AS1701, AS1706
Data Sheet - Detailed Description
8 Detailed Description
The AS1701/AS1706 bridged audio power-amplifiers can deliver 1.6W into 4Ω while operating from a single 2.7 to
5.5V supply. The devices consist of two high-output-current operational amplifiers configured as a bridge-tied load
(BTL) amplifier as shown in Figure 29.
Figure 29. AS1701 Typical Configuration Block Diagram
VDD
+
0.1µF
CS
20kΩ RF
VDD
CIN
IN-
RIN
20kΩ
Audio
Input
–
+
0.33µF
OUT+
OUT-
IN+
40kΩ
40kΩ
RL
4 or 8Ω
50kΩ
–
+
BIAS
VDD/2
0.1 to
1.0µF
+
CB
Av = -1
50kΩ
Bias
AS1701
SHDN
GND
The gain of the devices is set by the closed-loop gain of the input operational amplifier. As shown in Figure 29, the out-
put of the first amplifier serves as the input to the second amplifier, which is configured as an inverting unity-gain fol-
lower in both devices. This results in two outputs, identical in magnitude, and 180° out-of-phase.
Bias
The devices operate from a single 2.7 to 5.5V supply and contain an internally generated, common-mode bias voltage
of:
VDD/2
(EQ 1)
referenced to ground. Bias provides click-and-pop suppression and sets the DC bias level for the audio outputs. For
selection of the value for the bias bypass capacitor (CBIAS), see Bias Bypass Capacitor on page 13. Pin BIAS is inter-
nally connected to the non-inverting input of one amplifier, and should be connected to the non-inverting input of the
other amplifier for proper signal biasing (see Figure 29).
Shutdown
The integrated 100nA, low-power shutdown circuitry reduces quiescent current consumption. As shutdown com-
mences, the bias circuitry is automatically disabled, the device outputs go high impedance, and bias is driven to GND.
Note: Connect SHDN to GND for the AS1701 (active-high); connect SHDN to VDD for the AS1706 (active-low).
Current Limit
The AS1701/AS1706 current limit circuitry protects the device during output short-circuit and overload conditions.
When both amplifier outputs are shorted to either VDD or GND, the short-circuit protection is enabled and the amplifier
enters a pulsing mode, reducing the average output current to a safe level. The amplifier remains in this mode until the
short-circuit or overload condition is corrected.
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