Description of the LMP8601
Evaluation Board
The LMP8601 evaluation board requires a power supply with
a voltage between 3.0V and 5.5V , the supply current will be
<2 mA in normal operation with high impedance load on the
output of the part. The positive supply voltage is connected to
V
S
(P5) The negative supply voltage is connected to GND
(P6).
The offset voltage on the output of the LMP8601 is deter-
mined by the voltage on the offset pin which is connected to
pin2 of J1 and the offset voltage will be V
Offset
/2. This pin is
normally connected with a jumper to GND or V
S
, but this pin
can also be driven from a low impedance source (<10
Ω).
With a jumper on J1 between 1–2 the offset pin is connected
to V
S
and the offset voltage is half the value of V
S
. In this
configuration the LMP8601 can be used for measuring bidi-
rectional currents.
With a jumper on J1 between 2–3 the offset pin is connected
to GND and the output voltage is ground referenced. In this
configuration the LMP8601 is used for measuring unidirec-
tional currents.
The input signal is connected bIN (P1) and −IN (P2)
and the output signal is available at OUT (P3).
On the board there is the possibility to place a capacitor C2
which creates a low pass filter between the first and second
stage. This can be used to reduce the output noise and glitch-
es that might appear from switching large common mode
voltages with very fast transients at the input . (Please see the
application section of the LMP8601 data sheet for more de-
tails about this filter).
the Header J2 is normally shorted with a jumper and connects
the first stage to the second stage . The application section of
the LMP8601 data sheet explains more about the alternative
configurations that can be made after removing the jumper on
J2.
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FIGURE 2. Power Supply Connectors and Headers
PCB Layout Guidelines
This section provides general practical guidelines for PCB
layouts that use various power and ground traces. Designers
should note that these are only "rule-of-thumb" recommen-
dations and the actual results are predicated on the final
layout.
DIFFERENTIAL SIGNALS
The two input pins of the LMP8601 form a differential pair that
must be handled following the rules given below.
•
Keep both signals coupled by routing them closely
together and keeping them of equal length.
•
Do not allow any other signal in between these two signals
of the differential pair.
•
Keep all impedances in both traces of the signal equal.
POWER, GROUND AND DE-COUPLING
Keep the power supply de-coupling capacitor close to the
power supply pin (V
S
of the part.)
Make sure all return currents of the signals can flow next to
the originating signals
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