www.fairchildsemi.com AN-6066 FAN3800 Application Guide Objective Description The purpose of this document is to provide guidance for typical operation of and layout guidelines for the FAN3800. 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 SendEnd switching is also supported. 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 * 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 16 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 Dinput. 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. FAN3800 (c) 2008 Fairchild Semiconductor Corporation Rev. 1.0.0 * 2/21/08 www.fairchildsemi.com AN-6066 APPLICATION NOTE Overview amplifiers, multi-purpose button interface, mono/stereo switching, USB detection and identification, and muting. Figure 1 is a block diagram illustrating the device. 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 Figure 1. (c) 2008 Fairchild Semiconductor Corporation Rev. 1.0.0 * 2/21/08 Block Diagram www.fairchildsemi.com 2 AN-6066 APPLICATION NOTE Functional Description 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. 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. Layout Considerations When designing in the FAN3800, use the following guidelines to optimize the design: In mono mode, the ID line is in a low (<0.8V) state. The microphone audio is routed through the D+ line and the Dline 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. (c) 2008 Fairchild Semiconductor Corporation Rev. 1.0.0 * 2/21/08 1. When possible, use a four-layer board. 2. Place decoupling capacitors (0.1F and 1F) 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. www.fairchildsemi.com 3 AN-6066 APPLICATION NOTE DISCLAIMER FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE TO ANY PRODUCTS 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 PATENT RIGHTS, NOR THE RIGHTS OF OTHERS. LIFE SUPPORT POLICY FAIRCHILD'S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, or (c) whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in significant injury to the user. (c) 2008 Fairchild Semiconductor Corporation Rev. 1.0.0 * 2/21/08 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. www.fairchildsemi.com 4