MAX6457 Maxim, MAX6457 Datasheet - Page 11

• Manufacturer Part Number: MAX6457
• Description: High-Voltage / Low-Current Voltage Monitors in SOT Packages
• Manufacturer: Maxim

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