apa2058 Anpec Electronics Corporation, apa2058 Datasheet - Page 21

• Manufacturer Part Number: apa2058
• Description: 2.4w Stereo Fully Differential Audio Power Amplifier With Stereo Class Ab Cap-free Headphone Driver And Ldo
• Manufacturer: Anpec Electronics Corporation

APA2058
Function Description
Fully Differential Amplifier
The APA2058’ s power amplifier is a fully differential
amplifier with differential inputs and outputs. The fully
differential amplifier has some advantages versus tradi-
tional amplifier. Firstly, don’ t need the input coupling ca-
pacitors because the common-mode feedback will com-
pensate the input bias. The inputs can be biased from
0.5V to V
supply voltage of the power amplifier. If the inputs are
biased out of the input range, the coupling capacitors are
required. Secondly, the fully differential amplifier has out-
standing immunity against supply voltage ripple (217Hz)
caused by GSM RF transmitters’ signal, which is better
than the typical audio amplifier.
Gain Setting Function
For the convenient uses, the APA2058’ s power amplifiers
provide four gain setting options by GAIN0 and GAIN1
pins.
Headphone Mode Operation
Copyright
Rev. A.5 - Feb., 2010
Figure 1: The Cap-Free Headphone Driver’ s Operation
GAIN0
0
0
1
1
DD
Conventional Headphone Driver
-0.5V, and the outputs are still biased at mid-
Cap-free Headphone Driver
ANPEC Electronics Corp.
GAIN1
0
1
0
1
V
V
OUT
OUT
A
15.6
21.6
V
10
12
(dB)
Ri (k )
76
60
40
20
HV
Gnd
HV
HV
Gnd
V
SS
DD
DD
DD
Rf (k )
/2
240
240
240
240
21
The Cap-free headphone drivers use a charge pump to
invert the positive power supply (V
supply (V
operate at this bipolar power supply, and the outputs ref-
erence refers to the ground. This feature eliminates the
output capacitor that using in conventional single-ended
headphone amplifiers. In addition, the power supply rail
for Cap-free headphone drivers has almost 1.5X com-
pare to the single power supply rail headphone drivers.
Thermal Protection
The thermal protection circuit limits the junction tem-
perature of the APA2058. When the junction tempera-
ture exceeds T
amplifier, allowing the devices to cool. The thermal sen-
sor allows the amplifier to start-up after the junction tem-
perature down about 125
designed with a 25
during continuous thermal overload conditions, increas-
ing lifetime of the ICs.
Over-Current Protection (OCP)
When the over current occurs, the output buffers’ current
will be reduced and limited to a fold-back current level.
The power amplifier will go back to normal operation until
the over-current current situation has been removed. In
addition, if the over-current period is long enough and the
IC’ s junction temperature reaches the thermal protection
threshold, the IC enters thermal protection mode.
which monitors and controls P-channel MOS’ s gate
voltage, limiting the output current to 0.4A. For reliable
operation, the device should not be operated in current-
limit for extended period. When the output voltage drops
below 0.6V, which is caused by the over load or short
circuit, the internal short circuit current-limit circuitry lim-
its the output current down to 250mA. The short circuit
current-limit is used to reduce the power dissipation dur-
ing short circuit condition. The short circuit current-limit
has a blanking time feature after the under-voltage lock-
out threshold is reached, therefore, it will avoid the output
causing short circuit current-limit protection during start-
up; the blanking time is about 600 s.
The power amplifier monitors the output buffers’ current.
The LDO regulator provides a current-limit circuitry,
SS
) (see Figure 1). The headphone amplifiers
J
= +150
o
C hysteresis to lower the average T
o
C, a thermal sensor turns off the
o
C. The thermal protection is
DD
www.anpec.com.tw
) to negative power
J