TPS735: Supply noise due to current variation

Hi Waqas,

First it is important to operate within the recommended operating conditions.  For active mode for the 2.5V rail you are exceeding the 500mA rating of TPS735.  As such, this LDO may not perform as specified while in the active mode.

As with any regulator we only have a few options to improve the transient response at the system level (the LDO transient response is fixed by the internal design of the LDO).  We can reduce the magnitude and/or rate of the transient itself; however, this is often not a feasible option.  This leaves us with adjusting the capacitors.  Increasing the output capacitor will decrease the magnitude of the transient response; however, it will increase the duration of the transient response as shown in Figure 20.

With regards to the layout there are some best practices that will help your LDO performance.  First it is best practice to have a same layer ground path for the LDO and the related components which in your case are just capacitors.  This same layer ground path should be divided into an input plane and an output plane that meet at the GND pin of the LDO.  This helps to reduce the possibility of coupling through the ground plane from the input capacitor to the output capacitor and NR capacitor.

Very Respectfully,

Ryan

Hi Ryan,

Thanks for your response. The max current on the 2.5V rail is actually 455mA, not 520mA.

The longer transient response may not be too big of an issue and we can certainly try it out. In the meantime, we are designing the second version of our EVM. Are there any other parts in TI's portfolio that will perform better for the input/output needs of our system?