LM48820TM/NOPB National Semiconductor, LM48820TM/NOPB Datasheet - Page 13

• Manufacturer Part Number: LM48820TM/NOPB
• Description: IC AMP AUDIO PWR .095W AB 14USMD
• Manufacturer: National Semiconductor
• Series: Boomer®r
• Type: Class ABr

Specifications of LM48820TM/NOPB

• Output Type: Headphones, 2-Channel (Stereo)
• Max Output Power X Channels @ Load: 95mW x 2 @ 16 Ohm
• Voltage - Supply: 1.6 V ~ 4.5 V
• Features: Depop, Shutdown, Thermal Protection
• Mounting Type: Surface Mount
• Package / Case: 14-MicroSMD
• Amplifier Class: AB
• No. Of Channels: 1
• Output Power: 95mW
• Supply Voltage Range: 1.6V To 4.5V
• Load Impedance: 2kohm
• Operating Temperature Range: -40°C To +85°C
• Amplifier Case Style: SMD
• Rohs Compliant: Yes
• For Use With: LM48820TMBD - BOARD EVAL GROUND REF AUDIO AMP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LM48820TMTR

Charge Pump Capacitor Selection
Use low (<100mΩ) ESR (equivalent series resistance) ce-
ramic capacitors with an X7R dielectric for best performance.
Low ESR capacitors keep the charge pump output
impedance to a minimum, extending the headroom on the
negative supply. Higher ESR capacitors result in reduced
output power from the audio amplifiers.
Charge pump load regulation and output impedance are af-
fected by the value of the flying capacitor (C
C
charge pump output resistance. The switch-on resistance
dominates the output impedance for capacitor values above
2.2μF.
The output ripple is affected by the value and ESR of the out-
put capacitor (C
the negative power supply. Lower ESR capacitors minimize
the output ripple and reduce the output impedance of the
charge pump.
The LM48820 charge pump design is optimized for 2.2μF, low
ESR, ceramic, flying, and output capacitors.
Input Capacitor Value Selection
Amplifying the lowest audio frequencies requires high value
input coupling capacitors (C
value capacitor can be expensive and may compromise
C
(up to 3.3μF) improves load regulation and minimizes
SS
). Larger capacitors reduce output ripple on
INL
and C
INR
in Figure 1). A high
C
). A larger valued
13
space efficiency in portable designs. In many cases, however,
the speakers used in portable systems, whether internal or
external, have little ability to reproduce signals below 150Hz.
Applications using speakers with this limited frequency re-
sponse reap little improvement by using high value input and
output capacitors.
Besides affecting system cost and size, the input coupling
capacitor has an effect on the LM48820's click and pop per-
formance. The magnitude of the pop is directly proportional
to the input capacitor's size. Thus, pops can be minimized by
selecting an input capacitor value that is no higher than nec-
essary to meet the desired −3dB frequency.
As shown in Figure 1, the internal input resistor, R
input capacitor, C
cutoff frequency that is found using Equation (4).
Also, careful consideration must be taken in selecting a cer-
tain type of capacitor to be used in the system. Different types
of capacitors (tantalum, electrolytic, ceramic) have unique
performance characteristics and may affect overall system
performance.
f
–3dB
INL
and C
= 1 / 2πR
INR
, produce a -3dB high pass filter
i
C
IN
(Hz)
www.national.com
i
and the
(4)