TPA751

700-mW MONO LOW-VOLTAGE AUDIO POWER AMPLIFIER

WITH DIFFERENTIAL INPUTS

SLOS336C – DECEMBER 2000 – REVISED OCTOBER 2002

16

POST OFFICE BOX 655303

APPLICATION INFORMATION

application schematics (continued)

to shift slightly, which could influence the THD+N performance of the amplifier. Although an additional external

performance is only minimally affected by operating in the fully differential mode as shown in Figure 27. The

following sections discuss the selection of the components used in Figures 26 and 27.

component selection

(5)

BTL gain

+* 2

R

F

R

I

BTL mode operation brings about the factor 2 in the gain equation due to the inverting amplifier mirroring the

voltage swing across the load. Given that the TPA751 is a MOS amplifier, the input impedance is very high;

consequently input leakage currents are not generally a concern, although noise in the circuit increases as the

amplifier. Taken together it is recommended that the effective impedance seen by the inverting node of the

amplifier be set between 5 k

Ω and 20 kΩ. The effective impedance is calculated in equation 6.

(6)

Effective impedance

+

R

F

R

I

R

F )

R

I

As an example, consider an input resistance of 10 k

Ω and a feedback resistor of 50 kΩ. The BTL gain of the

amplifier would be –10 V/V and the effective impedance at the inverting terminal would be 8.3 k

Ω, which is well

within the recommended range.

For high performance applications, metal film resistors are recommended because they tend to have lower

50 k

Ω. This, in effect, creates a low-pass filter network with the cutoff frequency defined in equation 7.

(7)

–3 dB

fc

fc +

1

2

pR

F

C

F