MAX8216CSD データシートの表示（PDF） - Maxim Integrated
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MAX8216CSD Datasheet PDF : 12 Pages
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±5V, ±12V (±15V) Dedicated
Microprocessor Voltage Monitors
VTRIP2
INPUT VOLTAGE
VDD
(VS) VTRIP1
( )RA
VHYST 1 + RB
RA
+VS
7 DIN
RB
MAX8215
MAX8216
180k
DOUT 9
1.24V REFERENCE
( ) VTRIP = RA + RB (VREF)
RB
Figure 2. Undervoltage/Overvoltage Comparator Using the
Auxiliary Comparator
Adding hysteresis to a comparator creates two trip
points–one for the input voltage rising and one for the
input voltage falling. When the voltage at the
MAX8215/MAX8216 auxiliary comparator’s (noninvert-
ing) input falls, the threshold at which the comparator
switches equals the reference voltage connected to the
comparator’s inverting input. However, when the volt-
age at the noninverting input rises, the threshold
equals the reference voltage plus the amount of hys-
teresis voltage built into the part. The trip point is
somewhat more accurate when the hysteresis voltage
is not part of the threshold voltage (i.e., when the input
voltage is falling) because the tolerance of the hystere-
sis specification adds to the tolerance of the trip point.
Overvoltage and Undervoltage
Detection Circuits
Figure 2 shows connection of the auxiliary comparator
as either an undervoltage or overvoltage comparator.
Hysteresis makes this circuit more accurate when the
input voltage is dropping as opposed to rising. Figure
3 illustrates the comparator’s operation. The input volt-
age’s direction determines at which of two trip points
the comparator switches. Thus, the diagram includes
arrows that indicate whether the input voltage is rising
or falling. The formulas are provided for determining
trip-point voltages for specified resistors and for ease
in calculating appropriate resistor ratios for particular
trip points.
GND
OUTPUT
VOLTAGE
VDD
GND
TO DETERMINE THE TRIP VOLTAGES
FROM PARTICULAR RESISTOR
VALUES:
( ) VTRIP1 = VREF
1
+
RA
RB
( ) VTRIP2 = (VREF + VHYST)
1
+
RA
RB
VHYST = 16mV TYP
TO CALCULATE THE REQUIRED
RESISTOR RATIOS FOR PARTICULAR
TRIP VOLTAGES:
RA
RB
=
VTRIP1
VREF
-1
RA
RB
=
VTRIP2
VREF + VHYST
-1
Figure 3. Undervoltage/Overvoltage Detector Waveforms and
Formulas
2 GND
0.1µF
8
PGND
14
VDD
+VS
R1
3 +5V
MAX8215
MAX8216
13
OUT1
UNDERVOLTAGE
7 DIN
9
DOUT
OVERVOLTAGE
R2
+5V COMPARATOR IS ACTUATED WHEN VS FALLS TO THE
COMPARATOR'S SPECIFIED TRIP LEVEL. THE AUXILIARY
( ) COMPARATOR OUTPUT IS TRIPPED WHEN VS > R1 + R2 VREF
R2
Figure 4. Monitoring Supply Powering the MAX8215/MAX8216
with Undervoltage and Overvoltage Comparators
The MAX8215/MAX8216 comparator outputs correctly
display a low level down to 0.8V supply voltage. This is
useful in undervoltage applications where the monitored
power supply is also the supply connected to the VDD
pin. See the section Monitoring the Supply Voltage.
_______________________________________________________________________________________ 7
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