DRV411_15 Datasheet, PDF (17/34 Pages) Texas Instruments – Sensor Signal Conditioning IC for Closed-Loop Magnetic Current Sensors

DRV411
www.ti.com
SBOS693B – AUGUST 2013 – REVISED DECEMBER 2013
EXTERNAL GAIN AND COMPENSATION (OP-AMP MODE)
Op-amp mode allows several degrees of freedom for the sensor designer. In op-amp mode, the DRV411
functions like a conventional operation amplifier with high open loop gain (> 100 dB). The internal compensation
is disconnected, so that the sensor gain and compensation can be set externally. The DRV411 still provides a
stable excitation voltage of 0.74 V between terminals HALL1 and HALL3. The outputs of the Hall sensor must be
connected to terminal HALL2 and HALL4. The maximum current is limited to 10 mA to protect the Hall element.
The following list shows some ways to use op-amp mode:
• Op-amp mode can be used in cases where modes Gain_1 to Gain_3 do not lead to an acceptable frequency
response from the sensor module. In this mode, external compensation must be designed in to suit the
sensor requirements (see Figure 57).
• DRV411 can be used with symmetrical GaAs Hall sensors. However, because of the inherently low sensitivity
of GaAs sensors, the internal gain (compensation) may not be sufficient. In such cases, use op-amp mode to
make the system stable with external compensation. In op-amp mode, the excitation circuit provides a
constant 0.74 V across the HALL1 and HALL3 outputs, with HALL3 referred to GND. Connect the Hall
outputs to the HALL2 and HALL4 pins (see Figure 57). For Hall sensors with large input impedances, do not
exceed the common-mode input range of the op-amp inputs (see the Electrical Characteristics section).
• Op-amp mode can also be used for interfacing to nonsymmetrical Hall elements, which are Hall elements
where the input impedance and output impedance are not equal. Different Hall sensor input and output
impedances lead to very large sensor offsets that might be outside the correction range of the DRV411
excitation circuit. In this mode, the ERROR pin is disabled (see the Error Conditions for more details). For
Hall sensors with large input impedances, do not exceed the common-mode input range of the op amp inputs.
• If an external excitation circuit is required for the Hall sensor in op-amp mode, bypass the internal sensor by
ignoring the HALL1 and HALL3 terminals. Connect the Hall sensor outputs to the HALL2 and HALL4
terminals. For Hall sensors with large input impedances, do not exceed the common-mode input range of the
op amp inputs.
SHUNT SENSE AMPLIFIER
The differential (H-bridge) driver arrangement for the compensation coil requires a differential sense amplifier for
the shunt voltage. This differential amplifier offers wide bandwidth and a high slew rate for fast current sensors.
Excellent dc stability and accuracy result from an auto-zero technique. The voltage gain is 4 V/V, set by precisely
matched and stable internal resistors.
For gains of 4 V/V:
4 = ^R2 = ^{R4 + R5}
R₁ R_SHUNT + R₃
where:
• R₂ / R₁ = R₄ / R₃ = 4
• R₅ = R_SHUNT × 4
(1)
Both inputs of the differential amplifier are normally connected to the current shunt resistor. This resistor adds to
the internal 10-kΩ resistor, slightly reducing the gain in this signal path. For best common-mode rejection (CMR),
a dummy shunt resistor (R₅ = 4 x R_SHUNT) is placed in series with the REF_IN pin to restore matching of both
resistor dividers; see Figure 52.
Copyright © 2013, Texas Instruments Incorporated
Product Folder Links: DRV411
Submit Documentation Feedback
17