AnsweredAssumed Answered

AD5422 Vout is going to positive rail

Question asked by Photoman on Mar 2, 2015
Latest reply on Mar 5, 2015 by tjohnson

HI, I am using a Freescale Micro to write SPI to the AD5422.  When I initiate the following:


SPI2_Send3Chars(0x56, 0x00, 0x01); //RESET

SPI2_Send3Chars(0x55, 0x10, 0x00);   //OUTPUT ENABLE, select 0-5Vout

SPI2_Send3Chars(0x01, 0xFF, 0xFF);   //DATA REG WRITE Full Scale Output


10.23V appears on the output (which is the voltage applied to AVdd).  If I repeat the above, but with a data reg write of

SPI2_Send3Chars(0x01, 0xC5, 0xFF);

I get 3.88V output.  (reducing 0xC5 further gives expected results, i.e. writing SPI2_Send3Chars(0x01, 0x7F, 0xFF); gives 2.5V).  Somewhere between 0xC5 and 0xD0 it jumps up to ~10V.

As stated before, I have 5V output enabled, so how am I getting 10V?  If I increase AVdd, the output follows.

Connections to AD5422 Ref in tied to Ref out, using op amp to feed vout into vsense,Iout and Vout connected. DVCC=~4.8V (I will adjust this to 5.4 volts later when I tweak the power supply), I have -4.8V applied to AVSS1 & 2 & paddle.DVcc Sel= Gnd.  RSET 15k to gnd. 22nF caps from CAP1 and 2 to AVdd.

I had some wrong settings earlier, could I have damaged the part?  I accidentally had DVCC SEL floating with a 4.8V applied to DVcc, and didn't have Ref in and out tied.