DRV401_15 Datasheet, PDF (23/36 Pages) Texas Instruments – Sensor Signal Conditioning IC for Closed-Loop Magnetic Current Sensor

DRV401
www.ti.com
The connection example in Figure 8 illustrates the few
external components required for optimal performance.
Each component is described in the following list:
I_P is the primary current to be measured; K₁ and K₂
connect to the compensation coil. S1 and S2
connect to the magnetic field probe. The dots
indicate the winding direction on the sensor main
core.
R₁ and R₂ form the shunt resistor R_SHUNT. This
resistance is split into two to allow for adjustments
to the required R_SHUNT value. The accuracy and
temperature stability of these resistors are part of
the final system performance.
R₃ and R₄, together with C₃ and C₄, form a network
that reduces the remaining probe oscillator ripple in
the output signal. The component values depend
on the sensor type and are tailored for best results.
This network is not required for normal operation.
R₅ is the dummy shunt (R_D) resistor used to restore
the symmetry of both differential amplifier inputs.
R₅ = 4 × R_SHUNT, but the accuracy is less important.
R₆ and R₇ are pull-up resistors connected to the
logic outputs.
C₁ and C₂ are decoupling capacitors. Use low
ESR-type capacitors connected close to the pins.
Use low impedance printed circuit board (PCB)
traces, either avoiding vias (plated-through holes)
or using multiple vias. A combination of a large
(> 1µF) and a small (< 4.7nF) capacitor are
suggested. When selecting capacitors, make sure
to consider the large pulse currents handled from
the DRV401.
D₁ and D₂ are protection diodes for the differential
amplifier input. They are only needed if the voltage
drop at R_SHUNT exceeds 10V at the maximum
possible peak current.
SBVS070B − JUNE 2006 − REVISED MAY 2009
LAYOUT CONSIDERATIONS
The DRV401 operates with relatively large currents and
fast current pulses, and offers wide-bandwidth
performance. It is often exposed to large distortion energy
from both the primary signal and the operating
environment. Therefore, the wiring layout must provide
shielding and low-impedance connections between
critical points.
Use low ESR capacitors for power-supply decoupling. Use
a combination of a small capacitor and a large capacitor of
1µF or larger. Use low-impedance tracks to connect the
capacitors to the pins.
Both grounds should be connected to a local ground plane.
Both supplies can be connected together; however, best
results are achieved with separate decoupling (to the local
GND plane) and ferrite beads in series with the main
supply. The ferrite beads decouple the DRV401, reducing
interaction with other circuits powered from the same
supply voltage source.
The reference output is referred to GND2. A
low-impedance, star-type connection is required to avoid
the driver current and the probe current modulating the
voltage drop on the ground track.
The connection wires of the difference amplifier to the
shunt must be low resistance and of equal length. For best
accuracy, avoid current in this connection. Consider using
a Kelvin Contact-type connection. The required resistance
value can be set using two resistors.
Wires and PCB traces for S1 and S2 should be very close
or twisted. I_COMP1 and I_COMP2 should also be wired close
together. To avoid capacitive coupling, run a ground shield
between the S1/S2 and I_COMP wire pair or keep them
distant from each other.
The compensation driver outputs (I_COMP) are low
frequency only; however, the primary signal (with
high-frequency content present) is coupled into the
compensation winding, the shunt, and the difference
amplifier. Therefore, careful layout is recommended.
The output of REF_OUT and V_OUT can drive some capacitive
loads, but avoid large direct capacitive loads; these loads
increase internal pulse currents. Given the wide bandwidth
of the differential amplifier, isolate any large capacitive
load with a small series resistor. A small capacitor in the pF
range can improve the transient response on a high
resistive load.
The exposed thermal pad on the bottom of the package
must be soldered to GND because it is internally
connected to the substrate, which must be connected to
the most negative potential. It is also necessary to solder
the exposed pad to the PCB to provide structural integrity
and long-term reliability.
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