The MAX6880–MAX6883 dual-/triple-voltage monitors
are designed to sequence power supplies during
power-up condition. When all of the voltages exceed
their respective thresholds, these devices turn on voltages
to the system sequentially, enhancing n-channel
MOSFETs used as switches. The time between each
sequenced voltage is determined by an external
capacitor, thus allowing flexibility in delay timing. The
MAX6880/MAX6881 sequence three voltages and the
MAX6882/MAX6883 sequence two voltages.
These devices initially monitor all of the voltages and
when all of them are within their tolerances, the internal
charge pumps enhance external n-channel
MOSFETs in a sequential manner to apply the voltages
to the system. Internal charge pumps drive the
gate voltages 5V above the respective input voltage
thereby ensuring the MOSFETs are fully enhanced to
reduce the on-resistance.
The MAX6880–MAX6883 feature capacitor-adjustable
slew-rate control to provide controlled turn-on characteristics.
After all of the voltages reach 92.5% of their
final value, a power-good output (MAX6880/MAX6882)
signal is active. The power-good output (PG/RST-bar) can
be delayed with an external capacitor to create a
power-on reset delay. After the initial power-up phase,
the MAX6880–MAX6883 continue to monitor the voltages.
If any of the voltages falls below its threshold, the
MOSFETs are quickly turned off and the voltages are
tracked down together. An internal 100Ω pulldown
resistor ensures that the capacitance at the MOSFET's
source is discharged quickly. The power-good output
goes low to provide a system reset.
The MAX6880–MAX6883 are available in small 4mm x
4mm 24-pin and 16-pin thin QFN packages and specified
over the -40°C to +85°C extended operating temperature
range.
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