What is the adjustable reset timeout period suitable for various applications?

Last Update Time: 2021-07-17 11:58:32

All three monitors include an adjustable reset timeout period tRST. When all inputs are above its threshold, the reset timer is started. During tRST, / RST is low, and as long as the time between transients is less than the reset timeout period, / RST will remain low. In other words, the reset timeout prevents power supply transients with a frequency higher than 1 / tRST from causing undesirable level shifts on the / RST output. Keeping / RST low during these power supply transients will suppress false resets.

The reset timeout period is adjustable to suit various microprocessor applications. The reset timeout period tRST is configured by connecting a capacitor CRT between the CRT pin and GND. The value of the capacitor is determined by the following formula:

C_ {RT} = t_ {RST} / 2MΩ = 500 (pF / ms) • t_ {RST}

Floating the CRT pin will generate a minimum reset timeout of approximately 25μs. The maximum reset timeout is limited by the maximum available low-leakage capacitor.

Additional interference filtering

Although all six comparators have built-in interference filter processing circuits, it is still recommended to add bypass capacitors on the V1 and V2 inputs. Since two bypass capacitors are added, the input with the higher voltage will act as the entire chip VCC. If necessary, additional filter capacitors can be added to the V3, V4, V5, and V6 inputs to suppress unwanted noise.

Open drain reset

The / RST output on the LTC2930, LTC2931, and LTC2932 is an open drain and contains a weak pull-up current source to the V2 voltage. This open drain structure provides many advantages. For example, these outputs can be externally pulled up to a voltage higher than V2 using a pull-up resistor. This facilitates the use of multiple devices operating at different I / O voltages. In addition, multiple open-drain outputs can be configured in a "wire OR" format (in which the outputs are connected together). Figure 6 shows two LTC2930 monitors with their open drain / RST outputs connected together and pulled up to 5V using a 10k pull-up resistor. If one / RST output is pulled low due to a reset process, it will sink current and pull the other output low.

Comparator output provides separate power supply monitoring and sequencing support

The real-time comparator output on the LTC2931 and LTC2932 is used to indicate the status of each input. Similar to the / RST output, the comparator output is also an open-drain and has a weak pull-up current source to V2.

When an undervoltage event occurs on any monitored power supply, the / RST output will be pulled low, however, a comparator output will only be pulled low when its paired input is below its threshold voltage. In a multi-voltage system, the ability to monitor the status of each power supply is useful. Here, it is important to know which power supply failed.

Each comparator output also provides power sequencing. Figure 7 shows the application of LTC2932 in a five-power-on sequencer. When an input reaches its threshold, the corresponding comparator output will be pulled high and the next DC / DC converter will be enabled.

 

If you want to know more, our website has product specifications for capacitor, you can go to ALLICDATA ELECTRONICS LIMITED to get more information