MAX5921FESA+ Maxim Integrated Products, MAX5921FESA+ Datasheet - Page 10

• Manufacturer Part Number: MAX5921FESA+
• Description: IC HOT-SWAP CTRLR -48V 8-SOIC
• Manufacturer: Maxim Integrated Products
• Type: Hot-Swap Controllerr

Specifications of MAX5921FESA+

• Applications: General Purpose
• Internal Switch(s): No
• Voltage - Supply: -20 V ~ -80 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

If the voltage between V
rent-limit trip voltage (V
down the GATE and regulate the current through the
external MOSFET such that V
current drawn by the load drops below V
limit, the GATE voltage rises again. However, if the load
current is at the regulation limit of V
od of t
the MAX5921/MAX5939 to turn off the external MOSFET.
After an overcurrent fault condition, the MAX5921 auto-
matically restarts after t
circuit breaker is reset by toggling UV or by cycling
power. Unless power is cycled to the MAX5939, the
device waits until t
gate of the external FET.
The MAX5921/MAX5939 accomplish load-current regu-
lation by pulling current from GATE whenever V
V
the external MOSFET, thereby reducing the load current.
When V
GATE high by a 45µA (I
The MAX5921/MAX5939 provide an exponential pull-
down current to turn off the external FET in response to
overcurrent conditions. The GATE pulldown current
increases (see Typical Operating Characteristics) in
response to V
(V
-48V Hot-Swap Controllers with External
R
Figure 6b. Inrush Control Waveforms
10
EE
CL
SENSE
> V
).
______________________________________________________________________________________
PHLCL
SENSE
CL
. This decreases the gate-to-source voltage of
, the electronic circuit breaker trips, causing
SENSE
- V
EE
OFF
and High Gate Pulldown Current
< V
- V
4ms/div
Exponential Current Regulation
has elapsed before turning on the
PU
CL
OFF
CL
EE
EE
Load-Current Regulation
), the MAX5921/MAX5939 pull
) current.
, the MAX5921/MAX5939 pulls
potentials greater than 50mV
and SENSE reaches the cur-
has elapsed. The MAX5939
SENSE
CL
- V
/ R
INRUSH
CURRENT
1A/div
GATE - V
10V/div
DRAIN
50V/div
V
50V/div
EE
SENSE
EE
< V
CL
EE
for a peri-
/ R
CL
SENSE
. If the
SENSE
-
The MAX5921/MAX5939 devices also include a very
fast high-current pulldown source connected to GATE
(see Typical Operating Characteristics). The high-cur-
rent pulldown activates if V
650mV (typ) during a catastrophic overcurrent or short-
circuit fault condition. The high-current pulldown circuit
sinks as much as 450mA from GATE to turn off the
external MOSFET.
The MAX5921/MAX5939 guard against input voltage
steps on the input supply. A rapid increase in the input
supply voltage (V
step equal to I = C
voltage slew rate (∆V
V
MAX5939 current limit activates, pulling down the gate
voltage and limiting the load current to V
DRAIN voltage (V
the input voltage. As the drain voltage starts to slew
down, the drain-to-gate feedback capacitor C2 pushes
back on the gate, reducing the gate-to-source voltage
(V
Once the input supply reaches its final value, the DRAIN
slew rate (and therefore the inrush current) is limited by
the capacitor C2 just as it is limited in the startup condi-
tion (see the Power-Supply Ramping section). To ensure
correct operation, R
current limit larger than the sum of the load current and
the dynamic current into the load capacitance in the
slewing mode.
If the load current plus the capacitive charging current is
below the current limit, the circuit breaker does not trip.
Use UV and OV to detect undervoltage and overvoltage
conditions. UV and OV internally connect to analog com-
parators with 130mV (UV) and 50mV (OV) of hysteresis.
When the UV voltage falls below its threshold or the OV
voltage rises above its threshold, GATE pulls low. GATE
is held low until UV goes high and OV is low, indicating
that the input supply voltage is within specification. The
MAX5921/MAX5939 includes an internal lockout (UVLO)
that keeps the external MOSFET off until the input supply
voltage exceeds 15.4V, regardless of the UV input.
UV is also used to reset the circuit breaker after a fault
condition has occurred. Pull UV below V
circuit breaker.
CL
Undervoltage and Overvoltage Protection
GS
/ R
) and the current through the external MOSFET.
SENSE
Immunity to Input Voltage Steps
during an input voltage step, the MAX5921/
DRAIN
DD
L
SENSE
x ∆V
IN
- V
) then slews at a slower rate than
/ ∆t). If the load current exceeds
EE
Load Current Regulation
(Short-Circuit Condition)
IN
must be chosen to provide a
increasing) causes a current
/ ∆t, proportional to the input
SENSE
exceeds V
CL
UVL
/ R
to reset the
SENSE
EE
. The
by