A8285

· LNB selection and standby function
· Provides up to 500 mA load current
· Two-wire serial I2C interface
· Built-in tone oscillator, factory-trimmed to 22 kHz; facilitates DiSEqC™ 2.0 encoding
· Auxiliary modulation input
· 22 kHz tone detector facilitates DiSEqC™ decoding (A8287 only)
· Tracking switch-mode power converter for lowest dissipation
· LNB overcurrent protection and diagnostics
· Internal overtemperature protection
· LNB voltages (16 possible levels) compatible with all common standards

Load Supply Voltage, V_IN............................................16 V
Output Current, I_OUT ............................Internally Limited*
Output Voltage
- LNB, BOOST ............................................0.3 V to 28 V
- TOUT...................................................... 0.3 V to 22 V
Logic Input
- EXTM.........................................................0.3 V to 5 V
- Other....................................................... 0.3 V to 7 V
Logic Output ............................................... 0.3 V to 7 V
Package Power Dissipation .....See power dis sipation
information in the Application Information section
Operating Temperature
- Ambient, T_A.........................................20°C to +85°C
- Junction, T_J........................................20°C to +150°C
- Storage,T_S .......................................55°C to +150°C

Boost Converter/Linear Regulator. A current-mode boost converter provides the tracking regulator a supply voltage that tracks the requested LNB output voltage. The converter operates at 16 times the internal tone frequency, 352 kHz nominal.

The tracking regulator provides minimum power dissipation across the range of output voltages, assuming the input voltage is less than the output voltage, by adjusting the BOOST pin voltage 600 mV nominal above the LNB output voltage selected. Under conditions where the input voltage is greater than the output voltage, the tracking regulator must drop the differential voltage. When operating in this condition, care must be taken to ensure that the safe operating temperature range of the A8285/A8287 is not exceeded. For additional information, see Power Dissipation in the Application Information section.

Note: To conserve power at light loads, the boost converter operates in a pulse-skipping mode.

Intended for analog and digital satellite receivers, the LNB (low noise block) converter regulator is a monolithic linear and switching voltage regulator, specifically designed to provide power and interface signals to an LNB downconverter, via coaxial cable.

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

The A8285 is supplied in a 16-lead plastic power SOIC with internally fused leads for thermal dissipation. The A8287 is supplied in a 24-lead plastic power SOIC with internally fused leads. Both devices are also available in lead (Pb) free versions, with 100% matte tine leadframe plating.