DS1830/A DS183 DS1830/A Reset Sequence Pushbutton www.maxim-ic.com FEATURES 5V (DS1830) or 3.3V (DS1830A) power-on PIN ASSIGNMENT reset Excellent for systems that need power-on resets in a consistent sequence Asserts resets during power transients Pushbutton reset input for system override Selectable reset timing Reduces need for discrete components Precision temperature-compensated voltage reference 8-pin DIP, 8-pin SO, or space saving 8-pin SOP Operating temperature of -40C to +85C Open-drain, active-low inputs PIN DESCRIPTION - Pushbutton Reset Input 1 PBRST 2 TD - Time Delay Select Input 3 TOL - V Tolerance Select Input CC 4 GND - Ground 8 V - Power Supply CC - Reset 1 Output 7 RST1 - Reset 2 Output 6 RST2 - Reset 3 Output 5 RST3 DESCRIPTION The DS1830 Reset Sequencer monitors the power supply for an in-tolerance condition and the pushbutton reset input for a manual reset. First a precision temperature-compensated reference and comparator circuit monitors the status of the power supply and when an out-of-tolerance condition is detected, an internal power fail signal is generated that forces the reset lines to go to an active state. If the power supply returns to an in-tolerance condition, RST1 will release followed by RST2 and finally RST3 . Sequencing of resets allows for systems to power-up in an orderly manner providing superior reliability. Note: Some revisions of this device may incorporate deviations from published specifications known as errata. Multiple revisions of any device may be simultaneously available through various sales channels. For information about device errata, click here: D1830/A OPERATION POWER MONITOR The DS1830 provides the functions of detecting out-of-tolerance conditions on a power supply and warning a processor based system of impending power failure. When V is detected as out-of-tolerance CC all reset outputs will be forced active. When V returns to a valid state, RST1 will remain active for CC period of time based on the condition of the TD input. Reset outputs RST2 and RST3 follow RST1 , each one at the proper delays for the condition of the TD input. All resets will remain in the inactive state (high) until the next V out-of-tolerance condition or pushbutton reset. On power-up all resets are kept CC active for an appropriate period determined by the status of the TD input after the power supply inputs have reached the selected tolerance. This allows the power supply and system power to stabilize before the reset sequences are released. BLOCK DIAGRAM Figure 1 OPERATION TOLERANCE SELECT The DS1830/A provides a TOL input for individual customization of the DS1830x to specific application requirements (see Table 1). For the tolerance selection, see Table 1 below. The TOL input is only sampled while V is below the lowest potential trip value and can not be changed after the V voltage CC CC exceeds the lowest potential trip value. TOL TOLERANCE SELECT Table 1 TOL 5V (DS1830) 3.3V (DS1830A) V 5% 5% CC GND 10% 10% OPEN 15% 20% (N.C.) 2 of 7