximum k-factor) / 100μH = 240mA
Table 5 summarizes the minimum inductance value
needed to provide various output currents at several
minimum input voltages. Table 6 lists some suitable coil
types and manufacturers, but is not intended to be a
complete list.
Table 5. Maximum Inductance vs. I OUT and V BATT,MIN (20V output)
V BATT,MIN
1.8V
2.7V
3.6V
5.4V
7.2V
12V
5mA
10mA
100μH
56μH
150μH
82μH
220μH
100μH
330μH
150μH
390μH
220μH
680μH
330μH
IOUT
20mA
30mA
27μH
18μH
39μH
27μH
56μH
33μH
82μH
56μH
100μH
68μH
180μH
120μH
Table 6. Inductor List
COMPANY
Sumida
USA (847) 956-0666
Japan 81-3-3607-5111
Coilcraft
(847) 639-6400
TDK
(847) 390-4373
PART
CD43
CD54
CDRH62B
DO1608
DT1608
NLC565050
TPF0410
μH RANGE
Up to 68μH
Up to 220μH
Up to 330μH
Up to 1mH
Up to 400μH
Up to 1mH
Up to 1mH
SIZE IN mm (H x W x L)
3.2 x 4 diameter
4.5 x 5.2 diameter
3 x 6.2 x 6.2
3.18 x 4.45 x 6.6
3.18 x 4.45 x 6.6
5 x 5 x 5.6
4 diameter x 10 L
COMMENTS
Shielded
Shielded
Leaded coil
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17
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