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ADM1021A Folha de dados(PDF) 8 Page - ON Semiconductor |
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ADM1021A Folha de dados(HTML) 8 Page - ON Semiconductor |
8 / 16 page ADM1021A http://onsemi.com 8 To measure DVBE, the sensor is switched between operating currents of I and N I. The resulting waveform is passed through a 65 kHz low-pass filter to remove noise, and then to a chopper-stabilized amplifier that performs the functions of amplification and rectification of the waveform to produce a dc voltage proportional to DVBE. This voltage is measured by the ADC to give a temperature output in 8-bit, twos complement format. To reduce the effects of noise further, digital filtering is performed by averaging the results of 16 measurement cycles. Signal conditioning and measurement of the internal temperature sensor is performed in a similar manner. Differences Between the ADM1021 and the ADM1021A Although the ADM1021A is pin-for-pin compatible with the ADM1021, there are some differences between the two devices. Below is a summary of these differences and reasons for the changes. 1. The ADM1021A forces a larger current through the remote temperature sensing diode, typically 205 mA vs. 90 mA for the ADM1021. The primary reason for this is to improve the noise immunity of the part. 2. As a result of the greater remote sensor source current, the operating current of the ADM1021A is higher than that of the ADM1021, typically 205 mA vs. 160 mA. 3. The temperature measurement range of the ADM1021A is 0C to 127C, compared with −128C to +127C for the ADM1021. As a result, the ADM1021 should be used if negative temperature measurement is required. 4. The power-on reset values of the remote and local temperature values are −128C in the ADM1021A as compared to 0C in the ADM1021. As the part is powered up converting (except when the part is in standby mode, that is, Pin 15 is pulled low), the part measures the actual values of remote and local temperature and writes these to the registers. 5. The four MSBs of the revision register can be used to identify the part. The ADM1021 revision register reads 0x0x, and the ADM1021A reads 0x3x. 6. The power-on default value of the address pointer register is undefined in the ADM1021A and is equal to 0x00 in the ADM1021. As a result, a value must be written to the address pointer register before a read is performed in the ADM1021A. The ADM1021 is capable of reading back local temperature without writing to the address pointer register, as it defaulted to the local temperature measurement register at powerup. 7. Setting the mask bit (Bit 7 Config Reg) on the ADM1021A masks current and future ALERTs. On the ADM1021, the mask bit, masks only ALERTs. Any current ALERT has to be cleared using an ARA. Temperature Data Format One LSB of the ADC corresponds to 1C so the ADC can theoretically measure from −128C to +127C, although the device does not measure temperatures below 0C; therefore, the actual range is 0C to 127C. The temperature data format is shown in Table 5. The results of the local and remote temperature measurements are stored in the local and remote temperature value registers and are compared with limits programmed into the local and remote high and low limit registers. Table 5. TEMPERATURE DATA FORMAT Temperature (5C) Digital Output 0 0 000 0000 1 0 000 0001 10 0 000 1010 25 0 001 1001 50 0 011 0010 75 0 100 1011 100 0 110 0100 125 0 111 1101 127 0 111 1111 Registers The ADM1021A contains nine registers that are used to store the results of remote and local temperature measurements, and high and low temperature limits, and to configure and control the device. A description of these registers follows, and further details are given in Table 6 to Table 8. It should be noted that the ADM1021A’s registers are dual port and have different addresses for read and write operations. Attempting to write to a read address, or to read from a write address, produces an invalid result. Register addresses above 0x0F are reserved for future use or used for factory test purposes and should not be written to. Address Pointer Register The address pointer register does not have and does not require an address, because it is the register to which the first data byte of every write operation is written automatically. This data byte is an address pointer that sets up one of the other registers for the second byte of the write operation or for a subsequent read operation. Value Registers The ADM1021A has two registers to store the results of local and remote temperature measurements. These registers are written to by the ADC and can only be read over the SMBus. Status Register Bit 7 of the status register indicates when it is high that the ADC is busy converting. Bit 5 to Bit 3 are flags that indicate the results of the limit comparisons. |
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