Audio Subsystem

As cellular phones incorporate the ability to play music and video, they need to provide high-quality, undistorted sound with advanced acoustic performance. Transmitted and received voice signals must be filtered to maintain their audio quality. And provisions must be made to switch between handset voice signals, hands-free voice signals, ring-tones, and audio from music and video files – without interfering with the audio quality.

Providing effective amplification of audio signals, the NCP2820 Class D audio amplifier from ON Semiconductor delivers 1.4 W of continuous average power to an 8.0 Ohm load, with less than 1% total harmonic distortion. With more than 90% efficiency and very low shutdown current of 2.5 mA typical, the NCP2820 enables longer battery lifetime. With a 2.5 V to 5.5 V input voltage range, the device can be driven directly from a one-cell Li-ion battery, eliminating the need for an additional voltage regulator. The earpiece, speaker, and even the melody ringer can be driven with a single NCP2820 device. ON Semiconductor offers a portfolio of high performance audio amplifiers, including class AB and class D devices.

Advanced Double-Pole Double-Throw and Single-Pole Double-Throw analog switches provide the routing needed to provide pathways for the many audio signals required in today’s consumer handset market. The NLAS3799B Dual-Pole Double-Throw analog switch delivers high current switching for speaker outputs and earpieces. The switch can function directly from a Li-ion battery, so no voltage regulator is required. And the integrated ESD protection allows the device to be located in close proximity to I/O ports. The NLAS5223B offers similar performance from a space efficient μQFN-10 package, with a footprint of only 2.52 mm2, and a height of only 0.55 mm.

Audio Line Protection

To protect audio jacks, earpieces, and microphones from ESD, ON Semiconductor’s ESD5B5.0S transient voltage suppressor provides excellent clamping capability with fast response time. This device can clamp a contact input ESD pulse of up to 30 kV as measured by the IEC61000-4-2 standard. This performance is available in the ultra-small SOD-953 package, measuring only 1.2 mm x 0.8 mm x 0.7 mm, which provides designers with the flexibility to place the device near audio input jacks or ports for optimized protection.

Keypad Protection

Every button on a keypad is a source of potential ESD interference. ON Semiconductor’s ESD9X3.3S ESD protection diode is available in the SOD-923 package, measuring only 1.0 mm x 0.6 mm, with a 0.4 mm profile – which allows placement beneath the keypad.

Exceeding the highest standards for ESD protection, the ESD9X3.3S is capable of clamping a 30 kV contact discharge and complies with the IEC61000-4-2 Level 4 standard.

The ESD9X series from ON Semiconductor is available in the SOD-923 package in 3.3 V, 5 V, and 12 V versions. Each version offers the same excellent clamping capability, combined with a fast response time of < 1 ns typical.

Li-Ion Battery Charging

Cellular phones today need to be able to recharge their battery from a variety of charging sources, such as the USB port and various wall adapters. The NCP1835B battery charge control circuit has the flexibility to support these charging sources, due to its constant-current, constant-voltage charging profile, and its onboard thermal foldback circuitry.

For one-cell Li-ion batteries, the device generates a 4.2 V output voltage, with 1% regulation. Current regulation and end-of-charge detection are also provided to optimize battery life.

The NCP1835B provides a space efficient solution for charging circuits, as it does not require an external MOSFET, sense resistor, or blocking diode.

The ON Semiconductor portfolio includes battery charge circuits for a variety of battery chemistries and cell configurations.

Inductive Drive for LCD Backlighting

To enable circuits to drive up to five white LEDs with the most space-efficient design, the NCP5010 LED Driver from ON Semiconductor provides 500 mW of output power, in a tiny 1.7 mm x 1.7 mm board footprint. Optimized for use with small inductors and capacitors, and with integrated rectification, over-voltage protection, and short-circuit protection, the NCP5010 enables LED drive circuits with fewer external components than ever before – minimizing the bill-of-materials and enhancing the overall reliability of the handset.

The device uses true-cutoff circuitry to disconnect the load from the battery when the handset is put into standby mode, reducing the current demand on the battery.

Charge Pump Drive for Backlighting

The NCP5612 Dual-Channel White LED Driver was designed for LCD display backlighting. The device supports lighted icons on the handset that are controllable through a programmable dimming feature. The device is programmed through a single-wire serial link protocol.

Based on a highly efficient charge pump structure, the NCP5612’s built-in dc-dc converter provides peak efficiency of 87%. To maintain consistent brightness in the end product, this LED driver delivers 1% output current tolerance, and 0.2% matching tolerance.

Low Capacitance Analog Switches for Data Switching

Cellular phones need to manage more data than ever before, and that data can enter the handset from multiple sources, such as USB interfaces and UARTs. Designers must provide the means to switch between multiple data paths, and each data path needs to provide a route that is fast and interference-free. Analog switches and discrete protection devices from ON Semiconductor can help.

Supporting USB 2.0 High-Speed differential signals of 480 Mb/s, the NLAS7222 Dual Single-Pole Double-Throw Analog Switch features typical capacitance of 12 pF and channel-to-channel crosstalk rejection of -45 dB at 250 MHz, to ensure minimal noise interference.

In order to protect voltage sensitive components in data subsystems from ESD and transient voltage events, the uESD3.3D combines a Class 3 ESD rating, with low leakage and a typical response time of < 1 ns. Available in a SOD-723 package measuring 1.4 mm x 0.6 mm x 0.5 mm, these devices can be positioned close to data line connectors and interfaces to optimize board space.

The uESD series is available with working peak reverse voltages of 3.3 V, 5 V, 6 V, and 12 V.

EMI Filtering with ESD Protection for LCD Interface

Cellular phones in today’s market include high resolution color LCD displays. These displays require high bandwidth, low noise data lines, to prevent unwanted noise that can interfere with the displayed image.

ON Semiconductor’s NUF4001 four-line EMI filter array offers maximum attenuation filtering and protection from ESD, while allowing high-speed data signaling from the baseband chip-set to the LCD display. The device achieves better than -25 dB of attenuation, at frequencies from 800 MHz to 5 GHz, with no line loss.

With a high cut-off frequency of 150 MHz and low capacitance of 12 pF typical, the NUF4001 is ideal for filtering and protecting the LCD interface.

ON Semiconductor offers EMI filter arrays in four-channel, six-channel, and eight-channel versions to provide optimal reliability and design flexibility.

EMI Filtering with ESD Protection for Camera Interface

Before a new handset design reaches consumers, it must pass regulatory EMI and RFI testing. Designers consider EMI and RFI requirements important design parameters, but must include the necessary filtering within small physical spaces.

Developed to provide filtering and protection for data lines for camera interfaces, the eight-line NUF8001 EMI filter array from ON Semiconductor provides a cost efficient, space-saving solution. This low capacitance device filters signals with a maximum data rate up to 60 MHz. The device includes ESD protection to clamp transient voltage from static discharge and prevent damage to the data lines between the baseband and the camera interface. The NUF8001 is available in a μDFN package, providing a low profile and a small footprint to optimize board space.

Integrated Over-Voltage Protection

Handsets must include protection in their battery subsystems, which protect the battery during charging operations.

Representing a new level of safety and integration for cell phones, the NUS3045 from ON Semiconductor combines an advanced over-voltage protection circuit with a 30 V P-channel power MOSFET. Providing protection from over-voltage transients and power supply faults, the NUS3045 can quickly disconnect the input supply from the load in less than 1.0 µs, in case of a fault condition.

The analog control circuit and MOSFET of the NUS3045 are integrated into a low-profile DFN package, saving board space and reducing the bill-of-materials over existing discrete solutions.

This same high level of functionality is available with a 20 V MOSFET in the NUS2045, also from ON Semiconductor.