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ZHCSP80 December 2022 AFE78101 , AFE88101

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机械数据 (封装 | 引脚)

RRU|24
- MPQF588

散热焊盘机械数据 (封装 | 引脚)

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zhcsp80_oa

7.3.1.4 DAC Gain and Offset Calibration

The AFEx8101 provide DAC gain and offset calibration capability to correct for end-point errors present in the system. Implement the gain and offset calibration using two registers, DAC_GAIN.GAIN and DAC_OFFSET.OFFSET. Update DAC_DATA register after gain or offset codes are changed for the new values to take effect. The DAC_GAIN can be programmed from 0.5 to 1.499985 using Equation 2.

Equation 2.

D A C_G A I N = \frac{1}{2} + \frac{G A I N}{2^{N}}

where

N = DAC_GAIN resolution in bits: 16 for the AFE88101 and 14 for the AFE78101.
GAIN is the decimal value of the DAC_GAIN register setting.
GAIN data are left justified; the last two LSBs in the DAC_GAIN register are ignored for the AFE78101.

The example DAC_GAIN settings for the AFE88101 are shown in Table 7-3.

Table 7-3 DAC_GAIN Setting vs GAIN Code

DAC_GAIN	GAIN (HEX)
0.5	0x0000
1.0	0x8000
1.499985	0xFFFF

The DAC_OFFSET is stored in the DAC_OFFSET register using 2's-complement encoding. The DAC_OFFSET value can be programmed from –2^(N–1) to 2^(N–1) – 1 using Equation 3.

Equation 3.

D A C_O F F S E T = - {O F F S E T}_{M S B} \times 2^{(N - 1)} + \sum_{i = 0}^{(N - 2)} {O F F S E T}_{i} {\times 2}^{i}

where

N = DAC_OFFSET resolution in bits: 16 for the AFE88101 and 14 for the AFE78101.
OFFSET_MSB = MSB bit of the DAC_OFFSET register.
OFFSET_i = The rest of the bits of the DAC_OFFSET register.
i = Position of the bit in the DAC_OFFSET register.
OFFSET data are left justified; the last two LSBs in the DAC_OFFSET register are ignored for the device.

The most significant bit determines the sign of the number and is called the sign bit. The sign bit has the weight of –2^(N–1) as shown in Equation 3.

The example DAC_OFFSET settings for the AFE88101 are shown in Table 7-4.

Table 7-4 DAC_OFFSET Setting vs OFFSET Code

DAC_OFFSET	OFFSET (HEX)
32767	0x7FFF
1	0x0001
0	0x0000
–1	0xFFFF
–2	0xFFFE
–32768	0x8000

The following transfer function is applied to the DAC_DATA.DATA based on the DAC_GAIN and DAC_OFFSET values:

Equation 4.

D A C_C O D E = (D A T A \times D A C_G A I N) + D A C_O F F S E T

where

DAC_CODE is the internal signal applied to the DAC.
DATA is the decimal value of the DAC_DATA register.
DAC_GAIN and DAC_OFFSET are the user calibration settings.
DATA data are left justified; the last two LSBs in the DAC_DATA register are ignored for the AFE78101.

Substituting DAC_GAIN and DAC_OFFSET in Equation 4 with Equation 2 and Equation 3 results in:

Equation 5.

D A C_C O D E = (D A T A \times [\frac{1}{2} + \frac{G A I N}{2^{N}}]) - {O F F S E T}_{M S B} \times 2^{(N - 1)} + \sum_{i = 0}^{(N - 2)} {O F F S E T}_{i} {\times 2}^{i}

The multiplier is implemented using truncation instead of rounding. This truncation can cause a difference of one LSB if rounding is expected. Figure 7-2 shows the DAC calibration path.

Figure 7-2 DAC Calibration Path