ICL3224 데이터 시트보기 (PDF) - Intersil

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ICL3224

1 Microamp, +3V to +5.5V, 250kbps, RS-232 Transceivers with Enhanced Automatic Powerdown

Intersil 

ICL3224, ICL3226, ICL3238, ICL3244

Detailed Description

These ICL32XX interface ICs operate from a single +3V to

+5.5V supply, guarantee a 250kbps minimum data rate,

require only four small external 0.1µF capacitors, feature low

power consumption, and meet all ElA RS-232C and V.28

specifications. The circuit is divided into three sections: The

charge pump, the transmitters, and the receivers.

Charge-Pump

Intersil’s new ICL32XX family utilizes regulated on-chip dual

charge pumps as voltage doublers, and voltage inverters to

generate ±5.5V transmitter supplies from a VCC supply as

low as 3.0V. This allows these devices to maintain RS-232

compliant output levels over the ±10% tolerance range of

3.3V powered systems. The efficient on-chip power supplies

require only four small, external 0.1µF capacitors for the

voltage doubler and inverter functions at VCC = 3.3V. See

the “Capacitor Selection” section, and Table 3 for capacitor

recommendations for other operating conditions. The charge

pumps operate discontinuously (i.e., they turn off as soon as

the V+ and V- supplies are pumped up to the nominal

values), resulting in significant power savings.

Transmitters

The transmitters are proprietary, low dropout, inverting

drivers that translate TTL/CMOS inputs to EIA/TIA-232

output levels. Coupled with the on-chip ±5.5V supplies,

these transmitters deliver true RS-232 levels over a wide

range of single supply system voltages.

Transmitter outputs disable and assume a high impedance

state when the device enters the powerdown mode (see

Table 2). These outputs may be driven to ±12V when

disabled.

All devices guarantee a 250kbps data rate for full load

conditions (3kΩ and 1000pF), VCC ≥ 3.0V, with one

transmitter operating at full speed. Under more typical

conditions of VCC ≥ 3.3V, RL = 3kΩ, and CL = 250pF, one

transmitter easily operates at 1Mbps.

Transmitter inputs float if left unconnected, and may cause

ICC increases. Connect unused inputs to GND for the best

performance.

Receivers

All the ICL32XX devices contain standard inverting

receivers, but only the ICL3238 and ICL3244 receivers can

tristate, via the FORCEOFF control line. Additionally, the

ICL3238 and ICL3244 include a noninverting (monitor)

receiver (denoted by the ROUTB label) that is always active,

regardless of the state of any control lines. Both receiver

types 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.

8

The ICL3238 and ICL3244 inverting receivers disable during

forced (manual) powerdown, but not during automatic

powerdown (see Table 2). Conversely, the monitor receiver

remains active even during manual powerdown making it

extremely useful for Ring Indicator monitoring. Standard

receivers driving powered down peripherals must be

disabled to prevent current flow through the peripheral’s

protection diodes (see Figures 2 and 3). This renders them

useless for wake up functions, but the corresponding

monitor receiver can be dedicated to this task as shown in

Figure 3.

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

VOUT = VCC

GND

Tx

SHDN = GND

OLD

RS-232 CHIP

FIGURE 2. POWER DRAIN THROUGH POWERED DOWN

PERIPHERAL

VCC

TRANSITION

DETECTOR

TO

WAKE-UP

LOGIC

VCC

R2OUTB

RX

POWERED

DOWN

UART

TX

VOUT = HI-Z

R2OUT

T1IN

FORCEOFF = GND

ICL3238/44

R2IN

T1OUT

FIGURE 3. DISABLED RECEIVERS PREVENT POWER DRAIN

FN4876.10

March 1, 2006

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