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DRV401 Datasheet(PDF) 23 Page - Texas Instruments |
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DRV401 Datasheet(HTML) 23 Page - Texas Instruments |
23 / 36 page DRV401 SBVS070B − JUNE 2006 − REVISED MAY 2009 www.ti.com 23 The connection example in Figure 8 illustrates the few external components required for optimal performance. Each component is described in the following list: IP 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 RSHUNT. This resistance is split into two to allow for adjustments to the required RSHUNT 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 (RD) resistor used to restore the symmetry of both differential amplifier inputs. R5 = 4 × RSHUNT, 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 (< 4.7nF) 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 RSHUNT exceeds 10V 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. ICOMP1 and ICOMP2 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 (ICOMP) 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 REFOUT and VOUT 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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Descripción similar - DRV401_17 |
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