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ADM1026JST Datasheet(PDF) 11 Page - Analog Devices |
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ADM1026JST Datasheet(HTML) 11 Page - Analog Devices |
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11 / 56 page  ADM1026 Rev. A | Page 11 of 56 Fan Speed Control Outputs The ADM1026 has two outputs intended to control fan speed, though they can also be used for other purposes. Pin 18 is an open drain, pulse width modulated (PWM) output with a programmable duty cycle and an output frequency of 75 Hz. Pin 23 is connected to the output of an on-chip, 8-bit, digital-to- analog converter with an output range of 0 V to 2.5 V. Either or both of these outputs may be used to implement a temperature-controlled fan by controlling the speed of a fan using the temperature measured by the on-chip temperature sensor or remote temperature sensors. INTERNAL REGISTERS Table 4 describes the principal registers of the ADM1026. For more detailed information, see Table 11 to Table 124. Table 4. Principal Registers Type Description Address Pointer Contains the address that selects one of the other internal registers. When writing to the ADM1026, the first byte of data is always a register address, and is written to the address pointer register. Configuration Registers Provide control and configuration for various operating parameters. Fan Divisor Registers Contain counter prescaler values for fan speed measurement. DAC/PWM Control Registers Contain speed values for PWM and DAC fan drive outputs. GPIO Configuration Registers Configure the GPIO pins as input or output and for signal polarity. Value and Limit Registers Store the results of analog voltage inputs, temperature, and fan speed measurements, along with their limit values. Status Registers Store events from the various interrupt sources. Mask Registers Allow masking of individual interrupt sources. EEPROM The ADM1026 has 8 kB of nonvolatile, electrically erasable, programmable read-only memory (EEPROM) from register Addresses 8000h to 9FFFh. This may be used for permanent storage of data that is not lost when the ADM1026 is powered down, unlike the data in the volatile registers. Although referred to as read-only memory, the EEPROM can be written to (as well as read from) via the serial bus in exactly the same way as the other registers. The main differences between the EEPROM and other registers are • An EEPROM location must be blank before it can be written to. If it contains data, it must first be erased. • Writing to EEPROM is slower than writing to RAM. • Writing to the EEPROM should be restricted because its typical cycle life is 100,000 write operations, due to the usual EEPROM wear-out mechanisms. The EEPROM in the ADM1026 has been qualified for two key EEPROM memory characteristics: memory cycling endurance and memory data retention. Endurance qualifies the ability of the EEPROM to be cycled through many program, read, and erase cycles. In real terms, a single endurance cycle is composed of four independent, sequential events, as follows: 1. Initial page erase sequence 2. Read/verify sequence 3. Program sequence 4. Second read/verify sequence In reliability qualification, every byte is cycled from 00h to FFh until a first fail is recorded, signifying the endurance limit of the EEPROM memory. Retention quantifies the ability of the memory to retain its programmed data over time. The EEPROM in the ADM1026 has been qualified in accordance with the formal JEDEC Retention Lifetime Specification (A117) at a specific junction temperature (TJ = 55°C) to guarantee a minimum of 10 years retention time. As part of this qualification procedure, the EEPROM memory is cycled to its specified endurance limit described above before data retention is characterized. This means that the EEPROM memory is guaranteed to retain its data for its full specified retention lifetime every time the EEPROM is reprogrammed. Note that retention lifetime based on an activation energy of 0.6 V derates with TJ, as shown in Figure 16. JUNCTION TEMPERATURE (°C) 250 300 100 200 150 50 0 50 60 70 80 90 100 40 110 120 Figure 16. Typical EEPROM Memory Retention |
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