MAX6457 Maxim, MAX6457 Datasheet - Page 10

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

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 section).
When the voltage of the battery stack decreases so that
V
OUT (OUTA) goes low and disables the power supply to
the load. When the battery charger restores the voltage of
the 5-cell stack so that V
high and the power supply resumes driving the load.
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 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 over-
voltage 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.
High-Voltage, Low-Current Voltage Monitors in
SOT Packages
Figure 9. Overvoltage Shutdown Circuit (with External Pass
MOSFET)
10
IN
V
+ drops below V
SUPPLY
______________________________________________________________________________________
100kΩ
1µF
R1
R2
Applications Information
TH
IN+
CLEAR
- of the MAX6457–MAX6460, then
MAX6457–
IN
MAX6460
+ > V
Overvoltage Shutdown
V
GND
Undervoltage Lockout
CC
(OUTB FOR
MAX6459)
OUT
TH
+, OUT (OUTA) goes
R
PULLUP
LOAD
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
When V
(V
OUT asserts low.
The MAX6459 features two independent open-drain
outputs: OUTA (for undervoltage events) and OUTB (for
overvoltage events). When V
window, OUTA and OUTB assert high. When V
below V
Figure 10. Overvoltage Shutdown Circuit (with SCR Fuse)
Figure 11. Window Detection
TRIPLOW
V
SUPPLY
R1
R2
R3
V
CC
CC
TRIPLOW
FUSE
) or exceeds the upper limit (V
falls below the lower limit of the window
R1
R2
IN+
IN-
, OUTA asserts low while OUTB
IN+
CC
MAX6458
MAX6459
GND
V
CC
MAX6457–
MAX6460
is within the selected “window.”
GND
V
CC
MAX6458
MAX6459
(OUTB FOR
MAX6459)
OUTA
OUTB
ONLY
ONLY
OUT
CC
OUT
Window Detection
R
is within the selected
PULLUP
V
CC
R3
R
PULLUP
OUT
V
CC
SCR
TRIPHIGH
R
PULLUP
LOAD
OUTA
OUTB
CC
falls
),