TSV7721 datasheet(24/40 Pages) STMICROELECTRONICS

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Typical applications

6.1

Low-side current sensing

Power management mechanisms are found in most electronic systems. Current sensing is useful for protecting

applications. The low-side current sensing method consists of placing a sense resistor between the load and

the circuit ground. The resulting voltage drop is amplified using the TSV772x (see Figure 51. Low-side current

sensing schematic).

Figure 51. Low-side current sensing schematic

Vout can be expressed as follows:

VOut=Rsℎunt.I1− Rg2

Rg2+Rf2 . 1+Rf1Rg1 +Ip. Rg2.Rf2

Rg2+Rf2. 1+Rf1Rg1 −In.Rf1

−Vio. 1+Rf1Rg1

(4)

Assuming that Rf2 = Rf1 = Rf and Rg2 = Rg1 = Rg, this equation can be simplified as follows:

VOut=Rsℎunt.I.RfRg−Vio. 1+RfRg +Rf.Iio

(5)

The main advantage of using the TSV7722 for a low-side current sensing relies on its low Vio, compared to

general purpose operational amplifiers. For the same current and targeted accuracy, the shunt resistor can be

chosen with a lower value, resulting in lower power dissipation, lower drop in the ground path, and lower cost.

Particular attention must be paid to the matching and precision of Rg1, Rg2, Rf1, and Rf2, to maximize the

accuracy of the measurement. Furthermore, on the TSV7722, the Vio is trimmed, and thus reaches his minimum

value, at Vicm = 0 V. This allows optimized precision for low-side current sensing application without precision

degradation due to the CMRR.

TSV7721, TSV7722, TSV7723

Typical applications

DS13614 - Rev 3

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