Datasheet LTC1921 (Analog Devices) - 7
| Manufacturer | Analog Devices |
| Description | Dual –48V Supply and Fuse Monitor |
| Pages / Page | 12 / 7 — APPLICATIO S I FOR ATIO. Supply Monitoring. Undervoltage Lockout. Fuse … |
| File Format / Size | PDF / 179 Kb |
| Document Language | English |
APPLICATIO S I FOR ATIO. Supply Monitoring. Undervoltage Lockout. Fuse Monitoring. Figure 1. Supply Comparison
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LTC1921
U U W U APPLICATIO S I FOR ATIO Supply Monitoring
Monitoring for each supply, VA and VB, is independent of The LTC1921 is designed to monitor dual – 48V power the condition of the other supply. The LTC1921 can be supplies. This is accomplished with precision window powered equally from either VA, VB or both supplies. This comparators and an accurate bandgap reference, as well allows the LTC1921 to provide correct information at its as internal level shifting circuitry. The comparators are outputs as long as at least one supply is functional, preset to standard voltage thresholds in order to accu- whether or not the fuses are intact (see Figure 2). rately verify the status of each supply. These comparators
Undervoltage Lockout
also include precision hysteresis which allows accurate determination of voltage recovery. Status of the two If both supplies are active and their magnitude falls below supplies are indicated by the OUT A and OUT B pins. 13V, or if only one supply is active and its magnitude falls below 19V, the LTC1921 will lock all outputs into a fault The supply window comparison works in a straightfor- condition by closing all three output switches. This state ward way (Figure 1). As long as each supply magnitude will be held until one supply magnitude is driven above remains in the valid supply window (38.5V to 70V), the 19V or both are driven above 13V. outputs will indicate a valid supply condition by exhibiting a high internal impedance. If a supply magnitude falls
Fuse Monitoring
below the undervoltage threshold (38.5V), then its respec- tive output will short internally (OUT A to OUT F or OUT B In addition to monitoring two supplies, the LTC1921 can to OUT A) until that supply reaches the undervoltage monitor the condition of two supply fuses via the FUSE A recovery threshold, which is preset to –43V. At this time, (Pin 2) and FUSE B (Pin 7) inputs. Fuse monitoring is the output will return to a high impedance state. If a supply accomplished by comparing the potential at FUSE A to the magnitude rises above the overvoltage threshold (70V), potential at supply VA and comparing the potential at then its respective output will short internally, just as with FUSE␣ B to the potential at supply VB. If VFUSEA is within the an undervoltage condition. The output will return to its specified voltage window around VA and VFUSEB is within nominal state when the supply overcomes the overvoltage the specified voltage window around VB, the OUT F pin will hysteresis. indicate that the fuses are intact by exhibiting a high TIME 0 NOMINAL UNDERVOLTAGE VOLTAGE FAULT –38.5 –43 –48 UNDERVOLTAGE RECOVERY –68.7 SUPPLY VOLTAGE (V) –70 OVERVOLTAGE RECOVERY OVERVOLTAGE FAULT 1921 F01
Figure 1. Supply Comparison
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U U W U APPLICATIO S I FOR ATIO Supply Monitoring
Monitoring for each supply, VA and VB, is independent of The LTC1921 is designed to monitor dual – 48V power the condition of the other supply. The LTC1921 can be supplies. This is accomplished with precision window powered equally from either VA, VB or both supplies. This comparators and an accurate bandgap reference, as well allows the LTC1921 to provide correct information at its as internal level shifting circuitry. The comparators are outputs as long as at least one supply is functional, preset to standard voltage thresholds in order to accu- whether or not the fuses are intact (see Figure 2). rately verify the status of each supply. These comparators
Undervoltage Lockout
also include precision hysteresis which allows accurate determination of voltage recovery. Status of the two If both supplies are active and their magnitude falls below supplies are indicated by the OUT A and OUT B pins. 13V, or if only one supply is active and its magnitude falls below 19V, the LTC1921 will lock all outputs into a fault The supply window comparison works in a straightfor- condition by closing all three output switches. This state ward way (Figure 1). As long as each supply magnitude will be held until one supply magnitude is driven above remains in the valid supply window (38.5V to 70V), the 19V or both are driven above 13V. outputs will indicate a valid supply condition by exhibiting a high internal impedance. If a supply magnitude falls
Fuse Monitoring
below the undervoltage threshold (38.5V), then its respec- tive output will short internally (OUT A to OUT F or OUT B In addition to monitoring two supplies, the LTC1921 can to OUT A) until that supply reaches the undervoltage monitor the condition of two supply fuses via the FUSE A recovery threshold, which is preset to –43V. At this time, (Pin 2) and FUSE B (Pin 7) inputs. Fuse monitoring is the output will return to a high impedance state. If a supply accomplished by comparing the potential at FUSE A to the magnitude rises above the overvoltage threshold (70V), potential at supply VA and comparing the potential at then its respective output will short internally, just as with FUSE␣ B to the potential at supply VB. If VFUSEA is within the an undervoltage condition. The output will return to its specified voltage window around VA and VFUSEB is within nominal state when the supply overcomes the overvoltage the specified voltage window around VB, the OUT F pin will hysteresis. indicate that the fuses are intact by exhibiting a high TIME 0 NOMINAL UNDERVOLTAGE VOLTAGE FAULT –38.5 –43 –48 UNDERVOLTAGE RECOVERY –68.7 SUPPLY VOLTAGE (V) –70 OVERVOLTAGE RECOVERY OVERVOLTAGE FAULT 1921 F01
Figure 1. Supply Comparison
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