UTCL2949E

LINEAR INTEGRATED CIRCUIT

6

QW-R102-014,A

5V

0V

2V

5V

Vs

40V

Figure 2: Output Voltage vs.Input voltage

Figure 3: Quiescent Current vs.Supply Voltage

2.0

0

1.5

1.0

0.5

mA

Vs

5V

28V

Preregulator

To improve the transient immunity a preregulator stabilized the internal supply voltage to 5V.This internal voltage is

present at Pin3(Vz).This voltage should not be used as an output because the output capability is very small(≦10μ

A).

This output may be used as an option when a better transient behaviour for supply voltages less than 8V is

required(see also application note).

In this case a capacitor(100nF - 1μF) must be connected between Pin3 and GND.If this feature is not used Pin3

must be left open.

Reset Circuit

The block circuit diagram of the reset circuit is shown in Fig.4. the reset circuit supervises the output voltage.

The reset thereshold of 4.5V is defined with the internal reference voltage and standby output drivider.

CT● 2V

TRD=

2μA

The reactioin time of the reset circuit increases the noise immunity.Standby output voltagedrops below the reset

threshold only a bit longer than th reaction time results in a shorter reset delay time.

The nominal reset delay time will be generated for standby output voltage drops longer than approximately 50μs.

The typical reset output waveforms are shown in Fig.5.

Sense Comparator

The sense comparator compares an input signal with an internal voltage reference of typical 1.23V.The use of an

external voltage divider makes this comparator flexible in th application.

It can be used to supervise the input voltage either before or after the protection diode and to give additional

informations to the microprocessor like low voltage warnings.