MAX3381EEUP Просмотр технического описания (PDF) - Maxim Integrated

Номер в каталоге

Компоненты Описание

Список матч

MAX3381EEUP

+2.35V to +5.5V, 1µA, 2Tx/2Rx RS-232 Transceivers with ±15kV ESD-Protected I/O and Logic Pins

Maxim Integrated 

+2.35V to +5.5V, 1µA, 2Tx/2Rx RS-232 Transceivers

with ±15kV ESD-Protected I/O and Logic Pins

to IEC 1000-4-2 are generally lower than that measured

using the Human Body Model. Figure 6a shows the IEC

1000-4-2 model, and Figure 6b shows the current

waveform for the ±8kV IEC 1000-4-2 Level 4 ESD

Contact Discharge test.

The Air-Gap test involves approaching the device with

a charged probe. The Contact Discharge method con-

nects the probe to the device before the probe is ener-

gized.

Machine Model

The Machine Model for ESD tests all pins using a

200pF storage capacitor and zero discharge resis-

tance. Its objective is to emulate the stress caused by

contact that occurs with handling and assembly during

manufacturing. All pins require this protection during

manufacturing, not just RS-232 inputs and outputs.

Therefore, after PC board assembly, the Machine

Model is less relevant to I/O ports.

Applications Information

Capacitor Selection

The capacitor type used for C1–C4 is not critical for

proper operation. Polarized or nonpolarized capacitors

can be used. The charge pump requires 0.1µF capaci-

tors for +3.3V operation. For other supply voltages, see

Table 2 for required capacitor values. Do not use val-

ues smaller than those listed in Table 2. Increasing the

capacitor values (e.g., by a factor of 2) reduces ripple

on the transmitter outputs and slightly reduces power

consumption. C2, C3, and C4 can be increased without

changing C1’s value. However, do not increase C1

without also increasing the values of C2, C3, C4, and

C5 to maintain the proper ratios (C1 to the other capac-

itors).

When using the minimum required capacitor values,

make sure the capacitor value does not degrade

excessively with temperature. If in doubt, use capaci-

tors with a large nominal value. The capacitor’s equiva-

lent series resistance (ESR) usually rises at low

temperatures and influences the amount of ripple on

V+ and V-.

Table 2. Minimum Required Capacitor

Values

VCC (V)

+2.35 to +3.6

+4.5 to +5.5

+2.35 to +5.5

C1, C5 (µF)

0.1

0.047

0.22

C2, C3, C4 (µF)

0.1

0.33

1

Power-Supply Decoupling

In most circumstances, connect a 0.1µF capacitor from

VCC to GND. This capacitor is for noise reduction. If the

MAX3380E/MAX3381E are used in a data cable appli-

cation, add a 47µF capacitor from VCC to ground. The

47µF capacitor is used to ensure that the current need-

ed during power-up is supplied to the device. In appli-

cations that are sensitive to power-supply noise,

decouple VCC to ground with a capacitor of the same

value as charge-pump capacitor C1. Connect bypass

capacitors as close to the IC as possible.

Transmitter Outputs when Recovering

from Shutdown

Figure 7 shows two transmitter outputs when exiting

shutdown mode. As they become active, the two trans-

mitter outputs are shown going to opposite RS-232 lev-

els (one transmitter input is high, the other is low). Each

transmitter is loaded with 3kΩ in parallel with 1000pF.

The transmitter outputs display no ringing or undesir-

able transients as they come out of shutdown. Note that

the transmitters are enabled only when the magnitude

of V- exceeds approximately 3V.

High Data Rates

The MAX3380E/MAX3381E maintain the RS-232 ±5.0V

minimum transmitter output voltage even at high data

rates. Figure 8 shows a transmitter loopback test cir-

cuit. Figure 9 shows a loopback test result for the

MAX3380E at 460kbps with true RS-232 output voltage

levels (VCC = +4.2V). Figure 10 shows the same test

with RS-232-compatible levels (VCC = +2.5V). With

data rates as high as 460kbps, the MAX3380E is com-

patible with 2.5-Generation GSM standards.

5V/div

5V FORCEON =

0 FORCEOFF

6V T2OUT

2V/div

0

4µs/div

VCC = 3.3V, C1–C4 = 0.1µF, CLOAD = 1000pF

T1OUT

6V

Figure 7. Transmitter Outputs when Recovering from Shutdown

or Powering Up

______________________________________________________________________________________ 11

Share Link: