LowSide

CurrentSense

Phase

Current

Sense

HighSide

Current

Sense

LowSide

CurrentSense

Phase

Current

Sense

HighSide

Current

Sense

LowSide

CurrentSense

Phase

Current

Sense

HighSide

Current

Sense

Motor

INA282, INA283

INA284, INA285

INA286

SBOS485A – NOVEMBER 2009 – REVISED JULY 2010

www.ti.com

COMMON-MODE DYNAMICS AND CURRENT DIFFERENCING

Current sensing is frequently used on totem-pole output stages, such as those of bridge-type motor drives. We

can sense current in one of three locations on a totem-pole output: on the ground side (low-side sensing); on the

power-supply side (high-side sensing); or on the output (phase sensing). Only the output line reports the exact

load current. Obviously, the ground and supply-side sensing report only the current in the individual respective

phases. Figure 42 depicts these various methods on a three-phase motor driver.

NOTE: Motor drive current sensing can be done on the low side, phase side, or high side. Only the phase output gives

complete information regarding current in the motor, but is subject to common-mode transients that even the best

amplifiers do not reject completely.

Figure 42. Motor Drive Current Sensing

However, sensing on the output is subject to large common-mode voltage steps that result in feedthrough in

even the best amplifiers. The ground and supply-side sensing configurations are free of this problem, thanks to

the static common-mode environments. Sensing either ground or supply alone only provides partial information

regarding motor current, but sense them individually and sum them and we have the same information provided

by phase sensing, with an added advantage of not being subject to transient common-mode artifacts. See

Figure 43 for an illustration of two INA282 family devices connected in this manner. Technically, this

configuration is current differencing, though, because we want the upper sense to report a positive-going

excursion in the overall output, and the negative sense to report a negative-going excursion.

24

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