DRV421_16 Datasheet, PDF (21/44 Pages) Texas Instruments – Integrated Magnetic Fluxgate Sensor for Closed-Loop Current Sensing

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DRV421
SBOS704B – MAY 2015 – REVISED MARCH 2016
7.3.6 Voltage Reference
The internal precision voltage reference circuit offers low drift performance at the REFOUT output pin and is
used for internal biasing. The reference output is intended to be the common-mode voltage of the output (VOUT
pin) to provide a bipolar signal swing. This low-impedance output tolerates sink and source currents of ±5 mA.
However, fast load transients can generate ringing on this line. A small series resistor of a few ohms improves
the response, particularly for capacitive loads equal to or greater than 1 μF.
Adjust the value of the voltage reference output to the power supply of the DRV421 using mode selection pins
RSEL0 and RSEL1, as shown in Table 2.
Table 2. Reference Output Voltage Selection
MODE
V_REFOUT = 2.5 V
V_REFOUT = 1.65 V
Ratiometric output
RSEL1
0
0
1
RSEL0
0
1
x
DESCRIPTION
Use with sensor module supply of 5 V
Use with sensor module supply of 3.3 V
Provides output centered on V_DD / 2
In ratiometric output mode, an internal resistor divider divides the power supply voltage by a factor of two.
For current sensor modules with a reference input pin, the DRV421 also allows overwriting the internal reference
with an external reference voltage, V_EXT, as shown in Figure 58. If there is a significant difference between the
external and the internal voltage, resistor R₅ limits the current flow from the internal reference. In this case, the
internal reference sources current I_REFOUT shown in Equation 5:
I_REFOUT
V_REFOUT V_EXT
600
(5)
Current Sense Module
AINN
RSHUNT
Compensation
Coil
AINP
ICOMP2
ICOMP1
DRV421
_
Shunt Sense
Amplifier
+
Internal
Voltage
Reference
VDD
VDD
VOUT
VOUT
R5
(Dummy Shunt)
REFIN
R6
600
REFOUT
GND
REFIN
GND
External
Voltage
Reference
Figure 58. DRV421 with External Reference
The example of 600 Ω for R₆ was chosen for illustration purposes; different values are possible. If no external
reference is connected, R₆ has little impact on the common-mode rejection of the shunt sense amplifier;
therefore, use a resistor value that is as small as possible.
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