ISL28025 Datasheet, PDF (43/47 Pages) Intersil Corporation – Precision Digital Power Monitor with Real Time Alerts

ISL28025
TRACE ROUTING
It is always advised to make the distance between voltage
source, sense resistor and load as close as possible. The longer
the trace length between components will result in voltage drops
between components. The additional resistance will reduce the
efficiency of a system.
The bulk resistance, , of copper is 0.67µΩ/in or 1.7µΩ/cm at
+25°C. The resistance of trace can be calculated from
Equation 19.
R _trace
Trace _length
  _{Trace widthTrace thickness}
(EQ. 19)
Orthogonal routing for high current flow traces will result in
current crowding, localized heating of the trace and a change in
trace resistance.
CURRENT ^FLOW
CURRENT FLOW
Figure 84 illustrates each dimension of a trace.
TRACE
THICKNESS
TRACE
WIDTH
TLREANCGETH
FIGURE 84. ILLUSTRATION OF THE TRACE DIMENSIONS OF A STRIP
LINE TRACE
For example, assume a trace has 2oz. of copper or 2.8mil
thickness, a width of 100mil and a length of 0.5in. Using
Equation 19, the resistance of the trace is approximately 2mΩ.
Assume 1A of current is passing through the trace. A 2mV
voltage drop would result from trace routing.
Current flowing through a conductor will take the path of least
resistance. When routing a trace, avoid orthogonal connections
for current bearing traces.
FIGURE 86. USE ARCS AND 45° TRACES TO SAFELY ROUTE TRACES
WITH LARGE CURRENT FLOWS
The utilization of arcs and 45° traces in routing large current flow
traces will maintain uniform current flow throughout the trace.
Figure 86 illustrates the routing technique.
CONNECTING SENSE TRACES TO THE CURRENT SENSE
RESISTOR
Ideally, a 4 terminal current sense resistor would be used as the
sensing element. Four terminal sensor resistors can be hard to
find in specific values and in sizes. Often a two terminal sense
resistor is designed into the application.
Sense lines are high impedance by definition. The connection
point of a high impedance line reflects the voltage at the
intersection of a current bearing trace and a high impedance
trace.
The high impedance trace should connect at the intersection
where the sense resistor meets the landing pad on the PCB. The
best place to make current sense line connection is on the inner
side of the sense resistor footprint. The illustration of the
connection is shown in Figure 87. Most of the current flow is at
the outer edge of the footprint. The current ceases at the point
the sense resistor connects to the landing pad. Assume the
sense resistor connects at the middle of the each landing pad,
this leaves the inner half of the each landing pad with little
current flow. With little current flow, the inner half of each
landing pad is classified as high impedance and perfect for a
sense connection.
FIGURE 85. AVOID ROUTING ORTHOGONAL CONNECTIONS FOR
TRACES THAT HAVE HIGH CURRENT FLOWS.
Submit Document Feedback ₄₃
FN8388.3
June 17, 2015