LM25066APSQE/NOPB National Semiconductor, LM25066APSQE/NOPB Datasheet - Page 19

• Manufacturer Part Number: LM25066APSQE/NOPB
• Description: IC CTLR PM HOTSWAP 24-LLP
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM25066APSQE/NOPB

• Applications: Base Station-Networking Line Cards, Servers
• Current - Supply: 5.8mA
• Voltage - Supply: 2.9 V ~ 17 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: *
• Package / Case: *
• Input Voltage: 17V
• Internal Switch: No
• Supply Voltage Range: 2.9V To 5.5V
• Rohs Compliant: Yes
• Digital Ic Case Style: LLP
• No. Of Pins: 24
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LM25066APSQE/NOPBTR

cycles). The MOSFET manufacturer should be consulted for
guidelines.
- R
pation at maximum load current (I
its junction temperature above the manufacturer’s recom-
mendation.
- The gate-to-source voltage provided by the LM25066A can
be as high as 18.8V at turn-on when the output voltage is zero.
At turn-off the reverse gate-to-source voltage will be equal to
the output voltage at the instant the GATE pin is pulled low.
If the device chosen for Q
external zener diode must be added from its gate to source,
with the zener voltage less than the device maximum V
rating. The zener diode’s working voltage protects the MOS-
FET during turn-on, and its forward voltage protects the MOS-
FET during shutoff. The zener diode’s forward current rating
must be at least 190 mA to conduct the GATE pull-down cur-
rent when a circuit breaker condition is detected.
CURRENT LIMIT (R
The LM25066A monitors the current in the external MOSFET
Q
connected from VIN to SENSE. The required resistor value is
calculated from:
where I
across R
POWER LIMIT THRESHOLD
The LM25066A determines the power dissipation in the ex-
ternal MOSFET (Q
current in R
resistor at the PWR pin (R
sipation for Q
where P
Q
rent Limit section. For example, if R
desired power limit threshold is 20W, R
kΩ. If Q
is modulated to regulate the load current, keeping Q
from exceeding the threshold. For proper operation of the
power limiting feature, R
1
1
DS(on)
by measuring the voltage across the sense resistor (R
and R
LIM
1
R
’s power dissipation reaches the threshold, Q
MOSFET(LIM)
should be sufficiently low such that the power dissi-
S
S
PWR
reaches V
is the desired current limit threshold. If the voltage
is the current sense resistor described in the Cur-
S
) and the V
1
= 1.71 x 10
and is calculated from the following equation:
1
is the desired power limit threshold for
CL
S
) by monitoring the drain current (the
)
, the current limit circuit modulates the
DS
1
5
PWR
PWR
is not rated for these voltages, an
of Q
x R
) sets the maximum power dis-
must be
S
1
x P
LIM
(SENSE to OUT pins). The
2
MOSFET(LIM)
x R
S
PWR
≤
DS(on)
is 10 mΩ, and the
150 kΩ. While the
calculates to 34.2
FIGURE 7. Sense Resistor Connections
) does not raise
1
’s power
1
’s gate
(1)
(2)
S
GS
),
19
gate of Q
limiting circuit is active, the fault timer is active as described
in the Fault Timer & Restart section. For proper operation,
R
V
software. This setting defaults to use of CL pin which when
grounded is 25mV or high is 46mV. The value when powered
can
MFR_SPECIFIC_DEVICE_SETUP command, which de-
faults to the 25mV setting.
Once the desired setting is known, calculate the shunt based
on that input voltage and maximum current. While the maxi-
mum load current in normal operation can be used to deter-
mine the required power rating for resistor R
current limit value provides a more reliable design since the
circuit can operate near the current limit threshold continu-
ously. The resistor’s surge capability must also be considered
since the circuit breaker threshold is 1.8 or 3.6 times the cur-
rent limit threshold.
Connections from R
Kelvin techniques. In the suggested layout of
small pads at the lower corners of the sense resistor connect
only to the sense resistor terminals and not to the traces car-
rying the high current. With this technique, only the voltage
across the sense resistor is applied to VIN and SENSE, elim-
inating the voltage drop across the high current solder con-
nections.
power limiting circuit is active, the fault timer is active as de-
scribed in the Fault Timer & Restart section. Typically, power
limit is reached during startup or if the output voltage falls be-
casue of a severe overload or short circuit. The programmed
maximum power dissipation should have a reasonable mar-
gin from the maximum power defined by the SOA chart,
especially if retry is enabled since the MOSFET will be re-
peatedly stressed during fault restart cycles. The MOSFET
manufacturer should be consulted for guidelines. If the appli-
cation does not require use of the power limit function, the
PWR pin can be left open. The accuracy of the power limit
function at turn-on may degrade if a very low value power
dissipation limit is set. The reason for this caution is that the
voltage across the sense resistor, which is monitored and
regulated by the power limit circuit, is lowest at turn-on when
CL
S
must be less than 200 mΩ.
can be set to either 25mV or 46mV via hardware and/or
be
1
to regulate the current at I
set
S
to the LM25066A should be made using
via
30146019
the
PMBus
LIM
. While the current
S
, basing it on the
Figure
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with
7, the
the