DRV401-EP Datasheet, PDF (25/33 Pages) Texas Instruments – SENSOR SIGNAL CONDITIONING IC FOR CLOSED-LOOP MAGNETIC CURRENT SENSOR

DRV401-EP
www.ti.com............................................................................................................................................................................................... SBVS104 – JANUARY 2008
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(> 1 µF) and a small (< 4.7 nF) 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 needed only if the voltage drop at
R_SHUNT exceeds 10 V at the maximum possible peak current.
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 1 µF 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 ICOMP 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.
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): DRV401-EP
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