LTC4441 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC4441' PDF : 16 Pages View PDF
LTC4441/LTC4441-1
Applications Information
The 10-Lead LTC4441 includes an open-drain output that
can be used to extend this blanking interval. The 8-Lead
LTC4441-1 does not have this blanking function. Figure 3
shows the BLANK pin connection. The BLANK pin is con-
nected directly to the switching controller’s SENSE+ input.
Figure 4 shows the blanking waveforms. If the driver input
is low, the external power MOSFET is off and MB turns
on to hold SENSE+ low. If the driver input goes high, the
power MOSFET turns on after the driver’s propagation
delay. MB remains on, attenuating the ringing seen by the
controller’s SENSE+ input. After the programmed blanking
time, MB turns off to enable the current sense signal. MB
is designed to turn on and turn off at a controlled slew rate.
This is to prevent the gate switching noise from coupling
into the current sense signal.
VIN
DRIVER
LTC4441
OUT
LEADING
EDGE DELAY
BLANK
LOAD
INDUCTOR
POWER
MOSFET
R4
TO
SWITCHING
CONTROLLER’S
CURRENT
SENSE
INPUT
SENSE+
R3
SENSE–
RBLANK
R7
MB SGND
PGND
4441 F03
KEEP THIS
TRACE SHORT
Figure 3. Blanking Circuit
The blanking interval can be adjusted using resistor R7
connected to the RBLANK pin. A small resistance value
gives a shorter interval with a default minimum of 75ns.
The value of the resistor R4 and the on-resistance of MB
(typically 11Ω) form a resistive divider attenuating the
ringing. R4 needs to be large for effective blanking, but not
so large as to cause delay to the sense signal. A resistance
value of 1k to 10k is recommended.
For optimum performance, the LTC4441/LTC4441-1should
be placed as close as possible to the powerMOSFET and
current sense resistor, R3.
IN
OUT
POWER
MOSFET’s
CURRENT
POWER MOSFET’s
SOURCE TERMINAL
MB GATE
BLANK/SENSE+
BLANKING TIME
4441 F04
Figure 4. Blanking Waveforms
Power Dissipation
To ensure proper operation and long-term reliability, the
LTC4441/LTC4441-1 must not operate beyond its maxi-
mum temperature rating. The junction temperature can
be calculated by:
IQ(TOT) = IQ + ƒ • QG
PD = VIN • (IQ + ƒ • QG)
TJ = TA + PD • θJA
where:
IQ = LTC4441/LTC4441-1 static quiescent current,
typically 250µA
ƒ = Logic input switching frequency
QG = Power MOSFET total gate charge at corre-
sponding VGS voltage equal to DRVCC
VIN = LTC4441/LTC4441-1 input supply voltage
TJ = Junction temperature
TA = Ambient temperature
θJA = Junction-to-ambient thermal resistance. The
10-pin MSOP package has a thermal resistance of
θJA = 38°C/W.
44411fa
11
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