ZHCSDC6D November 2014 – February 2018 AMC7836
PRODUCTION DATA.
The AMC7836 device has an ADC with 21 analog inputs for external voltage sensing. Sixteen of these inputs are bipolar and the other five are unipolar. The bipolar inputs (ADC_0 through ADC_15) range is –12.5 to 12.5 V, and the unipolar analog inputs (LV_ADC16 through LV_ADC20) range is 0 to 2 × Vref. The ADC operates from an internal 2.5 V reference (Vref, measured at the REF_CMP pin). For additional noise filtering, a 4.7-µF capacitor should be connected between the REF_CMP and AGND2 pins. A high-quality ceramic type NP0 or X7R is recommended because of the optimal performance of the capacitor across temperature and very-low dissipation factor.
The ADC timing signals are driven from an on-chip temperature compensated 4-MHz oscillator. The on-chip oscillator is primarily responsible for the sampling frequency of the ADC. The sampling frequency of the ADC is dynamic and dependent on the acquisition and conversion time of each channel. Table 64 lists the relationship between the total update time and the internal oscillator frequency.
ADC CONVERSION RATE | ADC INPUT CHANNEL | ACQUISITION CLOCKS | CONVERSION CLOCKS | tS (ACQUISITION + CONVERSION)
NUMBER OF CLOCKS |
---|---|---|---|---|
00 | Bipolar | 124.5 | 13.5 | 138 |
Unipolar | 32.5 | 13.5 | 46 | |
Internal Temperature Sensor | — | — | 1025 | |
01 | Bipolar | 124.5 | 13.5 | 138 |
Unipolar | 78.5 | 13.5 | 92 | |
Internal Temperature Sensor | — | — | 1025 | |
10 | Bipolar | 124.5 | 13.5 | 138 |
Unipolar | 124.5 | 13.5 | 138 | |
Internal Temperature Sensor | — | — | 1025 | |
11 | Bipolar | 262.5 | 13.5 | 276 |
Unipolar | 262.5 | 13.5 | 276 | |
Internal Temperature Sensor | — | — | 1025 |
The minimum and maximum oscillator frequency specifications in conjunction with the number of clocks required for the unipolar, bipolar and temperature sensor inputs should be applied to Equation 5 to calculate the total update time range.
where
The following is an example of a complete calculation of the total update time range. In this example, the ADC conversion rate is set to 00 and the following ADC input channels are used:
Table 64 gives the total number of clocks required for each ADC input under the example conditions.
For the minimum specified oscillator frequency of 3.7 MHz, and with the ADC conversion rate set to 00, use Equation 6 to calculate the total maximum update time for this example.
For the maximum specified oscillator frequency of 4.3 MHz, use Equation 7 to calculate the total minimum update time for this example.
Therefore, the total update time range is 430.93 µs to 500.811 µs.
During the conversion, the input current per channel varies with the total update time which is determined by the number and type of channels (NCH) and the conversion rate setting of the CONV-RATE bit in the ADC configuration register (address 0x10).
NOTE
The source of the analog input voltage must be able to charge the input capacitance to a 12-bit settling level within the acquisition time.