ZNBG3211Q20TC

The ZNBG3211Q20TC from Diodes Incorporated is a specialized power management IC designed to meet the bias requirements of GaAs and HEMT FETs. It is commonly used in applications such as satellite receiver LNBs and PMR cellular telephones.

This device provides drain voltage and current control for up to three external grounded-source FETs, generating a regulated negative rail required for FET gate biasing from a single supply. The negative bias can be set to -3 volts and can also supply other external circuits. The ZNBG3211Q20TC includes bias circuits to drive up to three external FETs, with a control input allowing selection between two FETs using 0V gate switching methodology, while the third FET remains permanently active. This feature is particularly useful as an LNB polarization switch.

An integrated 22kHz tone detection and logic output feature is included, specifically designed for LNB applications to enable high and low band frequency switching. This detector is engineered to reject interference from low-frequency signals and DiSEqC tone bursts without additional external components. The drain current is user-selectable via an external resistor, ranging from 0 to 15mA. The ZNBG3211 series offers a choice in FET drain voltage; the ZNBG3211 provides 2 volts. The device operates over a temperature range of -40°C to 70°C and is available in a 20-QSOP surface mount package.

These devices are designed for unconditional stability over the full working temperature range when the recommended gate and drain capacitors are included, ensuring RF stability and minimal injected noise. The gate drive from the bias circuits is designed to prevent exceeding the range of -3.5V to 1V under any conditions, including power up/down transients. In case of a fault condition on the negative rail, such as overload or short circuit, the drain supply to the FETs will shut down to prevent excessive current flow.