TCF6000

3

MOTOROLA ANALOG IC DEVICE DATA

–0.3 V

+10 mA

IIK

0 V

–10 mA

Low

Impedance

High

Low

Impedance

Impedance

VCC+

0.75 V Typ

Vin

VCC

Figure 3. Clamping Characteristics

APPLICATIONS INFORMATION

Figure 4 depicts a typical application in a microcomputer

based automotive ignition system.

The TCF6000 is being used not only to protect the

system’s normal inputs but also the (bidirectional) serial

diagnostics port.

The value of the input resistors, Rin, is determined by the

clamping current and the anticipated value of the spikes.

Thus:

Rin =

Ω

V

IIK

where:

So, taking,

gives,

V

IIK

V

IIK

Rin

= Peak Volts (V)

= Clamping current (A)

= 300 V typically (SAE J1211)

= 10 mA (recommended)

= 30 k

Resistors of this value will not usually cause any problems

in MOS systems, but their presence needs to be taken into

account by the designer. Their effect will normally need to be

compensated for Bipolar systems.

Figure 4. Typical Automotive Application

Gnd

Gnd

VCC

Coil Drive

Coil Feedback

VCC

INT1

D1

D0

D2

B0

D6

B1

B2

VSS

Gnd

Serial Diagnostics

Ignition Module

Car

6X

Rin

3X

Cin

Gnd

Vbat

Vbat

RHall

Engine

Temperature

Hall

Effect

Pick Up

Pressure

Sensor

Battery

Volts

Gnd

MC6805S2