Maxim releases dual RF LDMOS bias controllers
A Maxim Integrated Products product story
Edited by the Electronicstalk editorial team Apr 6, 2009
Maxim Integrated Products has brought out the MAX1385 / MAX1386 / MAX11008 dual RF LDMOS bias controllers.
These devices measure 7 x 7mm, which Maxim claims makes them the industry's smallest LDMOS bias controllers to integrate all of the analogue-to-digital (A/D) and digital-to-analogue (D/A) interfaces and logic functions required for cellular base-station control.
The MAX1385 / MAX1386 / MAX11008 are suited to bias the power-amplifier power transistors employed in CDMA, GSM, EDGE and UMTS cellular base-stations.
These bias controllers integrate all the functions needed in a PA signal chain to achieve 25-microvolts (MAX1385 / MAX1386) or 50-microvolts (MAX11008) of resolution for self-calibration.
The MAX1385 / MAX1386 provide two gate-drive channels, each consisting of an eight-bit coarse DAC, a 10-bit fine DAC and a gate-drive amplifier with a gain of two (MAX1385) or four (MAX1386).
These channels generate a positive gate voltage to bias LDMOS devices, allowing up to 18 bits of resolution.
Each of the MAX11008's two gate-drive channels integrates a 12-bit DAC to generate this positive gate voltage.
The MAX1385 / MAX1386 / MAX11008 offer a seven-channel, 12-bit ADC, which includes three channels for temperature measurement.
In addition, each IC includes dual high-side current-sense amplifiers (32V, CMRR 90dB), which offer up to +/-0.5 per cent accuracy and one least-significant-bit (LSB) linearity at 12 bits.
These high-side current-sense amplifiers feature programmable gains of two, 10 and 25 to monitor the LDMOS drain current over the range of 20mA to 5A.
The temperature sensor offers 0.25C resolution with up to +/-1C accuracy.
The MAX11008 contains 4Kb of on-chip, non-volatile EEPROM, organised as 256 x 16 bits, to store lookup-table and register information.
The MAX11008 monitors current, voltage and temperature, logically deciding if the DAC output voltage should be adjusted to maintain the bias setting.
Other existing solutions require an external EEPROM, necessitating frequent communication with an external processor.
All three bias controllers offer self-calibration modes to minimise error over time, temperature and supply voltage.
Additionally, an internal reference provides a well-regulated, low-noise, +2.5V reference for the ADC, DAC and temperature sensors, while allowing the flexibility to operate from individual ADC and DAC external references.
These ICs communicate over a 20MHz, SPI-compatible, four-wire serial interface or a pin-selectable, 3.4MHz, I2C-compatible serial interface.
They operate from a +4.75 to +5.25V analogue supply and a +2.7V to +5.25V digital supply.
The MAX1385 / MAX1386 / MAX11008 are available in 7 x 7mm, 48-pin TQFN packages and are specified for the -40C to +85C temperature range.
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