11.1 Layout Guidelines

For best performance, place the 0.22-µF capacitor (C7, as shown in Figure 52) required for decoupling of the internal LDO output as close as possible to the ISO224 VCAP pin. The 0.1-µF ceramic decoupling capacitors for both power supplies (C8 and C9) are located as close as possible to the corresponding VDDx pins followed by the additional 1-µF ceramic capacitors for lower-frequency decoupling (C3 and C12). The resistor and capacitor used for the analog input (R1 and C2) are placed next to the decoupling capacitors. For best performance, use 0603-size or 1206-size, SMD-type, ceramic capacitors with low ESR. Connect the supply voltage sources in a way that allows the supply current to flow through the pads of the decoupling capacitors before powering the device.

Figure 52 shows this approach as implemented on the ISO224EVM. Capacitors C3 and C8 decouple the high-side supply VDD1 and capacitors C9 and C12 are used to support the low-side supply VDD2 of the ISO224.