MIC2589_05 Datasheet, PDF (25/29 Pages) Micrel Semiconductor – Single-Channel, Negative High-Voltage Hot Swap Power Controller/Sequencer

Micrel
PCB Layout Considerations
4-Wire Kelvin Sensing
Because of the low value typically required for the
sense resistor, special care must be used to measure
accurately the voltage drop across it. Specifically, the
measurement technique across each R_SENSE must
employ 4-wire Kelvin sensing. This is simply a means
of making sure that any voltage drops in the power
traces connecting to the resistors are not picked up by
the signal conductors measuring the voltages across
the sense resistors.
Figure 9 illustrates how to implement 4-wire Kelvin
sensing. As the figure shows, all the high current in
the circuit (from V_EE through R_SENSE, and then to the
source of the output MOSFET) flows directly through
the power PCB traces and R_SENSE. The voltage drop
resulting across R_SENSE is sampled in such a way that
the high currents through the power traces will not
introduce any parasitic voltage drops in the sense
leads. It is recommended to connect the hot swap
controller’s sense leads directly to the sense resistor’s
metalized contact pads.
Other Layout Considerations
Figure 10 is a suggested PCB layout diagram for the
MIC2589/MIC2595. Many hot swap applications will
require load currents of several amperes. Therefore,
MIC2589/MIC2595
the power (V_EE 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 to 25°C. The
return (or power ground) trace should be the same
width as the positive voltage power traces (input/load)
and isolated from any ground and signal planes so
that the controller’s power is common mode. Also,
these traces should be as short as possible in order to
minimize the IR drops between the input and the load.
Finally, the use of plated-through vias will be
necessary to make circuit connections to the power,
ground and signal planes of multi-layer PCBs.
PCB Track Width:
0.03" per Ampere
using 1oz Cu
Power Trace
From V_EE
R_SENSE metalized
contact pads
R_SENSE
Power Trace
To MOSFET Source
Signal Trace
to MIC2589/MIC2595 V_EE Pin
Signal Trace
to MIC2589/MIC2595 SENSE Pin
Note: Each SENSE lead trace shall be
balanced for best performance with equal
length/equal aspect ratio.
Figure 9. 4-Wire Kelvin Sense Connections for
R_SENSE
December 2005
25
M9999-120505
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