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CALIFORNIA MICRO DEVICES

CMC7101A

TAPE AND REEL SPECIFICATIONS

CMC7101A Benefits

3.0 High Side Current Sense

To monitor a load current it is necessary to insert a

current sense resistor in the power supply feed, as shown

in figure 4. The resulting voltage drop is proportional

to the load current, but as both ends of this resistor are

at (or very near to) the supply voltage, it is difficult to

use a conventional Op Amp.

The CMC7101A is ideal for this application as the inputs

can operate at either supply rail (or at ground when

used with a single supply). The output voltage is directly

proportional to current in the load, scaled by the gain

of the amplifier.

To reduce the power loss in the sense resistor and also

keep the supply voltage to the load immune to load

current variations, a small value Rsense is used.

An excellent application for this circuit is in a battery

charger, where the charging current is monitored to

detect end of charge (battery current will rise as the

cells ‘top off’), and charging must be reduced to prevent

damage (out gassing or over heating).

The sense resistor can be placed in the negative side

(known as Low Side Sensing), however this is less desirable

due to disruption of the ground path.

3.1 Rail To Rail Output Swing

Making smaller and lighter products requires the reduction

of battery size, lowering of battery voltage, or both. The

lower voltage products have less headroom, for a given

signal swing, and this demands better amplifier

performance. Rail To Rail Outputs help maintain the

existing signal level when products are redesigned for

lower voltage supplies.

3.2 Rail to Rail input Swing

When the amplifier is used as a buffer, the input of the

amplifier follows the input signal and if this is large

compared to the available supply voltage, it is important

that the Op Amp has a wide CMVR (Common Mode

Voltage Range). RRIO Op Amps have a CMVR equal (or

greater than) the supplies and this allows large signal

swings without clipping or distortion.

Figure 4 High Side Current Sense circuit

CMC7101A Physical Dimensions

For a complete mechanical drawing refer to http://www.calmicro.com/prod/data/package/sot-23.htm.