MAX3320ACAP Просмотр технического описания (PDF) - Maxim Integrated

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MAX3320ACAP

3V to 5.5V, up to 250kbps True RS-232 Transceiver with 4µA AutoShutdown Plus and Power-On Reset

Maxim Integrated 

3V to 5.5V, up to 250kbps True RS-232 Transceiver

with 4µA AutoShutdown Plus and Power-On Reset

VCC

MAX3320

VCC

GND

RESET

100k

2V/div

2V/div

FORCEON =

FORCEOFF

T2OUT

Figure 4. Ensuring RESET Valid to VCC = 0V

When using the minimum required capacitor values,

make sure the capacitor value does not degrade

excessively with temperatures outside the 0°C to +70°C

range. If in doubt, use capacitors with a larger nominal

value. The capacitor's equivalent series resistance

(ESR), which usually rises at low temperatures, influ-

ences the amount of ripple on V+ and V-.

Transmitter Outputs

when Exiting Shutdown

Figure 5 shows two transmitter outputs when exiting

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

mitter outputs go to opposite RS-232 levels (one trans-

mitter input is high; the other is low). Each transmitter is

loaded with 3kΩ in parallel with 2500pF. The transmitter

outputs display no ringing or undesirable transients as

they exit shutdown. Note that the transmitters are

enabled only when the magnitude of V- exceeds

approximately 3V.

High Data Rates

The MAX3320 maintains the RS-232 ±5V minimum

transmitter output voltage even at high data rates.

Figure 6 shows a transmitter loop-back test circuit.

Figure 7 shows a loop-back test result at 120kbps, and

Figure 8 shows the same test at 250kbps. For Figure 7,

both transmitters were driven simultaneously at

120kbps into RS-232 loads in parallel with 1000pF. For

Figure 8, a single transmitter was driven at 250kbps,

and both transmitters were loaded with an RS-232

receiver in parallel with 1000pF.

Interconnection with 3V and 5V Logic

The MAX3320 can directly interface with various 5V

logic families, including ACT and HCT CMOS. See

Table 4 for more information on possible combinations

of interconnections.

VCC = 3.3V

C1 - C4 = 0.1µF

5µs/div

T1OUT

Figure 5. Transmitter Outputs when Exiting Shutdown or

Powering Up

VCC

C1+

VCC

V+

C1

C3*

C1-

C2+

MAX3320

V-

C2

C4

C2-

T_ IN

T_ OUT

R_ OUT

R_ IN

FORCEON

5k

1000pF

VCC

FORCEOFF

GND

*C3 CAN BE RETURNED TO

VCC OR GND.

Figure 6. Loop-Back Test Circuit

Table 3. Required Minimum

Capacitance Values

VCC

(V)

3 to 3.6

4.5 to 5.5

3 to 5.5

C1

(µF)

0.1

0.047

0.1

C2, C3, C4, CBYPASS

(µF)

0.1

0.33

0.47

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