APA2068
Application Descriptions (Cont.)
voltage, are from 20dB to -80dB. Each gain step cor-
Output SE/BTL Operation (Cont.)
responds to a specific input voltage range, as shown
in table. To minimizethe effect of noise onthe volume
control pin, which can affect the selected gain level,
hysteresis and clock delay are implemented. The
amount of hysteresis corresponds to half of the step
width, as shown in volume control graph.
output impedance state, which configures the
APA2068 as SE driver from OUT+. IDD isreduced by
approximately one-half in SE mode.
Control of the SE/BTL input can be a logic-level TTL
source or a resistor divider network or the stereo
headphonejack with switchpin asshown inApplication
Circuit.
APA2068 DC Volume Control Curve (BTL)
20
10
0
1kW
VDD
Control
Pin
Forw ard
-10
Ring
100kW
SE/BTL
-20
Backw ard
-30
-40
Sleeve
Tip
Headphone Jack
-50
-60
-70
-80
Figure 2: SE/BTL input selection by phonejack plug
In Figure 2, input SE/BTL operates as follows :
When the phonejack plug is inserted, the 1kW resistor
is disconnected and the SE/BTL input is pulled high
and enables the SE mode. When the input goes high,
the OUT- amplifier isshutdown causing the speaker to
mute. The OUT+ amplifier then drives through the
output capacitor (CO) into the headphone jack. When
there is no headphone plugged into the system, the
contact pin of the headphone jack is connnected from
the signal pin, the voltage divider set up by resistors
100kW and 1kW.Resistor 1kW then pulls low the
SE/BTL pin, enabling the BTL function.
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
DC volume (V)
Figure 3: Gain setting vs VOLUME pin voltage
For highest accuracy, the voltage shown in the ‘rec-
ommended voltage’ column of the table is used to
select a desired gain. This recommended voltage is
exactly halfway between the two nearest transitions.
The gain levels are 2dB/step from 20dB to -40dB in
BTL mode, and the last step at -80dB as mute mode.
Input Resistance, Ri
Volume Control Function
The gain for each audio input of theAPA2068 isset by
the internal resistors (Ri and Rf) of volume control
amplifier ininverting configuration.
APA2068 hasan internal stereo volume control whose
setting is a function of the DC voltage applied to the
VOLUME input pin. The APA2068 volume control
consists of 32 steps that are individually selected by
a variable DC voltage level on the VOLUME control
pin. The range of the steps, controlled by the DC
RF
-
=
AV
(2)
(3)
SE Gain =
Ri
RF
Ri
-2 x
=
BTLGain
Copyright ã ANPEC Electronics Corp.
18
www.anpec.com.tw
Rev. A.2 - Jul., 2005
ANPEC [ ANPEC ELECTRONICS COROPRATION ]
