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VOUT

REFOUT

Internal

Voltage

Reference

600

REFIN

Current Sense Module

VDD

GND

External

Voltage

Reference

Shunt Sense

Amplifier

VOUT

REFIN

DRV421

(Dummy Shunt)

GND

VDD

AINN

RSHUNT

AINP

ICOMP2

Compensation

Coil

ICOMP1

REFOUT

EXT

REFOUT

600

DRV421

www.ti.com

SBOS704A – MAY 2015 – REVISED JULY 2015

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

RSEL1

RSEL0

DESCRIPTION

VREFOUT = 2.5 V

Use with sensor module supply of 5 V

VREFOUT = 1.65 V

Use with sensor module supply of 3.3 V

Ratiometric output

Provides output centered on VDD / 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, VEXT, 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 IREFOUT shown in Equation 5:

(5)

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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