DRV401_15 Datasheet, PDF (18/36 Pages) Texas Instruments – Sensor Signal Conditioning IC for Closed-Loop Magnetic Current Sensor

DRV401
SBVS070B − JUNE 2006 − REVISED MAY 2009
The reference input (REF_IN) is the reference node for the
exact output signal (V_OUT). Connecting REF_IN to the
reference output (REF_OUT) results in a live zero reference
voltage of 2.5V. Using the same reference for REF_IN and
the ADC avoids mismatch errors that exist between two
reference sources.
OVER-RANGE COMPARATOR
High peak current can overload the differential amplifier
connected to the shunt. The OVER-RANGE pin, an
open-drain output, indicates an over-voltage condition for
the differential amplifier by pulling low. The output of this
flag is suppressed for 3µs, preventing unwanted triggering
from transients and noise. This pin returns to high as soon
as the overload condition is removed (external pull-up
required to return the pin high).
This ERROR flag not only provides a warning about a
signal clipping condition, but is also a window comparator
output for actively shutting off circuits in the system. The
value of the shunt resistor defines the operating window for
the current. It sets the ratio between the nominal signal and
the trip level of the Over-Range flag. The trip current of this
window comparator is calculated using the following
example:
With a 5V supply, the output voltage swing is
approximately ±2.45V (load and supply
voltage-dependent).
The gain of 4V/V allows an input swing of ±0.6125V.
Thus, the clipping current is I_MAX = 0.6125V/R_SHUNT.
See the differential amplifier curve of the Typical
Characteristics, Output Voltage vs Output Current.
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The over-range condition is internally detected as soon as
the amplifier exceeds its linear operating range, not just a
set voltage level. Therefore, the error or the over-range
comparator level is reliably indicated in fault conditions
such as output shorts, low load or low supply conditions.
As soon as the output cannot drive the voltage higher, the
flag is activated. This configuration is a safety
improvement over a voltage level comparator.
NOTE: The internal resistance of the compensation coil
may prevent high compensation current from flowing
because of I_COMP driver overload. Therefore, the
differential amplifier may not overload with this current.
However, a fast rate of change of the primary current would
be transmitted through transformer action and safely
trigger the overload flag.
VOLTAGE REFERENCE
The precision 2.5V reference circuit offers low drift
(typically 10ppm/K) and is used for internal biasing; it is
also connected to the REF_OUT pin. The circuit is intended
as the reference point of the output signal to allow a bipolar
signal around it. This output is buffered for low impedance
and tolerates sink and source currents of ±5mA.
Capacitive loads can 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 1µF. Figure 6 shows the
transient load regulation with 1nF direct load.
The reference source is part of the integrated circuit and
referenced to GND2. Large current pulses driving the
compensation coil can generate a voltage drop in the GND
connection that would add on to the reference voltage.
Therefore, a low impedance GND layout is critical to
handle the currents and the high bandwidth of this IC.
Test Circuit:
REF_OUT
10kΩ
1nF
±5V
+2.5V
2.5µs/div
Figure 6. Pulse Response Test Circuit and Scope Shot of Reference
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