ZHCSIZ1G May 2010 – November 2018 LM98640QML-SP
PRODUCTION DATA.
The LM98640QML-SP provides two analog DACs per channel to provide flexibility in offset control. Each channel has a Coarse DAC and Fine DAC which have ±8-bit resolutions (8 bit + Sign). The two DACs can be used independently or as Coarse/Fine configuration. The Coarse DAC provides a sufficient range with moderate step sizes, while the Fine DAC is for designs which need a finely tuned offset. The correction voltage is applied to the "Video" level for both Sample & Hold and CDS input modes. Because of the DACs location in the signal path, the correction range lowers as CDS gain increases, and the output referred correction steps and ranges increase with PGA gain. Table 1 provides the range and step size of each DAC.
| CDS/SH GAIN | RANGE(1) | STEP SIZE(1) | OUTPUT ADC CODES | |
|---|---|---|---|---|
| Coarse DAC | 1x | ±250 mV | 1 mV | ±2048 |
| 2x | ±125 mV | 500 µV | ±2048 | |
| Fine DAC | 1x | ±5 mV | 20 µV | ±41 |
| 2x | ±2.5 mV | 10 µV | ±41 |
To use the Offset Correction DACs, the Coarse DAC and Fine DAC must be enabled using bits[6:5] of the Main Configuration Register (0x00). Then the desired correction value should be entered into the CDAC or FDAC register of the appropriate channel. The Offset Correction DACs use a signed binary format which is summarized in Table 2.
| CDAC / FDAC INPUT VALUE | CDAC CORRECTION (CODES) | FDAC CORRECTION (CODES) |
|---|---|---|
| 1 1111 1111 | +2048 | +41 |
| 1 0111 1111 | +1024 | +20 |
| 0 1111 1111 | 0 | 0 |
| 0 0111 1111 | –1024 | –20 |
| 0 0000 0000 | –2048 | –41 |