DRV421 datasheet(19/44 Pages) TI

19 / 44 page

SHUNT

R + R

4 =

+ R

Shunt Sense

Amplifier

VOUT

REFIN

AINN

RSHUNT

AINP

ICOMP2

Compensation

Coil

10 k

40 k

10 k

40 k

REFIN (compensated)

DRV421

500

optional

ADC

(Dummy Shunt)

10 nF

ICOMP1

DRV421

www.ti.com

SBOS704A – MAY 2015 – REVISED JULY 2015

7.3.3 H-Bridge Driver for Compensation Coil

The H-bridge compensation coil driver provides the current for the compensation coil at pins ICOMP1 and

ICOMP2. A fully-differential driver stage maximizes the driving voltage that is needed to overcome the wire

resistance and inductance of the coil with a single 3.3-V or 5-V supply. The low impedance of the H-bridge driver

outputs over a wide frequency range provides a smooth transition between the compensation frequency range of

the integrator-filter stage and the high-frequency range of the primary current that directly couples into the

compensation coil according to the winding ratio (transformer effect).

The common-mode voltage of the H-bridge driver outputs is set by the RSEL pins (see the Voltage Reference

section). Thus, the common-mode voltage of the shunt sense amplifier is matched if the internal reference is

used.

The two compensation driver outputs are protected and accept inductive energy. However, for high-current

sensors, add external protection diodes (see the Protection Recommendations section).

Consider the polarity of the compensation coil connection to the output of the H-bridge driver. If the polarity is

incorrect, the H-bridge output drives to the power supply rails, even at low primary-current levels. In this case,

interchange the connection of pins ICOMP1 and ICOMP2 to the compensation coil.

7.3.4 Shunt Sense Amplifier

The compensation coil current creates a voltage drop across the external shunt resistor, RSHUNT. The internal

differential amplifier senses this voltage drop. This differential amplifier offers wide bandwidth and a high slew

rate for fast current sensors. Excellent dc stability and accuracy result from an autozero technique. The voltage

gain is 4 V/V, set by precisely-matched and thermally-stable internal resistors.

Both AINN and AINP differential amplifier inputs are connected to the shunt resistor. This resistor, in series with

the internal 10-k

Ω resistor, affects the overall gain and causes an additional gain error; this gain error is often

negligible. However, if a common-mode rejection of 70 dB is desired, the match of both divider ratios must be

higher than 1/3000. Therefore, for best common-mode rejection performance, place a dummy shunt resistor (R5)

with a value higher than the shunt resistor in series with the REFIN pin to restore matching of both resistor

dividers, as shown in Figure 57.

Figure 57. Internal Difference Amplifier with Example of a Decoupling Filter

For an overall gain of 4 V/V, calculate the value of R5 using Equation 3:

where:

•

R2 / R1 = R4 / R3 = 4

•

R5 = RSHUNT × 4

(3)

Submit Documentation Feedback

Product Folder Links: DRV421

DRV421 Datasheet(PDF) 19 Page - Texas Instruments

DRV421 Datasheet(HTML) 19 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

Datasheet Download

Link URL