Tool/software:
Hi,
We are using your DAC7750 in our designs.
Upon design verification we've concluded that the current output is not doing what we expect.
It is configured as a 0-20mA output, and therefore we also use the 0-20mA CODE calculation method.
constexpr uint8_t RANGE_SELECTION = 0b110; // 0-20 mA
The method used to go from milli amps to the CODE is shown here:
uint16_t code = (uint16_t) ((current_ma / 20.0) *
pow(2, RESOLUTION)); // ((current_ma) << RESOLUTION) / 20;
// For DAC7750 the data is stored in DB15:DB4
// Therefore shift code by 4 to left.
// _value will be written by STATE_SET_OUTPUT
_value = code << 4;
When writing the CODE corresponding to 20mA (0x1000) to the device the current output is 10mA.
When writing the CODE corresponding to 10mA (0x0800) to the device the current output is 15mA.
When writing the CODE corresponding to 0mA (0x0000) to the device the current output is 10mA.
The codes are written to the chip using:
uint8_t data_msb = (_value >> 8) & 0xFF; // MSB
uint8_t data_lsb = _value & 0xFF; // LSB
_make_transaction(DATA_REGISTER, data_msb, data_lsb);
where make transaction, fills the spi buffer as:
_spi_tx[0] = reg;
_spi_tx[1] = msb;
_spi_tx[2] = lsb;
The output current is measured with a multimeter and a resistor in series on I_out.
The data is actually transmitted as we have measured that with a logic analyzer and verified with toggling OUTEN. Disabling OUTEN disables the current output (0 mA on the outputs.)
Any idea what we are doing wrong here?
