Datasheet

LMC6762
SNOS739D –JULY 1997–REVISED MARCH 2013 www.ti.com
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 kΩ). 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 V
CC
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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