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Original question:

TPS7A57: Output voltage not as expected

TPS7A94: SNS pin, LDO buffer TPS7A57 vs. TPS7A94

Arnav Shah
Prodigy 80 points
Part Number: TPS7A94
Other Parts Discussed in Thread: TPS7A57,

Hello,

I would like to ask the differences between TPS7A57 and TPS7A94 sensing. It seems SNS in TPS7A57 is used for output regulation connecting directly to the unity gain buffer; so I assume this means the trace must be low inductance and close to the output. But in TPS7A94, it seems the reference is connected to the buffer with a current clamp and the SNS is used for remote sensing. Please help to confirm this understanding, is it correct? The SNS can be a long trace? Why was remote sensing not implemented in TPS7A57? Is it due to delay in load regulation? 

TPS7A94:

TPS7A57:

  • TI__Mastermind 33205 points

    Hello Arnov,

    Both of these LDOs use the SNS pin as a remote sense pin.  The TPS7A94 block diagram shows the ESD diodes from the NR/SS node to the SNS node.  The TPS7A57 does not internally tie SNS to OUT - the diagram was meant to convey the external connection from SNS to OUT.  The input to the op-amp is high impedance (it is just the high impedance gate node of a MOSFET).  The inductance of the remote sense trace will still be low impedance with respect to this internal high impedance node.  In general you want your LDOs to always be placed as close to the load as possible to reduce IR drop and improve transient performance, but I would not expect the inductance on these remote sense traces to significantly degrade your performance.

    Thanks,

    Stephen