AnsweredAssumed Answered

AD9859 not responding

Question asked by stream99 on May 7, 2015
Latest reply on May 8, 2015 by stream99

I built a board that uses AD9859s, but I can not get them to respond to serial communication. I suspect that they are powered down.


I have the Evaluation Board that I'm controlling with an STM32. Everything works there as expected, so I'm guessing this isn't a software problem. The eval board setup:


25MHz sinusoidal ref clk 600mVPP

100kHz sclk

rb_enable jumper not present

ps1_dut1 grounded

ps2_dut1 grounded

osk_dut1 grounded

ioupdate -> fud_dut1

io_sync_dut1 grounded

pwrdwnctrl_dut1 grounded

clkmodesel_dut1 grounded

reset -> reset_dut1

cs1 -> csb_dut1


To initialize, I hold reset high for a period, then bring it low and write each of the registers.

CFR1 = 0x00000200

CFR2 = 0x000240

I've attached the logic analyzer capture for this.

The problem occurs when I try to use this same control on my board. When powered on, the DDS is pulling 26mA on the 1.8V line. This seems like a powered down state. Reads from any register returns all 0xFFs. With the PWRDWNCTL input low and CFR1<7,5,4> all 0, I believe the device should not be in a power down state. I have verified that the control lines are connected by probing the pins on the chip with a scope. Have I made an error in my schematic?