ICL3232CVZ datasheet(13/28 Pages) INTERSIL

13 / 28 page

FN4805.21

March 1, 2006

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 automatic powerdown functionality.

Devices with the automatic powerdown feature include an

INVALID output signal, which switches low to indicate that

invalid levels have persisted on all of the receiver inputs for

more than 30

µs (See Figure 7). 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. When automatic

powerdown is utilized, INVALID = 0 indicates that the

ICL32XX is in powerdown mode.

The time to recover from automatic powerdown mode is

typically 100

µs.

Receiver ENABLE Control (ICL3221/22/23/41 Only)

Several devices also feature an EN input to control the

receiver outputs. Driving EN high disables all the inverting

(standard) receiver outputs placing them in a high

impedance state. This is useful to eliminate supply current,

due to a receiver output forward biasing the protection diode,

when driving the input of a powered down (VCC = GND)

peripheral (See Figure 2). The enable input has no effect on

transmitter nor monitor (ROUTB) outputs.

Capacitor Selection

The charge pumps require 0.1

µF 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. C2, C3, and C4 can be

increased without increasing C1’s value, however, do not

increase C1 without also increasing C2, C3, and C4 to

maintain the proper ratios (C1 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 0.1

µF 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

ICL32XX transmitter outputs meet RS-562 levels (±3.7V), at

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

typically ensure interoperability with RS-232 devices.

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 3k

Ω in parallel with 2500pF. Note

that the transmitters enable only when the magnitude of the

supplies exceed approximately 3V.

FIGURE 6. DEFINITION OF VALID RS-232 RECEIVER LEVELS

0.3V

-0.3V

-2.7V

2.7V

INVALID LEVEL - POWERDOWN OCCURS AFTER 30ms

VALID RS-232 LEVEL - ICL32XX IS ACTIVE

INDETERMINATE - POWERDOWN MAY OR

MAY NOT OCCUR

RECEIVER

INPUTS

TRANSMITTER

OUTPUTS

INVALID

OUTPUT

V+

VCC

V-

VCC

tINVL

tINVH

INVALID

REGION

}

FIGURE 7. AUTOMATIC POWERDOWN AND INVALID

TIMING DIAGRAMS

AUTOPWDN

PWR UP

TABLE 3. REQUIRED CAPACITOR VALUES

VCC

(V)

(

µF)

C2, C3, C4

(

µF)

3.0 to 3.6

0.1

4.5 to 5.5

0.047

0.33

3.0 to 5.5

0.1

0.47

ICL3221, ICL3222, ICL3223, ICL3232, ICL3241, ICL3243

ICL3232CVZ Datasheet(PDF) 13 Page - Intersil Corporation

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