MAX976 View Datasheet(PDF) - Maxim Integrated
Part Name
Description
MFG CO.
MAX976 Datasheet PDF : 10 Pages
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MAX976/MAX978/MAX998
Single/Dual/Quad, SOT23, Single-Supply,
High-Speed, Low-Power Comparators
R3 VCC
R1
VIN
R2
VREF
0.1µF
VCC
OUT
GND
MAX976
MAX978
MAX998
Figure 2. Additional Hysteresis
2) Choose the hysteresis band required (VHB). For this
example, choose 100mV.
3) Calculate R1. R1 = R3 x (VHB / VCC). Plugging in the
values for this example,
R1 = 1.2MΩ x (100mV / 5.0V) = 24kΩ
4) Choose the trip point for VIN rising. This is the
threshold voltage at which the comparator switches
from low to high as VIN rises above the trip point. In
this example, choose 3.0V.
5) Calculate R2 as follows:
R2 =
R2 =
1
⎛
⎝⎜
VTHR ⎞
VREF x R1⎠⎟
−
1
R1
−
1
R3
1
⎛
⎝⎜
3.0V
1.2 x 24kΩ
⎞
⎠⎟
−
1
24kΩ
−
1
1.2M
= 16.2kΩ
Choose a standard value for R2 of 16kΩ.
6) Verify the trip voltage and hysteresis as follows:
VIN rising: VTHR =
VREF
x
R1
x
⎛1
⎝⎜ R1
+
1
R2
+
1⎞
R3 ⎠⎟
VIN falling:
VTHF =
VTHR
−
⎛ R1
⎝⎜
x VCC
R3
⎞
⎠⎟
Hysteresis = VTHR − VTHF
IR Receiver
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 RD.
When this voltage level crosses the voltage applied by the
voltage divider to the inverting input, the output transitions.
Maxim Integrated
Window Comparator
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
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.
2) Choose the overvoltage threshold (VOTH) when VIN
is rising, and calculate R2 and R3 with the following
formula:
RSUM = R2 + R3 = R1 x [VOTH / (VREF + VH) - 1]
where VH = 1/2VHYST.
3) Choose the undervoltage threshold (VUTH) when VIN
is falling, and calculate R2 with the following formula:
R2 = (R1 + RSUM) x [(VREF - VH) / VUTH] - R1
where VH = 1/2VHYST.
4) Calculate R3 with the following formula:
R3 = (RSUM) - R2
5) Verify the resistor values. The equations are as follows:
VOTH = (VREF + VH) x (R1 + R2 + R3) / R1
VUTH = (VREF - VH) x (R1 + R2 + R3) / (R1 + R2)
R3
82.1kΩ
1%
VIN
R2
24.9kΩ
VCC 1%
1
MAX6120 2
3
R1
100kΩ
1%
VCC
1
8
1/2
MAX976 7
2
5
0.1μF
UNDERVOLTAGE
POWER GOOD
3
1/2
6
MAX976
4
OVERVOLTAGE
Figure 3. Window Comparator
7
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