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HS574AT Datasheet(PDF) 9 Page - Sipex Corporation |
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HS574AT Datasheet(HTML) 9 Page - Sipex Corporation |
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9 / 14 page  11 Table 1. SPx74A Control Input Truth Table CE CS R/C 12/8 A 0 OPERATION 0 xxxx None x 1 x x x None 0 0 x 0 Initiate 12–Bit Conversion 0 0 x 1 Initiate 8–Bit Conversion 1 0 x 0 Initiate 12–Bit Conversion 1 0 x 1 Initiate 8–Bit Conversion 10 x 0 Initiate 12–Bit Conversion 10 x 1 Initiate 8–Bit Conversion 1 0 1 1 x Enable 12–Bit Output 1 0100 Enable 8 MSB's Only 1 0101 Enable 4 LSB's plus 4 Trailing Zeroes of these inputs in controlling the converter’s operation is shown in Table 1, and the internal control logic is shown in a simplified schematic in Figure 6. Conversion Start A conversion may be initiated by a logic transi- tion on any of the three inputs: CE, CS R/C, as shown in Table 1. The last of the three to reach the correct state starts the conversion, so one, two or all three may be dynamically controlled. The nominal delay from each is the same and all three may change state simultaneously. In order to assure that a particular input controls the start of conversion, the other two should be setup at least 50ns earlier. Refer to the convert mode timing specifications. The Convert Mode timing diagram is shown in Figure 8. The output signal STS is the status flag and goes high only when a conversion is in progress. While STS is high, the output buffers remain in a high impedance state so that data can not be read. Also, when STS is high, an additional Start Convert will not reset the converter or reinitiate a conversion. Note, if A 0 changes state after a conversion begins, an additional Start Convert command will latch the new state of A 0 and possibly cause a wrong cycle length for that conversion (8–versus 12–bits). CONTROLLING THE SPx74A The SPx74A can be operated by most micropro- cessor systems due to the control input pins and on–chip logic. It may also be operated in the “stand–alone” mode and enabled by the R/C input pin. Full microprocessor control consists of selecting an 8– or 12–bit conversion cycle, initiating the conversion, and reading the output data when ready. The output read has the options of choosing either 12–bits at once or 8–bits followed by 4–bits in a left–justified format. All five control inputs are TTL/CMOS compatible and include 12/8, CS, A 0, R/C and CE. The use log input to pin 13 for the 0V to 10V range or to pin 14 for the 0V to 20V range. Bipolar The gain and offset errors listed in the specifica- tions may be adjusted to zero using the potenti- ometers R 1 and R2 (See Figure 5). If adjustment is not needed, either or both pots may be replaced by a 50 Ω, 1% metal film resistor. To calibrate, connect the analog input signal to pin 13 for a ±5V range or to pin 14 for a ±10V range. First apply a DC input voltage 1⁄ 2 LSB above negative full scale which is –4.9988V for the ±5V range or –9.9976V for the ±10V range. Adjust the offset potentiometer R 1 for flicker between output codes 0000 0000 0000 and 0000 0000 0001. Next, apply a DC input voltage 11⁄ 2 LSB below positive full scale which is +4.9963V for the ±5 range or +9.9927V for the ±10V range. Adjust the gain potentiometer R 2 for flicker between codes 1111 1111 1110 and 1111 1111 1111. Alternative The 100 Ω potentiometer R 2 provides gain adjust for 10V and 20V ranges. In some applications, a full scale of 10.24V (for and LSB of 2.5mV) or 20.48 (for an LSB of 5.0mV) is more convenient. For these, replace R 2 by a 50Ω, 1% metal film resistor. Then to provide gain adjust for the 10.24 range, add a 200 Ω potentiometer and a 95Ω fixed resistor, all in series with pin 13. For the 20.48V range, add a 500 Ω potentiometer and a 200 Ω fixed resistor in series with pin 14. |
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