Datasheet

MAX6457–MAX6460
High-Voltage, Low-Current Voltage Monitors in
SOT Packages
11
Maxim Integrated
remains high. When V
CC
exceeds V
TRIPHIGH
, OUTB
asserts low while OUTA remains high. V
TRIPLOW
and
V
TRIPHIGH
are given by the following equations:
where R
TOTAL
= R1 + R2 + R3.
Use the following steps to determine the values for R1,
R2, and R3.
1) Choose a value for R
TOTAL
, the sum of R1, R2, and
R3. Because the MAX6458/MAX6459 have very
high input impedance, R
TOTAL
can be up to 5MΩ.
2) Calculate R3 based on R
TOTAL
and the desired
upper trip point:
3) Calculate R2 based on R
TOTAL
, R3, and the desired
lower trip point:
4) Calculate R1 based on R
TOTAL
, R3, and R2:
R1 = R
TOTAL
- R2 - R3
Example Calculations for Window
Detection
The following is an example for calculating R1, R2, and
R3 of Figure 11 for window detection. Select the upper
and lower trip points (V
TRIPHIGH
and V
TRIPLOW
).
V
CC
= 21V
V
TRIPHIGH
= 23.1V
V
TRIPLOW
= 18.9V
For 5% hysteresis, V
TH
+ = 1.228 and V
TH
- = 1.167.
1) Choose R
TOTAL
= 4.2MΩ = R1 + R2 + R3
2) Calculate R3
3) Calculate R2
R
VR
V
VM
V
k
TH TOTAL
TRIPHIGH
3
1 228 4 2
23 1
223 273
=
×
=
Ω
=Ω
+
(. )(. )
.
.
R
VR
V
R
TH TOTAL
TRIPLOW
23=
×
-
-
R
VR
V
TH TOTAL
TRIPHIGH
3 =
×
+
VV
R
RR
VV
R
R
TRIPLOW TH
TOTAL
TRIPHIGH TH
TOTAL
=
+
⎛
⎝
⎜
⎞
⎠
⎟
=
⎛
⎝
⎜
⎞
⎠
⎟
+
-
23
3
MAX6457–
MAX6460
V
MON
V
CC
V
CC
R1
R2
GND
R
PULLUP
IN+
OUT
(OUTA FOR
MAX6459)
OUT
(OUTA)
Figure 12. Monitoring Voltages Other than V
CC
MAX6457–
MAX6460
V
CC
GND
R
PULLUP
OUT/
OUTA/
OUTB
OUT/
OUTA/
OUTB
V
CC
(4V TO 28V)
V
OUT
(UP TO 28V)
Figure 13. Interfacing to Voltages Other than V
CC
MAX6460
V
CC
V
CC
R1
R2
GND
V
NEG
R
PULLUP
IN+
REF
IN-
OUT
OUT
Figure 14. Monitoring Negative Voltages