ICL3232IBZ datasheet(11/28 Pages) RENESAS

11 / 28 page

ICL3221, ICL3222, ICL3223, ICL3232, ICL3241, ICL3243

FN4805 Rev 22.00

Page 11 of 28

September 1, 2015

The INVALID output always indicates whether or not a valid

RS-232 signal is present at any of the receiver inputs (See

Table 2), giving the user an easy way to determine when the

interface block should power down. In the case of a

disconnected interface cable where all the receiver inputs

are floating (but pulled to GND by the internal receiver pull

down resistors), the INVALID logic detects the invalid levels

and drives the output low. The power management logic

then uses this indicator to power down the interface block.

Reconnecting the cable restores valid levels at the receiver

inputs, INVALID switches high, and the power management

logic wakes up the interface block. INVALID can also be

used to indicate the DTR or RING INDICATOR signal, as

long as the other receiver inputs are floating, or driven to

GND (as in the case of a powered down driver). Connecting

FORCEOFF and FORCEON together disables the

automatic powerdown feature, enabling them to function as

a manual SHUTDOWN input (See Figure 4).

With any of the above control schemes, the time required to

exit powerdown, and resume transmission is only 100

s. A

mouse, or other application, may need more time to wake up

from shutdown. If automatic powerdown is being utilized, the

RS-232 device will reenter powerdown if valid receiver levels

aren’t reestablished within 30

s of the ICL32XX powering

up. Figure 5 illustrates a circuit that keeps the ICL32XX from

initiating automatic powerdown for 100ms after powering up.

This gives the slow-to-wake peripheral circuit time to

reestablish valid RS-232 output levels.

Automatic Powerdown (ICL3221/23/43 Only)

Even greater power savings is available by using the

devices which feature an automatic powerdown function.

When no valid RS-232 voltages (See Figure 6) are sensed

on any receiver input for 30

s, the charge pump and

transmitters powerdown, thereby reducing supply current to

A. 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

powers back up whenever it detects a valid RS-232 voltage

level on any receiver input. This automatic powerdown

feature provides additional system power savings without

changes to the existing operating system.

FIGURE 2. POWER DRAIN THROUGH POWERED DOWN

PERIPHERAL

OLD

VCC

POWERED

GND

SHDN = GND

VCC

CURRENT

VOUT = VCC

FLOW

RS-232 CHIP

DOWN

UART

FIGURE 3. DISABLED RECEIVERS PREVENT POWER DRAIN

ICL324X

TRANSITION

R2OUTB

R2OUT

T1IN

FORCEOFF = GND

VCC

R2IN

T1OUT

VOUT = HI-Z

POWERED

OR SHDN = GND, EN = VCC

DETECTOR

DOWN

UART

WAKE-UP

LOGIC

FIGURE 4. CONNECTIONS FOR MANUAL POWERDOWN

WHEN NO VALID RECEIVER SIGNALS ARE

PRESENT

PWR

FORCEOFF

INVALID

CPU

I/O

FORCEON

ICL3221/23/43

MGT

LOGIC

UART

FIGURE 5. CIRCUIT TO PREVENT AUTO POWERDOWN FOR

100ms AFTER FORCED POWERUP

ICL3221/23/43

FORCEOFF

FORCEON

POWER

MASTER POWERDOWN LINE



0.1

F

MANAGEMENT

UNIT

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