DRV401-Q1 Datasheet, PDF (19/39 Pages) Texas Instruments – DRV401-Q1 Sensor Signal Conditioning Device for Closed-Loop Magnetic Current Sensor

www.ti.com
DRV401-Q1
SBOS814 – DECEMBER 2016
Feature Description (continued)
7.3.3 Compensation Driver
The compensation coil driver provides the driving current for the compensation coil. A fully-differential driver
stage offers high signal voltages to overcome the wire resistance of the coil with a 5-V supply. The compensation
coil is connected between I_COMP1 and I_COMP2, generating an analog voltage across the coil (shown in Figure 39)
that turns into current from the wire resistance (and eventually from the inductance). The compensation current
represents the primary current transformed by the turns ratio. A shunt resistor is connected in this loop and the
high-precision difference amplifier translates the voltage from the shunt to an output voltage.
Both compensation driver outputs provide low impedance over a wide frequency range to ensure smooth
transitions between the closed-loop compensation frequency range and the high-frequency range, where the
primary winding directly couples the primary current into the compensation coil at a rate set by the winding ratio.
The two compensation driver outputs are designed with protection circuitry to handle inductive energy. However,
additional external protection diodes may be necessary for high-current sensors.
For reliable operation, a wire break in the compensation circuit can be detected. If the feedback loop is broken,
the integrating filter drives the I_COMP1 and I_COMP2 outputs to the opposite rails. With one of these pins coming
within 300 mV to ground, a comparator tests for a minimum current flowing between I_COMP1 and I_COMP2. If the
current stays below the threshold current level for a minimum of 100 μs, the ERROR pin is asserted active (low).
The threshold current level for the test is less than 57 mA at 25°C and 65 mA at −40°C if the I_COMP pins are fully
railed, as shown in the Typical Characteristics section.
For sensors with high winding resistance (compensation coil resistance + R_SHUNT) or that are connected to an
external compensation driver, this function must be disabled by pulling the CCdiag pin low, as shown in
Equation 1:
V
R
MAX
=
OUT
65 mA
where:
• V_OUT equals the peak voltage between I_COMP1 and I_COMP2 at a 65-mA drive current; and
• R_MAX equals the sum of the coil and the shunt resistance
(1)
7.3.4 External Compensation Coil Driver
An external driver for the compensation coil connects to the I_COMP1 and I_COMP2 outputs. To prevent a wire break
indication, CCdiag must be asserted low.
An external driver provides a higher drive voltage and more drive current. The driver moves the power dissipation
to the external transistors, thereby allowing a higher winding resistance in the compensation coil and more
current. Figure 40 shows a block diagram of an external compensation coil driver. To drive the buffer, one or
both of the I_COMP outputs may be used. Note, however, that the additional voltage gain can cause instability of
the loop. Therefore, the internal gain may be reduced by approximately 8 dB by asserting the GAIN pin high.
R_SHUNT is connected to GND to allow for a single-ended external compensation driver. The differential amplifier
continues to sense the voltage, and is used for the gain and over-range comparator or ERROR flag.
V+
DRV401-Q1
I_COMP1
External
Buffer
I_COMP2
Compensation
Coil
V-
R_SHUNT
Copyright © 2016, Texas Instruments Incorporated
Figure 40. DRV401-Q1 with External Compensation Coil Driver and R_SHUNT Connected to GND
Copyright © 2016, Texas Instruments Incorporated
Submit Documentation Feedback
19
Product Folder Links: DRV401-Q1