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ADM1069ACPZ Datasheet(PDF) 15 Page - Analog Devices |
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ADM1069ACPZ Datasheet(HTML) 15 Page - Analog Devices |
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15 / 32 page  ADM1069 Rev. C | Page 15 of 32 The hysteresis value is given by VHYST = VR × NTHRESH/255 where: VHYST is the desired hysteresis voltage. NTHRESH is the decimal value of the 5-bit hysteresis code. Note that NTHRESH has a maximum value of 31. The maximum hysteresis for the ranges is listed in Table 6. INPUT GLITCH FILTERING The final stage of the SFDs is a glitch filter. This block provides time-domain filtering on the output of the SFD comparators, which allows the user to remove any spurious transitions such as supply bounce at turn-on. The glitch filter function is in addition to the digitally programmable hysteresis of the SFD comparators. The glitch filter timeout is programmable up to 100 μs. For example, when the glitch filter timeout is 100 μs, any pulse appearing on the input of the glitch filter block that is less than 100 μs in duration is prevented from appearing on the output of the glitch filter block. Any input pulse that is longer than 100 μs appears on the output of the glitch filter block. The output is delayed with respect to the input by 100 μs. The filtering process is shown in Figure 23. t0 tGF t0 tGF t0 tGF t0 tGF INPUT INPUT PULSE SHORTER THAN GLITCH FILTER TIMEOUT INPUT PULSE LONGER THAN GLITCH FILTER TIMEOUT OUTPUT PROGRAMMED TIMEOUT PROGRAMMED TIMEOUT INPUT OUTPUT Figure 23. Input Glitch Filter Function SUPPLY SUPERVISION WITH VXx INPUTS The VXx inputs have two functions. They can be used as either supply fault detectors or digital logic inputs. When selected as analog (SFD) inputs, the VXx pins have functionality that is very similar to the VH and VPx pins. The primary difference is that the VXx pins have only one input range: 0.573 V to 1.375 V. Therefore, these inputs can directly supervise only the very low supplies. However, the input impedance of the VXx pins is high, allowing an external resistor divide network to be connected to the pin. Thus, potentially any supply can be divided down into the input range of the VXx pin and supervised. This enables the ADM1069 to monitor other supplies, such as +24 V, +48 V, and −5 V. An additional supply supervision function is available when the VXx pins are selected as digital inputs. In this case, the analog function is available as a second detector on each of the dedi- cated analog inputs, VPx and VH. The analog function of VX1 is mapped to VP1, VX2 is mapped to VP2, and so on. VX4 is mapped to VH. In this case, these SFDs can be viewed as secondary or warning SFDs. The secondary SFDs are fixed to the same input range as the primary SFDs. They are used to indicate warning levels rather than failure levels. This allows faults and warnings to be gener- ated on a single supply using only one pin. For example, if VP1 is set to output a fault when a 3.3 V supply drops to 3.0 V, VX1 can be set to output a warning at 3.1 V. Warning outputs are available for readback from the status registers. They are also OR’ed together and fed into the SE, allowing warnings to generate interrupts on the PDOs. Therefore, in this example, if the supply drops to 3.1 V, a warning is generated, and remedial action can be taken before the supply drops out of tolerance. VXx PINS AS DIGITAL INPUTS As discussed in the Supply Supervision with VXX Inputs section, the VXx input pins on the ADM1069 have dual functionality. The second function is as a digital logic input to the device. Therefore, the ADM1069 can be configured for up to four digital inputs. These inputs are TTL-/CMOS-compatible. Standard logic signals can be applied to the pins: RESET from reset generators, PWRGD signals, fault flags, manual resets, and so on. These signals are available as inputs to the SE and, therefore, can be used to control the status of the PDOs. The inputs can be configured to detect either a change in level or an edge. When configured for level detection, the output of the digital block is a buffered version of the input. When configured for edge detection, a pulse of programmable width is output from the digital block once the logic transition is detected. The width is programmable from 0 μs to 100 μs. The digital blocks feature the same glitch filter function that is available on the SFDs. This enables the user to ignore spurious transitions on the inputs. For example, the filter can be used to debounce a manual reset switch. When configured as digital inputs, each VXx pin has a weak (10 μA) pull-down current source available for placing the input into a known condition, even if left floating. The current source, if selected, weakly pulls the input to GND. DETECTOR VXx (DIGITAL INPUT) GLITCH FILTER VREF = 1.4V TO SEQUENCING ENGINE + – Figure 24. VXx Digital Input Function |
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