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© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com
Rev. 1.0.0 • 2/21/08
AN-6066
FAN3800 Application Guide
Objective
The purpose of this document is to provide guidance for
typical operation of and layout guidelines for the FAN3800.
Features
• Regulated Positive Supply
• Negative Supply Generator Allows for Ground-centered
Output Swing
• Dual Speaker Drivers with Mono/Stereo Switch
Capability
• Complete External Microphone Interface
• Manual and Remote Send-End Switch Interface
• Pop and Click Suppression
• Single 2.7V to 4.5V Operation
• 2kV ESD (HBM) Protection
• MLP 24 Pin Package
Applications
• One-piece Stereo/Mono Headset with Microphone
• 3.5mm Stereo Headphone Adapter
• 2.5 or 3.5 Adapter for Stereo Headset with Microphone
Related Datasheets
• FAN3800
Description
The FAN3800 is a low-cost solution to integrate the many
discreet parts currently used in stereo and mono headset
applications. It provides mono/stereo speaker drivers and a
complete microphone interface. Manual and remote Send-
End switching is also supported.
The FAN3800 speaker drivers are designed to operate with
a ground-centered output signal. This allows for the removal
of large and expensive DC blocking capacitors. In addition,
it allows for interfacing with externally powered speakers.
The speaker drivers are capable of driving up to 15.6mWRMS
with 16Ω loads.
The FAN3800 delivers a complete solution for interfacing
an external microphone. The microphone interface provides
a regulated, high PSRR supply, differential input sense to
single-ended output driver amplifiers and output muting.
Gain is fixed at 38dB and can be attenuated externally with
a resistor divider network on Micout.
Send-End switching automatically routes the microphone
output to the D+ output. When activated, the speakers
switch from stereo to mono mode, both driven by the D-
input. Pop and click noise are minimized during power on,
power off, and mode switching. Send-End information can
be generated manually through an external switch.
AN-6066 APPLIC ATION NOTE
© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com
Rev. 1.0.0 • 2/21/08 2
Overview
The FAN3800 is intended for headset applications using
Universal Serial Bus (USB) connectivity. The main purpose
of the FAN3800 is to reduce the discrete components
currently being used in these applications. The FAN3800
includes an internal power supply, speaker and microphone
amplifiers, multi-purpose button interface, mono/stereo
switching, USB detection and identification, and muting.
Figure 1 is a block diagram illustrating the device.
Figure 1. Block Diagram
AN-6066 APPLIC ATION NOTE
© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com
Rev. 1.0.0 • 2/21/08 3
Functional Descr i pti on
When a FAN3800 headset, configured as shown in Figure 1,
is connected to a device (such as a phone); a pull-down
resistor in the headset pulls ID down below the device’s
supply rail. This change in the ID voltage informs the device
that a headset is attached. The FAN3800 headset provides a
USB low (<0.8V) on D+. The device then looks for a USB
low from the headset. Once acknowledged, the device
provides VBUS to the FAN3800 headset. The FAN3800
reacts by providing a USB low (<0.8V) on D- and USB high
(>2.0V) on D+. With the FAN3800 headset detected, the
device pulls the ID line higher, >1.2V, to switch the headset
to stereo mode. The headset then places a USB low (<0.8V)
on D+. The device verifies a USB low (<0.8V) on both D+
and D-. This acknowledges a FAN3800 headset is present.
In mono mode, the ID line is in a low (<0.8V) state. The
microphone audio is routed through the D+ line and the D-
line routes speaker audio to both the right and left speakers.
In stereo mode, the ID voltage is increased (>1.2V), which
tells the headset to switch to stereo mode. The right speaker
channel from the D+ is routed to the right speaker output and
the left speaker channel from the D- line is routed to the left
speaker output. In stereo mode, the microphone is muted.
In standby, the device turns off the VBUS voltage and
configures the D- line to the internal supply rail. ID
remains biased so the device may detect when the headset
is disconnected.
Layout Considerati ons
When designing in the FAN3800, use the following
guidelines to optimize the design:
1. When possible, use a four-layer board.
2. Place decoupling capacitors (0.1µF and 1µF) as close to
the power (Vs) pins as possible.
3. Place RF bypass capacitors (33pF-100pF) on all I/O
pins, as close to the device as possible.
4. Connect all ground pins as tightly as possible,
preferably with a large ground plane.
5. Minimize all trace lengths to reduce series inductance.
AN-6066 APPLIC ATION NOTE
© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com
Rev. 1.0.0 • 2/21/08 4
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HEREIN TO IMPROVE RELIABILITY, FUNCTION, OR DESIGN. FAIRCHILD DOES NOT ASSUME ANY LIABILITY ARISING OUT OF THE
APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN; NEITHER DOES IT CONVEY ANY LICENSE UNDER ITS
PATE NT RIGHTS, NOR THE RIGHTS OF OTHE RS .
LIFE SUPPORT POLICY
FAIRCHILD’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS
WITHOUT THE EXPRESS WRI T T E N APPROVA L OF T HE PRESIDENT OF F AIRCHILD SE MI CONDUCT OR CORPORATION.
As us ed herei n:
1. Life support devices or s ystems are devices or systems
which, (a) are intended for surgical i mplant into the body, or
(b) support or s ustain lif e, or (c) whose failure t o perform
when properly used in accordance with instruc t i ons for use
provided in the label i ng, can be reasonably expected to
result i n significant injury to the user.
2. A crit i cal component is any c omponent of a l i fe support
device or system whose f ai l ure to perform can be
reasonably expected to cause the f ai l ure of the life s upport
device or system, or to affect its safety or eff ectiveness .
