DS14C335

SNLS090C – MARCH 2000 – REVISED APRIL 2013

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EXTERNAL DC-DC CONVERTOR COMPONENTS

The DS14C335 with it's unique DC-DC Convertor triples the power supply voltage (3.0V) to +9.3V and then

inverts it to a

−9V potential. This unique convertor ONLY requires 5 external surface mount 0.47 μF capacitors.

The five identical components were chosen to simplify PCB layout and the procurement of components. The

DS14C335's DC-DC Convertor also provides a larger signal swing (higher at RS-232 standard data rates) which

translates to more noise margin for the rejection of ground potential differences, induced noise, and crosstalk

compared to other DC-DC convertor schemes which only provide limited signal swing and limited noise margin.

DC-DC CONVERTOR CAPACITORS

The use of polarized capacitors is not required. However, if they are used, the polarity indicated in the

DS14C335 Functional Diagram must be honored for proper operation. Surface mount capacitors or ceramic

capacitors may be used, however, for optimal efficiency, capacitors with a low effective series resistance (ESR)

should be used. Values in the low Ohms(

Ω) is normally acceptable.

INTEROPERATION WITH +5V UARTS

The DS14C335 provides full RS-232 driver output levels and a single chip solution for the popular 9-pin defacto

serial port. This device may be used in either pure +3V applications or mixed power supplied +3V/+5V

applications. The Driver Input (DIN) and ShutDown (SD) input pins can directly accept full +5V levels without the

need for any external components. The Receiver Output (ROUT) is specified at 2.4V minimum while sourcing 1

mA. This level is compatible with standard TTL thresholds. For a complete discussion on “Interoperation of the

DS14C335 with +5V UARTs” please see TI Application Note AN-876 (SNLA163).

POWER DISSIPATION IN REAL RS-232 APPLICATIONS

The DS14C335 DC-DC Convertor uses special circuitry that helps limit the increase in power supply current as

frequency increases. A complete description of power dissipation and calculations for RS-232 applications can

be found in TI Application Note AN-914 (SNLA037) titled “Understanding Power Requirements in RS-232

Applications”. Typical performance curves are also located in this datasheet for quick reference.

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