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ADM1068ACP-REEL Fiches technique(PDF) 11 Page - Analog Devices |
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ADM1068ACP-REEL Fiches technique(HTML) 11 Page - Analog Devices |
11 / 28 page Preliminary Technical Data ADM1068 Rev. PrB | Page 11 of 28 INPUTS SUPPLY SUPERVISION The ADM1068 has eight programmable inputs. Four of these are dedicated supply fault detectors (SFDs). These dedicated inputs are called VH and VP1–3 by default. The other four inputs are labeled VX1–VX4 and have dual functionality. They can be used as either supply fault detectors, with similar functionality to VH and VP1–3, or CMOS/TTL-compatible logic inputs to the devices. Therefore, the ADM1068 can have up to eight analog inputs, a minimum of four analog inputs and four digital inputs, or a combination. If an input is used as an analog input, it cannot be used as a digital input. Therefore, a configuration requiring eight analog inputs has no digital inputs available. Table 5 shows the details of each of the inputs. + – + – UV COMPARATOR VREF FAULT TYPE SELECT OV COMPARATOR FAULT OUTPUT GLITCH FILTER VPn MID LOW RANGE SELECT ULTRA LOW Figure 15. Supply Fault Detector Block PROGRAMMING THE SUPPLY FAULT DETECTORS The ADM1068 has up to eight supply fault detectors (SFDs) on its eight input channels. These highly programmable reset generators enable the supervision of up to eight supply voltages. The supplies can be as low as 0.573 V and as high as 14.4 V. The inputs can be configured to detect an undervoltage fault (the input voltage droops below a preprogrammed value), an overvoltage fault (the input voltage rises above a preprogrammed value) or an out-of-window fault (undervoltage or overvoltage). The thresholds can be programmed to an 8-bit resolution in registers provided in the ADM1068. This translates to a voltage resolution that is dependent on the range selected. The resolution is given by Step Size = Threshold Range/255 Therefore, if the high range is selected on VH, the step size can be calculated as follows: (14.4 V − 4.8 V)/255 = 37.6 mV Table 4 lists the upper and lower limit of each available range, the bottom of each range (VB), and the range itself (VR). Table 4. Voltage Range Limits Voltage Range (V) VB (V) VR (V) 0.573 to 1.375 0.573 0.802 1.25 to 3.00 1.25 1.75 2.5 to 6.0 2.5 3.5 4.8 to 14.4 4.8 9.6 The threshold value required is given by VT = (VR × N)/255 + VB where: VT is the desired threshold voltage (UV or OV). VR is the voltage range. N is the decimal value of the 8-bit code. VB is the bottom of the range. Reversing the equation, the code for a desired threshold is given by N = 255 × (VT − VB)/VR For example, if the user wants to set a 5 V OV threshold on VP1, the code to be programmed in the PS1OVTH register (discussed in the AN-698 application note) is given by N = 255 × (5 − 2.5)/3.5 Therefore, N = 182 (1011 0110 or 0xB6). Table 5. Input Functions, Thresholds, and Ranges Input Function Voltage Range (V) Maximum Hysteresis Voltage Resolution (mV) Glitch Filter (µs) VH High V Analog Input 2.5–6.0 425 mV 13.7 0–100 4.8–14.4 1.16 V 37.6 0–100 VPn Positive Analog Input 0.573–1.375 97.5 mV 3.14 0–100 1.25–3.00 212 mV 6.8 0–100 2.5–6.0 425 mV 13.7 0–100 VXn High Z Analog Input 0.573–1.375 97.5 mV 3.14 0–100 Digital Input 0–5 N/A N/A 0–100 |
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