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參數(shù)資料
| 型號(hào)： | AD1994ACPZ |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | Class-D Audio Power Amplifier |
| 中文描述： | 25 W, 2 CHANNEL, AUDIO AMPLIFIER, QCC64 |
| 封裝： | 9 X 9 MM, LEAD FREE, MO-220VMMD-4, LFCSP-64 |
| 文件頁(yè)數(shù)： | 10/16頁(yè) |
| 文件大?。?/td> | 389K |
| 代理商： | AD1994ACPZ |
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AD199x
Preliminary Technical Data
FUNCTIONAL DESCRIPTION
DEVICE ARCHITECTURE
The AD199x is an audio quality, switching amplifier with an
integrated sigma-delta modulator. The power stage of the
AD199x is arranged internally as four transistor pairs, which
are used as two H-bridge outputs to provide stereo
amplification. The transistor pairs are driven by the output of
the
∑
modulator. A user selectable non-overlap time is
provided between the switching of the high side transistor and
low side transistor to ensure that both transistors are never on at
the same time. The AD199x implements turn on pop
suppression to eliminates any pops or clicks following a reset
or un-mute.
Rev. PrA – 1/20/05 | Page 10 of 16
Analog Input Section
The analog input section uses an internal amplifier to bias the
input signal to the reference level. A DC blocking capacitor
should be connected as shown in Figure 15 to remove any
external DC bias contained in the input signal
1.25V
AINL/
AINR
0V
+
71046-0007
Figure 15. Normal Operation
The Sigma-Delta Modulator
Detailed description pending on patents pending, as well as
announcements, conference proceedings and other scheduled
public disclosures.
Selecting Stereo or Mono Mode
Driving the H-Bridge
Each channel of the switching amplifier is controlled by a 4
transistor H-bridge to give a differential output stage. The
outputs of the H-bridges, OUTR+, OUTR-, OUTL+ and
OUTL- will switch between PVDD and PGND as determined
by the sigma delta modulator. The power supply that is used to
drive the power stage of the AD199x should be typically in the
range of +8 V to +20 V and should be capable of supplying
enough current to drive the load. This power supply is
connected across the PVDD and PGND pins. The feedback
pins, NFR+, NFR-, NFL+ and NFL-, are used to supply
negative feedback to the modulator. The pins are connected to
the outputs of the H-bridge via a resister divider network as
shown in Figure 16. See the section on Selecting the Modulator
Gain for more information.
External schottky diodes can be used to reduce power loss
during the non-overlap time when neither of the high-side or
low-side transistors is on. During this time neither transistor is
driving the OUTx pin. The nature of the inductors is to keep
current flowing. For example the OUTx pin may approach and
pass the PGND level to achieve this. When the voltage at the
OUTx pin is 0.7V below PGND the parasitic diode associated
with the low-side transistor will become forward biased and
turn on. When the high-side transistor turns on the voltage at
OUTx will rise to PVDD and will reverse bias the parasitic
diode. However, by its nature the parasitic diode has a long
reverse recovery time and current will continue to flow through
it to PGND thus causing the entire circuit to draw more current
than necessary. The addition of the schottky diodes prevents
this happening. When the OUTx pin goes more than 0.3V
below PGND the schottky diode becomes forward biased.
When the high-side transistor turns on the schottky diode
becomes reverse biased. The reverse recovery time of the
schottky diode is significantly faster than the parasitic diode so
far less current is wasted. A similar effect happens when the
inductor induces a current which drives the OUTx pin above
PVDD. Figure 16 shows how the external components of a
system are connected to the pins of the AD199x to form the H-
bridge configuration.
AMPLIFIER GAIN
Selecting the Modulator Gain
The AD199x modulator can be thought of as a switching
analog amplifier with a voltage gain controlled by two external
resistors forming a resistor divider between the OUTxx pins
and PGND. The centre of the resistor divider is connected to
the appropriate feedback pin NFx. Selecting the gain along
with the PVDD Voltage will determine how much power can be
delivered to a load for a fixed input signal. The gain of the
modulator is controlled by the values of R1 and R2 (see Figure
16) according to the equation below.
Gain = (R1 + R2)/R2
The gain should be selected such that a 1Vrms input signal
doesn’t cause the modulator to generate an output signal which
has a peak to peak value greater than 90% of PVDD. Selecting
a gain that meets this criteria will ensure that the modulator
remains in a stable operating condition.
PVDD
OUTx+
PGND
NFx+
OUTx-
PGND
NFx-
71046-0004
EXTERNAL COMPONENTS
D3
D4
PVDD
Figure 16. H-Bridge Configuration
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