SNIU028D February 2016 – September 2020 UCD3138 , UCD3138064 , UCD3138064A , UCD3138128 , UCD3138A , UCD3138A64
The ADC 12 in UCD3138 digital controller is a 12 bit, high speed analog to digital converter. It comes equipped with the following features:
The control module, shown in Figure 8-1, contains the control and conversion logic for auto-sequencing a series of conversions. The sequencing is fully configurable for any combination of 16 possible ADC channels through an analog multiplexer embedded in the ADC12 block. Once converted, the selected channel value is stored in the result register associated with the sequence number. Input channels can be sampled in any desired order or programmed to repeat conversions on the same channel multiple times during a conversion sequence. Selected channel conversions are also stored in the result registers in order of conversion, where the result 0 register is the first conversion of a 16-channel sequence and result 15 register is the last conversion of a 16-channel sequence. The number of channels converted in a sequence can vary from 1 to 16.
Unlike the EADC converters in the Digital Power Peripherals portion of UCD3138, which feature a substantially faster conversion rate and hence are primarily designed for closing high speed voltage/current feedback loops of the power supply, the ADC12 is not usually used for loop compensation purposes. The ADC12 features make it best suited for monitoring and detection of currents, voltages, temperatures and faults.
Unbuffered multiplexed input is a popular option in CMOS switched capacitor ADCs. Compared with buffered inputs, the power consumption of unbuffered option is much lower. But there exists several problems: First, in general, the input impedance of this kind of ADC is very high at low frequency range and rolls off when frequency gets higher. Second, in unbuffered multiplexed ADC, the charge injection from the internal sampling capacitors and network reflects a small amount of signal, which is packed with high frequency content back onto the front-end circuitry and incoming signal. This may cause settling errors for the elements connected to the analog inputs of the converter. Another problem is that all the sampling channels use the same S/H capacitor in a sequence, if the sampling speed is very high, the charge remain on the S/H capacitor of one conversion may affect the result of the next conversion channel.