ICL3226EIAZ Datasheet ATA6624C-PGQW-1, ICL3226EIAZ, ICL3244EIAZ | P10-P12

Powerdown Functionality

This 3V family of RS-232 interface devices requires a

nominal supply current of 0.3mA during normal operation

(not in powerdown mode). This is considerably less than the

5mA to 11mA current required of 5V RS-232 devices. The

already low current requirement drops significantly when the

device enters powerdown mode. In powerdown, supply

current drops to 1µA, because the on-chip charge pump

turns off (V+ collapses to V

, V- collapses to GND), and

the transmitter outputs three-state. Inverting receiver outputs

may or may not disable in powerdown; refer to Table 2 for

details. This micro-power mode makes these devices ideal

for battery powered and portable applications.

Software Controlled (Manual) Powerdown

These devices allow the user to force the IC into the low

power, standby state, and utilize a two pin approach where

the FORCEON and FORCEOFF

inputs determine the IC’s

mode. For always enabled operation, FORCEON and

FORCEOFF

are both strapped high. To switch between

active and powerdown modes, under logic or software

control, only the FORCEOFF

input need be driven. The

FORCEON state isn’t critical, as FORCEOFF

dominates

over FORCEON. Nevertheless, if strictly manual control over

powerdown is desired, the user must strap FORCEON high

to disable the enhanced automatic powerdown circuitry.

ICL3244E inverting (standard) receiver outputs also disable

when the device is in powerdown, thereby eliminating the

possible current path through a shutdown peripheral’s input

protection diode (see Figures 2 and 3).

Connecting FORCEOFF

and FORCEON together disables

the enhanced 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 100µs.

When using both manual and enhanced automatic

powerdown (FORCEON = 0), the ICL32XXE won’t power up

from manual powerdown until both FORCEOFF

and

FORCEON are driven high, or until a transition occurs on a

receiver or transmitter input. Figure 5 illustrates a circuit for

ensuring that the ICL32XXE powers up as soon as

FORCEOFF

switches high. The rising edge of the Master

Powerdown signal forces the device to power up, and the

ICL32XXE returns to enhanced automatic powerdown mode

an RC time constant after this rising edge. The time constant

isn’t critical, because the ICL32XXE remains powered up for

30 seconds after the FORCEON falling edge, even if there

are no signal transitions. This gives slow-to-wake systems

(e.g., a mouse) plenty of time to start transmitting, and as

long as it starts transmitting within 30 seconds both systems

remain enabled.

FIGURE 2. POWER DRAIN THROUGH POWERED DOWN

PERIPHERAL

OLD

POWERED

GND

SHDN

= GND

CURRENT

OUT

FLOW

RS-232 CHIP

DOWN

UART

FIGURE 3. DISABLED RECEIVERS PREVENT POWER DRAIN

ICL3244E

TRANSITION

OUTB

OUT

FORCEOFF = GND

OUT

HI-Z

POWERED

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

ICL32XXE

MGT

LOGIC

UART

ICL3224E, ICL3226E, ICL3244E

INVALID Output

The INVALID output always indicates (see Table 2) whether

or not 30µs have elapsed with invalid RS-232 signals (see

Figures 6 and 8) persisting on all of the receiver inputs,

giving the user an easy way to determine when the interface

block should power down. Invalid receiver levels occur

whenever the driving peripheral’s outputs are shut off

(powered down) or when the RS-232 interface cable is

disconnected. 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).

Enhanced Automatic Powerdown

Even greater power savings is available by using these

devices which feature an enhanced automatic powerdown

function. When the enhanced powerdown logic determines

that no transitions have occurred on any of the transmitter

nor receiver inputs for 30 seconds, the charge pump and

transmitters powerdown, thereby reducing supply current to

1µA. The ICL32XXE automatically powers back up

whenever it detects a transition on one of these inputs. This

automatic powerdown feature provides additional system

power savings without changes to the existing operating

system.

Enhanced 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 via the overriding

FORCEOFF

input. Table 2 summarizes the enhanced

automatic powerdown functionality.

Figure 7 illustrates the enhanced powerdown control logic.

Note that once the ICL32XXE enters powerdown (manually

or automatically), the 30 second timer remains timed out

(set), keeping the ICL32XXE powered down until FORCEON

transitions high, or until a transition occurs on a receiver or

transmitter input.

The INVALID

output signal switches low to indicate that

invalid levels have persisted on all of the receiver inputs for

more than 30µs (see Figure 8), but this has no direct effect

on the state of the ICL32XXE (see the next sections for

methods of utilizing INVALID

to power down the device).

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.

The time to recover from automatic powerdown mode is

typically 100µs.

Emulating Standard Automatic Powerdown

If enhanced automatic powerdown isn’t desired, the user can

implement the standard automatic powerdown feature

(mimics the function on the ICL3221E/23E/43E) by

connecting the INVALID

output to the FORCEON and

FORCEOFF

inputs, as shown in Figure 9. After 30µs of

invalid receiver levels, INVALID

switches low and drives the

ICL32XXE into a forced powerdown condition. INVALID

switches high as soon as a receiver input senses a valid

RS-232 level, forcing the ICL32XXE to power on. See the

“INVALID

DRIVING FORCEON AND FORCEOFF” section

of Table 2 for an operational summary. This operational

mode is perfect for handheld devices that communicate with

FIGURE 5. CIRCUIT TO ENSURE IMMEDIATE POWER UP

WHEN EXITING FORCED POWERDOWN

FORCEOFF FORCEON

POWER

MASTER POWERDOWN LINE

1MΩ

0.1µF

MANAGEMENT

UNIT

ICL32XXE

FIGURE 6. DEFINITION OF VALID RS-232 RECEIVER LEVELS

0.3V

-0.3V

-2.7V

2.7V

INVALID LEVEL - INVALID

= 0

VALID RS-232 LEVEL - INVALID

= 1

VALID RS-232 LEVEL - INVALID

= 1

INDETERMINATE

FIGURE 7. ENHANCED AUTOMATIC POWERDOWN LOGIC

30s

TIMER

FORCEOFF

AUTOSHDN

FORCEON

R_IN

T_IN

EDGE

DETECT

EDGE

DETECT

ICL3224E, ICL3226E, ICL3244E

another computer via a detachable cable. Detaching the

cable allows the internal receiver pull-down resistors to pull

the inputs to GND (an invalid RS-232 level), causing the

30µs timer to time-out and drive the IC into powerdown.

Reconnecting the cable restores valid levels, causing the IC

to power back up.

Hybrid Automatic Powerdown Options

For devices which communicate only through a detachable

cable, connecting INVALID

to FORCEOFF (with

FORCEON = 0) may be a desirable configuration. While the

cable is attached INVALID

and FORCEOFF remain high, so

the enhanced automatic powerdown logic powers down the

RS-232 device whenever there is 30 seconds of inactivity on

the receiver and transmitter inputs. Detaching the cable

allows the receiver inputs to drop to an invalid level (GND),

so INVALID

switches low and forces the RS-232 device to

power down. The ICL32XXE remains powered down until

the cable is reconnected (INVALID

= FORCEOFF = 1) and a

transition occurs on a receiver or transmitter input (see

Figure 7). For immediate power up when the cable is

reattached, connect FORCEON to FORCEOFF

through a

network similar to that shown in Figure 5.

Ready Output (ICL3224E and ICL3226E only)

The Ready output indicates that the ICL322XE is ready to

transmit. Ready switches low whenever the device enters

powerdown, and switches back high during power-up when

V- reaches -4V or lower.

Capacitor Selection

The charge pumps require 0.1µF capacitors for 3.3V

operation. For other supply voltages refer to Table 3 for

capacitor values. Do not use values smaller than those listed

in Table 3. Increasing the capacitor values (by a factor of 2)

reduces ripple on the transmitter outputs and slightly

reduces power consumption. C

, C

, and C

can be

increased without increasing C

’s value, however, do not

increase C

without also increasing C

, C

, and C

maintain the proper ratios (C

to the other capacitors).

RECEIVER

INPUTS

TRANSMITTER

OUTPUTS

INVALID

OUTPUT

V+

V-

INVL

INVH

FIGURE 8. ENHANCED AUTOMATIC POWERDOWN, INVALID AND READY TIMING DIAGRAMS

READY

OUTPUT

TRANSMITTER

INPUTS

AUTOPWDN

INVALID

REGION

}

FIGURE 9. CONNECTIONS FOR AUTOMATIC POWERDOWN

WHEN NO VALID RECEIVER SIGNALS ARE

PRESENT

FORCEOFF

INVALID

CPU

I/O

FORCEON

ICL32XXE

UART

ICL3224E, ICL3226E, ICL3244E

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P20

ICL3226EIAZ

Mfr. #:

Buy ICL3226EIAZ

Manufacturer:

Renesas / Intersil

Description:

RS-232 Interface IC RS232 3V 1D/1R 15KV E-DWN IND

Lifecycle:

New from this manufacturer.

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ICL3226EIAZ

ICL3226EIAZ

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