MAX16050_08 Datasheet, PDF (15/21 Pages) Maxim Integrated Products – Voltage Monitors/Sequencer Circuits with Reverse-Sequencing Capability

Voltage Monitors/Sequencer Circuits with
Reverse-Sequencing Capability
Charge-Pump Output (CP_OUT)
The MAX16050/MAX16051 feature an on-chip charge
pump that drives its output voltage to 5V above V_CC,
and it can be used as a pullup voltage to drive one or
more external n-channel MOSFETs (see the Typical
Operating Circuit). The charge-pump output can be
modeled as a 25µA current source with a compliance
voltage of (V_CC + 5V); the slew rate can be controlled
by connecting a capacitor from the gate of the MOSFET
to ground. When using CP_OUT to provide the pullup
voltage for multiple MOSFETs, ensure that the voltage
is enough to enhance a MOSFET despite the load of
the other pullup resistors (which may be connected to
outputs that are deasserted low).
Disabling Channels
If any channel is not used, connect the associated SET_
input to ABP. Connect DISC_ of the disabled channel to
GND or leave it unconnected. The channel exclusion
feature adds more flexibility to the device in a variety of
different applications.
SHDN and EN Inputs
The shutdown input (SHDN) initiates a reverse
sequencing event. When SHDN is brought low, the
device will sequentially power down in reverse order.
During this period, all DISC_ inputs are monitored to
make sure the voltage of each supply falls below
250mV before allowing the next supply to shut down.
The next OUT_ goes low as soon as the previous DISC_
input drops below 250mV without any capacitor-adjust-
ed delay. This continues until all supplies are turned off.
SHDN is internally pulled up to ABP.
When EN falls below its threshold, the device performs
a simultaneous power-down and does not reverse
sequence. When either SHDN or EN initializes the
power-down event, the reset output (RESET) immedi-
ately asserts. At the end of the power-down event,
when all DISC_ voltages are below 250mV, the bus
removal output (REM) goes high impedance.
Reset Output (RESET)
The MAX16050/MAX16051 include a reset output.
RESET is an open-drain output and requires an external
pullup resistor.
When any of the monitored voltages falls below its
threshold, SHDN is pulled low, EN falls below its thresh-
old, or FAULT is pulled low, RESET asserts and stays
asserted for at least the minimum reset timeout period
after all of these conditions are removed. Connect a
capacitor from TIMEOUT to GND to adjust the reset
timeout period. Connect TIMEOUT to ABP for the fixed
timeout of 128ms (typ). Leave TIMEOUT unconnected
for a 10µs (typ) timeout period.
FAULT Input/Output
The FAULT input/output asserts to signal a fault if any of
the SET_ monitored voltages falls below its threshold
while EN = SHDN = high. FAULT is internally pulled up
to ABP by a 100kΩ resistor. FAULT also can be used as
an input. Pull FAULT low to simultaneously shut down
the OUT_ outputs .
For multichip solutions, all of the FAULT input/outputs
can be connected together. In case of a fault condition,
all outputs on every device are turned off and the inter-
nal pulldown circuitry is activated simultaneously.
Overvoltage Fault Output (OV_OUT)
The MAX16050/MAX16051 include an overvoltage fault
output. OV_OUT is an open-drain output and requires
an external pullup resistor. When any of the SET_ volt-
ages exceed their 0.55V overvoltage threshold,
OV_OUT goes low. When all of the SET_ voltages are
below their overvoltage threshold, OV_OUT goes high
impedance after a short propagation delay.
Discharge Inputs (DISC_)
The discharge inputs (DISC_) discharge power-supply
capacitors during a power-down or fault event and mon-
itor power-supply output voltages during reverse
sequencing. When an OUT_ output goes low, the asso-
ciated DISC_ activates an 85mA pulldown current to dis-
charge any output capacitors. This helps the
power-supply output drop below the 250mV level so the
next power supply can be turned off. During normal
operation, DISC_ is high impedance and will not load
the circuit.
Bus Removal Output (REM)
The MAX16050/MAX16051 include an open-drain bus
removal output (REM) that indicates when it is safe to
disconnect the input power after a controlled power-
down operation. REM monitors DISC_ voltages and
goes low when any DISC_ input voltage goes above the
DISC_ power low threshold (V_{TH_PL}). REM goes high
when all DISC_ inputs are below the DISC_ power low
threshold (V_{TH_PL}). For a visual signal of when it is
unsafe to remove a powered board from the bus, con-
nect an LED to REM.
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