MIC2584/2585
Micrel
PCB Layout Considerations
Becauseofthelowvaluesofthesenseresistorsusedwiththe
MIC2584/85 controllers, special attention to the layout must
be used in order for the device’s circuit breaker function to
operate properly. Specifically, the use of a 4-wire Kelvin
a 12V application. Many hot swap applications will require
load currents of several amperes. Therefore, the power (V
CC
andReturn)tracewidths(W)needtobewideenoughtoallow
the current to flow while the rise in temperature for a given
copper plate (e.g., 1oz. or 2oz.) is kept to a maximum of
10°C ~ 25°C. Also, these traces should be as short as
possible in order to minimize the IR drops between the input
and the load. For a starting point, there are many trace width
calculation tools available on the web such as the following
link:
connectiontoaccuratelymeasurethevoltageacrossR
SENSE
is highly recommended. Kelvin sensing is simply a means of
making sure that any voltage drops in the power traces
connecting to the resistors does not get picked up by the
traces themselves. Additionally, these Kelvin connections
should be isolated from all other signal traces to avoid
introducing noise onto these sensitive nodes. Figure 14
http://www.aracnet.com/cgi-usr/gpatrick/trace.pl
illustratesarecommended, multi-layerlayoutfortheR
,
SENSE
Power MOSFET, timer(s), and feedback network connec-
tions. The feedback network resistor values are selected for
Finally, the use of plated-through vias will be needed to make
circuitconnectionstopowerandgroundplaneswhenutilizing
multi-layer PC boards.
Current Flow
to the Load
Current Flow
to the Load
*POWER MOSFET
*SENSE RESISTOR
(2512)
(SO-8)
D
G
D
D
S
S
W
W
D
S
Via to
GND plane
**RGATE
**CGATE
12.4k
1%
93.1k
1%
16
15
14
13
12
11
10
9
Via to
GND plane
Current Flow
from the Load
W
DRAWING IS NOT TO SCALE
Similar considerations should be used for Channel 2.
*See Table 5 for part numbers and vendors.
**Optional components.
Trace width (W) guidelines given in "PCB Layout Recommendations" section of the datasheet.
Figure 14. Recommended PCB Layout for Sense Resistor, Power MOSFET and Feedback Network
MIC2584/2585
26
March 2005
MICREL [ MICREL SEMICONDUCTOR ]
