MAX690(1994) 查看數據表（PDF） - Maxim Integrated
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MAX690 Datasheet PDF : 12 Pages
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3.0V/3.3V Microprocessor Supervisory Circuits
VIN
R1
R2
VCC
PFI MAX690T/S/R
MAX704T/S/R
R3
MAX802T/S/R
MAX804T/S/R
MAX805T/S/R
C1*
PFO MAX806T/S/R
GND
TO µP
*OPTIONAL
VIN
R1
R2
VCC
PFI MAX690T/S/R
MAX704T/S/R
R3
MAX802T/S/R
MAX804T/S/R
C1*
MAX805T/S/R
MAX806T/S/R
PFO
GND
TO µP
*OPTIONAL
PFO
0V
0V
VL
VH
VIN
VTRIP
( ) VTRIP = VPFT
R1 + R2
R2
WHERE VPFT = 1.237V
( ) VH = (VPFT + VPFH) (R1)
111
++
R1 R2 R3
VPFH = 10mV
( ) VL = R1 VPFT
111
++
– VCC
R1 R2 R3
R3
a
PFO
0V
0V
VTRIP
VH
VIN
( ) VTRIP = VPFT
R1 + R2
R2
( ) VH = R1 (VPFT + VPFH)
111
++
R1 R2 R3
– (VCC - VD)
R3
WHERE VPFT = 1.237V
VPFH = 10mV
VD = DIODE FORWARD VOLTAGE DROP
b
VL = VTRIP
Figure 4. a) Adding Additional Hysteresis to the Power-Fail Comparator b) Shifting the Additional Hysteresis above VPFT
3.0V OR 3.3V
R1
VCC
PFI
MAX690T/S/R
MAX704T/S/R
PFO
MAX802T/S/R
R2
MAX804T/S/R
MAX805T/S/R
MAX806T/S/R
GND
V-
VCC
PFO
V-
VL VTRIP
0V
( ) VTRIP = R2 (VPFT + VPFH)
11
+
R1 R2
– VCC
R1
( ) VL = R2 (VPFT)
11
+
R1 R2
– VCC
R1
a
WHERE VPFT = 1.237V
VPFH = 10mV
NOTE: VTRIP IS NEGATIVE
VIN
R1
R2
3.0V OR 3.3V
VCC
PFI
MAX690T/S/R
MAX704T/S/R
PFO
MAX802T/S/R
MAX804T/S/R
MAX805T/S/R
MAX806T/S/R
MR
*
GND
VCC
PFO
VTRIP VH
( ) VTRIP = VPFT
R1 + R2
R2
( ) VH = (VPFT + VPFH)
R1 + R2
R2
b
VIN
* MAX704T/S/R,
MAX806T/S/R ONLY
Figure 5. Using the Power-Fail Comparator to Monitor an Additional Power Supply
10 ______________________________________________________________________________________
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