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ICL7129 Datasheet(PDF) 9 Page - Intersil Corporation |
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ICL7129 Datasheet(HTML) 9 Page - Intersil Corporation |
9 / 11 page 3-39 In low resolution applications, where the converter uses only 31/2 digits and 100µV resolution, an R-C type oscillator is ade- quate. In this application a C of 51pF is recommended and the resistor value selected from fOSC = 0.45/RC. However, when the converter is used to its full potential (41/2 digits and 10µV resolution) a crystal oscillator is recommended to prevent the noise from increasing as the input signal is increased due to frequency jitter of the R-C oscillator. Both R-C and crystal oscil- lator circuits are shown in Figure 12. Powering the ICL7129 The ICL7129 may be operated as a battery powered hand-held instrument or integrated into larger systems that have more sophisticated power supplies. Figures 13, 14, and 15 show various powering modes that may be used with the ICL7129. The standard supply connection using a 9V battery is shown in the Typical Application Schematic. The power connection for systems with +5V and -5V sup- plies available is shown in Figure 13. Notice that measure- ments are with respect to ground. COMMON is also tied to INLO to remove any common-mode voltage swing on the integrator amplifier inputs. It is important to notice that in Figure 13, digital ground of the ICL7129 (DGND pin 36) is not directly connected to power supply ground. DGND is set internally to approximately 5V less than the V+ terminal and is not intended to be used as a power input pin. It may be used as the ground reference for external logic, as shown in Figure 4 and 5. In Figure 4, DGND is used as the negative supply rail for external logic provided that the supply current for the external logic does not cause excessive loading on DGND. The DGND output can be buff- ered as shown in Figure 5. Here, the logic supply current is shunted away from the ICL7129 keeping the load on DGND low. This treatment of the DGND output is necessary to insure compatibility when the external logic is used to interface directly with the logic inputs and outputs of the ICL7129. When a battery voltage between 3.8V and 6V is desired for operation, a voltage doubling circuit should be used to bring the voltage on the ICL7129 up to a level within the power sup- ply voltage range. This operating mode is shown in Figure 14. Again measurements are made with respect to COMMON since the entire system is floating. Voltage doubling is accomplished by using an ICL7660 CMOS voltage converter and two inexpensive electrolytic capacitors. The same princi- ple applies in Figure 15 where the ICL7129 is being used in a system with only a single +5V power supply. Here mea- surements are made with respect to power supply ground. ICL7129 2 40 75k Ω 51pF 1 ICL7129 2 40 27k Ω 10pF 1 120kHz 5pF V+ V- CRYSTAL MODE: PARALLEL RS < 50kΩ CL < 12pF CO < 5pF FIGURE 12. RC AND CRYSTAL OSCILLATOR CIRCUITS ICL7129 24 34 35 28 33 32 23 36 ICL8089 +5V -5V 0.1 µF 0.1 µF 0.1 µF VIN V- V+ REF HI REF LO DGND COM IN HI IN LO FIGURE 13. POWERING THE ICL7129 FROM +5V AND -5V ICL7129 24 34 35 28 33 32 23 36 10 µF VIN V- V+ + - 2 4 5 + 10 µF ICL7660 3 + 8 3.8V TO 6V + - REF HI REF LO DGND COM IN HI IN LO FIGURE 14. POWERING THE ICL7129 FROM A 3.8V TO 6V BATTERY ICL7129 24 34 35 28 33 32 23 36 ICL8089 +5V 10 µF 0.1 µF 0.1 µF VIN V- V+ + - 2 4 5 + 10 µF ICL7660 3 + 8 FIGURE 15. POWERING THE ICL7129 FROM A SINGLE POLARITY POWER SUPPLY ICL7129 |
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