MAX6497ATA+T Maxim Integrated Products, MAX6497ATA+T Datasheet - Page 10

• Manufacturer Part Number: MAX6497ATA+T
• Description: IC CNTRLR PROT SW 8-TDFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX6497ATA+T

• Voltage - Working: 72V
• Technology: Mixed Technology
• Power (watts): 1.45W
• Number Of Circuits: 1
• Applications: General Purpose
• Package / Case: 8-TDFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Clamping: -

72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
where I
is the load current at startup, and C
capacitor.
Select external MOSFETs according to the application
current level. The MOSFET’s on-resistance (R
should be chosen low enough to have a minimum volt-
age drop at full load to limit the MOSFET power dissipa-
tion. Determine the device power rating to
accommodate an overvoltage fault when operating the
MAX6495/MAX6496/MAX6499 in overvoltage-limit mode.
During normal operation, the external MOSFET dissi-
pates little power. The power dissipated in the MOSFET
during normal operation is:
where P is the power dissipated in the MOSFET, I
is the output load current, and R
source resistance of the MOSFET.
Most power dissipation in the MOSFET occurs during a
prolonged overvoltage event when operating the
MAX6495/MAX6496/MAX6499 in voltage-limiter mode.
The power dissipated across the MOSFET is as follows
(see the Thermal Shutdown in Overvoltage-Limiter
Mode section):
where V
and source.
The MAX6495–MAX6499 thermal-shutdown feature
turns off GATE if it exceeds the maximum allowable
thermal dissipation. Thermal shutdown also monitors
the PC board temperature of the external n-channel
MOSFET when the devices sit on the same thermal
island. Good thermal contact between the MAX6495–
MAX6499 and the external n-channel MOSFET is essen-
tial for the thermal-shutdown feature to operate effec-
tively. Place the n-channel MOSFET as close to
possible to OUTFB.
When the junction temperature exceeds T
the thermal sensor signals the shutdown logic, turning
off the GATE output and allowing the device to cool.
The thermal sensor turns the GATE on again after the
IC’s junction temperature cools by 20°C. Thermal-over-
load protection is designed to protect the MAX6495–
MAX6499 and the external MOSFET in the event of cur-
rent-limit fault conditions. For continuous operation, do
10
______________________________________________________________________________________
GATE
DS
is the voltage across the MOSFET’s drain
is GATE’s 100µA sourcing current, I
P = I
P = V
LOAD
DS
2
x I
x R
LOAD
Thermal Shutdown
MOSFET Selection
DS(ON)
DS(ON)
OUT
is the drain-to-
is the output
J
= +160°C,
DS(ON)
LOAD
LOAD
)
not exceed the absolute maximum junction-temperature
rating of T
The MAX6495–MAX6499 activate an internal 100mA
pulldown on GATE when SHDN goes low, OVSET
exceeds its threshold or UVSET falls below its threshold.
Once the voltage on GATE falls below the OUTFB volt-
age, current begins to flow from OUTFB to the 100mA
pulldown through the internal clamp diode, discharging
the output capacitors.
Depending on the output capacitance and the initial volt-
age, a significant amount of energy may be dissipated
by the internal 100mA pulldown. To prevent damage to
the device ensure that for a given overvoltage threshold,
the output capacitance does not exceed the limit provid-
ed in Figure 4. This output capacitance represents the
sum of all capacitors connected to OUTFB, including
reservoir capacitors and DC-DC input filter capacitors.
When operating the MAX6495/MAX6496/MAX6499 in
overvoltage-limit mode for a prolonged period of time, a
thermal shutdown is possible. The thermal shutdown is
dependent on a number of different factors:
• The device’s ambient temperature
• The output capacitor (C
• The output load current (I
• The overvoltage threshold limit (V
Figure 4. Safe Operating Area for 100mA Pulldown.
Thermal Shutdown in Overvoltage-Limiter Mode
100,000
J
10,000
1000
= +150°C.
100
10
0
MAXIMUM OUTPUT CAPACITANCE
Peak Power-Dissipation Limit
SAFE OPERATING AREA
vs. OVERVOLTAGE THRESHOLD
10
OVERVOLTAGE THRESHOLD (V)
20
OUT
OUT
30
)
)
40
OV
50
)
60
70