TPS7A7100 current sensing

Hi Paul,

Can you please post a schematic of what you have in mind? This will enable me to help you better. Thanks

Regards,

Kartik

Hi Kartik,

Please see below.

Hi Paul,

Using the TPS7A7100 in the above configuration may throw off your Vout. As can be seen in the diagram below Rsense will be in parallel to 32R which in turn changes the  the 

value of the voltage divider that sets Vout. Your best option would be to use the TPS7A7100 as an adjustable LDO as discribed on page 16 of the PDS and use R1 as the current sense resistor. Hope this helps.

Regards,

Kartik

Hi Kartik,

I guess I could use the SNS line as below?

Hi Paul,

Now Rsense is in series with 32R again modifying the resistor divider. your thinking is correct, placing Rsense in the feedback loop, but the resistor divider spoils things for us. 

Can you place the Rsense in series with the LDO input? The input current  = output current + GND current.

GND is very small and you can calibrate in your system.

Regards,

Kartik

Hi Kartik,

That's an interesting idea however we have to measure the current very accurately and down to very small levels (<0.1uA). The GND current will change according to load and temperature and would be very difficult to compensate for.

I've just realised that the internal resistors are higher than I thought! For example I thought 32R was 32 ohms but the note against Fig 1 says it's actually 32 x 3.2K i.e. 102K and so a sense resistor of say 200 ohms in series (as per my post Jul 17 2013 06:00 AM) will only have a small (and predictable i.e. independent of load) effect on the output voltage. Does this sound OK?

Inidentally, I now see that Fig 1 has values for the internal resistors which are 10 times what is shown on the other figures in the datasheet (Mar 2012 - revised Jan 2013). Which is correct?

Thanks again,

Paul

Thanks for the confirmation Kartik. I guess the datasheet will be corrected at some point.

Regards,

Paul