LTC1644
22
1644f
APPLICATIO S I FOR ATIO
WUU
U
Table 7. Manufacturers’ Web Site
MANUFACTURER WEB SITE
International Rectifier www.irf.com
ON Semiconductor www.onsemi.com
IRC-TT www.irctt.com
Vishay-Dale www.vishay.com
Vishay-Siliconix www.vishay.com
Diodes, Inc. www.diodes.com
Obtaining Information on Specific Parts
For more information regarding or to request a copy of the
CompactPCI specification, contact the PCI Industrial Com-
puter Manufacturers Group at:
PCI Industrial Computer Manufacturers Group
Wakefield, MA 01880 USA
Phone: 01 (617) 224-1100
Web Site: http://www.picmg.com
TransZorb SMAJ12CA and diodes BAV99 are supplied by:
Diodes, Incorporated
Westlake Village, CA 91362 USA
Phone: 01 (805) 446-4800
Web Site: http://www.vishay-liteon.com or
http://www.diodes.com
Transistors MMBT2222A and TVS 1PMT5.0AT3 are
supplied by:
Semiconductor Components Industries, LLC
Phoenix, AZ 85008 USA
Phone: 01 (602) 244-6600
Web Site: http://www.onsemi.com
PCB Layout Considerations
For proper operation of the LTC1644’s circuit breaker
operation, 4-wire Kelvin-sense connections between the
sense resistor and the LTC1644’s 5V
IN
and 5V
SENSE
pins
and 3V
IN
and 3V
SENSE
pins are strongly recommended.
The PCB layout should be balanced and symmetrical to
minimize wiring errors. In addition, the PCB layout for the
sense resistors and the power MOSFETs should include
good thermal management techniques for optimal device
power dissipation.
A recommended PCB layout for the sense resistor, the
power MOSFET and the GATE drive components around
the LTC1644 is illustrated in Figure 18. In Hot Swap
applications where load currents can be 10A, narrow PCB
tracks exhibit more resistance than wider tracks and
operate at more elevated temperatures. Since the sheet
resistance of 1 ounce copper foil is approximately
0.45mΩ/■■, track resistances add up quickly in high
current applications. Thus, to keep PCB track resistance
and temperature rise to a minimum, the suggested trace
width in these applications for 1 ounce copper foil is 0.03"
for each ampere of DC current.
In the majority of applications, it will be necessary to use
plated-through vias to make circuit connections from
component layers to power and ground layers internal to
the PC board. For 1 ounce copper foil plating, a general rule
is 1 ampere of DC current per via, making sure the via is
properly dimensioned so that solder completely fills any
void. For other plating thicknesses, check with your PCB
fabrication facility.
Power MOSFET and Sense Resistor Selection
Table 8 lists some current sense resistors that can be used
the LTC1644’s circuit breakers and Table 9 list some
power MOSFET transistors that are available. Table 7 lists
supplier web site addresses for discrete component men-
tioned throughout the LTC1644 data sheet.
