ICL3221, ICL3222, ICL3223, ICL3232, ICL3241, ICL3243

4. Application Information

FN4805 Rev.23.00

Page 18 of 36

Apr.26.19

power-down for 100ms after powering up, which gives the slow-to-wake peripheral circuit time to re-establish valid

RS-232 output levels.

4.5.3 Automatic Powerdown (ICL3221/23/43 Only)

Even greater power savings are available by using the ICL3221, ICL3223, or ICL3243's automatic powerdown

function. When no valid RS-232 voltages (See Figure 12) are sensed on any receiver input for 30

μs, the

charge-pump and transmitters powerdown, thereby reducing supply current to 1µA. Invalid receiver levels occur

whenever the driving peripheral’s outputs are shut off (powered down) or when the RS-232 interface cable is

disconnected. The ICL32xx devices power back up whenever they detect a valid RS-232 voltage level on any

receiver input, which provides additional system power savings without changes to the existing operating system.

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 15 summarizes the automatic powerdown functionality.

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

that invalid levels have persisted on all of the receiver inputs for more than 30µs (See Figure 13). INVALID

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

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

When automatic powerdown is used, INVALID = 0 indicates that the ICL32xx is in powerdown mode.

Figure 11. Circuit to Prevent Auto Powerdown for 100ms After Forced Power-UP

Figure 12. Definition of Valid RS-232 Receiver Levels

ICL3221/23/43

FORCEOFF

FORCEON

Power

Master Powerdown Line

1MΩ

0.1µF

Management

Unit

0.3V

-0.3V

-2.7V

2.7V

Invalid Level - Powerdown Occurs After 30ms

Valid RS-232 Level - ICL32xx is Active

Valid RS-232 Level - ICL32xx is Active

Indeterminate - Powerdown May or

Indeterminate - Powerdown May or

May Not Occur

May Not Occur