Current Sinking DAC

Regarding your question – You can certainly operate the AD5398 at a reduced current settling but unfortunately you will no longer be able to get 10 bits of resolution. It might be worth considering the AD5750 ?  This ADI IC is a current/voltage output driver with 20mA and 24mA sink capability. Primarily targeting industrial applications, It operates from dual supplies ±12 V to ±24 V. This product does not integrate a DAC however but you could choose a 10/12-bit external DAC (like the AD5620 for example) and drive the AD5750 directly. You will need to set-up the device in +/-20mA Mode. (software selectable over the SPI interface)

The advantage of this IC is very low drift and low Total Unadjusted error as well as a small footprint.

http://www.analog.com/en/amplifiers-and-comparators/instrumentation-amplifiers/ad5750/products/product.html

http://www.analog.com/en/amplifiers-and-comparators/instrumentation-amplifiers/ad5750-1/products/product.html

http://www.analog.com/en/digital-to-analog-converters/da-converters/ad5620/products/product.html

-Liam