
NCP4896
http://onsemi.com
12
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 below 140
°
C.
The NCP4896 is unitygain stable and requires no
external components besides gainsetting resistors, an
input coupling capacitor and a proper bypassing capacitor
in the typical application.
Both internal amplifiers are externally configurable (RF
and R
in
) with 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 VP/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
the voltage seen by the load and V
inrms
is the rms value of
the input differential signal.
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
Vorms
.
V
orms
is the rms value of
Porms
(Vopeak is the peak differential
is 500 mA
Iopeak
.
GainSetting Resistor Selection (R
in
and RF)
R
in
and RF
set the closedloop gain of both amplifier.
In order to optimize device and system performance, the
NCP4896 should be used in low gain configurations.
The low gain configuration minimizes THD + noise
values and maximizes the signal to noise ratio, and the
amplifier can still be used without running into the
bandwidth limitations.
A closed loop gain in the range from 2 to 5 is
recommended to optimize overall system performance.
An input resistor (R
in
) value of 22 k is realistic in most
of applications, and doesn’t require the use of a too large
capacitor C
in
.
Input Capacitor Selection (C
in
)
The input coupling capacitor blocks the DC voltage at
the amplifier input terminal. This capacitor creates a
highpass filter with Rin, the cutoff frequency is given by
1
2 *
*Rin* Cin
The value of the capacitor must be high enough to ensure
good coupling at low frequencies without attenuation.
However a large input coupling capacitor requires more
time to reach its quiescent DC voltage (VP/2) and can
increase the turnon pops.
An input capacitor value between 0.1 and 0.39 F
performs well in many applications (With R
in
= 22 k ).
fc
.
Bypass Capacitor Selection (Cby)
The bypass capacitor Cby provides halfsupply filtering
and determines how fast the NCP4896 turns on.
This capacitor is a critical component to minimize the
turnon pop. A 1.0
F bypass capacitor value
(C
in
= < 0.39 F) should produce clickless and popless
shutdown transitions. The amplifier is still functional with
a 0.1 F capacitor value but is more susceptible to “pop and
click” noises.
Thus, a 1.0 F bypassing capacitor is recommended.