ICL3221EM, ICL3221EF

4. Application Information

FN7552 Rev.2.00

Page 15 of 22

May.29.19

When using minimum required capacitor values, make sure that capacitor values do not degrade excessively with

temperature. If in doubt, use capacitors with a larger nominal value. The capacitor’s Equivalent Series Resistance

(ESR) usually rises at low temperatures and it influences the amount of ripple on V+ and V-.

4.8

Power Supply Decoupling

In most circumstances a 0.1µF bypass capacitor is adequate. In applications that are particularly sensitive to

power supply noise, decouple VCC to ground with a capacitor of the same value as the charge-pump capacitor C1.

Connect the bypass capacitor as close as possible to the IC.

4.9

Operation Down to 2.7V

The ICL3221EM and ICL3221EF transmitter outputs meet RS-562 levels (±3.7V), at full data rate, with VCC as low

as 2.7V. RS-562 levels typically ensure interoperability with RS-232 devices.

4.10 Transmitter Outputs when Exiting Powerdown

Figure 12 shows the response of two transmitter outputs when exiting powerdown mode. As they activate, the two

transmitter outputs properly go to opposite RS-232 levels, with no glitching, ringing, nor undesirable transients.

Each transmitter is loaded with 3kΩ in parallel with 2500pF. Note: The transmitters enable only when the

magnitude of the supplies exceed approximately 3V.

Table 6.

Required Capacitor Values

VCC (V)

C1 (µF)

C2, C3, C4 (µF)

3.0 to 3.6

0.1

0.1

Figure 12. Transmitter Outputs When Exiting Powerdown

Time (20µs/Div)

T1

T2

2V/Div

5V/Div

VCC = +3.3V

FORCEOFF

C1 - C4 = 0.1µF