MIC2588_05 Datasheet, PDF (18/21 Pages) Micrel Semiconductor – Single-Channel, Negative High-Voltage Hot Swap Power Controllers

MIC2588/MIC2594
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 8 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 9 is a suggested PCB layout diagram for the MIC2588/
MIC2594. Many hot swap applications will require load currents
of several amperes. Therefore, the power (V_EE and Return)
trace widths (W) need to be wide enough to allow the current
Micrel
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 MIC2588/MIC2594 V_EE Pin
Signal Trace
to MIC2588/MIC2594 SENSE Pin
Note: Each SENSE lead trace shall be
balanced for best performance with equal
length/equal aspect ratio.
Figure 8. 4-Wire Kelvin Sense Connections for R_SENSE
Current Flow
to the Load
W
Via to the
Return (VDD)
plane
^R1
GROUND
PAD
MIC2588-2BM
/PWRGD
VDD
R3
Via to the
bottom side
Via to the
Return (VDD)
plane
OV
R2
UV
VEE
D1
C1
Current Flow
from the Load
DRAIN
GATE
SENSE
Via to the
power (VEE output)
plane
RFDBK
CFDBK
Via to the
power (VEE output)
plane
C3
R4
W
*SENSE RESISTOR
(WSR-2 or
WSL2512)
- DRAWING IS NOT TO SCALE-
*See Table 1 for part numbers and vendors
^R1 placed on bottom side
Power Plane -------- (red)
Ground Plane ------- (black)
Trace width (W) guidelines and additional information given in
"PCB Layout Recommendations" section of the datasheet
W
Via to the
ground plane
*POWER MOSFET
(TO-263)
Figure 9. Recommended PCB Layout for Sense Resistor, Power MOSFET, Overvoltage/Undervoltage Resistive
Divider Network, and Timer Capacitors
September 2005
18
M9999-083005