SBOS710D October 2014 – February 2018 LMH5401
The LMH5401 operates using split supplies. One of the most common supply configurations is ±2.5 V. In this case, VS+ is connected to 2.5 V, VS– is connected to –2.5 V, and the GND pins are connected to the system ground. As with any device, the LMH5401 is impervious to what the levels are named in the system. In essence, using split supplies is simply a level shift of the power pins by –2.5 V. If everything else is level-shifted by the same amount, the device does not detect any difference. With a ±2.5-V power supply, the CM range is 0 V ±1 V; the input has a slightly larger range of –2.5 V to 1 V. This design has certain advantages in systems where signals are referenced to ground, and as shown in the ADC Input Common-Mode Voltage Considerations : DC-Coupled Input section, for driving ADCs with low input common-mode voltage requirements in DC-coupled applications. With the GND pin connected to the system ground, the power-down threshold is 1.2 V, which is compatible with most logic levels from 1.5-V CMOS to 2.5-V CMOS.
As noted previously, the absolute supply voltage values are not critical. For example, using a 4-V VS+ and a
–1-V VS– still results in a 5-V supply condition. As long as the input and output common-mode voltages remain in the optimum range, the amplifier can operate on any supply voltages from 3.3 V to 5.25 V. When considering using supply voltages near the 3.3-V total supply, take care to ensure that the amplifier performance is adequate. Setting appropriate common-mode voltages for large-signal swing conditions becomes difficult when the supply voltage is below 4 V.