MIC2584 Datasheet, PDF (26/28 Pages) Micrel Semiconductor – Dual-Channel Hot Swap Controller/Sequencer

MIC2584/2585
PCB Layout Considerations
Because of the low values of the sense resistors used with the
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
connection to accurately measure the voltage across R_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
illustrates a recommended, multi-layer layout for the R_SENSE,
Power MOSFET, timer(s), and feedback network connec-
tions. The feedback network resistor values are selected for
Micrel
a 12V application. Many hot swap applications will require
load currents of several amperes. Therefore, the power (V_CC
and Return) trace widths (W) need to be wide enough to allow
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:
http://www.aracnet.com/cgi-usr/gpatrick/trace.pl
Finally, the use of plated-through vias will be needed to make
circuit connections to power and ground planes when utilizing
multi-layer PC boards.
Current Flow
to the Load
W
*SENSE RESISTOR
(2512)
*POWER MOSFET
(SO-8)
Current Flow
to the Load
D
G
D
S
D
S
W
D
S
**R_GATE
Via to
GND plane
**C_GATE
12.4k
1%
16 15 14 13 12 11 10 9 Via to
GND plane
93.1k
1%
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