参数资料
型号: LTC2908ITS8-B1#TRMPBF
厂商: Linear Technology
文件页数: 11/18页
文件大小: 0K
描述: IC MON SIX SUPPLY PREC TSOT23-8
标准包装: 500
类型: 多压监控器
监视电压数目: 6
输出: 开路漏极或开路集电极
复位: 低有效
复位超时: 最小为 160 ms
电压 - 阀值: 1.403V,1.683V,2.338V,3.086V,可调,可调
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: SOT-23-8 薄型,TSOT-23-8
供应商设备封装: TSOT-23-8
包装: 带卷 (TR)
其它名称: LTC2908ITS8-B1#PBF
LTC2908ITS8-B1#PBF-ND
LTC2908
APPLICATIONS INFORMATION
Adjustable Input
The noninverting input on the V ADJ comparator is set to
0.5V. And the high impedance inverting input directly ties
to the V ADJ pin.
In a typical application, this pin connects to a tap point on an
external resistive divider between the positive voltage being
monitored and ground (see Figure 3). The following formula
derives the value of the R1 resistor in the divider from a
particular value of R2 and the desired trip voltage:
In an application with less than six supply voltages, the
unused supervisor inputs should be tied to the closest
higher supply voltage available.
Threshold Accuracy
Specifying system voltage margin for worst-case operation
requires the consideration of three factors: power supply
tolerance, IC supply voltage tolerance and supervisor reset
threshold accuracy. Highly accurate supervisors ease the
design challenge by decreasing the overall voltage margin
R1 =
V TRIP
0.5V
– 1 R2
required for reliable system operation.
Consider a 5V system with a ±5% power supply tolerance
R2 = 100k is recommended. Table 1 shows suggested
1% resistor values for various adjustable applications and
their corresponding trip thresholds.
Table 1. Suggested 1% Resistor Values for the V ADJ Inputs
band. System ICs powered by this supply must operate
reliably within this band (and a little more, as explained
below). The bottom of the supply tolerance band, at 4.75V
(5% below 5V), is the exact voltage at which a perfectly
accurate supervisor generates a reset (see Figure 4).
V SUPPLY (V)
12
10
8
7.5
6
V TRIP (V)
11.25
9.4
7.5
7
5.6
R1 (kΩ)
2150
1780
1400
1300
1020
R2 (kΩ)
100
100
100
100
100
Such a perfectly accurate supervisor does not exist—the
actual reset threshold may vary over a speci?ed band
(±1.5% for the LTC2908 supervisors). Figure 5 shows
the typical relative threshold accuracy for all six inputs
overtemperature.
5
3.3
3
4.725
3.055
2.82
845
511
464
100
100
100
5.000V
MINIMUM SUPPLY IDEAL
RELIABLE TOLERANCE SUPERVISOR
SYSTEM
THRESHOLD
VOLTAGE
NOMINAL
SUPPLY
VOLTAGE
2.5
1.8
1.5
2.325
1.685
1.410
365
237
182
100
100
100
4.750V
±1.5%
THRESHOLD 4.675V
BAND
4.600V
REGION OF POTENTIAL MALFUNCTION
–5.0%
–6.5%
–8.0%
±2.5%
THRESHOLD
BAND
1.2
1.120
124
100
4.500V
WITH 2.5% MONITOR
2908 F04
–10%
1.0
0.933
86.6
100
0.9
0.8
0.7
0.6
0.840
0.750
0.655
0.561
68.1
49.9
30.9
12.1
100
100
100
100
Figure 4. Threshold Band Diagram
1.5
1.0
V TRIP
R1
1%
V ADJ
R2
1%
LTC2908-A1/LTC2908-B1/LTC2908-C1
0.5
0
–0.5
+
–1.0
+
0.5V
–1.5
–50
–25
0 25 50
75
100
TEMPERATURE (°C)
2908 F03
Figure 3. Setting the Adjustable Trip Point
2908 F05
Figure 5. Typical Threshold Accuracy vs Temperature
2908fd
11
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