The LTC1921 monitors two independent -48V supplies, including their fuses, and drives up to three optoisolators to indicate status, in accordance with standard backplane specifications. It features dual supply overvoltage and undervoltage detection circuits, and can ignore fast supply transients to eliminate false detection. The LTC1921 operates from -10V to -80V with a typical power dissipation of less than 10mW. It is available in an 8-pin MSOP package.
The LTC1921 is a dual -48 V supply and fuse monitor designed for telecom and networking backplanes. It provides independent monitoring of two supplies, detects undervoltage, overvoltage, and fuse conditions, and drives up to three optoisolators or LEDs.
The device operates from -10 V to -80 V, tolerates supply reversals, and includes built‑in comparators, a bandgap reference, and precision hysteresis. Typical applications show how the monitor can be used to indicate supply status and fuse integrity with simple external components.
| Supply Voltage Range | -10 V to -80 V |
|---|---|
| Undervoltage Threshold | -39.5 V to -37.5 V |
| Overvoltage Threshold | -71.5 V to -68.5 V |
| Input Resistance (Fuse A/B) | 11 MΩ |
| Package | 8‑Lead Plastic MSOP |
| Operating Temperature Range | -40 °C to 85 °C |
| Maximum Junction Temperature | 150 °C |
It monitors supplies from –10 V to –80 V, with a specified voltage window of 38.5 V to 70 V for normal operation.
The OUT F pin (Pin 4) goes low when either fuse voltage is outside its valid window, signalling a fuse open condition.