ISL83387EIVZ Datasheet ISL83387EIVZ, ISL83387EIVZ-T, ISL83387EIV | P7-P9

FN6040.1

July 8, 2005

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

constant isn’t critical, because the ISL83387E 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.

Logic Supply Input

Unlike other RS-232 interface devices where the CMOS

outputs swing between 0 and V

, the ISL83387E features

a separate logic supply input (V

; 1.8V to 5V, regardless of

) that sets V

for the receiver and INVALID outputs.

Connecting V

to a host logic supply lower than V

prevents the ISL83387E outputs from forward biasing the

input diodes of a logic device powered by that lower supply.

Connecting V

to a logic supply greater than V

ensures

that the receiver and INVALID

output levels are compatible

even with the CMOS input V

of AC, HC, and CD4000

devices. Note that the V

supply current increases to 100µA

with V

= 5V and V

= 3.3V (see Figure 16). V

also

powers the transmitter and logic inputs, thereby setting their

switching thresholds to levels compatible with the logic

supply. This separate logic supply pin allows a great deal of

flexibility in interfacing to systems with different logic

supplies. If logic translation isn’t required, connect V

to the

ISL83387E V

INVALID Output

The INVALID output always indicates (see Table 2) whether

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

TABLE 2. POWERDOWN LOGIC TRUTH TABLE

RCVR OR XMTR

EDGE WITHIN 30

SEC?

FORCEOFF

INPUT

FORCEON

INPUT

TRANSMITTER

OUTPUTS

RECEIVER

OUTPUTS

RS-232 LEVEL

PRESENT AT

RECEIVER INPUT?

INVALID

OUTPUT MODE OF OPERATION

NO H H Active Active NO L Normal Operation (Enhanced

Auto Powerdown Disabled)

NO H H Active Active YES H

YES H L Active Active NO L Normal Operation (Enhanced

Auto Powerdown Enabled)

YES H L Active Active YES H

NO H L High-Z Active NO L Powerdown Due to Enhanced

Auto Powerdown Logic

NO H L High-Z Active YES H

X L X High-Z Active NO L Manual Powerdown

X L X High-Z Active YES H

INVALID

DRIVING FORCEON AND FORCEOFF (EMULATES AUTOMATIC POWERDOWN)

X NOTE 3 NOTE 3 Active Active YES H Normal Operation

X NOTE 3 NOTE 3 High-Z Active NO L Forced Auto Powerdown

NOTES:

3. Input is connected to INVALID

Output.

FIGURE 2. CONNECTIONS FOR MANUAL POWERDOWN

PWR

FORCEOFF

, FORCEON

CPU

I/O

ISL83387E

MGT

LOGIC

UART

I/O CHIP

POWER SUPPLY

INVALID

FIGURE 3. CIRCUIT TO ENSURE IMMEDIATE POWER UP

WHEN EXITING FORCED POWERDOWN

FORCEOFF FORCEON

POWER

MASTER POWERDOWN LINE

1MΩ

0.1µF

MANAGEMENT

UNIT

ISL83387E

FN6040.1

July 8, 2005

Figures 4 and 7) 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).

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.

Enhanced Automatic Powerdown

Even greater power savings is available by using the

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

ISL83387E 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 5 illustrates the enhanced powerdown control logic.

Note that once the ISL83387E enters powerdown (manually

or automatically), the 30 second timer remains timed out

(set), keeping the ISL83387E powered down until

FORCEON transitions high, or until a transition occurs on a

receiver or transmitter input.

As stated previously, the INVALID

output switches low

whenever invalid levels have persisted on all of the receiver

inputs for more than 30µs (see Figure 7), but this has no

direct effect on the state of the ISL83387E (see the next

sections for methods of utilizing INVALID

to power down the

device).

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 6. After 30µs of

invalid receiver levels, INVALID

switches low and drives the

ISL83387E into a forced powerdown condition. INVALID

switches high as soon as a receiver input senses a valid

FIGURE 4. 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 5. ENHANCED AUTOMATIC POWERDOWN LOGIC

30s

TIMER

FORCEOFF

AUTOPWDN

FORCEON

R_IN

T_IN

EDGE

DETECT

EDGE

DETECT

FIGURE 6. CONNECTIONS FOR AUTOMATIC POWERDOWN

WHEN NO VALID RECEIVER SIGNALS ARE

PRESENT

FORCEOFF

INVALID

CPU

I/O

FORCEON

ISL83387E

UART

ISL83387E

FN6040.1

July 8, 2005

RS-232 level, forcing the ISL83387E 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 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 ISL83387E remains powered down until

the cable is reconnected (INVALID

= FORCEOFF = 1) and a

transition occurs on a receiver or transmitter input (see

Figure 5). For immediate power up when the cable is

reattached, connect FORCEON to FORCEOFF

through a

network similar to that shown in Figure 3.

Capacitor Selection

The ISL83387E charge pumps require only 0.1µF capacitors

for the full operational voltage range. Table 3 lists other

acceptable capacitor values for various supply voltage

ranges. 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.

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

Powerdown

Figure 8 shows the response of two transmitter outputs

when exiting powerdown 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.

RECEIVER

INPUTS

TRANSMITTER

OUTPUTS

INVALID

OUTPUT

V+

V-

INVL

INVH

FIGURE 7. ENHANCED AUTOMATIC POWERDOWN AND INVALID TIMING DIAGRAMS

TRANSMITTER

INPUTS

AUTOPWDN

INVALID

REGION

}

TABLE 3. REQUIRED CAPACITOR VALUES

(V)

(µF)

, C

(µF)

3.0 to 3.6 0.1 0.1

4.5 to 5.5 0.047 0.33

3.0 to 5.5 0.22 1

ISL83387E

P1-P3 P4-P6 P7-P9 P10-P12 P13-P13

ISL83387EIVZ

Mfr. #:

Buy ISL83387EIVZ

Manufacturer:

Renesas / Intersil

Description:

RS-232 Interface IC W/ANNEAL RS232 3V 3D /3R 15KV SHTDWN 24LD

Lifecycle:

New from this manufacturer.

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ISL83387EIVZ

ISL83387EIVZ

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