When using the minimum recommended capacitor

values, make sure the capacitance value does not

degrade excessively as the operating temperature

varies.

If in doubt, use capacitors with a

larger nominal value (for example, 2 times larger).

The effective series resistance (ESR) of the capaci-

tors may vary over temperature and increase

when below 0°C. ESR influences the amount of rip-

ple on V+ and V-, so if low ripple is required over

wide temperature ranges, use larger capacitors or

low-ESR types.

To reduce the output impedance at V+ and V-, use

larger capacitors (up to 10µF). This can be useful

when “stealing” power from V+ or from V-.

Driver Outputs when Exiting Shutdown

Figure 3 shows the MAX214 driver outputs when exiting

shutdown. As they become active, the two driver out-

puts are shown going to opposite RS-232 levels (one

driver input is high, the other is low). Each driver is

loaded with 3k

Ω in parallel with 2.5nF.

Power-Supply Bypassing

value as the charge-pump capacitors.

V+ and V- as Power Supplies

A small amount of power can be drawn from V+ and V-,

although this will reduce noise margins. See the

Output Voltage vs. Load Current graph in the

Typical

Operating Characteristics. Increasing the charge-

pump capacitor sizes up to 10µF reduces the imped-

ance of the V+ and V- outputs.

High Data Rates

The MAX214 maintains the RS-232 ±5.0V minimum

driver output voltage even at high data rates. The

Typical Operating Characteristics show transmitter out-

put voltage levels driving 3k

Ω in parallel with various

capacitive loads at data rates up to 120kbps.

Programmable DTE/DCE,

+5V RS-232 Transceiver

_______________________________________________________________________________________

9

+5V

A

B

C

+10V

+5V

0V

-10V

0V

A = TRANSMITTER OUTPUT HIGH, +5V/div

B = TRANSMITTER OUTPUT LOW, +5V/div

C = SHDN INPUT, +5V/div

HORIZONTAL = 200

µs

-5V

Figure 3. Transmitter Outputs When Exiting Shutdown