LMC6762

SNOS739D – JULY 1997 – REVISED MARCH 2013

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Shoot-Through Current

The shoot-through current is defined as the current surge, above the quiescent supply current, between the

positive and negative supplies of a device. The current surge occurs when the output of the device switches

states. This transient switching current results in glitches in the supply voltage. Usually, glitches in the supply

lines are compensated by bypass capacitors. When the switching currents are minimal, the values of the bypass

capacitors can be reduced considerably.

Figure 27. LMC6762 Circuit for Measurement of the Shoot-Through Current

Figure 28. Measurement of the Shoot-Through Current

From Figure 27 and Figure 28 the shoot-through current for the LMC6762 can be approximated to be 0.2 mA

(200 mV/1 k

Ω). The duration of the transient is measured as 1 μs. The values needed for the local bypass

capacitors can be calculated as follows:

Area of

Δ = ½ (1 μs × 200 μA)

= 100 pC

If the local bypass capacitor has to provide this charge of 100 pC, the minimum value of the local capacitor to

prevent local degradation of VCC can be calculated. Suppose that the maximum voltage droop that the system

can tolerate is 100mV,

ΔQ

= C * (

ΔV)

→C

= (

ΔQ/ΔV)

= 100 pC/100 mV

= 0.001

μF

The low internal feedthrough current of the LMC6762 thus requires lower values for the local bypass capacitors.

In applications where precision is not critical, this is a significant advantage, as lower values of capacitors result

in savings of board space, and cost.

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