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ADT7488A Arkusz danych(PDF) 12 Page - Analog Devices |
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ADT7488A Arkusz danych(HTML) 12 Page - Analog Devices |
12 / 16 page ADT7488A Rev. 0 | Page 12 of 16 VOLTAGE MEASUREMENT The ADT7488A has two external voltage measurement channels. It can also measure its own supply voltage, VCC. Pins 7 and 8 measure the supplies of the processor core voltage (VCCP), and 2.5V pins, respectively. The VCC supply voltage measurement is carried out through the VCC pin (Pin 1). The 2.5V pin can be used to monitor a chipset supply voltage in a computer system. ANALOG-TO-DIGITAL CONVERTER All analog inputs are multiplexed into the on-chip, successive approximation, analog-to-digital converter (ADC). This has a resolution of 10 bits. The basic input range is 0 V to 2.25 V, but the inputs have built-in attenuators to allow measurement of 2.5 V, 3.3 V, 5 V, 12 V, and the processor core voltage (VCCP) without any external components. To allow for the tolerance of these supply voltages, the ADC produces a specific output for each nominal input voltage and therefore has adequate headroom to cope with overvoltages. The full-scale voltage that can be recorded for each channel is shown in Table 10. Table 10. Maximum Reported Input Voltages Voltage Channel Full-Scale Voltage VCC 4 V 2.5V 4 V VCCP 4 V Input Circuitry The internal structure for the analog inputs is shown in Figure 15. The input circuit consists of an input protection diode and an attenuator, plus a capacitor that forms a first- order, low-pass filter to provide input immunity to high frequency noise. 35pF 30pF 30pF MUX 68kΩ 71kΩ 3.3VIN 2.5VIN VCCP 45kΩ 94kΩ 17.5kΩ 52.5kΩ Figure 15. Internal Structure of Analog Inputs Voltage Measurement Command Codes The voltage measurement command codes are detailed in Table 11. Each voltage measurement has a read length of two bytes in little endian format (LSB followed by MSB). All voltages can be read together by addressing Command Code 0x12 with a read length of 0x06. The data is retrieved in the order listed in Table 11. Table 11. Voltage Measurement Command Codes Voltage Channel Command Code Returned Data VCC 0x12 LSB, MSB 2.5V 0x13 LSB, MSB VCCP 0x14 LSB, MSB Voltage Data Format The returned voltage value is in twos complement, 16-bit, binary format. The format is structured so that voltages in the range of ±32 V can be reported. In this way, the reported value represents the number of 1/1024 V in the actual reading, allowing a resolution of approximately 1 mV. Table 12. Analog-to-Digital Output Code vs. VIN Twos Complement Voltage MSB LSB 3.3 0000 1101 0011 0011 3 0000 1100 0000 0000 2.5 0000 1010 0000 0000 1 0000 0100 0000 0000 0 0000 0000 0000 0000 |
Podobny numer części - ADT7488A |
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Podobny opis - ADT7488A |
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