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參數(shù)資料
| 型號： | NCP9002 |
| 廠商： | ON SEMICONDUCTOR |
| 英文描述： | 1.3 Watt Audio Power Amplifier with Fast Turn On Time |
| 中文描述： | 1.3瓦音頻功率放大器具有快速準時打開 |
| 文件頁數(shù)： | 11/13頁 |
| 文件大?。?/td> | 147K |
| 代理商： | NCP9002 |
NCP9002
http://onsemi.com
11
APPLICATION INFORMATION
Detailed Description
The NCP9002 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
load (V
p
= 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 NCP9002 is basically composed of
two identical internal power amplifiers; the first one is
externally configurable with gainsetting resistors R
in
and
R
f
(the closedloop gain is fixed by the ratios of these
resistors) and the second is internally fixed in an inverting
unitygain configuration by two resistors of 20 k . So the
load is driven differentially through OUTA and OUTB
outputs. This configuration eliminates the need for an
output coupling capacitor. The NCP9002 has around 10 k
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
(R
on
) of the NMOS and PMOS transistors does not exceed
0.6
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.
TurnOn and TurnOff Transitions
A cycle with a turnon and turnoff 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 turnon the device is
optimized in terms of rejection of “pop and click” noises.
The device has the same behavior when it is turnedoff
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 F 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 s after the falling edge on
the shutdown pin.
With 1 F 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.
NCP9002 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 on each
output.
Current Limit Circuit
The maximum output power of the circuit (Porms =
1.0 W,
V
p
= 5.0 V, R
L
= 8.0 ) requires a peak current in
the load of 500 mA.
In order to limit the excessive power dissipation in the
load when a shortcircuit occurs, the current limit in the
load is fixed to 800 mA. The current in the four output MOS
transistors are realtime 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 NCP9002 is unitygain stable and requires no
external components besides gainsetting resistors, an
input coupling capacitor and a proper bypassing capacitor
in the typical application.
The first amplifier is externally configurable (R
f
and
R
in
), while the second is fixed in an inverting unity gain
configuration.
The differentialended amplifier presents two major
advantages:
The possible output power is four times larger (the
output swing is doubled) as compared to a singleended
amplifier under the same conditions.
Output pins (OUTA and OUTB) are biased at the same
potential V
p
/2, this eliminates the need for an output
coupling capacitor required with a singleended
amplifier configuration.
The differential closed loopgain of the amplifier is
Rf
Rin
Vinrms
Output power delivered to the load is given by
(Vopeak)2
2 *RL
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
Vopeak
RL
given by
Avd
2 *
Vorms
.
Porms
(Vopeak is the peak differential
is 500 mA
Iopeak
.
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