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PDF MAX921 Data sheet ( Hoja de datos )
| Número de pieza | MAX921 | |
| Descripción | Ultra Low-Power / Single/Dual-Supply Comparators | |
| Fabricantes | Maxim Integrated | |
| Logotipo |  |
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19-0115; Rev 3; 3/95
Ultra Low-Power,
Single/Dual-Supply Comparators
_______________General Description
The MAX921–MAX924 single, dual, and quad micro-
power, low-voltage comparators feature the lowest
power consumption available. These comparators draw
less than 4µA supply current over temperature
(MAX921/MAX922), and include an internal 1.182V
±1% voltage reference, programmable hysteresis, and
TTL/CMOS outputs that sink and source current.
Ideal for 3V or 5V single-supply applications, the
MAX921–MAX924 operate from a single +2.5V to +11V
supply (or a ±1.25V to ±5V dual supply), and each
comparator’s input voltage range swings from the
negative supply rail to within 1.3V of the positive
supply.
The MAX921–MAX924’s unique output stage con-
tinuously sources as much as 40mA. And by eliminating
power-supply glitches that commonly occur when com-
parators change logic states, the MAX921–MAX924
minimize parasitic feedback, which makes them easier to
use.
The single MAX921 and dual MAX923 provide a unique
and simple method for adding hysteresis without
feedback and complicated equations, simply by using
the HYST pin and two resistors.
MAX921
MAX922
MAX923
MAX924
Yes
No
Yes
Yes
1
Yes
8-Pin
DIP/SO/µMAX
2
No
8-Pin
DIP/SO/µMAX
2
Yes
8-Pin
DIP/SO/µMAX
4
No
16-Pin
DIP/SO/µMAX
________________________Applications
Battery-Powered Systems
Threshold Detectors
Window Comparators
Oscillator Circuits
____________________________Features
o µMAX Package—Smallest 8-Pin SO
(MAX921/MAX922/MAX923)
o Ultra-Low 4µA Max Quiescent Current
Over Extended Temp. Range (MAX921)
o Power Supplies:
Single +2.5V to +11V
Dual ±1.25V to ±5.5V
o Input Voltage Range Includes Negative Supply
o Internal 1.182V ±1% Bandgap Reference
o Adjustable Hysteresis
o TTL/CMOS-Compatible Outputs
o 12µs Propagation Delay (10mV Overdrive)
o No Switching Crowbar Current
o 40mA Continuous Source Current
______________Ordering Information
PART
TEMP. RANGE
PIN-PACKAGE
MAX921CPA
0°C to +70°C
8 Plastic DIP
MAX921CSA
0°C to +70°C
8 SO
MAX921CUA
0°C to +70°C
8 µMAX
MAX921C/D
0°C to +70°C
Dice*
MAX921EPA
-40°C to +85°C
8 Plastic DIP
MAX921ESA
-40°C to +85°C
8 SO
MAX921MJA
-55°C to +125°C 8 CERDIP**
Ordering Information continued at end of data sheet.
* Dice are tested at TA = +25°C, DC parameters only.
** Contact factory for availability and processing to MIL-STD-883.
__________Typical Operating Circuit
VIN
7
V+
3 IN+
4 IN-
OUT 8
5 HYST
6 REF
V-
2
MAX921
GND
1
THRESHOLD DETECTOR
________________________________________________________________ Maxim Integrated Products 1
Call toll free 1-800-998-8800 for free samples or literature.
1 page  
Ultra Low-Power,
Single/Dual-Supply Comparators
__________________________________________Typical Operating Characteristics
(V+ = 5V, V- = GND, TA = +25°C, unless otherwise noted).
REFERENCE VOLTAGE
vs. TEMPERATURE
1.22
1.21 MILITARY TEMP. RANGE
EXTENDED TEMP. RANGE
1.20
1.19 COMMERCIAL
TEMP. RANGE
1.18
1.17
1.16
1.15
1.14
-60 -40 -20 0 20 40 60 80 100 120 140
TEMPERATURE (°C)
MAX923
SUPPLY CURRENT vs. TEMPERATURE
5.0
4.5
MAX921
SUPPLY CURRENT vs.
TEMPERATURE
4.5
IN+ = IN- + 100mV
4.0
V+ = 5V, V- = - 5V
3.5
3.0
V+ = 3V, V- = 0V
2.5
2.0
-60
V+ = 5V, V- = 0V
-20 20 60 100
TEMPERATURE (°C)
140
MAX924
SUPPLY CURRENT vs. TEMPERATURE
10
IN+ = (IN- + 100mV)
9
MAX922
SUPPLY CURRENT vs. TEMPERATURE
4.5
IN+ = (IN- + 100mV)
4.0
3.5
V+ = 10V, V- = 0V
3.0
2.5
2.0
1.5
-60
10
V+ = 5V, V- = 0V
V+ = 3V, V- = 0V
-20 20 60 100
TEMPERATURE (°C)
MAX924
SUPPLY CURRENT vs.
LOW SUPPLY VOLTAGES
140
4.0
V+ = 5V, V- = 0V
3.5
3.0
8
7
V+ = 5V, V- = -5V
6
5
V+ = 5V, V- = 0V
1
0.1
2.5
2.0
-60
V+ = 3V, V- = 0V
-20 20 60 100
TEMPERATURE (°C)
140
4
3
-60
V+ = 3V, V- = 0V
-20 20 60 100
TEMPERATURE (°C)
0.01
140 1.0
1.5 2.0
SINGLE-SUPPLY VOLTAGE (V)
2.5
HYSTERESIS CONTROL
80
60
OUTPUT HIGH
40
20
0 NO CHANGE
-20
-40
OUTPUT LOW
-60
-80
0
10 20 30 40
VREF -VHYST (mV)
50
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
-0.3
TRANSFER FUNCTION
100k
10µF
V0
-0.2 -0.1 0 0.1 0.2
IN+ INPUT VOLTAGE (mV)
0.3
RESPONSE TIME vs.
LOAD CAPACITANCE
18
V- = 0V
16
14
VOHL
12
10
8
VOLH
6
4
2
0
20 40 60 80
LOAD CAPACITANCE (nF)
100
_______________________________________________________________________________________ 5
5 Page 
Ultra Low-Power,
Single/Dual-Supply Comparators
4.5V TO 6.0V
MOMENTARY
SWITCH
7
V+
6 REF
MAX921
IN+ 3
47k
5 HYST
CR
1.1M
4 IN-
100k V-
2
OUT 8
GND
1
VBATT -0.15V
10mA
Figure 5. Auto-off power switch operates on 2.5µA quiescent
current.
6. Verify the threshold voltages with these formulas:
VIN rising :
VTHR
=
VREF
×
R1
×
1
R1
+
1
R2
+
1
R3
VIN falling :
( )R1 × V +
VTHF = VTHR −
R3
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.
_______________Typical Applications
Auto-Off Power Source
Figure 5 shows the schematic for a 40mA power supply
that has a timed auto power-off function. The
comparator output is the switched power-supply
output. With a 10mA load, it typically provides a
voltage of (VBATT – 0.12V), but draws only 3.5µA
quiescent current. This circuit takes advantage of the
four key features of the MAX921: 2.5µA supply current,
an internal reference, hysteresis, and high current
output. Using the component values shown, the three-
resistor voltage divider programs the maximum ±50mV
of hysteresis and sets the IN- voltage at 100mV. This
gives an IN+ trip threshold of approximately 50mV for
IN+ falling.
The RC time constant determines the maximum power-
on time of the OUT pin before power-down occurs.
This period can be approximated by:
R x C x 4.6sec
For example: 2MΩ x 10µF x 4.6 = 92sec. The actual
time will vary with both the leakage current of the
capacitor and the voltage applied to the circuit.
Window Detector
The MAX923 is ideal for making window detectors
(undervoltage/overvoltage detectors). The schematic
is shown in Figure 6, with component values selected
for an 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. OUTA provides an active-low undervoltage
indication, and OUTB gives an active-low overvoltage
indication. ANDing 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 (MAX921/MAX923) 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.
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet MAX921.PDF ] | |
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