MAX976-MAX998 Maxim, MAX976-MAX998 Datasheet - Page 7

• Manufacturer Part Number: MAX976-MAX998
• Description: Single/Dual/Quad / SOT23 / Single-Supply / High-Speed / Low-Power Comparators
• Manufacturer: Maxim

2) Choose the hysteresis band required (V
3) Calculate R1. R1 = R3 x (V
4) Choose the trip point for V
5) Calculate R2 as follows:
6) Verify the trip voltage and hysteresis as follows:
The Typical Operating Circuit shows an application using
the MAX998 as an infrared receiver. The infrared photo-
diode creates a current relative to the amount of infrared
light present. This current creates a voltage across R
When this voltage level crosses the voltage applied by the
voltage divider to the inverting input, the output transitions.
Figure 2. Additional Hysteresis
Hysteresis
V rising: V
V falling
R2 =
R2 =
example, choose 100mV.
values for this example,
threshold voltage at which the comparator switches
from low to high as V
this example, choose 3.0V.
Choose a standard value for R2 of 16kΩ.
IN
IN
V
IN
R1 = 1.2MΩ x (100mV / 5.0V) = 24kΩ
1.2 x 24k
V
:
REF
R1
V
V
3.0V
THR
THR
THF
V
x R1
R2
THR
_______________________________________________________________________________________
Single/Dual/Quad, SOT23, Single-Supply,
= V
V
1
REF
THR
V
IN
REF
1
V
High-Speed, Low-Power Comparators
R1
1
24k
THF
rises above the trip point. In
x R1 x
1
R3
HB
R x V
R3
/ V
GND
IN
1
V
V
1
CC
CC
R1
R
CC
1
rising. This is the
1.2M
3
). Plugging in the
1
CC
OUT
IR Receiver
MAX976
MAX978
MAX998
R
0.1 F
1
2
HB
16.2k
). For this
R
1
3
D
.
The MAX976 is ideal for making a window detector
(undervoltage/overvoltage detector). The schematic
shown in Figure 3 uses a MAX6120 reference and com-
ponent values selected for a 2.0V undervoltage thresh-
old and a 2.5V overvoltage threshold. Choose different
thresholds by changing the values of R1, R2, and R3.
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) Select R1. The leakage current into INB- is normally
2) Choose the overvoltage threshold (V
3) Choose the undervoltage threshold (V
4) Calculate R3 with the following formula:
5) Verify the resistor values. The equations are as follows:
Figure 3. Window Comparator
V
IN
75nA, so the current through R1 should exceed
1.0µA for the thresholds to be accurate. R1 values in
the 50kΩ to 100kΩ range are typical.
is rising, and calculate R2 and R3 with the following
formula:
where V
is falling, and calculate R2 with the following formula:
where V
MAX6120
1
3
R
R2 = (R1 + R
R3 = (R
V
V
V
CC
OTH
UTH
82.1k, 1%
SUM
R3
24.9k,
100k,
H
H
= (V
= (V
1%
1%
= R2 + R3 = R1 x [V
R2
2
R1
= 1/2V
= 1/2V
SUM
REF
REF
) - R2
SUM
HYST
HYST
+ V
- V
1
2
3
4
MAX976
MAX976
H
) x [(V
H
1/2
) x (R1 + R2 + R3) / (R1 + R2)
.
.
1/2
) x (R1 + R2 + R3) / R1
V
CC
8
Window Comparator
REF
5
7
OTH
6
- V
0.1 F
H
/ (V
) / V
OTH
REF
UTH
UNDERVOLTAGE
UTH
OVERVOLTAGE
) when V
) when V
+ V
POWER GOOD
] - R1
H
) - 1]
IN
IN
7