ncp4896 ON Semiconductor, ncp4896 Datasheet - Page 11

• Manufacturer Part Number: ncp4896
• Description: 1w Audio Amplifier With Earpiece Driving Capability
• Manufacturer: ON Semiconductor

Detailed Description
until 5.5 V power supply. It delivers 320 mW rms output
power to 4.0 W load (VP = 2.6 V) and 1.0 W rms output
power to 8.0 W load (VP = 5.0 V).
two identical internal power amplifiers. Both are externally
configurable with gain−setting resistors R
closed−loop gain is fixed by the ratios of these resistors).
So the load is driven differentially through OUTA and
OUTB outputs. This configuration eliminates the need for
an output coupling capacitor.
Internal Power Amplifier
were designed to deliver the output power of the
specifications without clipping. The channel resistance
(R
0.6 W when they drive current.
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
illustrated with plots that show both single ended signals on
the previous page.
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 slowly
(20 ms). This way to turn−on the device is optimized in
terms of rejection of “pop and click” noises.
the following formula.
by a logic low on the shutdown pin. During the shutdown
mode, amplifier outputs are connected to the ground.
However, to cut totally the output audio signal, you only
need to wait for 20 ms.
The NCP4896 audio amplifier can operate from 2.2 V
The structure of the NCP4896 is basically composed of
The output Pmos and Nmos transistors of the amplifier
The structure of the internal power amplifier is
A cycle with a turn−on and turn−off transition is
In order to eliminate “pop and click” noises during
A theoretical value of turn−on time at 25 C is given by
C
R: internal 150 k resistor with a 25% accuracy
The device has the same behavior when it is turned−off
on
by
) of the Nmos and Pmos transistors does not exceed
T
: bypass capacitor
on
= 0.95 * R * C
by
in
APPLICATION INFORMATION
and RF (the
http://onsemi.com
NCP4896
11
Shutdown Function
signal is low. During the shutdown mode, the Dc quiescent
current of the circuit is typically 10 nA.
Current Limit Circuit
(Porms = 1.0 W, VP = 5.0 V, R
current in the load of 500 mA.
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.
Single−Ended Operation
output (OUTA). The gain is set by the ration between RF
and Ri.
block the common mode voltage at the output of the
amplifier, thus avoiding DC currents in the load. As for the
high pass filter due to the input capacitor and the Ri resistor,
the load gives with Co another first order high pass filter,
the cut−off frequency of which is given by:
SE/BTL Operation
SE/BTL pin, the NCP4896 allows a cost saving for
application which requires to drive a example an 8.0 W
BTL and a 32 W Single−Ended load.
could occur in both BTL and Singled−Ended loads during
transitions from SE to BTL and BTL to SE.
The device enters shutdown mode when the shutdown
The
In order to limit the excessive power dissipation in the
In SE mode, the load is driven from the primary amplifier
In this SE mode, an output capacitor (Co) is required to
Due to the internal control of each amplifier through
The internal circuitry avoids “pop and click” noises that
maximum
SE Gain + − Rf
Fc +
output
2pR L @ Co
L
1
power
= 8.0 W) requires a peak
Ri
of
the
circuit