MAX6872/MAX6873
EEPROM-Programmable, Hex/Quad,
Power-Supply Sequencers/Supervisors
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Program each output to assert on any voltage-detector
input, general-purpose logic input, watchdog timer,
manual reset, or other output stages. Programmable
timing-delay blocks configure each output to wait
between 25µs and 1600ms before deasserting. A fault
register logs the conditions that caused each output to
assert (undervoltage, overvoltage, manual reset, etc.).
The MAX6872/MAX6873 feature two watchdog timers,
adding flexibility. Program each watchdog timer to assert
one or more programmable outputs. Program each
watchdog timer to clear on a combination of one GPI_
input and one programmable output, one of the GPI_
inputs only, or one of the programmable outputs only.
The initial and normal watchdog timeout periods are
independently programmable from 6.25ms to 102.4s.
A virtual diode-ORing scheme selects the input that pow-
ers the MAX6872/MAX6873. The MAX6872/MAX6873
derive power from IN1 if V
IN1
> +6.5V or from the highest
voltage on IN3–IN6 if V
IN1
< +2.7V. The power source
cannot be determined if +4V < V
IN1
< +6.5V and one
of V
IN3
through V
IN6
> +2.7V. The programmable out-
puts maintain the correct programmed logic state for
V
ABP
> V
UVLO
. One of IN3 through IN6 must be
greater than +2.7V or IN1 must be greater than +4V for
device operation.
Powering the MAX6872/MAX6873
The MAX6872/MAX6873 derive power from the positive
voltage-detector inputs: IN1 or IN3–IN6. A virtual diode-
ORing scheme selects the positive input that supplies
power to the device (see the Functional Diagram). IN1
must be at least +4V or one of IN3–IN6 (MAX6872)/
IN3–IN4 (MAX6873) must be at least +2.7V to ensure
device operation. An internal LDO regulates IN1 down
to +5.4V.
The highest input voltage on IN3–IN6 (MAX6872)/
IN3–IN4 (MAX6873) supplies power to the device, unless
V
IN1
≥ +6.5V, in which case IN1 supplies power to the
device. For +4V < V
IN1
< +6.5V and one of V
IN3
through
V
IN6
> +2.7V, the input power source cannot be deter-
mined due to the dropout voltage of the LDO. Internal
hysteresis ensures that the supply input that initially pow-
ered the device continues to power the device when
multiple input voltages are within 50mV of each other.
ABP powers the analog circuitry; bypass ABP to GND
with a 1µF ceramic capacitor installed as close to the
device as possible. The internal supply voltage, mea-
sured at ABP, equals the maximum of IN3–IN6
(MAX6872)/IN3–IN4 (MAX6873) if V
IN1
= 0, or equals
+5.4V when V
IN1
> +6.5V. Do not use ABP to provide
power to external circuitry.
The MAX6872/MAX6873 also generate a digital supply
voltage (DBP) for the internal logic circuitry and the
EEPROM; 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 MAX6872/MAX6873 contain multiple logic and volt-
age-detector inputs. Each voltage-detector input is
simultaneously monitored for primary and secondary
thresholds. The primary threshold must be an under-
voltage threshold. The secondary threshold may be an
undervoltage or overvoltage threshold. Table 1 summa-
rizes these various inputs.
Set the primary and secondary threshold voltages for
each voltage-detector input with registers 00h–0Bh.
Each primary threshold voltage must be an undervolt-
age threshold. Configure each secondary threshold
voltage as an undervoltage or overvoltage threshold
(see register 0Ch). Set the threshold range for each
voltage detector with register 0Dh.
High-Voltage Input (IN1)
IN1 offers threshold voltages of +2.5V to +13.2V in
50mV increments, or +1.25V to +7.625V in 25mV incre-
ments. Use the following equations to set the threshold
voltages for IN1:
where V
TH
is the desired threshold voltage and x is the
decimal code for the desired threshold (Table 2). For
the +2.5V to +13.2V range, x must equal 214 or less,
otherwise the threshold exceeds the maximum operat-
ing voltage of IN1.
Bipolar-Voltage Input (IN2)
IN2 offers negative thresholds from -2.5V to -15.25V in
50mV increments, or from -1.25V to -7.625V in 25mV
increments. Alternatively, IN2 offers positive thresholds
from +2.5V to +15.25V in 50mV increments, or +1.25V
to +7.625V in 25mV increments. Use the following
equations to set the threshold voltages for IN2:
