LMH6401 DC to 4.5 GHz, Fully-Differential, Digital Variable-Gain Amplifier (Rev. A)
SBOS730A – April2015 – revisedMay 2015
11 Power-Supply Recommendations
The LMH6401 supports both single- or split-supply operation with a total recommended supply operating range [(VS+) – (VS–)] from 4.0 V to 5.25 V. Note that supply voltages do not need to be symmetrical when using split supplies, provided the total supply voltage is within the recommended operating range. Any combination of positive (VS+) and negative (VS–) supply voltages is acceptable, as long as the minimum positive (VS+) supply voltage to ground is 2 V, or greater.
Using a single 5-V power supply gives the best balance of performance and power dissipation. If power dissipation is a critical design parameter, a power supply as low as 4.0 V (±2.0 V) can be used. The input common-mode and output swing limitations of the device scale with supply voltage. TI recommends studying the common-mode voltage and output swing limitations (see the Electrical Characteristics table) before deciding to use a lower supply voltage.
11.1 Single-Supply Operation
The device supports single-ended supply voltages with VS+ connected to a positive voltage from 4.0 V to 5.25 V and VS– connected to ground reference. When using a single supply, check to make sure the input and output common-mode voltages are within the operating range of the device. Best performance is achieved when the input and output common-mode voltages are centered close to mid-supply.
11.2 Split-Supply Operation
Using split supplies provides the most flexibility in system design. To operate on split supplies, apply the positive supply voltage to VS+, the negative supply voltage to VS–, and the ground reference to GND. Note that supply voltages do not need to be symmetrical, as long as the minimum positive (VS+) supply voltage to ground is 2 V, or greater. The split-supply operation is often beneficial when the output common-mode of the device must be set to a particular voltage. For best performance (see Figure 21 and Figure 22), TI recommends that the power-supply voltages be symmetrical around the desired output common-mode voltage. The input common-mode voltage range is much more flexible than the output. For example, if the LMH6401 is used to drive an ADC with a 1.0-V input common mode, then the ideal supply voltages are 3.5 V and –1.5 V with the output common-mode voltage of the LMH6401 centered at 1.0 V for best linearity and noise performance. The GND pin can then be connected to the system ground and the PD pin and SPI pins are ground referenced.
TI recommends powering up the device with low-noise, LDO-type regulators. If a switching-type regulator is used to improve system power efficiency, following the switching-type regulator with a low-noise LDO is recommended to provide the best possible filtering of the switching noise. An example low-noise switcher and LDO for generating negative supply voltages are the LMR70503 and TPS72301, respectively. In a system with multiple devices being powered on from the same voltage regulator, a high possibility of noise being coupled between the multiple devices exists. Additionally, when operated on a board with high-speed digital signals, isolation must be provided between the digital signal noise and the LMH6401 supply pins. Therefore, adding additional series ferrite beads or isolation devices and decoupling capacitors is recommended to filter out any power-supply noise and improve isolation.
Power-supply decoupling is critical to filter out high-frequency switching noise coupling into the supply pins. Decoupling the supply pins with low ESL, 0306-size ceramic capacitors of X7R-type 0.01-µF and 2200-pF values are recommended. In addition to the decoupling capacitors, the supply bypassing can be provided by the PCB, as illustrated in Layout Guidelines section.
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