KingborTechnologyCo.,Ltd
TEL:(86)0755-83095458 FAX:(86)0755-88364052
KB4863
(Continued)
Application Information
*
Refer to the section Proper Selection of External Components, for a detailed discussion of C size.
B
FIGURE 1. Typical Audio Amplifier Application Circuit
Pin out shown for DIP and SO packages. Refer to the Connection Diagrams for the pinout of the TSSOP,
Exposed-DAP TSSOP, and Exposed-DAP LLP packages.
BRIDGE CONFIGURATION EXPLANATION
Another advantage of the differential bridge output is no net
DC voltage across the load. This is accomplished by biasing
channel A’s and channel B’s outputs at half-supply. This
eliminates the coupling capacitor that single supply,
single-ended amplifiers require. Eliminating an output cou-
pling capacitor in a single-ended configuration forces a
single-supply amplifier’s half-supply bias voltage across the
load. This increases internal IC power dissipation and may
permanently damage loads such as speakers.
As shown in Figure 1, the KB4863 consists of two pairs of
operational amplifiers, forming a two-channel (channel A and
channel B) stereo amplifier. (Though the following discusses
channel A, it applies equally to channel B.) External resistors
Rf and Ri set the closed-loop gain of Amp1A, whereas two
internal 20kΩ resistors set Amp2A’s gain at -1. The KB4863
drives a load, such as a speaker, connected between the two
amplifier outputs, -OUTA and +OUTA.
Figure 1 shows that Amp1A’s output serves as Amp2A’s
input. This results in both amplifiers producing signals iden-
tical in magnitude, but 180˚ out of phase. Taking advantage
of this phase difference, a load is placed between -OUTA
and +OUTA and driven differentially (commonly referred to
as ’bridge mode’). This results in a differential gain of
POWER DISSIPATION
Power dissipation is a major concern when designing a
successful single-ended or bridged amplifier. Equation (2)
states the maximum power dissipation point for a single-
ended amplifier operating at a given supply voltage and
driving a specified output load
AVD = 2 x (Rf / Ri)
(1)
2
PDMAX = (VDD
)
/ (2π2 RL) Single-Ended
(2)
Bridge mode amplifiers are different from single-ended am-
plifiers that drive loads connected between a single amplifi-
er’s output and ground. For a given supply voltage, bridge
mode has a distinct advantage over the single-ended con-
figuration: its differential output doubles the voltage swing
across the load. This produces four times the output power
when compared to a single-ended amplifier under the same
conditions. This increase in attainable output power as-
sumes that the amplifier is not current limited or that the
output signal is not clipped. To ensure minimum output sig-
nal clipping when choosing an amplifier’s closed-loop gain,
refer to the Audio Power Amplifier Design section.
However, a direct consequence of the increased power de-
livered to the load by a bridge amplifier is higher internal
power dissipation for the same conditions.
The KB4863 has two operational amplifiers per channel. The
maximum internal power dissipation per channel operating in
the bridge mode is four times that of a single-ended ampli-
fier. From Equation (3), assuming a 5V power supply and an
4Ω load, the maximum single channel power dissipation is
1.27W or 2.54W for stereo operation.
2
PDMAX = 4 x (VDD
)
/ (2π2 RL) Bridge Mode
(3)
The LM4973’s power dissipation is twice that given by Equa-
tion (2) or Equation (3) when operating in the single-ended
Rev: 1.1
12/19
2005-12-05
KINGBOR [ KINGBOR TECHNOLOGY CO ]
