MAX6892/MAX6893/MAX6894
Detailed Description
The MAX6892/MAX6893/MAX6894 pin-selectable, mul-
tivoltage supply sequencers/supervisors monitor sever-
al voltage detector inputs and one watchdog input,
asserting the outputs when the respective input thresh-
olds have been reached or a timeout occurs. All ver-
sions have an enable manual reset and margin input
disable. The MAX6892/MAX6893/MAX6894 voltage
thresholds are selected by logic inputs and/or an exter-
nal voltage-divider. A RESET output ensures all moni-
tored inputs are above the pin-selected/adjustable
thresholds. Watchdog and reset timeout periods can
use factory default settings or are independently
adjustable by connecting external capacitors. In addi-
tion, all devices can be powered through the voltage
detector inputs alone, or externally supplied from a
constant supply on the V
CC
pin (see the
Powering the
MAX6892/MAX6893/MAX6894
section). The outputs
are factory configured as open drain.
Powering the
MAX6892/MAX6893/MAX6894
The MAX6892/MAX6893/MAX6894 derive power from
the voltage detector inputs: IN2–IN5 (MAX6892/
MAX6893), IN2–IN4 (MAX6894), or through an external-
ly supplied V
CC
. A virtual diode-ORing scheme selects
the positive input that supplies power to the device
(see the
Functional Diagram
). The highest input voltage
on IN2–IN5 (MAX6892/MAX6893)/IN2–IN4 (MAX6894)
supplies power to the device. One of IN2–IN5
(MAX6889/MAX6890)/IN2–IN4 (MAX6891) or V
CC
must
be at least 2.7V to ensure proper operation.
Internal hysteresis ensures that the supply input that
initially powered the device continues to power the
device when multiple input voltages are within 50mV of
each other.
V
CC
powers the analog circuitry and is the bypass con-
nection for the MAX6892/MAX6893/MAX6894 internal
supply. Bypass V
CC
to GND with a 1µF ceramic capac-
itor installed as close to the device as possible. The
internal supply voltage, measured at V
CC
, equals the
maximum of IN2–IN5. If V
CC
is externally supplied, V
CC
must be at least 200mV higher than any voltage
applied to IN2–IN5 and V
CC
must be brought up first.
V
CC
always powers the device when all IN_ are factory
set as “ADJ.” Do not use the internally generated V
CC
to provide power to external circuitry.
The MAX6892/MAX6893/MAX6894 also generate a dig-
ital supply voltage (DBP) for the internal logic circuitry
and the output stages. Bypass DBP to GND with a 1µF
ceramic capacitor installed as close to the device as
possible. The nominal DBP output voltage is 2.55V. Do
not use DBP to provide power to external circuitry.
Inputs
The MAX6892/MAX6893/MAX6894 contain multiple
logic and voltage detector inputs. Each voltage detec-
tor input is monitored for undervoltage thresholds.
Voltage Detector Inputs (IN_)
The MAX6892/MAX6893/MAX6894 offer several moni-
tor options with both pin-selectable and adjustable
reset thresholds. The threshold voltage at each
adjustable IN_ input is typically 0.6V. To monitor a volt-
age > 0.6V, connect a resistor-divider network to the
circuit as shown in Figure 1:
V
IN_TH
= V
TH
(R
1
+ R
2
)/R
2
(Equation 1)
where V
IN_TH
is the desired reset threshold voltage for
the respective IN_ and V
TH
is the input threshold
(0.6V).
Resistors R
1
and R
2
can have high values to minimize
current consumption due to low-leakage currents. Set
R
2
to some conveniently high value (10kΩ, for exam-
ple) and calculate R
1
based on the desired reset
threshold voltage, using the following formula:
R
1
= R
2
x (V
IN_TH
/V
TH
- 1)
Pin-Selectable, Octal/Hex/Quad, Power-Supply
Sequencers/Supervisors
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