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AD9117 coarse gain setting

Category: Hardware

Hello,

we are playing the gain control of an AD9117 DAC.

Config: VDD is 3.3V, Vref is 1V, IRSET is enabled and we have IV converter with 49.9 ohm resistors at the DAC outputs. CMPLx grounded, RLxP/N open.

Stated in datasheet rev. E p.38:

Changes the value of the on-chip IRSET resistor; this scales the full-scale current of the DAC in ~0.25 dB steps twos complement (nonlinear), see Figure 99.

000000 (default): IRSET = 2 kΩ.

011111: IRSET = 8 kΩ.

100000: IRSET = 1.6 kΩ.

111111: IRSET = 2 kΩ.

Q1: How is it possible to have same IRSET values (2k) with different register codes (000000, 111111)? They seem one step far, so the resistance must be differ.

Q2: If IRSET equals 2k then the IOUTFS shouldn't be 32*Vref/2k = 16mA (as per page 45)? Figure 99. looks different.

Q3. Where is the tolerance of xRSET? (I didn't find it on the datasheet.)

Thank you.

Top Replies

    •  Analog Employees 
    May 17, 2023 in reply to molnar +2 verified

    Hello ,

    Thank you for patiently waiting. Regarding xRset (Q2), we've confirmed on bench that the correct xRset for 0b000000 and 0b111111 should be 4kΩ, not 2kΩ. The graph in Fig. 99…

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