Maxim Integrated MAX1402 - Manual (Page 5)

Calibration Tool
The MAX1402 EV kit software can average the mea-
surements from the calibration channels and use the
measured values to correct the voltage displays. The
calibration algorithm assumes that the CALOFF inputs
are externally connected together, and that the
CALGAIN inputs are externally connected to the refer-
ence voltage (VREF). View the calibration tool by
selecting it from the Show menu.
The software automatically disables calibration if either
of the calibration channels reports a code of 0 or
262143. This is to prevent erroneous calibration when
using a transfer function that does not include both 0V
and VREF.
When Use CALOFF and CALGAIN for Calibration is
checked, the software averages the raw A/D codes for
the CALOFF and CALGAIN channels. The average is
calculated as a weighted sum of the new data and the
old average value. The Slower/Faster slide bar controls
the weight of the new data vs. the weight of the old
average.
The EV kit software assumes that all three transfer func-
tion registers are set to the same value.
This calibration affects only the displayed voltage, not
the raw code numbers. The average CALOFF and
CALGAIN code values are used as the endpoints of a
linear interpolation, with CALOFF measuring zero volts
and CALGAIN measuring VREF.
The linear interpolation formula is as follows:
Sampling Tool
To sample data at full speed, select Sample from the
main display menu, make your selections, and click on
the Begin Sampling button. Sampling rate is controlled
by the Configuration tool. Sample size is restricted to a
power of two. Sample Size controls the number of sam-
ples collected on each selected channel. After the
samples have been collected, the data is automatically
uploaded to the host and is graphed. Once displayed,
the data may be saved to a file.
While the Sampling tool is open, the other windows are
locked out. Close the Sampling tool by clicking the
Close icon in the upper corner.
Register Display Tool
This tool displays all of the internal registers of the
MAX1400/MAX1402. Modify any bit value by checking
or unchecking its box. (The START bit and the zero bits
in the special function register (SFR) cannot be modi-
fied). The Read All Registers button causes the soft-
ware to read all of the MAX1400/MAX1402’s registers.
(Not functional when the MDOUT or FULLPD bit is set.)
Refer to Table 4, Guide to Register Bit Functions.
Communications Register (COMMS)
Setting the FSYNC control bit inhibits the MAX1400/
MAX1402 from performing its self-timed measurements.
If FSYNC = 1 when it is time to perform a measurement,
the MAX1400/MAX1402 simply skips that measure-
ment. Thus, power line frequency rejection is not affect-
ed by the FSYNC bit.
Setting the STDBY bit places the part in low-power
standby mode. The serial interface and the CLK oscilla-
tor continue to operate. The part can be restored to
normal operation by clearing the STDBY bit.
Special Function Register (SFR)
Setting the MDOUT bit causes the raw modulator output
to be driven out the DOUT pin; however, the EV kit soft-
ware cannot read data from the MAX1402 in this mode.
Setting the FULLPD bit in the SFR register places the
part in full power-down mode. The master oscillator
does not run. To restore normal operation, click on the
Reset menu item in the main display. This causes the
68HC16 software to pulse the MAX1402 RESET pin.
Transfer Function Registers (TF1, TF2, TF3)
The three Transfer Function registers (TF1, TF2, TF3)
control how input voltage is mapped to code values. The
transfer function registers control a programmable-gain
amplifier (PGA) and an offset correction DAC.
If U/B = 1, the transfer function maps unipolar voltages
between 0V and VREF. If U/B = 0, then the transfer
function maps bipolar voltages between -VREF and
+VREF. Next, the PGA increases the code-per-volt pro-
cessing gain, reducing the full-scale voltage range by a
factor of 1, 2, 4, 8, 16, 32, 64, or 128. Finally, the offset
correction DAC offsets the voltage range by up to ±7/6
of the full-scale voltage range.
Input pins AIN1 and AIN2 are controlled by TF1. Input
pins AIN3 and AIN4 are controlled by TF2. Input pin
AIN5 is controlled by TF3. Input pin AIN6 is the analog
common.
When SCAN = 1, the CALOFF and CALGAIN channels
are controlled by TF3. When SCAN = 0, the CALOFF
and CALGAIN channels are controlled by one of the
transfer function registers, as selected by the A1 and
A0 bits.
Voltage
VREF Code CALOFFcode
CALGAINcode CALOFFcode PGAgain
=
−
−
⋅
⋅
( )
( )
Evaluate: MAX1400/MAX1402
MAX1402 Evaluation Kit/Evaluation System
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