Part Number:ADS1248
I am having trouble reading from RTDs. All reads return a 7FFFFF value. No voltage can be read across the RTDs leading me to believe the IDAC current is not outputting. I tried adding an ammeter in the line and read no current either.
Here is the circuit we are using on our pcb:
and the process is:
Power up
set reset pin high
wait 16ms
write reset opcode
wait 1ms
write SDATAC opcode
write register values
Reg 0 MUX0 = 0x01 (Burnout off, ADC positive input = AIN0, ADC negative input = AIN1 )
Reg 1 VBIAS = 0x00 (VBIAS off)
Reg 2 MUX1 = 0x20 (Internal reference always on, REFP0 and REFN0, Normal operation)
Reg 3 SYS0 = 0x14 (PGA =2, Data rate = 80)
Reg 4 OFC0 = 0x00 (No offset)
Reg 5 OFC1 = 0x00 (No offset)
Reg 6 OFC2 = 0x00 (No offset)
Reg 7 FSC0 = 0x00 (Gain set by PGA to 0x402000)
Reg 8 FSC1 = 0x02 (Gain set by PGA to 0x402000)
Reg 9 FSC2 = 0x40 (Gain set by PGA to 0x402000)
Reg a IDAC0 = 0x94 (Data out only, IDAC magnitude = 500uA)
Reg b IDAC1 = 0x8F (IDAC1 = IEXC1, IDAC2 = Disconnected)
Reg c GPIOCFG = 0x00 (NO gpio)
Reg d GPIODIR = 0x00 (NO gpio)
Reg e GPIODAT = 0x00 (NO gpio)
pulse start pin high for 20us
wait for drdy interrupt
send RDATA opcode followed by 24 clocks
I have double checked the initialization several times and it seems right to me, but I cannot measure any excitation current or voltage across the RTDs. I also tried IEXC2 with a resistor to ground. Am I doing something wrong? Are there any problems with the circuit? Also I mistakenly set REFSELT[1:0] to Internal reference selected and internally connected to REFP0 and REFN0 pins, is it possible this damaged the current supply?