ICL3221EM, ICL3221EF

4. Application Information

FN7552 Rev.2.00

Page 14 of 22

May.29.19

Automatic powerdown operates when the FORCEON input is low, and the FORCEOFF input is high. Tying

FORCEON high disables automatic powerdown, but manual powerdown is always available using the overriding

FORCEOFF input. Table 5 on page 11 summarizes the automatic powerdown functionality.

Devices with the automatic powerdown feature include an INVALID output signal that switches low to indicate that

invalid levels have persisted on all of the receiver inputs for more than 30µs (see Figure 11). INVALID switches

high 1µs after detecting a valid RS-232 level on a receiver input. INVALID operates in all modes (forced or

automatic power-down, or forced on), so it is also useful for systems employing manual powerdown circuitry.

When automatic powerdown is used, INVALID = 0 indicates that the ICL3221EM and ICL3221EF are in

power-down mode.

The time to recover from automatic powerdown mode is typically 100µs.

4.6

Receiver ENABLE Control

The ICL3221EM and ICL3221EF also feature an EN input to control the receiver outputs. Driving EN high

disables all the inverting (standard) receiver outputs placing them in a high impedance state, which is useful to

eliminate supply current, due to a receiver output forward biasing the protection diode, when driving the input of a

powered down (VCC = GND) peripheral (see Figure 6 on page 12).

4.7

Capacitor Selection

The charge pumps require 0.1µF capacitors for 3.3V operation. For other supply voltages, see Table 6 on page 15

for capacitor values. Do not use values smaller than those listed in Table 6. Increasing the capacitor values (by a

factor of 2) reduces ripple on the transmitter outputs and slightly reduces power consumption. C2, C3, and C4 can

be increased without increasing C1’s value; however, do not increase C1 without also increasing C2, C3, and C4 to

maintain the proper ratios (C1 to the other capacitors).

Figure 10. Definition of Valid RS-232 Receiver Levels

Figure 11. Automatic Powerdown and INVALID Timing Diagrams

0.3V

-0.3V

-2.7V

2.7V

Invalid Level - Powerdown Occurs

Valid RS-232 Level - ICL3221EM and ICL3221EF are Active

Valid RS-232 Level - ICL3221EM and ICL3221EF are Active

Indeterminate - Powerdown Can Occur

Indeterminate - Powerdown Can Occur

After 30µs

Receiver

Inputs

Transmitter

Outputs

INVALID

Output

V+

VCC

0

V-

VCC

0

tINVL

tINVH

Invalid

Region

}

AUTOPWDN

PWR UP