ISL4244EIRZ-T Datasheet ISL4238EIRZ-T, ISL4238EIRZ, ISL4244EIRZ | P10-P12

FN8038.5

May 13, 2010

Power-down Functionality

The already low current requirement drops significantly

when the device enters power-down mode. In power-down,

supply current drops to 10nA, because the on-chip charge

pump turns off (V+ collapses to V

, V- collapses to GND),

and the transmitter outputs tristate. Inverting receiver

outputs disable only in manual power-down; refer to Table 2

for details. This micro-power mode makes these devices

ideal for battery powered and portable applications.

Software Controlled (Manual) Power-down

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 power-down 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

power-down is desired, the user must strap FORCEON high

to disable the enhanced automatic power-down circuitry.

ISL4238E, ISL4244E, ISL4245 inverting (standard) receiver

outputs also disable when the device is in manual power-

down, 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 power-down feature, enabling them

to function as a manual SHUTDOWN

input (see Figure 4).

With any of the previous mentioned control schemes, the

time required to exit power-down, and resume transmission

is only 100µs.

When using both manual and enhanced automatic power-

down (FORCEON = 0), the ISL4238E, ISL4244E, ISL4245

won’t power up from manual power-down 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 ISL4238E,

ISL4244E, ISL4245 powers up as soon as FORCEOFF

switches high. The rising edge of the Master Power-down

signal forces the device to power up, and the ISL4238E,

ISL4244E, ISL4245 returns to enhanced automatic power-

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

time constant isn’t critical, because the ISL4238E,

ISL4244E, ISL4245 remains powered up for 30s 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 30s both systems remain enabled.

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 9) 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

FIGURE 3. DISABLED RECEIVERS PREVENT POWER DRAIN

ISL4238E

TRANSITION

OUTB

OUT

FORCEOFF = GND

OUT

HI-Z

POWERED

DETECTOR

DOWN

UART

WAKE-UP

LOGIC

ISL4244E

ISL4245

FIGURE 4. CONNECTIONS FOR MANUAL POWER-DOWN

WHEN NO VALID RECEIVER SIGNALS ARE

PRESENT

PWR

FORCEOFF

INVALID

CPU

I/O

FORCEON

ISL4238E

MGT

LOGIC

UART

ISL4244E

ISL4245

FIGURE 5. CIRCUIT TO ENSURE IMMEDIATE POWER UP

WHEN EXITING FORCED POWER-DOWN

FORCEOFF FORCEON

POWER

MASTER POWER-DOWN LINE

1MΩ

0.1µF

MANAGEMENT

UNIT

ISL4238E, ISL4244E, ISL4245

ISL4238E, ISL4244E, ISL4245E

FN8038.5

May 13, 2010

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).

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 power-down circuitry.=

Enhanced Automatic Power-down

Even greater power savings is available by using these devices

which feature an enhanced automatic power-down function.

When the enhanced power-down logic determines that no

transitions have occurred on any of the transmitter nor receiver

inputs for 30 seconds, the charge pump and transmitters

power-down, thereby reducing supply current to

10nA. The

ISL4238E, ISL4244E, ISL4245 automatically powers back up

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

automatic power-down feature provides additional system

power savings without changes to the existing operating

system.

Enhanced automatic power-down operates when the

FORCEON input is low, and the FORCEOFF

input is high.

Tying FORCEON high disables automatic power-down, but

manual power-down is always available via the overriding

FORCEOFF

input. Table 2 summarizes the enhanced

automatic power-down functionality.

Figure 7 illustrates the enhanced power-down control logic.

Note that once the ISL4238E, ISL4244E, ISL4245 enters

power-down (manually or automatically), the 30 second

timer remains timed out (set), keeping the ISL4238E,

ISL4244E, ISL4245 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 9), but this has no direct effect on the state of

the ISL4238E, ISL4244E, ISL4245 (see the next sections for

methods of utilizing INVALID

to power down the device).

The time to recover from automatic power-down mode is

typically 100µs.

Emulating Standard Automatic Power-down

If enhanced automatic power-down isn’t desired, the user can

implement the standard automatic power-down feature (mimics

the function on the ISL4243E) by connecting the INVALID

output to the FORCEON and FORCEOFF

inputs, as shown in

Figure 8. After 30µs of invalid receiver levels, INVALID

switches

low and drives the ISL4238E, ISL4244E, ISL4245 into a forced

power-down condition. INVALID

switches high as soon as a

receiver input senses a valid RS-232 level, forcing the

ISL4238E, ISL4244E, ISL4245 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 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 power-down. Reconnecting the cable

restores valid

levels, causing the IC to power back up.

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 POWER-DOWN LOGIC

30sec

TIMER

FORCEOFF

AUTOPWDN

FORCEON

R_IN

T_IN

EDGE

DETECT

EDGE

DETECT

FIGURE 8. CONNECTIONS FOR AUTOMATIC POWER-DOWN

WHEN NO VALID RECEIVER SIGNALS ARE

PRESENT

FORCEOFF

INVALID

CPU

I/O

FORCEON

ISL4238E

UART

ISL4244E

ISL4245

ISL4238E, ISL4244E, ISL4245E

FN8038.5

May 13, 2010

Hybrid Automatic Power-down 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 power-down 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

ISL4238E, ISL4244E, ISL4245 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.

Capacitor Selection

The ISL4238E charge pumps require 0.1μF, or greater,

capacitors for 3.3V (5% tolerance) operation. For other

supply voltages refer to Table 3 for capacitor values. Do not

use values smaller than those listed in Table 3.

The ISL4244E/45E charge pumps require 0.1

µF capacitors

for proper operation. 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).

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-.

Power Supply Decoupling

In most circumstances a 0.1µF bypass capacitor is

adequate. In applications that are particularly sensitive to

power supply noise, decouple V

to ground with a

capacitor of the same value as the charge-pump capacitor C

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

Transmitter Outputs when Exiting

Power-down

Figure 10 shows the response of two transmitter outputs

when exiting power-down 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

that the transmitters enable only when the magnitude of the

supplies exceed approximately 3V.

Operation Down to 2.7V

ISL4238E, ISL4244E, ISL4245 transmitter outputs meet

RS-562 levels (±3.7V), at the full data rate, with V

as low

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

RS-232 devices.

TABLE 3. REQUIRED CAPACITOR VALUES (ISL4238E)

(V) C

(µF) C

, C

(µF)

3.0 to 3.6 (3.3V ±10%) 0.22 0.22

3.15 to 3.6 (3.3V ±5%) 0.1 0.1

4.5 to 5.5 0.047 0.33

3.0 to 5.5 0.22 1

RECEIVER

INPUTS

TRANSMITTER

OUTPUTS

INVALID

OUTPUT

V+

V-

INVL

INVH

FIGURE 9. ENHANCED AUTOMATIC POWER-DOWN AND INVALID TIMING DIAGRAMS

OUTPUT

TRANSMITTER

INPUTS

AUTOPWDN

INVALID

REGION

}

ISL4238E, ISL4244E, ISL4245E

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P17

ISL4244EIRZ-T

Mfr. #:

Buy ISL4244EIRZ-T

Manufacturer:

Renesas / Intersil

Description:

RS-232 Interface IC RS232 3V 3D/5R 15KV E-DWN 32QFN INDEL

Lifecycle:

New from this manufacturer.

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ISL4244EIRZ-T

ISL4244EIRZ-T

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