A8291

• 2-wire serial I²C™-compatible interface: control (write) and status (read)
• LNB voltages (16 programmable levels) compatible with all common standards
• Tracking switch-mode power converter for lowest dissipation
• Integrated converter switches and current sensing
• Provides up to 500 mA load current
• Static current limit circuit allows full current at startup and 13→18 V output transition; reliably starts wide load range
• Push-pull output stage minimizes 13→18 V and 18→13 V output transition times for highly capacitive loads
• Adjustable rise/fall time via external timing capacitor
• Built-in tone oscillator, factory-trimmed to 22 kHz facilitates DiSEqC™ tone encoding, even at no-load
• Four methods of 22 kHz tone generation, via I²C™ data bits and/or external pin
• Filter bypass MOSFET minimizes losses during tone transmit
• 22 kHz tone detector facilitates DiSEqC™ 2.0 decoding
• Auxiliary modulation input
• LNB overcurrent with timer
• Diagnostics for output voltage level, input supply UVLO, and DiSEqC™ tone output
• Cable disconnect diagnostic

Description

Intended for analog and digital satellite receivers, this single low noise block converter regulator (LNBR) A8291 is a monolithic linear and switching voltage regulator, specifically designed to provide the power and the interface signals to an LNB down converter via coaxial cable. The A8291 requires few external components, with the boost switch and compensation circuitry integrated inside of the device. A high switching frequency is chosen to minimize the size of the passive filtering components, further assisting in cost reduction. The high levels of component integration ensure extremely low noise and ripple figures.

The A8291 has been designed for high efficiency, utilizing the Allegro advanced BCD process. The integrated boost switch has been optimized to minimize both switching and static losses. To further enhance efficiency, the voltage drop across the tracking regulator has been minimized.

The A8291 has integrated tone detection capability, to support full two-way DiSEqCcommunications. Several schemes are available for generating tone signals, all the way down to no-load, and using either the internal clock or an external time source. A DiSEqC filter bypass switch is also integrated, to minimize the output impedance during tone generation.

A comprehensive set of fault registers are provided, which comply with all the common standards, including: overcurrent, thermal shutdown, undervoltage, cable disconnect, power not good, and tone detect.

The device uses a 2-wire bidirectional serial interface, compatible with the I2C standard, that operates up to 400 kHz.

The A8291 is supplied in a lead (Pb) free 28-lead MLP/QFN.