It is often necessary in complex designs to provide a sequence of reset pulses to different parts of a circuit to ensure the whole design functions reliably. The DS1830 from Maxim (www.maxim-ic.com) provides three sequenced open-drain reset outputs. This chip is designed for 5 V systems but a 3.3 V version (DS1830A) is also available. Both are offered in a range of package outlines including DIP, SO and µSOP. Two inputs give the chip some degree of programmability of its characteristics: The TOL input defines the chips tolerance to power supply fluctuations before a reset sequence is triggered.
Circuit diagram:
Reset Sequencer Circuit Diagram
| TOL | 5V | 3,3 V | TD | Tr1 | Tr2 | Tr3 |
| + Ub | Ub .0.95 | Ub .0.95 | 0 V | 10 ms | 50 ms | 100 ms |
| 0 V | Ub .0.90 | Ub .0.90 | Open | 20 ms | 100 ms | 200 ms |
| Open | Ub .0.85 | Ub .0.80 | + Ub | 50 ms | 250 ms | 500 ms |
Jumper JP1 allows the TOL to be connected to Ub (Vcc), ground or left open circuit and will result in the following three reset thresholds: The TD input allows the length of the reset signal to be programmed and jumper JP2 gives the following three possibilities: The PBRST (pushbutton reset) allows a manual reset button to be connected to the chip. This input has a built-in 40 k? pull up resistor and can also be driven by a digital output or used to cascade additional devices to provide more sequenced reset signals.
Author: Gregor Kleine Copyright: Elektor Electronics
