Semiconductor Group

6

Digital / Analog Converter, Loudness and Junction Control

The DAC converts the 4-bit words from the logic into the appropriate staircase currents with the

particular tone frequency. The sum current

I

generator produces the DAC reference current

I

external resistor to ground. The chip temperature is monitored by the junction control. At

temperatures of more then approx. 170 ˚C the stop input will switch the output current

I

output current is enabled again once the chip has cooled down to approx. 150 ˚C.

Current Amplifier

The current amplifier with a gain of 1600 boosts the current

I

approx. 750 mA maximum. The output stage consists of an NPN transistor with its emitter on power

GND and collector on pin Q.

The current control insures that the output stage only conducts defined currents. In conjunction with

the integrated thermal shutdown, this makes the configuration shortcircuit-protected within wide

limits. Because of the absence of feedback the circuit is also extremely stable and therefore

uncritical in applications. Resistor

R

resistive component of the loudspeaker impedance

R

The output amplitude of the current

I

(only 3 tone mode), so

R

The following applies:

I

3 x B x (

V

the result is:

R

with: B = 1600

R

with: K = 4800

SAE 800