VDD

DC VOL

4

LM4952

62 k:

50 k:

RVOL

LM4040-4.1

LM4952

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SNAS230A – AUGUST 2004 – REVISED MAY 2013

Using an LM4040–4.1 to set the maximum DC volume control voltage and attenuate power supply variations when

using unregulated supplies that would otherwise perturb the volume setting.

Figure 47.

Same conditions and waveforms as shown in Figure 46, except that a 4700

μF capacitor has been connected

between the VDD pin and GND (Trace A).

Figure 48.

SELECTING EXTERNAL COMPONENTS

Input Capacitor Value Selection

Two quantities determine the value of the input coupling capacitor: the lowest audio frequency that requires

amplification and desired output transient suppression.

The amplifier's input resistance and the input capacitor (CIN) produce a high pass filter cutoff frequency that is

found using Equation 5.

FCIN = 1/(2πRINCIN)

(5)

As an example when using a speaker with a low frequency limit of 50Hz and based on the LM4952's 44k

Ω

nominal minimum input resistance, CIN, using Equation 5 is 0.072μF. The 0.39μF CINA shown in Figure 40 allows

the LM4952 to drive high efficiency, full range speaker whose response extends below 30Hz.

Similarly, the output coupling capacitor and the load impedance also form a high pass filter. The cutoff frequency

formed by these two components is found using Equation 6.

fCOUT = 1/(2πRLOADCOUT)

(6)

Expanding on the example above and assuming a nominal speaker impedance of 4

Ω, response below 30Hz is

assured if the output coupling capacitors have a value, using Equation 6, greater than 1330

μF.

Bypass Capacitor Value

Besides minimizing the input capacitor size, careful consideration should be paid to value of CBYPASS, the

capacitor connected to the BYPASS pin. Since CBYPASS determines how fast the LM4952 settles to quiescent

operation, its value is critical when minimizing turn-on pops. The slower the LM4952’s outputs ramp to their

quiescent DC voltage (nominally VDD/2), the smaller the turn-on pop. Choosing CBYPASS equal to 4.7μF along with

a small value of CIN (in the range of 0.1μF to 0.39μF) produces a click-less and pop-less shutdown function. As

discussed above, choosing CIN no larger than necessary for the desired bandwidth helps minimize clicks and

pops.

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