MAX6457_V5 Datasheet, PDF (11/15 Pages) Maxim Integrated Products – High-Voltage, Low-Current Voltage Monitors in SOT Packages

High-Voltage, Low-Current Voltage Monitors in
SOT Packages
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:
V_TRIPLOW
=
V_TH-
⎛
⎝⎜
R_TOTAL
R2 + R3
⎞
⎠⎟
V_TRIPHIGH
=
V_TH+
⎛
⎝⎜
R_TOTAL
R3
⎞
⎠⎟
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:
R3 = ^{VTH+ × RTOTAL}
V_TRIPHIGH
3) Calculate R2 based on R_TOTAL, R3, and the desired
lower trip point:
R2 = ^{VTH- × RTOTAL} - R3
V_TRIPLOW
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
R3 = ^{VTH+ × RTOTAL} = ^{(1.228V) (4.2MΩ)}
V_TRIPHIGH
23.1V
= 223.273kΩ
3) Calculate R2
V_CC (4V TO 28V)
V_CC
MAX6457–
MAX6460
V_OUT (UP TO 28V)
OUT/
OUTA/
OUTB
R_PULLUP
OUT/
OUTA/
OUTB
GND
V_MON
R1
R2
V_CC
V_CC
MAX6457–
MAX6460
IN+
OUT
(OUTA FOR
MAX6459)
R_PULLUP
OUT
(OUTA)
GND
Figure 12. Monitoring Voltages Other than V_CC
Figure 13. Interfacing to Voltages Other than V_CC
V_CC
V_CC
IN-
MAX6460
OUT
REF
R_PULLUP
OUT
R1
IN+
GND
R2
V_NEG
Figure 14. Monitoring Negative Voltages
11