MAX9728AETC+ Maxim Integrated Products, MAX9728AETC+ Datasheet - Page 7

• Manufacturer Part Number: MAX9728AETC+
• Description: IC AMP AUDIO .06W STER AB 12TQFN
• Manufacturer: Maxim Integrated Products
• Series: DirectDrive™r
• Type: Class ABr

Specifications of MAX9728AETC+

• Output Type: Headphones, 2-Channel (Stereo)
• Max Output Power X Channels @ Load: 60mW x 2 @ 32 Ohm
• Voltage - Supply: 4.5 V ~ 5.5 V
• Features: Depop, Short-Circuit and Thermal Protection, Shutdown
• Mounting Type: Surface Mount
• Package / Case: 12-TQFN Exposed Pad
• Product: General Purpose Audio Amplifiers
• Output Power: 60 mW
• Thd Plus Noise: 0.02 %
• Operating Supply Voltage: 4.5 V to 5.5 V
• Supply Current: 3.5 mA
• Maximum Power Dissipation: 1177 mW
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• Supply Voltage (max): 5.5 V
• Supply Voltage (min): 4.5 V
• Amplifier Class: AB
• No. Of Channels: 2
• Supply Voltage Range: 4.5V To 5.5V
• Load Impedance: 32ohm
• Operating Temperature Range: -40°C To +85°C
• Amplifier Case Style: TQFN
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The MAX9728A/MAX9728B stereo headphone ampli-
fiers feature Maxim’s DirectDrive architecture, eliminat-
ing the large output-coupling capacitors required by
conventional single-supply headphone amplifiers.
These devices consist of two 60mW Class AB head-
phone amplifiers, undervoltage lockout (UVLO)/shut-
down control, charge pump, and comprehensive
click-and-pop suppression circuitry (see the Functional
Diagram/Typical Operating Circuits ). The charge pump
inverts the positive supply (V
supply (PV
these bipolar supplies with their outputs biased about
SGND (Figure 1). The benefit of this SGND bias is that
the amplifier outputs do not have a DC component. The
large DC-blocking capacitors required with convention-
al headphone amplifiers are unnecessary, conserving
board space, reducing system cost, and improving fre-
quency response. The MAX9728A/MAX9728B feature
an undervoltage lockout that prevents operation from
an insufficient power supply and click-and-pop sup-
pression that eliminates audible transients on startup
and shutdown. The MAX9728A/MAX9728B also feature
thermal-overload and short-circuit protection.
Conventional single-supply headphone amplifiers have
their outputs biased about a nominal DC voltage (typical-
ly half the supply) for maximum dynamic range. Large-
coupling capacitors are needed to block this DC bias
from the headphone. Without these capacitors, a signifi-
cant amount of DC current flows to the headphone,
resulting in unnecessary power dissipation and possible
damage to both headphone and headphone amplifier.
Maxim’s DirectDrive architecture uses a charge pump
to create an internal negative supply voltage, allowing
the MAX9728A/MAX9728B outputs to be biased about
SGND. With no DC component, there is no need for the
large DC-blocking capacitors. The MAX9728A/
MAX9728B charge pumps require two small ceramic
capacitors, conserving board space, reducing cost,
and improving the frequency response of the head-
phone amplifier. See the Output Power vs. Load
Resistance and Charge-Pump Capacitor Size graph in
the Typical Operating Characteristics for details of the
possible capacitor sizes. There is a low DC voltage on
the amplifier outputs due to amplifier offset. However,
the offsets of the MAX9728A/MAX9728B are typically
1.5mV, which, when combined with a 32Ω load, results
in less than 47µA of DC current flow to the head-
phones.
SS
). The headphone amplifiers operate from
_______________________________________________________________________________________
Detailed Description
60mW, DirectDrive, Stereo Headphone
DD
), creating a negative
DirectDrive
Amplifier with Shutdown
The MAX9728A/MAX9728B feature a low-noise charge
pump. The 270kHz switching frequency is well beyond
the audio range and does not interfere with audio sig-
nals. The switch drivers feature a controlled switching
speed that minimizes noise generated by turn-on and
turn-off transients. The di/dt noise caused by the para-
sitic bond wire and trace inductance is minimized by
limiting the switching speed of the charge pump.
Although not typically required, additional high-fre-
quency noise attenuation can be achieved by increas-
ing the value of C2 (see the Functional Diagram/Typical
Operating Circuits ).
In conventional single-supply audio amplifiers, the out-
put-coupling capacitor contributes significantly to audi-
ble clicks and pops. Upon startup, the amplifier charges
the coupling capacitor to its bias voltage, typically half
the supply. Likewise, on shutdown, the capacitor is dis-
charged. This results in a DC shift across the capacitor,
which appears as an audible transient at the speaker.
Figure 1. Conventional Driver Output Waveform vs.
MAX9728A/MAX9728B Output Waveform
V
SGND
SGND
-V
DD
V
V
DD
DD
DD
/2
V
V
OUT
OUT
CONVENTIONAL DRIVER-BIASING SCHEME
Click-and-Pop Suppression
DirectDrive BIASING SCHEME
2V
Charge Pump
V
DD
DD
7