Other Parts Discussed in Thread: TMUX1511
Dear sirs
I'm using the ADS1261B's internal constant current source to drive a 3.5K pressure sensor bridge. Please see attached schematic. The multiplexer is a TI TMUX1511. I've configured the IMUX register for IDAC1 to be connected to AINCOM (0xFA) and IMAG for an output of 1000uA (1mA) (0x06). I'm just starting the firmware development, so I've set the reference to the 5vdc supply and AIN2 and AIN3 to outputs with AIN2 set low and AIN3 set to high. Please see attached code snippet. I've read back the registers to make sure they were written correctly. Yet I'm not getting any current out of AINCOM. I should be able to read a 3.5vdc voltage drop across the bridge. Am I missing something in the setup procedure? I have five identical circuits on the PCA and they all behave the same.
//
// Reset all the ADS1261s.
// Drives the reset pin low for 1mS.
//
for(i=1; i<6; i++)
{
ADC_RST(i);
}
//
// Read the STATUS register
//
for(i=1; i<6; i++)
{
ui32RegData = ADC_Read_Reg(SPI0, REG_ADDR_STATUS, i);
Dennis_UARTprintf("ADS1261 #%i Status output is %x\n", i, ui32RegData);
}
//
// Write the MODE0 register
//
for(i=1; i<6; i++)
{
ADC_Write_Reg(SPI0, REG_ADDR_MODE0, i, (MODE0_DR_1200_SPS | MODE0_SINC4));
}
//
// Write the MODE2 register
// Enables AIN2 and 3 as outputs.
//
for(i=1; i<6; i++)
{
ADC_Write_Reg(SPI0, REG_ADDR_MODE2, i, (MODE2_GPIOCON_AIN3_ENABLE_MASK | MODE2_GPIOCON_AIN2_ENABLE_MASK));
}
//
// Write the MODE3 register
// Set AIN3's output to high. AIN2's output is default low.
//
for(i=1; i<6; i++)
{
ADC_Write_Reg(SPI0, REG_ADDR_MODE3, i, MODE3_GPIODAT_AIN3_DATA_MASK);
}
//
// Write the REF register
//
for(i=1; i<6; i++)
{
ADC_Write_Reg(SPI0, REG_ADDR_REF, i, (REF_RMUXP_AVDD | REF_RMUXN_AVSS));
}
//
// Write the IMUX register
// Select IDAC1 to be connected to AINCOM.
//
for(i=1; i<6; i++)
{
ADC_Write_Reg(SPI0, REG_ADDR_IMUX, i, (IMUX_IMUX2_NOCONNECT | IMUX_IMUX1_AINCOM));
}
//
// Write the IMAG register
// Set IDAC1 output to 1000uA (1mA)
//
for(i=1; i<6; i++)
{
ADC_Write_Reg(SPI0, REG_ADDR_IMAG, i, (IMAG_IMAG2_OFF | IMAG_IMAG1_1000_uA));
}
//
// Write the PGA register
// Set the PGA gain to 16.
//
for(i=1; i<6; i++)
{
ADC_Write_Reg(SPI0, REG_ADDR_PGA, i, PGA_GAIN_16);
}
//
// Write the INPMUX register
// Set AIN6 and 7 to plus and minus analog inputs respectively.
//
for(i=1; i<6; i++)
{
ADC_Write_Reg(SPI0, REG_ADDR_INPMUX, i, (INPMUX_MUXP_AIN6 | INPMUX_MUXN_AIN7));
}
