TLE 4226 G

Semiconductor Group

5

Circuit Description

Input Circuits

The control inputs and the preferred-state input consist of TTL-compatible Schmitt triggers with

hysteresis. Driven by these stages the buffer amplifiers convert the logic signal necessary for driving

the NPN power transistors.

Switching Stages

The output stages consist of NPN power transistors with open collectors. Each stage has its own

protective circuit for limiting power dissipation and shorted load current, which makes the outputs

shorted load protected to the supply voltage throughout the operating range. Integrated clamp-

diodes limit positive voltage spikes that occur when inductive loads are discharged. Output currents,

caused through negative voltages at the outputs, are compensated up to 50 mA for all outputs in

total.

Monitoring and Protective Functions

Each output is monitored (for overload) in its activated status. For the switches 1 to 4 overload is

detected, if the switches are activated and the output voltage at the transistor is higher than 4.1 V

for more than 10

µs. The concerned output will be shutdown and both status outputs will be set. The

switch can only be activated again if the corresponding input is switched off and then on again. If

the output voltage does not exide 4.1 V, the output is not shutdown and the status outputs are not

set, although an overload may occur. The switches 5 and 6 are protected through a SOA-circuit. It

is suppressed for at least 10

µs when the switch is turned on before it can start limiting the overload

current. The status outputs also monitor openload or shorted load to ground at the switches 5 and

6 in deactivated mode.

An analog signal is applied to the analog status output only when protection function is active. If

several malfunctions appear coincident, the highest voltage level of the analog status output will

dominate. Simultaniously the digital status output will be set.

The IC is also protected against thermal overload. If a chip temperature of typically 155 ˚C is

attained, the status outputs monitor overtemperature. If the temperature continues to increase, the

inputs and outputs of the switches 5 and 6 are shutdown. The switches 1 to 4 will not shutdown, so

precaution has to be taken in the application to prevent a further increase of the chiptemperature,

which may destroy the IC. After cooling down below 140 ˚C the overtemperature monitoring will be

reseted and the outputs of the switches 5 and 6 can be activated again.

If the minimum supply voltage for operation is not maintained, the outputs are deactivated. At a

supply voltage of higher than 1.8 V, the outputs 1 to 4 are switched on, if pin 14 (PREFST) is

connected to ground over a resistance smaller 1 M

Ω. The outputs 1 to 4 can be controlled via the

inputs, if pin 14 (PREFST) is switched to high or not connected. Characteristics may be beyond the

specified values. Full function is guaranteed in the supply voltage range of 5 V

± 5%.