Maxim's integrated IC for power transistor bias control in cellular base station infrastructure

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Maxim introduces the MAX1385/MAX1386*/MAX11008 dual-channel RF LDMOS bias controllers. These highly integrated devices are available in a 7mm x 7mm package and are the industry's smallest LDMOS bias for all analog to digital (A/D), digital to analog (D/A) interfaces and logic functions required for cellular base station control. Controller. The MAX1385/MAX1386/MAX11008 are ideal for biasing power transistors in power amplifiers in CDMA, GSM, EDGE, and UMTS cellular base stations.

These bias controllers integrate all the features required in the PA signal chain with a self-calibrating resolution of 25μV (MAX1385/MAX1386) or 50μV (MAX11008). The MAX1385/MAX1386 provide two gate drive channels, each with an 8-bit coarse-tuned DAC, a 10-bit fine-tuned DAC, and a gate-driver with a gain of 2 (MAX1385) or 4 (MAX1386). These two channels generate a positive gate voltage to bias the LDMOS device with a resolution of up to 18 bits. MAX

The 11 gate's 2 gate drive channels integrate a 12-bit DAC to generate a positive gate voltage.

The MAX1385/MAX1386/MAX11008 include a 7-channel, 12-bit ADC with 3 channels for temperature measurement. In addition, each IC features two high-side current-sense amplifiers (32V, 90dB CMRR) with an accuracy of ±0.5% and a linearity of 1 least significant bit (LSB) at 12-bit. These high-side current-sense amplifiers feature 2, 10, and 25 times programmable gain to monitor LDMOS drain current from 20mA to 5A. The temperature sensor has a resolution of 0.25 ° C and an accuracy of ± 1 ° C.

The MAX11008 contains 4Kb of on-chip nonvolatile EEPROM divided into 256-bit x 16-bit bits for storing lookup tables and register information. The MAX11008 determines whether to adjust the DAC output voltage to maintain the bias setting by monitoring current, voltage, and temperature. Other existing solutions require an external EEPROM and must also communicate frequently with an external processor.

Each of the three bias controllers provides a self-calibration mode that reduces errors over time, temperature, and supply voltage. In addition, the internal reference provides a stable, low noise, +2.5V reference for the ADC, DAC, and temperature sensor, and allows the ADC and DAC to use the external reference flexibly and independently. It communicates with the IC via a 20MHz, SPI? compatible 4-wire serial interface or a pin-selectable 3.4MHz, I2C compatible serial interface. The device operates from a +4.75V to +5.25V analog supply and a +2.7V to +5.25V digital supply.

The MAX1385/MAX1386/MAX11008 are available in a 7mm x 7mm, 48-pin TQFN package and operate over the -40°C to +85°C temperature range.