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# DAC query

Category: Hardware
Product Number: LTC2664HUH-12#PBF, LTC2664

In my circuit, the DAC LTC2664CUH-12#PBF output is connected to 301ohms series resistor. When the load current of 66uA given at DAC resistor out,  i could see a voltage drop at 301 ohms series resistor out side. example: the expected DAC output voltage is 10V. In my board, i could see at DAC IC output, the voltage received is 9.999V but the voltage at 301ohms series resistor out side is 9.9862V when 66uA load current is given at DAC series resistor out. So kindly tell what could be the reason ? have attached the image of the circuit.

• Also to add up is it fine to give 0R series resistor at DAC output instead of 301R ?

•   is currently looking at this query and will get back to you soon. Thanks for your support and patience.

Best Regards,

Den

• If you source a 66uA load at AO, that's going to cause a voltage drop across your series resistor equal to 301*66u =~19mV. Is there a reason why you need the series resistor at the output of the DAC?

Best regards,

Ian

• Hi lan,

As you could see in the circuit diagram,it is a RC filter circuit only at DAC output. We could observe by tuning this resistor value from 301R to 0R in bench testing, there is not voltage drop observed. Is it ok to change the DAC output series resistor to 0R ? Will this change to 0R affect the DAC IC ?

• kindly reply soon...it is very important and high priority for us

• Hi,

I understand that this is for filtering, and if the load at the RC (AO_x) is high impedance then there should be no drop as you observe in your bench test. But if the load presents some current draw, it will cause voltage drop due to the R in your RC filter

Is it ok to change the DAC output series resistor to 0R ? Will this change to 0R affect the DAC IC ?

Are you referring to the R32 in your diagram? or the R17? if R17, then the voltage drop would disappear but you won't have your RC filter anymore.

Best regards,

Ian

• The LTC2664HUH12PBF DAC's output load capacitance is 1000pF. According to the end application a max. of 10000pF load is expected. So whether any additional circuit is required to be implemented for avoiding oscillations and keep the VOUT stable for 10000pF capacitive load?

• The capacitance load spec is based on maintaining the noise performance of the DAC stated in the specs table. Going beyond 1000pF, we can't guarantee the stability of the DAC. In my opinion, the safest way is install an additional buffer amplifier at the output that is stable at higher than 10000pF.

• Kindly provide the LTSPICE simulation of this DAC circuit to VOUT