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ADM1068 Datenblatt(PDF) 11 Page - Analog Devices |
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ADM1068 Datenblatt(HTML) 11 Page - Analog Devices |
11 / 24 page ADM1068 Rev. C | Page 11 of 24 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 VPx (VP1 to VP3) by default. The other four inputs are labeled VXx (VX1 to VX4) and have dual functionality. They can be used either as SFDs, with functionality similar to the VH and VPx, or as CMOS-/TTL-compatible logic inputs to the device. Therefore, the ADM1068 can have up to eight analog inputs, a minimum of four analog inputs and four digital inputs, or a combination thereof. 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 available digital inputs. Table 6 shows the details of each input. PROGRAMMING THE SUPPLY FAULT DETECTORS The ADM1068 can have up to eight 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 drops below a preprogrammed value), an overvoltage fault (the input voltage rises above a preprogrammed value), or an out-of-window fault (the input voltage is outside a preprogrammed range). The thresh- olds 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 − 6.0 V)/255 = 32.9 mV Table 5 lists the upper and lower limits of each available range, the bottom of each range (VB), and the range itself (VR). Table 5. 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 6.0 to 14.4 6.0 8.4 The threshold value required is given by VT = (VR × N)/255 + VB where: VT is the desired threshold voltage (undervoltage or overvoltage). 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 overvoltage threshold on VP1, the code to be programmed in the PS1OVTH register (as discussed in the AN-721 Application Note at www.analog.com) is given by N = 255 × (5 − 2.5)/3.5 Therefore, N = 182 (1011 0110 or 0xB6). INPUT COMPARATOR HYSTERESIS The UV and OV comparators shown in Figure 15 are always monitoring VPx. To avoid chatter (multiple transitions when the input is very close to the set threshold level), these comparators have digitally programmable hysteresis. The hysteresis can be programmed up to the values shown in Table 6. + – + – UV COMPARATOR VREF FAULT TYPE SELECT OV COMPARATOR FAULT OUTPUT GLITCH FILTER VPx MID LOW RANGE SELECT ULTRA LOW Figure 15. Supply Fault Detector Block The hysteresis is added after a supply voltage goes out of tolerance. Therefore, the user can program the amount above the undervoltage threshold to which the input must rise before an undervoltage fault is deasserted. Similarly, the user can program the amount below the overvoltage threshold to which an input must fall before an overvoltage fault is deasserted. Table 6. Input Functions, Thresholds, and Ranges Input Function Voltage Range (V) Maximum Hysteresis Voltage Resolution (mV) Glitch Filter (μs) VH High Voltage Analog Input 2.5 to 6.0 425 mV 13.7 0 to 100 6.0 to 14.4 1.02 V 32.9 0 to 100 VPx Positive Analog Input 0.573 to 1.375 97.5 mV 3.14 0 to 100 1.25 to 3.00 212 mV 6.8 0 to 100 2.5 to 6.0 425 mV 13.7 0 to 100 VXx High-Z Analog Input 0.573 to 1.375 97.5 mV 3.14 0 to 100 Digital Input 0 to 5.0 N/A N/A 0 to 100 |
Ähnliche Teilenummer - ADM1068_15 |
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Ähnliche Beschreibung - ADM1068_15 |
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