Zywyn Corporation

ZT230E

Specifications subject to change without notice

Zywyn

5

August 2004

rev. 02

Circuit Description

Proprietary Switch-Capacitor Regulated Voltage

Converter

Different from other suppliers, Zywyn uses a patent pending

switch-capacitor voltage-controlled source and sink current

generators design to provide powerful bipolar voltages to

maintain compliant EIA/RS232 levels regardless of power

supply fluctuations. The design consists of an internal

regulated oscillator, a two phase clock cycling, regulated

complementary MOS switches, fast switching diode and

switch capacitors.

The switch capacitor bi-directional current generators oper-

ate with Zywyn’s proprietary smartly regulated complemen-

tary MOS switches and fast switching diode from its

proprietary high voltage process technology. The efficiency

of these bi-directional current generators is well over 70%.

The switching frequency is generated by an internal oscilla-

tor and regulated by the current loads. The switch capacitor

pump design delivers higher negative bucked voltage than

the positive boosted voltage to achieve a balanced voltage

controlled source and sink current generators resulting a

balanced bipolar voltage supplies to the chip.

With its unique proprietary design technique, Zywyn’s

interface product series provide a better power efficient,

stable and compliant EIA/RS232 levels with superior low

power consumption.

Controlled Enable and Power-Down

The ZT211E and ZT213E both feature an enable input, which

allows the receiver outputs to be either tri–stated or en-

abled. This can be especially useful when the receiver is tied

directly to a microprocessor data bus. For the ZT211E,

enable is active low, in which a logic LOW applied to the EN

pin will enable the receiver outputs. For the ZT213E, enable

is active high in which a logic HIGH applied to the EN pin will

enable the receiver outputs.

ZT211E and ZT213E have a low-power shutdown mode

controlled by the SD pin. During shutdown the driver output

and the switch-capacitor regulated voltage converter are

disabled with the supply current falls to less than 1µA.

ZT213E includes a wakeup function (see Table 1) that

enables two receivers during a shutdown state. With only

the receivers active during the shutdown state, the devices

draw 5-10µA of supply current. A typical application is when

a RS232 cable is connected or when the peripheral is

enabled such as a modem, the devices will automatically

become active again. The ring indicator signal from the

modem could be passed through an active receiver in the

ZT213E that is itself in the shutdown mode. The ring

indicator signal would propagate through the ZT213E to the

power management circuitry of the computer to power up

the microprocessor and the ZT213E drivers. After the supply

voltage to the ZT213E reaches +5.0V, the SD pin can be

disabled, taking the ZT213E out of the shutdown mode. All

receivers that are active during shutdown maintain 500mV

(typ.) of hysteresis.

ESD Immunity

Electro-Static Discharge (ESD) is an important factor when

implementing a serial port into a system. In some applica-

tions, it is crucial that the ESD protection for the system

must meet a certain tolerance level. Since RS232 trans-

ceiver devices are exposed to the outside world, there are

many environmental factors that can effect the serial port

and even subject it to transients that could potentially

damage the transceiver itself.

The RS232 transceiver is usually routed from the serial port

connector to the transceiver IC through the metal trace on

the printed circuit board. This trace will have some small

amount of resistance that will add some protection in terms

of limiting transient current to the IC. However for added

voltage protection, transient voltage suppressors (TVS) or

transzorbs, which are back-to-back diode arrays clamp, are

usually necessary to protect the serial port circuity.

To further reduce cost within their system, more engineers

are requiring higher ESD tolerances from the transceiver ICs

themselves without having to add costly TVS circuitry.

Zywyn's RS232 transceivers includes built-in transient volt-

age suppression where external ESD circuitry is not neces-

sary to meet the MIL-STD-883, Method 3015, Human Body

Model and the EN61000-4-2 Air/Contact Discharge tests.

The Human Body Model has been the generally accepted

ESD testing method for semiconductors. This test is in-

tended to simulate the human body’s potential to store

electrostatic energy and discharge it to an integrated circuit

upon close proximity or contact. This method will test the

IC’s capability to withstand an ESD transient during normal

handling such as in manufacturing areas where the ICs tend

to be handled frequently.

EN61000-4-2 is used for testing ESD on equipment and

systems. For system manufacturers, they must guarantee

a certain amount of ESD protection since the system itself

is exposed to the outside environment and human pres-

ence. EN61000-4-2 specifies that the system is required to

withstand an amount of static electricity when ESD is

applied to exposed metal points and surfaces of the equip-

ment that are accessible to personnel during normal usage.

The transceiver IC receives most of the ESD current when

the ESD source is applied to the connector pins.

There are two methods within EN61000-4-2, the Air Dis-

charge method and the Contact Discharge method. With

the Air Discharge Method, an ESD voltage is applied to the

equipment under test through air, which simulates an

electrically charged person ready to connect a cable onto

the rear of the system and the high energy potential on the

person discharges through an arcing path to the rear panel

of the system before he or she even touches the system.

The Contact Discharge Method applies the ESD current

directly to the EUT. This method was devised to reduce the

unpredictability of the ESD arc. The discharge current rise

time is constant since the energy is directly transferred

without the air-gap arc inconsistencies.