LMC7215, LMC7225

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SNOS882E – SEPTEMBER 1999 – REVISED MARCH 2013

SHOOT-THROUGH

Shoot-through is a common occurrence on digital circuits and comparators where there is a push-pull output

stage. This occurs when a signal is applied at the same time to both the N-channel and P-channel output

transistors to turn one off and turn the other on. (See Figure 15.) If one of the output devices responds slightly

faster than the other, the fast one can be turned on before the other has turned off. For a very short time, this

allows supply current to flow directly through both output transistors. The result is a short spike of current drawn

from the supply.

Figure 15.

The LMC7215 produces a small current spike of 300

μA peak for about 400 ns with 2.7V supply and 1.8 mA

peak for 400 ns with a 5V supply. This spike only occurs when the output is going from high to low. It does not

occur when going from low to high. Figure 16 and Figure 17 show what this current pulse looks like on 2.7V and

5V supplies. The upper trace is the output voltage and the lower trace is the supply current as measured with the

circuit in Figure 18.

If the power supply has a very high impedance, a bypass capacitor of 0.01

μF should be more than enough to

minimize the effects of this small current pulse.

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