DESCRIPCIÓN

The LTC1727 is a triple supply monitor intended for systems with multiple supply voltages. Each supply monitor has its own open-drain output for individual supply monitoring. A common open-drain reset output remains low until all three supplies have been in compliance for 200ms. Tight 1.5% accuracy specifications and glitch immunity ensure reliable reset operation without false triggering.The RST output is guaranteed to be in the correct state for VCC5/VCC25/VCC18 or VCC3 down to 1V. The LTC1727 may also be configured to monitor any one or two VCC inputs instead of three, depending on system requirements.Very low (10µA typical) supply current makes the LTC1727 ideal for power conscious systems. The LTC1727 is available in an 8-lead MSOP or SO package and the LTC1728 is available in a 5-lead SOT-23 package.

 

CARACTERÍSTICAS

Monitors Three Inputs Simultaneously

LTC1727-5: 5V, 3.3V and ADJ

±1.5% Threshold Accuracy Over Temperature

Very Low Supply Current: 10µA Typ

200ms Reset Time Delay

Active Low RESET Output

Power Supply Glitch Immunity

Guaranteed RESET for VCC3 ≥ 1V  or VCC5/VCC25/VCC18 ≥ 1V

LTC1727 Includes Monitor Output for Each Supply

LTC1727: 8-Lead MSOP and SO Packages

 

APLICACIONES

Desktop Computers

Notebook Computers

Intelligent Instruments

Portable Battery-Powered Equipment

Network Servers

 

INFORMACIÓN SOBRE APLICACIONES

Supply Monitoring

The LTC1727 is a low power, high accuracy triple supply monitoring circuit with three monitor outputs and a 200ms microprocessor reset output.All three VCC inputs must be above predetermined thresholds for reset not to be invoked. The LTC1727 will assert reset during power-up, power-down and brownout conditions on any one or all of the VCC inputs.

Power Detect.The LTC1727 is powered from the 3.3V/3V input pin (VCC3), the 1.8V input pin (VCC18), the 2.5V input pin (VCC25) or the 5V input pin (VCC5), whichever pin has the highest potential. This ensures the part pulls the RST pin low as soon as either input pin is ≥1V.

Power-Up

Upon power-up, either the VCC5/VCC25/VCC18 or VCC3 pin, can power the part. This ensures that RST will be low when either VCC5/VCC25/VCC18 or VCC3 reaches 1V. As long as any one of the VCC inputs is below its predetermined threshold, RST will stay a logic low. Once all of the VCC inputs rise above their thresholds, an internal timer is started and RST is released after 200ms.RST is reasserted whenever any one of the VCC inputs drops below its predetermined threshold and remains asserted until 200ms after all of the VCC inputs are above their thresholds.On the LTC1727, each of the comparator outputs will be low until the VCC input that is monitored by that comparator rises above the appropriate predetermined threshold. The COMP3, and COMP5/COMP25 outputs are guaranteed to be in the correct logic state for either VCC3 or VCC5/VCC25 greater than 1V. The COMPA output requires the internal bandgap reference to be valid before the correct logic state can be output. Therefore, the COMPA output will be held low until VCCA is above 1V and VCC3 or VCC5/VCC25 is greater than 2V (typ).

Power-Down

On power-down, once any of the VCC inputs drop below its threshold, RST is held at a logic low. A logic low of 0.3V is guaranteed until both VCC3 and VCC5/VCC25/VCC18 drop below 1V.

Glitch Immunity

The RST output of the LTC1727/LTC1728 have two forms of glitch immunity built in. First, the input monitors require the input voltage to transition at least 10% of the input threshold (0.1 • VRTH) below the input threshold for approximately 50µs in order to force the monitor output low. The duration of the transition must be longer for voltage transitions of lesser magnitude (see Figure 1). Secondly, the reset pulse width of approximately 200ms acts to debounce the RST output ensuring that the RST output will always be in the correct state.The individual monitor outputs of the LTC1727 do not have hysteresis and will track the monitor inputs relative to the monitor’s input threshold (VRTA, VRT25, VRT3 and VRT5). A very slow moving input voltage with ripple riding on it may cause the individual monitor outputs (COMPA, COMP25, COMP3 and COMP5) to toggle on the ripple as the input voltage passes the input threshold. The slow response time of the LTC1727’s input monitors has a tendency to integrate signals on the inputs improving their immunity to noise and ripple.