Datasheet

MAX6457–MAX6460
High-Voltage, Low-Current Voltage Monitors in
SOT Packages
9
Maxim Integrated
Hysteresis
Hysteresis adds noise immunity to the voltage monitors
and prevents oscillation due to repeated triggering
when V
IN
is near the threshold trip voltage. The hystere-
sis in a comparator creates two trip points: one for the
rising input voltage (V
TH
+) and one for the falling input
voltage (V
TH
-). These thresholds are shown in Figure 6.
The internal hysteresis options of the MAX6457/
MAX6458/MAX6459 are designed to eliminate the need
for adding an external hysteresis circuit.
Timeout Period
The timeout period (t
TP
) for the MAX6457 is the time
from when the input (IN+) crosses the rising input
threshold (V
TH
+) to when the output goes high (see
Figures 6 and 7). For the MAX6458, the monitored volt-
age must be in the “window” before the timeout starts.
The MAX6459 and MAX6460 do not offer the extended
timeout option (150ms). The extended timeout period is
suitable for overvoltage protection applications requir-
ing transient immunity to avoid false output assertion
due to noise spikes.
Latched-Output Operation
The MAX6457 features a digital latch input (CLEAR) to
latch any overvoltage event. If the voltage on IN+ (V
IN
+)
is below the internal threshold (V
TH
-), or if V
CC
is below
4V, OUT remains low regardless of the state of CLEAR.
Drive CLEAR high to latch OUT high when V
IN
+ exceeds
V
TH
+. When CLEAR is high, OUT does not deassert if
V
IN
+ drops back below V
IN
-. Toggle CLEAR to deassert
OUT. Drive CLEAR low to make the latch transparent
(Figure 7). CLEAR must be low when powering up the
MAX6457. To initiate self-clear at power-up, add a 100kΩ
pullup resistor from CLEAR to V
CC
and a 1µF capacitor
from CLEAR to GND to hold CLEAR low. Connect
CLEAR to GND when not used. See Figure 9.
IN+
OUT
>V
TH+
<V
TH-
V
CC
V
CC
0
0
t
TP
t
TP
t
TP
CLEAR
Figure 7. Timing Diagram (MAX6457)
5-CELL
Li+
BATTERY
STACK
BATTERY
CHARGER
DC-DC
CONVERTER
LOAD
R1
R2
R
PULLUP
IN OUT
+21V
V
CC
GND
IN+ OUT
(OUTA FOR
MAX6459)
MAX6457–
MAX6460
SHDN
Figure 8. Undervoltage Lockout Typical Application Circuit