MAX6457 Maxim, MAX6457 Datasheet - Page 8

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

Each of the MAX6457–MAX6460 high-voltage (4V to
28V), low-power voltage monitors include a precision
bandgap reference, one or two low-offset-voltage com-
parators, internal threshold hysteresis, internal timeout
period, and one or two high-voltage open-drain outputs.
Two external resistors set the trip voltage, V
V
V
MAX6460’s high input impedance allows large-value
resistors without compromising trip-voltage accuracy.
To minimize current consumption, select a value for R2
between 10kΩ and 1MΩ, then calculate R1 as follows:
where V
threshold trip voltage (V
or V
Use the MAX6460 voltage reference (REF) to set the
trip threshold by connecting IN+ or IN- through a volt-
age divider (within the inputs common-mode voltage
range) to REF. Small leakage currents into the com-
parators inputs allows use of large value resistors to
prevent loading the reference and affecting its accura-
cy. Figure 5b shows an active-high power-good output.
Use the following equation to determine the resistor val-
ues when connecting REF to IN-:
High-Voltage, Low-Current Voltage Monitors in
SOT Packages
Figure 5a. Programming the Trip Voltage
8
TRIP
CC
_______________________________________________________________________________________
TH
) toggles OUT. The MAX6457/MAX6458/MAX6459/
is the point at which the applied voltage (typically
Programming the Trip Voltage (V
- for undervoltage detection).
R1
R2
TRIP
V
CC
= desired trip voltage (in volts), V
R
1
IN+
GND
=
V
TRIP
R
2
Detailed Description
= V
MAX6457–
MAX6460



TH
TH
V
V
V
TRIP
CC
TH
R1 + R2
+ for overvoltage detection
(OUTB FOR
R2
MAX6459)
-
1
OUT



TRIP
R
PULLUP
OUT
(OUTB)
(Figure 5).
TRIP
TH
=
)
where V
V
old in (in volts).
For an active-low power-good output, connect the
resistor divider R1 and R2 to the inverting input and the
reference-divider network to the noninverting input.
Alternatively, connect an external reference less than
1.4V to either input.
Figure 6. Input and Output Waveforms (Noninverting Input Varied)
Figure 5b. Programming the MAX6460 Trip Voltage
REFD
V
V
IN+
OUT
V
V
V
R1
R2
TH+
CC
TH-
0
V
= divided reference, V
TRIP
REF
V
HYST
V
REFD
R3
R4
= reference output voltage (2.25V, typ),
V
R
REFD
1
=
R
t
TP
2
=
IN+
REF
IN-



V
V
REF
V
REFD
TRIP
MAX6460



GND
R
TRIP
V
CC
−
3
R
1
+



4
R
= desired trip thresh-
4
OUT



R
PULLUP
OUT
t
TP