Figure 5.

For example: if signal frequency is 20hz, C = 2200

µF, Rl = 8Ohm , Vcc = 20V (+-20V) from [3] the peak

modulation of any supply is DV ~ 1.8V. (measured ~2V)

NOTE1 : From this formula it is clear that the IC is not able to deliver dc current without generating uncontrolled increase of the supply voltage

(Tsinewave=infinite-->Dv=infinite).

This condition happens if the dc current on the load is bigger than the current sinked by the IC. For ex-

ample a short circuit to gnd with the IC not supplied by any signal. In this case the offset of the IC on the

short cicuit generates a dc current and so a supply voltage increase.

To avoid the sure breakdown of the IC there is an internal comparator that senses the total supply and

put the IC in st-by if the total supply is over 55V (TYP)

This means that the electrolityc capacitor to be used must have the maximum operating voltage over the

maximum of [ 55V - (Vcc) ] and Vcc

To summarize the parameter of the electrolitic capacitors:

- Good ESR,ESL at switching frequency (around 100Khz)

- Value consistent with the formula [3]

- Maximum operating voltage of max[(55v-(Vcc); (Vcc)].

NOTE2 : Appl icationin dummy split supply (fig. 7)

The circuit must be supplied with +Vcc, GND, -Vcc. The GND is half of the overall supply.

Using a single supply it is possible to obtain, by the use of a resistive/capacitive devider, the half Vcc to

be used as GND. The schematic can be the following:

Figure 7

Figure 6.

AN1013 APPLICATION NOTE

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