ISL83385ECA-T 查看數據表（PDF） - Intersil

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ISL83385ECA-T

±15kV ESD Protected, +3V to +5.5V, 1 Microamp, 250kbps, RS-232 Transmitters/Receivers

Intersil 

ISL83385E

hysteresis to increase noise immunity and decrease errors

due to slow input signal transitions.

VCC

RXIN

-25V ≤ VRIN ≤ +25V

5kΩ

GND

RXOUT

GND ≤ VROUT ≤ VCC

FIGURE 1. INVERTING RECEIVER CONNECTIONS

Low Power Operation

This 3V device requires 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 ISL83385E in new designs.

Powerdown Functionality

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 VCC, V- collapses to GND),

and the transmitter outputs three-state. This micro-power

mode makes these devices ideal for battery powered and

portable applications.

Software Controlled (Manual) Powerdown

The ISL83385E may be forced into its low power, standby

state via a simple shutdown (SHDN) pin (see Figure 2).

Driving this pin high enables normal operation, while driving

it low forces the IC into it’s powerdown state. The time

required to exit powerdown, and resume transmission is less

than 100µs. Connect SHDN to VCC if the powerdown

function isn’t needed.

PWR

MGT

LOGIC

SHDN

ISL83385E

Capacitor Selection

These charge pumps only require 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-.

TABLE 3. REQUIRED CAPACITOR VALUES

VCC

(V)

C1

C2, C3, C4

(µF)

(µF)

3.0 to 3.6

0.1

0.1

4.5 to 5.5

0.047

0.33

3.0 to 5.5

0.1

0.47

Power Supply Decoupling

In most circumstances a 0.1µF bypass capacitor is

adequate. In applications that are particularly sensitive to

power supply noise, decouple VCC to ground with a

capacitor of the same value as the charge-pump capacitor C1.

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

Operation Down to 2.7V

ISL83385E transmitter outputs meet RS-562 levels (±3.7V),

at the full data rate, with VCC as low as 2.7V. RS-562 levels

typically ensure inter operability with RS-232 devices.

Transmitter Outputs when Exiting

Powerdown

Figure 3 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.

CPU

I/O

UART

FIGURE 2. CONNECTIONS FOR MANUAL POWERDOWN

6

FN6001.4

January 16, 2005

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