参数资料
型号: MAX984ESE+T
厂商: Maxim Integrated Products
文件页数: 3/17页
文件大小: 0K
描述: IC COMPARATOR OD 16-SOIC
产品培训模块: Lead (SnPb) Finish for COTS
Obsolescence Mitigation Program
标准包装: 2,500
类型: 带电压基准
元件数: 4
输出类型: 开路漏极
电压 - 电源,单路/双路(±): 2.5 V ~ 11 V,±1.25 V ~ 5.5 V
电压 - 输入偏移(最小值): 10mV @ 5V
电流 - 输出(标准): 0.015mA @ 5V
电流 - 静态(最大值): 8.5µA
CMRR, PSRR(标准): 80dB CMRR,80dB PSRR
工作温度: -40°C ~ 85°C
封装/外壳: 16-SOIC(0.154",3.90mm 宽)
安装类型: 表面贴装
包装: 带卷 (TR)
MAX971–MAX974/MAX981–MAX984
Ultra-Low-Power, Open-Drain,
Single/Dual-Supply Comparators
______________________________________________________________________________________
11
__________Applications Information
Hysteresis
Hysteresis increases the comparators’ noise margin by
increasing the upper threshold and decreasing the
lower threshold (Figure 2).
Hysteresis (MAX9_1/MAX982/MAX9_3)
To add hysteresis to the MAX9_1, MAX982, or MAX9_3,
connect resistor R1 between REF and HYST, and
connect resistor R2 between HYST and V- (Figure 3). If
no hysteresis is required, connect HYST to REF. When
hysteresis is added, the upper threshold increases by
the same amount that the lower threshold decreases.
The hysteresis band (the difference between the upper
and lower thresholds, VHB) is approximately equal to
twice the voltage between REF and HYST. The HYST
input can be adjusted to a maximum voltage of REF
and to a minimum voltage of (REF - 50mV). The
maximum difference between REF and HYST (50mV)
will therefore produce a 100mV (max) hysteresis band.
Use the following equations to determine R1 and R2:
where IREF (the current sourced by the reference)
should not exceed the REF source capability, and
should be significantly larger than the HYST input
current. IREF values between 0.1A and 4A are usually
appropriate. If 2.4M
is chosen for R2 (IREF = 0.5A),
the equation for R1 and VHB can be approximated as:
When hysteresis is obtained in this manner for the
MAX982/MAX9_3, the same hysteresis applies to both
comparators.
Hysteresis (MAX972/MAX9_4)
Hysteresis can be implemented with any comparator
using positive feedback, as shown in Figure 4. This
approach generally draws more current than circuits
using the HYST pin on the MAX9_1/MAX982/MAX9_3,
and the high feedback impedance slows hysteresis. In
addition, because the output does not source current,
any increase in the upper threshold is dependent on
the
load
or
pullup
resistor
on
the
output.
Board Layout and Bypassing
Power-supply bypass capacitors are not needed if the
supply impedance is low, but 100nF bypass capacitors
should be used when the supply impedance is high or
when the supply leads are long. Minimize signal lead
lengths to reduce stray capacitance between the input
and output that might cause instability. Do not bypass
the reference output.
Window Detector
The MAX9_3 is ideal for making window detectors
(undervoltage/overvoltage detectors). The schematic is
shown in Figure 5, with component values selected for a
4.5V undervoltage threshold and a 5.5V overvoltage
threshold. Choose different thresholds by changing the
values of R1, R2, and R3. To prevent chatter at the
output when the supply voltage is close to a threshold,
hysteresis has been added using R4 and R5. Taken
alone, OUTA would provide an active-low undervoltage
indication, and OUTB would give an active-low
overvoltage indication. Wired-ORing the two outputs
provides an active-high, power-good signal.
The design procedure is as follows:
1) Choose the required hysteresis level and calculate
values for R4 and R5 according to the formulas in
the Hysteresis (MAX9_1/MAX982/MAX9_3) section.
In this example, ±5mV of hysteresis has been added
at the comparator input (VH = VHB/2). This means
that the hysteresis apparent at VIN will be larger
because of the input resistor divider.
R1 (k ) = V
(mV)
HB
R1 =
V
2
I
R2 =
1.182 –
V
2
I
HB
REF
HB
REF
×
()
GND
V-
V+
MAX9_4
OUT
RH
RPULLUP
VREF
VIN
V+
Figure 4. External Hysteresis
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