ICL3217E Просмотр технического описания (PDF) - Intersil

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ICL3217E

+/- 15kV ESD Protected, +3V to +5.5V, Low Power, 250kbps, RS-232 Transmitters/Receivers

Intersil 

ICL3207E, ICL3217E

Receivers

The ICL32X7E each contain inverting receivers that convert

RS-232 signals to CMOS output levels and accept inputs up

to ±25V while presenting the required 3kΩ to 7kΩ input

impedance (see Figure 1) even if the power is off

(VCC = 0V). The receivers’ Schmitt trigger input stage uses

hysteresis to increase noise immunity and decrease errors

due to slow input signal transitions.

Receivers on the ICL3207E are always active. The

ICL3217E receivers disable when in the automatic

powerdown state, thereby eliminating the possible current

path through a shutdown peripheral’s input protection diode

(see Figures 2 and 3).

Low Power Operation

These 3V devices require a nominal supply current of

0.3mA, even at VCC = 5.5V, during normal operation (not in

powerdown mode). This is considerably less than the 11mA

current required by comparable 5V RS-232 devices,

allowing users to reduce system power simply by replacing

the old style device with the ICL3207E.

Low Power, Pin Compatible Replacement

Pin compatibility with existing 5V products (e.g., MAX207E),

coupled with the wide operating supply range, make the

ICL32X7E potential lower power, higher performance drop-

in replacements for existing ‘2X7E 5V applications. As long

as the ±5V RS-232 output swings are acceptable, the

ICL32X7E devices should work in most 5V applications.

VCC

RXIN

-25V ≤ VRIN ≤ +25V

5kΩ

GND

RXOUT

GND ≤ VROUT ≤ VCC

FIGURE 1. INVERTING RECEIVER CONNECTIONS

VCC

VCC

VCC

CURRENT

FLOW

Rx

POWERED

DOWN

UART

Tx

GND

VOUT = VCC

SHDN = GND

OLD

RS-232 CHIP

FIGURE 2. POWER DRAIN THROUGH POWERED DOWN

PERIPHERAL

VCC

TRANSITION

DETECTOR

TO

WAKE-UP

LOGIC

VCC

ICL3217E

V-

RX

POWERED

DOWN

UART TX

VOUT = HI-Z*

* IN AUTOMATIC

POWERDOWN

FIGURE 3. DISABLED RECEIVERS PREVENT POWER DRAIN

When replacing a ‘207E or ‘237E device in an existing 5V

application, it is acceptable to terminate C3 to VCC as shown

on the Typical Operating Circuit. Nevertheless, terminate C3

to GND if possible, as slightly better performance results

from this configuration.

Automatic Powerdown (ICL3217E Only)

Even greater power savings is available by using the

ICL3217E which features an automatic powerdown function.

When no valid RS-232 voltages (see Figure 4) are sensed

on any receiver input for 30µs, the ICL3217E automatically

enters its powerdown state (see Figure 5). In powerdown,

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

pump turns off (V+ collapses to VCC, V- collapses to GND),

and the receiver and transmitter outputs three-state (see

Table 2). This micro-power mode makes the ICL3217E ideal

for battery powered and portable applications. 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 ICL3217E powers back

up whenever it detects a valid RS-232 voltage level on any

receiver input (such as when the RS-232 cable is

reconnected). The time to recover from automatic

powerdown mode is typically 100µs.

TABLE 2. ICL3217E AUTOMATIC POWERDOWN OPERATION

RS-232 SIGNAL

PRESENT AT

RECEIVER

INPUT?

MODE

TRANSMITTER RECEIVER

OF

OUTPUTS OUTPUTS OPERATION

YES

Active

Active Normal

Operation

NO

High-Z

High-Z Powerdown

Due to Auto

Powerdown

Logic

6

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