max97220a Maxim Integrated Products, Inc., max97220a Datasheet - Page 12

• Manufacturer Part Number: max97220a
• Description: Differential Input Directdrive Line Drivers/headphone Amplifiers
• Manufacturer: Maxim Integrated Products, Inc.

Differential Input DirectDrive
Line Drivers/Headphone Amplifiers
The MAX97220_ is a fully differential input line driver/
headphone amplifier for set-top boxes, LCD TV, and
home theater applications where audio fidelity is of pri-
mary importance. Power consumption of the amplifier is
reduced while maintaining high SNR and THD+N per-
formance. The MAX97220A/MAX97220B require exter-
nal input and feedback resistors to set amplifier gain.
The MAX97220C/MAX97220D feature internal input and
feedback resistors for a set gain of +6dB. Output swings
of 3V
are perfect for line driver applications.
High fidelity is maintained through the differential input
connection. An output noise voltage of 7FV
for 112dB SNR when powered from 5V and 109dB SNR
when powered from 3.3V. The IC has better than 90dB
THD+N across the entire audio bandwidth.
The MAX97220_ operates from a single supply ranging
from 2.5V to 5.5V. An on-chip charge pump inverts the
positive supply (PVDD), creating an equal magnitude
negative supply (PVSS). The headphone amplifiers
Figure 1. Conventional Driver Output Waveform vs.
MAX97220_ Output Waveform
12
RMS
V
V
with a 5V supply and 2V
OUT
OUT
CONVENTIONAL DRIVER-BIASING SCHEME
DirectDrive BIASING SCHEME
Detailed Description
RMS
with a 3.3V supply
PVDD
PVDD/2
PGND
+PVDD
PGND
-PVDD
RMS
allows
operate from bipolar supplies with their outputs biased
about PGND (Figure 1). The benefit of this PGND bias is
that the amplifier outputs do not have a DC component,
typically PVDD/2. The large DC-blocking capacitors
required with conventional headphone amplifiers are
unnecessary, thus conserving board space, reducing
system cost, and improving frequency response. Output
power of 125mW into 32I is achievable from a 5V sup-
ply. The device features an undervoltage lockout that
prevents operation from an insufficient power supply
and click-and-pop suppression that eliminates audible
transients on startup and shutdown.
The IC can be configured as differential or pseudo-
differential input amplifiers (Figures 2 and 3), making
it compatible with all codecs. A differential input offers
improved noise immunity over a single-ended input. In
devices such as cellular phones, high-frequency signals
from the RF transmitter can couple into the amplifier’s
input traces. The signals appear at the amplifier’s inputs
as common-mode noise. A differential input amplifier
amplifies the difference of the two inputs while signals
common to both inputs are cancelled. Configured dif-
ferentially, the gain of the MAX97220A/MAX97220B is
set by:
The common-mode rejection ratio (CMRR) is limited by
the external resistor matching, and if used, input capaci-
tor matching at low frequencies. For example, the worst-
case variation of 1% tolerant resistors results in 40dB
CMRR, while 0.1% resistors result in 60dB CMRR. For
best matching, use resistor arrays.
Figure 2. Differential Input Configuration
IN+
R
*R
IN-
IN1
IN1
= R
AND R
IN2
, R
F1
F1
ARE INTERNAL FOR MAX97220C/MAX97220D
R
R
= R
IN1*
IN2
F2
A
V
= R
R
F2
F
/R
IN
R
F1*
Differential Input
OUT