MAX6457–MAX6460
High-Voltage, Low-Current Voltage Monitors in
SOT Packages
10
Maxim Integrated
Applications Information
Undervoltage Lockout
Figure 8 shows the typical application circuit for detecting
an undervoltage event of a 5-cell Li+ battery stack.
Connect OUT of the MAX6457/MAX6458/MAX6460
(OUTA of the MAX6459) to the shutdown input of the DC-
DC converter to cut off power to the load in case of an
undervoltage event. Select R1 and R2 to set the trip volt-
age (see the
Programming the Trip Voltage (V
TRIP
)
sec-
tion). When the voltage of the battery stack decreases so
that V
IN
+ drops below V
TH
- of the MAX6457–MAX6460,
then OUT (OUTA) goes low and disables the power sup-
ply to the load. When the battery charger restores the volt-
age of the 5-cell stack so that V
IN
+ > V
TH
+, OUT (OUTA)
goes high and the power supply resumes driving the load.
Overvoltage Shutdown
The MAX6457–MAX6460 are ideal for overvoltage shut-
down applications. Figure 9 shows a typical circuit for
this application using a pass P-channel MOSFET. The
MAX6457–MAX6460 are powered directly from the sys-
tem voltage supply. Select R1 and R2 to set the trip volt-
age (see the
Programming the Trip Voltage (V
TRIP
)
section). When the supply voltage remains below the
selected threshold, a low logic level on OUT (OUTB for
MAX6459) turns on the p-channel MOSFET. In the case
of an overvoltage event, OUT (OUTB) asserts high, turns
off the MOSFET, and shuts down the power to the load.
Figure 10 shows a similar application using a fuse and
a silicon-controlled rectifier (SCR). An overvoltage
event turns on the SCR and shorts the supply to
ground. The surge of current through the short circuit
blows the fuse and terminates the current to the load.
Select R3 so that the gate of the SCR is properly biased
when OUT (OUTB) goes high impedance.
Window Detection
The MAX6458/MAX6459 include undervoltage and
overvoltage comparators for window detection (Figures
2 and 3). The circuit in Figure 11 shows the typical con-
figuration for this application. For the MAX6458, OUT
asserts high when V
CC
is within the selected “window.”
When V
CC
falls below the lower limit of the window
(V
TRIPLOW
) or exceeds the upper limit (V
TRIPHIGH
),
OUT asserts low.
The MAX6459 features two independent open-drain
outputs: OUTA (for undervoltage events) and OUTB (for
overvoltage events). When V
CC
is within the selected
window, OUTA and OUTB assert high. When V
CC
falls
below V
TRIPLOW
, OUTA asserts low while OUTB
