5

Application recommendation

When high speed comparators are used, it is strongly recommended to place a capacitor as close as possible to

the supply pins. Decoupling has two main advantages for this application: it helps to reduce electromagnetic

interference and rejects the ripple that may appear on the output.

A bypass capacitor combination, composed of 100 nF in addition to 10 nF and 1 nF in parallel is recommended

because it eliminates spikes on the supply line better than a single 100 nF capacitor. Each millimeter of the PCB

track plays an important role. Bypass capacitors must be placed as close as possible to the comparator supply

pin.

The smallest value capacitor should be preferably placed closer to the supply pin.

In addition, important values of input impedance in series with parasitic PCB capacity and input comparator

capacity create an additional RC filter. It generates an additional propagation delay.

For high speed signal applications, PCB must be designed with great care taking into consideration low resistive

grounding, short tracks and quality SMD capacitors featuring low ESR. Bypass capacitor stores energy and

provides a complementary energy tank when spikes occur on the power supply line. If the input signal frequency

is far from the resonant frequency, impedance strongly increases and the capacitor loses bypassing capability.

Placing different capacitors with different resonant frequencies allows a wide frequency bandwidth to be covered.

It is also recommended to implement an unbroken ground plane with low inductance.

Figure 21. High speed layout recommendation

TS3011

Application recommendation

DS8604 - Rev 9

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