MAX6889/MAX6890/MAX6891
EEPROM-Programmable, Octal/Hex/Quad,
Power-Supply Sequencers/Supervisors
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Output Stage Configurations
Independently configure each programmable output as
active-high or active-low (Table 17). Additionally, config-
ure each programmable output as open drain or weak
pullup (Table 18). Finally, set the PO_ timeout period for
each programmable output (Table 19). The programma-
ble outputs can sink up to 4mA.
Weak Pullup Output Configuration
The MAX6889/MAX6890/MAX6891s’ programmable outputs
have a pullup resistance (10kΩ, typ) connected to the inter-
nal 2.55V LDO output to provide weak pullup outputs.
Open-Drain Output Configuration
Connect an external pullup resistor from the program-
mable output to an external voltage when configured as
an open-drain output. Open-drain configured outputs
may be pulled up to 13.2V. Choose the pullup resistor
depending on the number of devices connected to the
open-drain output and the allowable current consump-
tion. The open-drain output configuration allows wire-
ORed connections, and provides flexibility in setting the
pullup current.
Configuring the Watchdog Timer
(Registers 29h–2Ah)
A watchdog timer monitors microprocessor software
execution for a stalled condition and resets the micro-
processor if it stalls. The output of the watchdog timer
(one of the programmable outputs) connects to the reset
input or a nonmaskable interrupt of the microprocessor.
Registers 29h–2Ah configure the watchdog functionali-
ty of the MAX6889/MAX6890/MAX6891. Program the
watchdog timer to assert one or more programmable
outputs (see Tables 7–16). Program the watchdog timer
to reset on one of the GPI_ inputs, one of the program-
mable outputs, or a combination of one GPI_ input and
one programmable output.
The watchdog timer features independent initial and
normal watchdog timeout periods. The initial watchdog
timeout period applies immediately after power-up,
after a software reboot, after a reset event takes place,
or after enabling the watchdog timer. The initial watch-
dog timeout period allows the microprocessor to per-
form its initialization process. If no pulse occurs during
the initial watchdog timeout period, the microprocessor
is taking too long to initialize, indicating a potential
problem.
The normal watchdog timeout period applies after the
initial watchdog timeout period occurs. The normal
watchdog timeout period monitors a pulsed output of
the microprocessor that indicates when normal proces-
sor behavior occurs. If no pulse occurs during the nor-
mal watchdog timeout period, this indicates that the
processor has stopped operating or is stuck in an infi-
nite execution loop.
Register 2Ah programs the initial and normal watchdog
timeout periods, and enables or disables the watchdog
timer. See Tables 20 and 21 for a summary of the
watchdog behavior.
Configuration Lock
Lock the configuration register bank and configuration
EEPROM contents after initial programming by setting
the lock bit high (see Table 22). Locking the configura-
tion prevents write operations to all registers except the
configuration lock register. Clear the lock bit to reconfig-
ure the device.
Internal/External V
CC
Power
The MAX6889/MAX6890/MAX6891 can generate an
internal V
CC
, or V
CC
can be externally supplied (see
Table 22). To internally generate V
CC
from the highest
voltage on IN1–IN5 set register 2Eh and EEPROM
address AEh Bit[2] = 0. To use an externally supplied,
always-on V
CC
ensure register 2Eh and EEPROM
address AEh Bit[2] =1 (see the
Powering the MAX6889/
MAX6890/MAX6891
section).
Write Disable
A unique write-disable feature protects the MAX6889/
MAX6890/MAX6891 from inadvertent user-EEPROM
writes. As input voltages that power the serial interface,
a microprocessor, or any other writing-devices fall,
unintentional data may be written onto the data bus.
The user-EEPROM write-disable function (see Table 23)
ensures that unintentional data does not corrupt the
MAX6889/MAX6890/MAX6891 EEPROM data.
