MAX5921EESA+ Maxim Integrated Products, MAX5921EESA+ Datasheet - Page 12

• Manufacturer Part Number: MAX5921EESA+
• Description: IC HOT-SWAP CTRLR -48V 8-SOIC
• Manufacturer: Maxim Integrated Products
• Type: Hot-Swap Controllerr

Specifications of MAX5921EESA+

• 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

The MAX5921/MAX5939 feature an overcurrent fault inte-
grator. When an overcurrent condition is detected, an
internal digital counter is incremented. The clock period
for the digital counter is 32µs for the 500µs maximum
current-limit duration version and 128µs for 2ms maxi-
mum current-limit duration devices. An overcurrent of
less than 32µs is interpreted as an overcurrent of 32µs.
When the counter reaches 500µs (the maximum current-
limit duration) for the MAX5921/MAX5939A, an overcur-
rent fault is generated. If the overcurrent fault does not
last 500µs, then the counter begins decrementing at a
rate 128 (maximum current-limit duty cycle) times slower
than the counter was incrementing. Repeated overcur-
rent conditions generate a fault if the duty cycle of the
overcurrent condition duty ratio is greater than the maxi-
mum current-limit duty cycle (see Figure 14).
The MAX5921/MAX5939 include internal die-tempera-
ture monitoring. When the die temperature reaches the
thermal-shutdown threshold, T
MAX5939 pull GATE low and turn off the external MOS-
FET. If a good thermal path is provided between the
MOSFET and the MAX5921/MAX5939, the device offers
thermal protection for the external MOSFET. Placing the
-48V Hot-Swap Controllers with External
R
Figure 9. Automatic Restart After a Short Circuit
12
SENSE
______________________________________________________________________________________
Overcurrent Fault Integrator
and High Gate Pulldown Current
10ms/div
Thermal Shutdown
OT
, the MAX5921/
V
2V/div
I
2A/div
D
GATE
(Q1)
- V
EE
MAX5921/MAX5939 near the drain of the external MOS-
FET offers the best thermal protection because most of
the power is dissipated in its drain.
After a thermal shutdown fault has occurred, the
MAX5921_ turns the external FET off for a minimum
time of t
MAX5921_ device restarts after the temperature drops
20°C below the thermal-shutdown threshold.
The MAX5939_ latches off after a thermal shutdown
fault. The MAX5939_ can be restarted by toggling UV
low or cycling power. However, the device keeps the
external FET off for a minimum time of t
gling UV.
The circuit-breaker current-limit threshold is set to 50mV
(typ). Select a sense resistor that causes a drop equal
to or above the current-limit threshold at a current level
above the maximum normal operating current. Typically,
set the overload current to 1.5 to 2.0 times the nominal
load current plus the dynamic load-capacitance charg-
ing current during startup. Choose the sense resistor
power rating to be greater than (V
Figure 10. Undervoltage and Overvoltage Sensing
V
V
OFF
UV
OV
= 1.255
= 1.255
, allowing the MOSFET to cool down. The
-48V RTN
Applications Information
R4 + R5 + R6
R4 + R5 + R6
(SHORT PIN)
R5 + R6
-48V
-48V RTN
R6
R4
R5
R6
3
2
CL
UV
OV
)
Sense Resistor
2
MAX5921
MAX5939
/ R
V
V
DD
EE
SENSE
8
4
OFF
when tog-
.