Datasheet LTC1921 (Analog Devices) - 8
| Hersteller | Analog Devices |
| Beschreibung | Dual –48V Supply and Fuse Monitor |
| Seiten / Seite | 12 / 8 — APPLICATIO S I FOR ATIO. Output Pins. SUPPLY A. SUPPLY B. STATUS. FUSE A. … |
| Dateiformat / Größe | PDF / 179 Kb |
| Dokumentensprache | Englisch |
APPLICATIO S I FOR ATIO. Output Pins. SUPPLY A. SUPPLY B. STATUS. FUSE A. FUSE B. FUSE STATUS. Figure 2
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LTC1921
U U W U APPLICATIO S I FOR ATIO
internal impedance to the return (RTN) pin. The applica- series, one for each output. In this configuration tion must be designed so that an open fuse condition will (Figure␣ 2), a diode connected between OUT F and RTN will force the fuse input (FUSE A or FUSE B) to be outside the indicate the condition of both fuses. A diode connected specified window around the supply pins, such as with a between OUT A and OUT F will indicate the condition of weak pull-up resistor to RTN, so that the LTC1921 can supply A (VA) and a diode connected between OUT B and properly indicate a fault at OUT F. If supply diodes that OUT A will indicate the condition of supply B (VB). A exhibit high reverse leakage, such as Schottky diodes, are resistor connected from OUT B to the negative supply is used, then the values of the pull-up resistors must be required to bias the diodes. The LTC1921 is designed to reduced accordingly. allow the current from this resistor to flow through the diodes during normal supply conditions and intact fuses, The FUSE A and FUSE B pins may also be used in and will shunt this current away from the proper diodes conjunction with VA and VB for simple window compari- during a fault condition. These diodes will further clamp son, provided that one of the circuit nodes to be compared the output pin potentials to RTN in order to keep the can provide the small amount of supply current required outputs within rated voltages. If LEDs are used instead of to bias the IC. The LTC1921 is ideally suited for compari- optoisolators, they should be green since they will be lit son functions in a circuit where only high supply voltages when the supplies are within the proper voltage range. are available. The LTC1921 may be connected in such a way as to OR
Output Pins
various outputs to allow the use of fewer optocouplers or The output pins in the LTC1921 are designed to shunt LEDs (Figures 3a and 3b). One and two diode circuits are external optoisolator diodes or LEDs during a supply or shown. fuse fault condition. Up to three diodes may be used in 47k –48V 5V RETURN FUSE STATUS R1 R2 100k 100k 3 MOC207
SUPPLY A SUPPLY B
RTN 47k
V V STATUS STATUS
1 4
A B
5V V OUT F A OK OK 0 0 SUPPLY A OK UV OR OV 0 1 STATUS 8 UV OR OV OK 1 0 VB UV OR OV UV OR OV 1 1 LTC1921 OK: WITHIN SPECIFICATION MOC207 2 OV: OVERVOLTAGE FUSE A 47k UV: UNDERVOLTAGE 5V 7 5 FUSE B OUT A
V V FUSE A FUSE B FUSE STATUS
SUPPLY B STATUS = V = V 0 A B = VA ≠ V 1 B ≠ V = V 1 A B MOC207 ≠ VA ≠ V 1* 6 B OUT B R3 0: LED/PHOTODIODE ON 47k 1: LED/PHOTODIODE OFF F1 D1 1/4W *IF BOTH FUSES (F1 AND F2) ARE OPEN, SUPPLY A –48V OUT ALL STATUS OUTPUTS WILL BE HIGH –48V SINCE R3 WILL NOT BE POWERED F2 D2 SUPPLY B = LOGIC COMMON 1921 F02 –48V
Figure 2.
1921f 8
U U W U APPLICATIO S I FOR ATIO
internal impedance to the return (RTN) pin. The applica- series, one for each output. In this configuration tion must be designed so that an open fuse condition will (Figure␣ 2), a diode connected between OUT F and RTN will force the fuse input (FUSE A or FUSE B) to be outside the indicate the condition of both fuses. A diode connected specified window around the supply pins, such as with a between OUT A and OUT F will indicate the condition of weak pull-up resistor to RTN, so that the LTC1921 can supply A (VA) and a diode connected between OUT B and properly indicate a fault at OUT F. If supply diodes that OUT A will indicate the condition of supply B (VB). A exhibit high reverse leakage, such as Schottky diodes, are resistor connected from OUT B to the negative supply is used, then the values of the pull-up resistors must be required to bias the diodes. The LTC1921 is designed to reduced accordingly. allow the current from this resistor to flow through the diodes during normal supply conditions and intact fuses, The FUSE A and FUSE B pins may also be used in and will shunt this current away from the proper diodes conjunction with VA and VB for simple window compari- during a fault condition. These diodes will further clamp son, provided that one of the circuit nodes to be compared the output pin potentials to RTN in order to keep the can provide the small amount of supply current required outputs within rated voltages. If LEDs are used instead of to bias the IC. The LTC1921 is ideally suited for compari- optoisolators, they should be green since they will be lit son functions in a circuit where only high supply voltages when the supplies are within the proper voltage range. are available. The LTC1921 may be connected in such a way as to OR
Output Pins
various outputs to allow the use of fewer optocouplers or The output pins in the LTC1921 are designed to shunt LEDs (Figures 3a and 3b). One and two diode circuits are external optoisolator diodes or LEDs during a supply or shown. fuse fault condition. Up to three diodes may be used in 47k –48V 5V RETURN FUSE STATUS R1 R2 100k 100k 3 MOC207
SUPPLY A SUPPLY B
RTN 47k
V V STATUS STATUS
1 4
A B
5V V OUT F A OK OK 0 0 SUPPLY A OK UV OR OV 0 1 STATUS 8 UV OR OV OK 1 0 VB UV OR OV UV OR OV 1 1 LTC1921 OK: WITHIN SPECIFICATION MOC207 2 OV: OVERVOLTAGE FUSE A 47k UV: UNDERVOLTAGE 5V 7 5 FUSE B OUT A
V V FUSE A FUSE B FUSE STATUS
SUPPLY B STATUS = V = V 0 A B = VA ≠ V 1 B ≠ V = V 1 A B MOC207 ≠ VA ≠ V 1* 6 B OUT B R3 0: LED/PHOTODIODE ON 47k 1: LED/PHOTODIODE OFF F1 D1 1/4W *IF BOTH FUSES (F1 AND F2) ARE OPEN, SUPPLY A –48V OUT ALL STATUS OUTPUTS WILL BE HIGH –48V SINCE R3 WILL NOT BE POWERED F2 D2 SUPPLY B = LOGIC COMMON 1921 F02 –48V
Figure 2.
1921f 8