LTC4271IUF#PBF Linear Technology, LTC4271IUF#PBF Datasheet - Page 27

• Manufacturer Part Number: LTC4271IUF#PBF
• Manufacturer: Linear Technology

Specifications of LTC4271IUF#PBF

• Operating Temperature (max): 85C
• Operating Temperature (min): -40C
• Pin Count: 24
• Mounting: Surface Mount
• Package Type: QFN EP
• Case Length: 4mm
• Screening Level: Industrial
• Lead Free Status / Rohs Status: Compliant

APPLICATIONS INFORMATION
External MOSFET
Careful selection of the power MOSFET is critical to system
reliability. LTC recommends either Fairchild IRFM120A,
FDT3612, FDMC3612 or Philips PHT6NQ10T for their
proven reliability in Type 1 and Type 2 PSE applications.
SOA curves are not a reliable specification for MOSFET
selection. Contact LTC Applications before using a MOSFET
other than one of these recommended parts.
Sense Resistor
The LTC4270/LTC4271 is designed to use 0.25Ω current
sense resistors to reduce power dissipation. Four com-
monly available 1Ω resistors (sized according to power
dissipation) can be used in parallel in place of a single
NO ISOLATION
REQUIRED ON
I
2
C INTERFACE
GP0
GP1
MID
RESET
MSD
AUTO
INT
SCL
SDAIN
SDAOUT
AD0
AD1
AD2
AD3
AD6
DGND
LTC4271
V
3.3V
DD33
CAP1
1μF
0.1μF
CND
DPD
DND
CPD
Figure 15. LTC4270/LTC4271 Proprietary Isolation
3.3V
3.3V
100Ω
100Ω
100Ω
100Ω
2nF , 2kV
T1
T2
100Ω
100Ω
100Ω
100Ω
0.25Ω resistor. In order to meet the I
required by the IEEE specification, the sense resistors
should have ±1% tolerance or better, and no more than
±200ppm/°C temperature coefficient. In addition, the sense
resistors must meet strict layout guidelines.
Port Output Cap
Each port requires a 0.22μF cap across its outputs to keep
the LTC4270 stable while in current limit during startup or
overload. Common ceramic capacitors often have signifi-
cant voltage coefficients; this means the capacitance is
reduced as the applied voltage increases. To minimize this
problem, X7R ceramic capacitors rated for at least 100V
are recommended and must be located close to the PSE.
–54V
–54V
0.1μF
CPA
CNA
DPA
DNA
CAP2
–54V
V
EE
XIO0
VSSK
LTC4270
1μF
LTC4270/LTC4271
XIO1
AGND
SENSEn
SENSE1
GATEn
GATE1
BULK CAP
OUTn
OUT1
SYSTEM
>47μF
–54V
+
CUT
0.25Ω
0.25Ω
0.22μF
100V
0.22μF
100V
and I
LIM
S1B
S1B
S1B
S1B
accuracy
27
–54V
–54V
42701 F16
PORTn
PORT1
42701f