Datasheet

Calculate resistor values for Figure 3 as follows:
1) Choose a value for R1. Typical values are in
the 10kΩ to 10MΩ range.
2) Calculate R2 for the desired upper trip point
V
U
using the formula:
3) Calculate R3 for the desired amount of
hysteresis, where V
L
is the lower trip point:
or, if V+ = V
IN
:
Figure 5 shows an alternate circuit, suitable only when the
voltage being detected is also the power-supply voltage
for the MAX8211 or MAX8212.
Calculate resistor values for Figure 5 as follows:
1) Choose a value for R1. Typical values are in
the 10kΩ to 10MΩ range.
2) Calculate R2:
3) Calculate R3:
Low-Voltage Detector for Logic Supply
The circuit of Figure 5 will detect when a 5.0V (nominal)
supply goes below 4.5V, which is the V
MIN
normally
specified in logic systems. The selected resistor values
ensure that false undervoltage alarms will not be gener-
ated, even with worst-case threshold trip values and
resistor tolerances. R3 provides approximately 75mV of
hysteresis.
R3 R1
(V
U
V
L
)
1.15V
=×
−
R2 R1
(V
L
V
TH
)
V
TH
R1
(V
L
1.15V)
1.15V
=×
−
=×
−
R3 R2
(V
L
V
TH
)
(V
U
V
L
)
R2
(V
L
1.15V)
(V
U
V
L
)
=×
−
−
=×
−
−
R3 R2
(V V
TH
)
(V
U
V
L
)
R2
(V + 1.15V)
(V
U
V
L
)
=×
+−
−
=×
−
−
R2 = R1
(V
U
V
TH
)
V
TH
R1
(V
U
1.15V)
1.15V
×
−
=×
−
MAX8211/MAX8212
Microprocessor Voltage Monitors
with Programmable Voltage Detection
________________________________________________________________________________________ 5
-55
T
A
(
°
C)
V
TH
(V)
1.250
1.230
1.210
1.190
1.170
1.150
1.130
1.110
1.090
1.070
1.050
MAX8211,8212-FIG 4
-25 25 75 125
V+ = 16.5V
V+ = 2V
Figure 4. MAX8211/MAX8212 Threshold Trip Voltage vs.
Ambient Temperature
V
IN
HYST
MAX8211
OUT
GND
V+
R3
48.7k
Ω
1%
R2
2.2M
Ω
1%
R1
750k
Ω
1%
V
OUT
(LOW FOR
V
IN
< 4.5V)
THRESH
Figure 5. MAX8211 Logic-Supply Low-Voltage Detector