STCC05-BD4 datasheet(9/13 Pages) STMICROELECTRONICS

9 / 13 page

STCC05-B

9/13

■ STCC05 POWER PERFORMANCE VERSUS ITS THERMAL CAPABILITY

The main heat sources of the circuit during operation are the voltage regulator and the relay coil drivers.

Depending of the power supply voltage VPS, the ambient temperature TAMB, and the thermal of resistance

of the package Rth(j-a), the sum of all the coil driver currents

ΣIM is linked to the output regulator current

IDD. In order to avoid spurious thermal shutdown of the system, it is advised to respect this relationship as

shown on figures 7 and 8.

■ EXTENSION OF THE REGULATOR CURRENT CAPABILITY

The output current capability of the STCC05 voltage regulator can be increased in a cost effective manner

by adding an external ballast transistor and two biasing resistors. With such a circuit, the output voltage

regulation remains at 5V 5%, and the current limitation is still active.

Such a topology generates also power losses in the external power transistor especially when the supply

voltage VPS is high or the regulator is in current limiting mode. Therefore it is advised to use a package

with a suitable thermal resistance (Rth j-a).

An example is proposed in the following figure doubling the regulator current capability of the solution to

100mA while producing a current limitation typically at 110mA.

■ FLOATING BUZZER OPERATION

The sound produced by the buzzer is controlled by the frequency of the square signal applied to the INBZ

input pin.

The external RS CS network connected to the BZ2 output pin produces a soft sound by smoothing the

buzzer supplying envelope at power up and power down. Contrary to basic drivers, which directly apply

Figure 11: Driver current sum versus regulator

current at TAMB = 85°C for VPS = 12, 14, 16, 18V

Figure 12: Driver current sum versus regulator

current at TAMB = 70°C for VPS = 12, 14, 16, 18V

0.01

0.02

0.03

0.04

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Σ I

M(A)

AMB =85°C

DD(A)

VPS=18V

VPS=16V

VPS=14V

VPS=12V

0.01

0.02

0.03

0.04

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Σ I

M(A)

DD(A)

AMB =70°C

VPS=18V

VPS=12V & 14V

VPS=16V

Figure 13: Circuit diagram to extend the

STCC05 regulator current to 100mA

Figure 14: Application diagram of the buzzer

drive

VDD

20Ω ¼W

STCC05

5V-50mA

Regulator

Ω ½W

BD136

OH =1kΩ

BZ= 1kΩ

10 k

Ω

S=47 µF

S= 560 Ω

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