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NCP2892 Datasheet(PDF) 12 Page - ON Semiconductor

Part No. NCP2892
Description  1.3 Watt Audio Power Amplifier with Fast Turn On Time
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Maker  ONSEMI [ON Semiconductor]
Homepage  http://www.onsemi.com
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NCP2892 Datasheet(HTML) 12 Page - ON Semiconductor

 
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NCP2892 Series
http://onsemi.com
12
APPLICATION INFORMATION
Detailed Description
The NCP2892 audio amplifier can operate under 2.6 V
until 5.5 V power supply. With less than 1% THD+N, B
version can deliver up to 1.2 W rms output power to an
8.0
W load (Vp = 5.0 V). If application allows to reach 10%
THD+N, then 1.6 W can be provided using a 5.0 V power
supply.
The structure of the NCP2892 is basically composed of
two identical internal power amplifiers; the first one is
externally configurable with gain−setting resistors Rin and
Rf (the closed−loop gain is fixed by the ratios of these
resistors) and the second is internally fixed in an inverting
unity−gain configuration by two resistors of 20 k
W. So the
load is driven differentially through OUTA and OUTB
outputs. This configuration eliminates the need for an
output coupling capacitor. The NCP2892A has around
100
W and the NCP2892B has around 10 kW output
impedance in the shutdown mode.
Internal Power Amplifier
The output PMOS and NMOS transistors of the amplifier
were designed to deliver the output power of the
specifications without clipping. The channel resistance
(Ron) of the NMOS and PMOS transistors does not exceed
0.6
W when they drive current.
The structure of the internal power amplifier is
composed of three symmetrical gain stages, first and
medium gain stages are transconductance gain stages to
obtain maximum bandwidth and DC gain.
Turn−On and Turn−Off Transitions
A cycle with a turn−on and turn−off transition is
illustrated with plots that show both single ended signals on
the previous page.
In order to eliminate “pop and click” noises during
transitions, output power in the load must be slowly
established or cut. When logic high is applied to the
shutdown
pin, the bypass voltage begins to rise
exponentially and once the output DC level is around the
common
mode
voltage,
the
gain
is
established
instantaneously. This way to turn−on the device is
optimized in terms of rejection of “pop and click” noises.
The device has the same behavior when it is turned−off
by a logic low on the shutdown pin. During the shutdown
mode, amplifier outputs are connected to the ground.
When a shutdown low level is applied, with 1
mF bypass
capacitor, it takes 65 ms before the DC output level is tied
to Ground on each output. However, no audio signal will be
provided to the BTL load only 1
ms after the falling edge on
the shutdown pin.
With 1
mF bypass capacitor, turn on time is set to 90 ms.
This fast turn on time added to a very low shutdown current
saves battery life and brings flexibility when designing the
audio section of the final application.
NCP2892 is a zero pop noise device when using a
differential audio input. In case of a single ended one, there
is no audible pop click noise, especially when the input cut
off frequency is higher than 100 Hz.
Shutdown Function
The device enters shutdown mode when shutdown signal
is low. During the shutdown mode, the DC quiescent
current of the circuit does not exceed 100 nA. In this
configuration, the output impedance is 10 k
W on each
output.
Current Limit Circuit
The maximum output power of the circuit (Porms =
1.0 W, Vp = 5.0 V, RL = 8.0
W) requires a peak current in
the load of 500 mA.
In order to limit the excessive power dissipation in the
load when a short−circuit occurs, the current limit in the
load is fixed to 800 mA. The current in the four output MOS
transistors are real−time controlled, and when one current
exceeds 800 mA, the gate voltage of the MOS transistor is
clipped and no more current can be delivered.
Thermal Overload Protection
Internal
amplifiers
are
switched
off
when
the
temperature exceeds 160
°C, and will be switched on again
only when the temperature decreases fewer than 140
°C.
The NCP2892 is unity−gain stable and requires no
external components besides gain−setting resistors, an
input coupling capacitor and a proper bypassing capacitor
in the typical application.
The first amplifier is externally configurable (Rf and
Rin), while the second is fixed in an inverting unity gain
configuration.
The differential−ended amplifier presents two major
advantages:
− The possible output power is four times larger (the
output swing is doubled) as compared to a single−ended
amplifier under the same conditions.
− Output pins (OUTA and OUTB) are biased at the same
potential Vp/2, this eliminates the need for an output
coupling
capacitor required with a single−ended
amplifier configuration.
The differential closed loop−gain of the amplifier is
given by Avd + 2*
Rf
Rin
+
Vorms
Vinrms
.
Output power delivered to the load is given by
Porms +
(Vopeak)2
2* RL
(Vopeak is the peak differential
output voltage).
When choosing gain configuration to obtain the desired
output power, check that the amplifier is not current limited
or clipped.
The maximum current which can be delivered to the load
is 500 mA Iopeak +
Vopeak
RL
.


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