6

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 TSZ151 and TSZ152.

Figure 62. Low-side current sensing schematic

Vout can be expressed as follows:

Vout=Rsℎunt⋅I1− Rg2

Rg2+rf2 ⋅ 1+Rf1Rf2 +Ip⋅ Rg2⋅Rf2

Rg2+Rf2

⋅ 1+Rf1Rg1 −In⋅Rf1−Vio⋅ 1+Rf1rg1

(3)

Assuming that Rf2 = Rf1 = Rf and Rg2 = Rg1 = Rg, equation 4 can be simplified as follows:

Vout=Rsℎunt⋅I⋅RfRg−Vio⋅ 1+RfRg +Rf⋅Iio

(4)

The main advantage of using the TSZ151 and TSZ152 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 precision of Rg1 and Rf1, to maximize the accuracy of the

measurement.

Note that the open loop gain of TSZ151 and TSZ152 are defined close to the rail. It enables measurements over

a wide range of currents.

TSZ151, TSZ152

Typical applications

DS14459 - Rev 4

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