NCP2817
www.onsemi.com
8
Under Voltage Lockout
When the battery voltage decreases below 1.4 V, the
amplifiers are turned off. The hysteresis to turn back on the
device is 100 mV.
Pop and Click Suppression Circuitry
The NCP2817 includes a special circuitry to eliminate any
pop and click noise during turn on and turn off time.
During uncontrolled turn on and turn off sequences,
normal amplifiers would create an output offset. This offset
drives the loudspeaker and generates a parasitic noise called
“pop and click noise”.
The NCP2817 carefully controls the amplifier output
stages during turn on and off sequences to eliminate this
problem.
Input capacitor selection
The input coupling capacitor blocks the DC voltage at the
amplifier input terminal. This capacitor creates a high−pass
filter with the R
IN
input resistor (10 kW for NCP2817).
The size of the capacitor must be large enough to cut off
low frequencies without severe attenuation in the audio
bandwidth (20 Hz − 20 kHz).
The cut off frequency for the input high−pass filter is:
F
c
+
1
2pR
in
C
in
With R
IN
= 10 kW
A F
c
< 20 Hz is recommended.
Charge Pump Capacitor Selection
Use ceramic capacitor with low ESR for better
performances. X5R / X7R capacitor is recommended.
The C
FLY
flying capacitor serves to transfer charge during
the generation of the negative voltage and directly affects
load regulation and charge pump output impedance. A too
low value results in poor current performance while higher
value increases charge pump regulation and lowers output
impedance (until internal switches R
DS(on)
becomes
predominant). We recommend 1 mF, but lower values can be
uses in systems with lower audio power requirements.
The C
PVM
capacitor must be equal at least to the C
FLY
capacitor to allow maximum transfer charge. In addition, the
ESR of C
PVM
capacitor directly affects ripple on P
VM
as
well as charge pump output impedance. We recommend
1 mF, but lower values can be uses in systems with lower
audio power requirements.
Table 1. SUGGEST TYPICAL VALUE AND
MANUFACTURER
Value Reference Package
Manufac-
turer
1 mF
C1005X5R0J105K 0402 TDK
1 mF
GRM155R60J105K19 0402 Murata
Power Supply Decoupling Capacitor (C1)
The NCP2817 is a NOCAP amplifier and proper power
supply bypassing is critical to reduce noise, high THD+N
and PSRR performances. It is recommended to use a 1uF
X5R / X7R ceramic capacitor and place it as close as
possible to the V
P
pin.
Shutdown Function
The device enters in shutdown mode when shutdown
signal is low. During the shutdown mode, the DC quiescent
current of the circuit does not exceed 1 mA. In this
configuration, the output impedance is 20 kW on each
output.
Layout Recommendation
Minimize trace impedance of the power, the ground and
all output traces. The voltage drop between NCP2817 and
the headset load results in decrease of output power and
efficiency. We strongly recommend using wide traces for
power supply inputs to optimize the power supplies
efficiency and regulation performances. Good ground
connection improves the amplifier immunity to external
switching noise, improves crosstalk between channels as
well as general audio performances. We also recommend
wide PCB traces for the power outputs routing. If possible,
we recommend to use local Ground and power planes.
The power supply decoupling capacitor C
BYP
will help to
minimize the input voltage ripple during fast load transients.
It is important to minimize traces impedances from C
BYP
to
GND plane and from C
BYP
to V
P
pin as close as possible of
the V
P
pin. C
BYP
should be placed as close as possible to the
V
P
pin.
The charge pump creates the VPM negative voltage that
supplies the amplifiers. C
FLY
and C
PVM
capacitors location
and access impedances are also critical. Connect C
FLY
and
C
PVM
as close as possible of the NCP2817 and route their
terminal to the associated pin with wide traces to minimize
impedance and optimize the charge pump ripple and
efficiency performances. In addition, the C
FLY
and C
PVM
capacitors as well as the traces connecting capacitors to the
device should be kept away from the audio input and output
traces to avoid any switching noise coupling with the audio
signal.
A
GND
is the ground reference for all internal analog
features so, particular attention should govern the A
GND
pin
connection to the Ground reference plane. A
GND
pin should
be directly connected to the board Ground reference plane
and keep it separated from other ground connections. The
A
GND
to GND ground reference plane trace should not be
shared with the trace between S
GND
or P
GND
and the Ground
plane.
