ICL3237 Просмотр технического описания (PDF) - Intersil

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ICL3237

1 Microamp Supply-Current, +3V to +5.5V, 1Mbps, RS-232 Transmitters/Receivers

Intersil 

ICL3237

Receiver ENABLE Control

This device also features 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.

VCC

VCC

VCC

CURRENT

FLOW

POWERED

DOWN

UART

GND

VOUT = VCC

Rx

Tx

SHDN = GND

OLD

RS-232 CHIP

FIGURE 2. POWER DRAIN THROUGH POWERED DOWN

PERIPHERAL

VCC

TRANSITION

DETECTOR

TO

WAKE-UP

LOGIC

VCC

R1OUTB

RX

POWERED

DOWN

UART TX

VOUT = HI-Z

R1OUT

T1IN

ICL3237

R1IN

T1OUT

SHDN = GND, EN = VCC

FIGURE 3. DISABLED RECEIVERS PREVENT POWER DRAIN

MegaBaud Selection

In normal operating mode (MBAUD = GND), the ICL3237

transmitters guarantee a 250kbps data rate with worst-case

loads of 3kΩ in parallel with 1000pF. This provides

compatibility with PC-to-PC communication software, such

as Laplink™.

For higher speed serial communications, the ICL3237

features MegaBaud operation. In MegaBaud operating

mode (MBAUD = VCC), the ICL3237 transmitters guarantee

a 1Mbps data rate with worst-case loads of 3kΩ in parallel

with 250pF for 3.0V < VCC < 4.5V. For 5V ±10% operation,

the ICL3237 transmitters guarantee a 1Mbps data rate into

worst-case loads of 3kΩ in parallel with 1000pF.

Capacitor Selection

The charge pumps require 0.1µF 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-.

TABLE 3. REQUIRED CAPACITOR VALUES

VCC (V)

3.0 to 3.6

C1 (µF)

0.22

C2, C3, C4 (µF)

0.22

3.15 to 3.6

0.1

0.1

4.5 to 5.5

0.047

0.33

3.0 to 5.5

0.22

1.0

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.

Transmitter Outputs when Exiting

Powerdown

Figure 4 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.

High Data Rates

The ICL3237 maintains the RS-232 ±5V minimum

transmitter output voltages even at high data rates. Figure 5

7

Laplink® is a registered trademark of Traveling Software.

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