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MAX1261AEEI Datasheet(PDF) 10 Page - Maxim Integrated Products |
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MAX1261AEEI Datasheet(HTML) 10 Page - Maxim Integrated Products |
10 / 20 page Analog Input Protection Internal protection diodes, which clamp the analog input to VDD and GND, allow each input channel to swing within (GND - 300mV) to (VDD + 300mV) without damage. However, for accurate conversions near full scale, both inputs must not exceed (VDD + 50mV) or be less than (GND - 50mV). If an off-channel analog input voltage exceeds the sup- plies by more than 50mV, limit the forward-bias input current to 4mA. Track/Hold The MAX1261/MAX1263 T/H stage enters its tracking mode on the rising edge of WR. In external acquisition mode, the part enters its hold mode on the next rising edge of WR. In internal acquisition mode, the part enters its hold mode on the fourth falling edge of clock after writing the control byte. Note that, in internal clock mode, this occurs approximately 1µs after writing the control byte. In single-ended operation, IN- is connect- ed to COM and the converter samples the positive (+) input. In pseudo-differential operation, IN- connects to the negative (-) input, and the difference of (IN+) - (IN-) is sampled. At the beginning of the next conversion, the positive input connects back to IN+ and CHOLD charges to the input signal. The time required for the T/H stage to acquire an input signal depends on how quickly its input capacitance is charged. If the input signal’s source impedance is high, the acquisition time lengthens, and more time must be allowed between conversions. The acquisition time, tACQ, is the maximum time the device takes to acquire the signal and is also the minimum time required for the signal to be acquired. Calculate this with the following equation: tACQ = 9(RS + RIN)CIN where RS is the source impedance of the input signal, RIN (800 Ω) is the input resistance, and CIN (12pF) is the ADC’s input capacitance. Source impedances below 3k Ω have no significant impact on the MAX1261/ MAX1263s’ AC performance. Higher source impedances can be used if a 0.01µF capacitor is connected to the individual analog inputs. Together with the input impedance, this capacitor forms an RC filter, limiting the ADC’s signal bandwidth. Input Bandwidth The MAX1261/MAX1263 T/H stage offers a 250kHz full- linear and a 3MHz full-power bandwidth, enabling these parts to use undersampling techniques to digitize high-speed transients and measure periodic signals with bandwidths exceeding the ADC’s sampling rate. To avoid high-frequency signals being aliased into the frequency band of interest, anti-alias filtering is recom- mended. Starting a Conversion Initiate a conversion by writing a control byte that selects the multiplexer channel and configures the MAX1261/MAX1263 for either unipolar or bipolar opera- tion. A write pulse (WR + CS) can either start an acqui- sition interval or initiate a combined acquisition plus 250ksps, +3V, 8-/4-Channel, 12-Bit ADCs with +2.5V Reference and Parallel Interface 10 ______________________________________________________________________________________ CH0 CH2 CH1 CH3 CH4 CH6 CH7 CH5 COM CSWITCH TRACK T/H SWITCH RIN 800 Ω CHOLD HOLD 12-BIT CAPACITIVE DAC REF ZERO COMPARATOR – + 12pF SINGLE-ENDED MODE: IN+ = CH0–CH7, IN- = COM PSEUDO-DIFFERENTIAL MODE: IN+ AND IN- SELECTED FROM PAIRS CH0/CH1, CH2/CH3, CH4/CH5, AND CH6/CH7 AT THE SAMPLING INSTANT, THE MUX INPUT SWITCHES FROM THE SELECTED IN+ CHANNEL TO THE SELECTED IN- CHANNEL. INPUT MUX Figure 3a. MAX1261 Simplified Input Structure CH0 CH1 CH2 CH3 COM CSWITCH TRACK T/H SWITCH RIN 800 Ω CHOLD HOLD 12-BIT CAPACITIVE DAC REF ZERO COMPARATOR – + 12pF SINGLE-ENDED MODE: IN+ = CH0–CH3, IN- = COM PSEUDO-DIFFERENTIAL MODE: IN+ AND IN- SELECTED FROM PAIRS CH0/CH1 AND CH2/CH3 AT THE SAMPLING INSTANT, THE MUX INPUT SWITCHES FROM THE SELECTED IN+ CHANNEL TO THE SELECTED IN- CHANNEL. INPUT MUX Figure 3b. MAX1263 Simplified Input Structure |
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