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ADS7861 Datasheet(PDF) 10 Page - Texas Instruments |
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ADS7861 Datasheet(HTML) 10 Page - Texas Instruments |
10 / 33 page ADS7861 10 SBAS110D Code (decimal) 8000 7000 6000 5000 4000 3000 2000 1000 0 2044 2045 2046 2047 2048 FIGURE 5. Histogram of 8,000 Conversions of a DC Input. FIGURE 6. Test Circuits for Timing Specifications. FIGURE 7. Level Shift Circuit for Bipolar Input Ranges. TRANSITION NOISE Figure 5 shows a histogram plot for the ADS7861 following 8,000 conversions of a DC input. The DC input was set at output code 2046. All but one of the conversions had an output code result of 2046 (one of the conversions resulted in an output of 2047). The histogram reveals the excellent noise performance of the ADS7861. BIPOLAR INPUTS The differential inputs of the ADS7861 were designed to accept bipolar inputs (–VREF and +VREF) around the internal reference voltage (2.5V), which corresponds to a 0V to 5V input range with a 2.5V reference. By using a simple op amp circuit featuring a single amplifier and four external resis- tors, the ADS7861 can be configured to except bipolar inputs. The conventional ±2.5V, ±5V, and ±10V input ranges can be interfaced to the ADS7861 using the resistor values shown in Figure 7. TIMING AND CONTROL The operation of the ADS7861 can be configured in four different modes by using the address pins M0, M1 and A0. The M0 pin selects between two- and four-channel operation (in two-channel operation, the A0 pin selects between Chan- nels 0 and 1; in four-channel operation the A0 pin is ignored and the channels are switched automatically after each conversion). The M1 pin selects between having serial data transmitted simultaneously on both the Serial A data output and the Serial B data output or having both channels output data through the Serial A port. The A0 pin selects either Channel 0 or Channel 1 (see Pin Descriptions and Serial Output Truth Table for more information). The next four sections will explain the four different modes of operation. Mode I (M0 = 0, M1 = 0) With the M0 and M1 pins both set to ‘0’, the ADS7861 will operate in two-channel operation (the A0 pin must be used to switch between Channels A and B). A conversion is initiated by bringing CONVST HIGH for a minimum of 15ns. It is very important that CONVST be brought HIGH a minimum of 10ns prior to a rising edge of the external clock or 5ns after the rising edge. If CONVST is brought R 1 R 2 +IN –IN REF OUT 2.5V 4k Ω 20k Ω Bipolar Input BIPOLAR INPUT R 1 R 2 ±10V 1k Ω 5k Ω ±5V 2k Ω 10k Ω ±2.5V 4k Ω 20k Ω OPA132 ADS7861 DATA 1.4V Test Point 3k Ω 100pF C LOAD t R DATA Voltage Waveforms for DATA Rise and Fall Times t R, and tF. V OH V OL t F DESCRIPTION ANALOG INPUT Full-Scale Input Span –VREF to +VREF(1) Least Significant (–VREF to +VREF)/4096(2) Bit (LSB) +Full Scale 4.99878V 0111 1111 1111 7FF Midscale 2.5V 0000 0000 0000 000 Midscale – 1 LSB 2.49878V 1111 1111 1111 FFF –Full Scale 0V 1000 0000 0000 800 NOTES: (1) –VREF to +VREF around VREF. With a 2.5V reference, this corre- sponds to a 0V to 5V input span. (2) 1.22mV with a 2.5V reference. TABLE I. Ideal Input Voltages and Output Codes. DIGITAL OUTPUT BINARY TWO’S COMPLEMENT BINARY CODE HEX CODE |
Número de pieza similar - ADS7861_14 |
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Descripción similar - ADS7861_14 |
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