The MAX881R is a low-noise, inverting power supply designed for biasing GaAsFET power amplifiers in portable wireless applications. It has an input voltage range of 2.5V to 5.5V and the output is preset at -2.0V or can be set to any voltage from -0.5V to (-VIN + 0.6V) using two resistors. It can deliver up to 4mA of current. The internal linear regulator also filters the output to 1mVp-p ripple and noise. Other features include a power-OK (POK) output that signals when the negative voltage is within 7.5% of its set point. It protects the GaAsFET by not allowing power to be applied to the GaAsFET’s drain until it is properly biased. The signal can be routed either to a microcontroller or directly to a switch at the GaAsFET drain. The MAX881R is available in a 10-pin µMAX package.
The MAX881R low‑noise, inverting power supply is designed for biasing GaAsFET power amplifiers in portable wireless applications. It combines a charge‑pump inverter with a negative linear regulator, providing a preset –2 V output or an adjustable output from –0.5 V to (‑VIN + 0.6 V). The device delivers up to 4 mA with an output ripple of only 1 mV p‑p and includes a Power‑OK (POK) signal for safe startup.
The part is offered in a 10‑pin µMAX package and features a shutdown mode that reduces supply current to less than 1 µA. Typical startup time from shutdown is about 0.5 ms. Detailed pin functions, layout recommendations, and capacitor selection guidelines are provided to achieve low noise and ripple performance.
| Input voltage range | 2.5 V to 5.5 V |
|---|---|
| Preset output voltage | -2.0 V |
| Adjustable output voltage range | -0.5 V to (‑VIN + 0.6 V) |
| Maximum output current | 4 mA |
| Output ripple and noise | 1 mV p‑p |
| Power‑OK (POK) output threshold | 92.5 % of set point |
| Shutdown supply current | < 1 µA |
| Startup time from shutdown | ≈ 0.5 ms |
| Package | 10‑pin µMAX |
The device operates with an input voltage between 2.5 V and 5.5 V.
It can deliver up to 4 mA of negative output current.
The output is preset at –2 V, or it can be adjusted between –0.5 V and (‑VIN + 0.6 V) using a resistor divider on the FB pin.
POK goes low when the output reaches 92.5 % of the regulated voltage, signalling that the bias is within the required range.