Could you please help me in understanding DPC feature in DAC IC AD5755 ?
and how is it helpful in giving us better efficiency at lowerCurrent output loads as compared to Conventional DAC IC without DPC feature ?
For sake of clarity I have ignored any efficency losses in the explanation above, but it is easy to see the benefits of the DPC. The worst case power dissipation from the output stage has dropped from 720mW per channel to 178mW per channel. This results in better efficiancy of the current output and thus less heating within a module.
Hi Deerick ,
Thanks for your earlier reply !!
As i understand from your above explanation that DPC feature helps in reducing Power disssipation in the Output stage at the expense of few more components and an additional AVcc Power supply .
Since Cost and PCB carpet area are the main consideration in our design , we are thinking of not using DPC feature of DAC IC AD5755.
As a result of which the maximum Power Dissipation at the Current output stage comes out to be 315mW /Channel ( 15V Suppply * 21mA Maximum Iout ) and if we configure all channels as Current Output then total Max Power dissipation comes out to be 315mW * 4 = 1.26W .
Now my questions to you are :-
a) Is it Ok to use DAC AD5755 IC without DPC feature when dissipating around 1.5W power ?
b) What PCB guidelines ( general as well as specific to LFCSP package ) should we follow so as to disspiate that much amount of heat ?
Our main Concern is that under above condition accuracy shouldn't get affected and DAC IC should work normally .
To answer your questions below
a) Yes it is ok to dissipate this power on chip. However it is important that the Exposed paddle be connected to a solder plane to dissipate the heat.
there is a value of Theta JA of 20degreeC per Watt. If the ambient temperature varies this increase in heat due to power dissipation will add to
this temperature. The part has maximum specifications at 105degrees C.
b) The Exposed paddle with dissipate any heat generated on chip. It is recommended that this pad be thermally connected to a copper plane for
enhanced thermal performance.
It is important that most our specifications are maximum over temperature. By minimizing any temperature variations greater accuracy can be achieved. See list of specifications that are listed with PPM FSR / degree C for example.
See attached link to a comprehensive Applications Note on
On the AD5755 without the DPC being used (high load resistance, slow slew rate, and not all channels using current mode) what is the proper way to power a current channel without using the DPC. Do you just apply 28V to V boost and nothing to AVcc. Any other not used pins should be taken care of?
If you are not using the DPC feature you must still connect 5V to AVcc.
It is also recommended that 5V be connected to the Vboost terminal. (or 15V if available).
It is important that this pin is not left floating. As the other pins not being used are outputs (SW etc.)
these are ok to leave floating.
Michael (PDA Applications)
Just a side note in addition to the above response. If DPC is not being used, AVcc only needs to be in the range of 2.7V to 5.5V and therefore can be tied directly to DVdd (2.7V to 5.5V). In non-DPC configuration the load current on the output is derived from AVdd and AVss.
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