DRV401-Q1 Datasheet, PDF (21/39 Pages) Texas Instruments – DRV401-Q1 Sensor Signal Conditioning Device for Closed-Loop Magnetic Current Sensor

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DRV401-Q1
SBOS814 – DECEMBER 2016
7.3.7 Voltage Reference
The precision 2.5-V reference circuit offers low drift (typically 10 ppm/K), used for internal biasing, and connects
to the REF_OUT pin. The circuit is intended as the reference point of the output signal to allow a bipolar signal
around it. The output is buffered for low impedance and tolerates sink and source currents of ±5 mA. Capacitive
loads may be directly connected, but generate ringing on fast load transients. A small series resistor of a few
ohms improves the response, especially for a capacitive load in the range of 1 μF. Figure 41 illustrates this circuit
configuration and the transient load regulation with 1-nF direct load.
The reference source is part of the integrated circuit and referenced to GND2. Large current pulses driving the
compensation coil generates a voltage drop in the GND connection that may add on to the reference voltage.
Therefore, a low impedance GND layout is critical to handle the currents and the high bandwidth of the device.
Test Circuit:
REF_OUT
10 kW
1 nF
±5 V
+2.5 V
2.5 ms/div
Figure 41. Pulse Response: Test Circuit and Scope Shot of Reference
7.3.8 Demagnetization
Iron cores are not immune to residual (remanence) magnetism. The residual remanence produces a signal offset
error, especially after strong current overload, which goes along with high magnetic field density. Therefore, the
DRV401-Q1 device includes a signal generator for a demagnetization cycle. The digital control pin, DEMAG,
starts the cycle on demand after the pin is held high for at least 25.6 μs. Shorter pulses are ignored. The cycle
lasts for approximately 110 ms. During this time, the ERROR flag is asserted low to indicate that the output is not
valid. When DEMAG is high during power-on, a demagnetization cycle immediately initiates (12 μs) after power-
on (V_DD > 4 V). Holding DEMAG low avoids this cycle at power-up. See the Power-On and Brownout section for
more information.
The probe circuit is in normal operation and oscillates during the demagnetization cycle. The PWM and PWM
outputs are active accordingly.
A demagnetization cycle can be aborted by pulling DEMAG low, filtered by 25 μs to ignore glitches, as shown in
Figure 46. In a typical circuit, the DEMAG pin may be connected to the positive supply, which enables a degauss
cycle every time the unit is powered on.
The degauss cycle is based on an internal clock and counter logic. The maximum current is limited by the
resistance of the connected coil in series with the shunt resistor. The DEMAG logic input requires a 5-V, CMOS-
compatible signal.
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