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AD5535B driven capacity

Question asked by wqiang on Feb 4, 2015
Latest reply on Feb 5, 2015 by MCollins

We use the AD5535B evaluation board to provide 32 channel bias voltage for our silicon photon sensors(MPPC from Hamamatsu) that have a working voltage ranges from 65 to 70 volts with consumed current around 1 mA.
The AD5535B only provide a maximum source current around 550 uA. We tried to directly drive our photon sensor and it only goes up to about 64.4 volts.

I check the datasheet and found AD5535B provide much larger sink current, around -2 mA. My idea is to increase the driven capacity of the DAC output with a pull up resistor that connected to 100 V power source. Assuming the output voltage is 67 V, the input high voltage Vpp is 100 V, the pull up resistor with 17.5 k Ohms gives 2 mA current, then 1 mA goes to the photon sensor and the other 1 mA goes to the DAC as a sink current. I tested the output and found it only goes up to 67.2 V and can not goes up anymore. The datasheet only gives the Output Amplifier Source and Sink Capability with output voltage of 70 V, I want to know how it will change for different output voltage setting? Is there a detailed circuit diagram of the chip's output stage? Could you give some other suggestions to increase the chip's current driven capacity?