CPC7512

10

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R01

3. Functional Description

3.1 Introduction

The CPC7512 Dual, 1Form-A, Shunt-Isolated

High-Voltage, High-Frequency, Analog Switch has two

symmetrical switch arrays with four operating states to

facilitate switching of high-frequency, high-voltage

signals using the AB and C switch states and the

flexibility to provide a variety of alternative switching

solutions for low-frequency high-voltage signal

applications. Operational states and logical behavior

of the device is shown in the “Truth Table” on

page 8. Switch organization consists of two channels,

each having three switches.

Within each channel there is an independent LATCH

input and a common Thermal Shutdown circuit that is

shared by the two channels. Other than the shared

TSD circuit, switch functionality under normal

operating conditions within each channel is

independent of the other channel. In designs where

the switches will be required to carry high load

currents or operate in higher temperature

environments, the thermal specifications should be

reviewed because the TSD circuit is shared by both

channels. An excess thermal condition in one channel

resulting in an active TSD event will cause an

interruption in the other channel as well when the TSD

protection circuit activates.

Solid-state switch construction of the CPC7512 offers

clean, bounce-free switching with simple TTL logic

level input control to provide access to high voltage

interfaces without the impulse noise generated by

traditional electromechanical switching techniques.

TTL logic level input control eliminates the additional

driver circuitry required by traditional techniques.

switches utilized in the AB switch state are configured

improved performance when differential access is

required. Their symmetrical construction provides an

additional degree of design flexibility allowing either

side of the switch to be connected to the high voltage

network.

Integrated into the CPC7512 switches are high

frequency dynamic current limiting and thermal

shutdown mechanisms to provide protection for the

electronics being connected to a high voltage network

during a fault condition. High frequency positive and

negative transient currents such as lightning are

reduced by the dynamic current limiting function while

protection from prolonged low frequency power-cross

and DC currents is provided by the thermal shutdown

circuitry.

To protect against a high voltage fault in excess of the

CPC7512’s maximum voltage rating, use of an

over-voltage protector is required. The protector must

limit the voltage seen at the switch terminals to a level

less than the switches’ breakdown voltage. To

minimize the stress on the solid-state contacts, use of

a foldback or crowbar type protector is highly

recommended. With proper selection of the protector,

telecom applications using the CPC7512 will meet all

relevant ITU, LSSGR, TIA/EIA and IEC protection

requirements.

Operating from a single +5V supply the CPC7512 has

extremely low power consumption.

3.2 Under-Voltage Switch Lock-Out Circuitry

Smart logic in the CPC7512 provides for switch state

control during both power up and power loss

transients to prevent undesired connections to high

voltage networks. This is done by setting the switches’

logic to the All-Off state. An internal detector evaluates

determine when to de-assert the under-voltage switch

the under-voltage switch lock-out circuitry with a falling

the lock-out circuit overrides user switch control by

blocking the external information applied to the input

pins, output by the internal latch, and conditioning the

internal switch commands to the All-Off state. Upon

made.

internal logic is properly biased and functional before

accepting external switch commands from the inputs.

assure proper logic and switch behavior up to the

moment the switches are forced off and external

inputs are suppressed.