DS1846 Просмотр технического описания (PDF) - Maxim Integrated

Номер в каталоге

Компоненты Описание

производитель

DS1846

NV Tri-Potentiometer, Memory, and MicroMonitor

Maxim Integrated 

DEVICE OPERATION

DS1846

Power Monitor

The DS1846 detects out-of-tolerance power-supply conditions and warns a processor-based system of an

impending power failure. When VCC falls below the minimum VCC tolerance, a comparator asserts the

RST and RST signals. On power-up, RST and RST are kept active for a minimum of tRST to allow the

power supply and processor to stabilize.

Pushbutton Reset

The DS1846 provides an input pin for direct connection to a pushbutton reset (see Figure 4). The

pushbutton reset input requires an active-low signal. Internally, this input is debounced and timed such

that RST and RST signals of at least tRST minimum are generated. The tRST delay commences as the

pushbutton reset input is released from the low level. The pushbutton can be initiated by connecting the

NMI output to the PBRST input as shown in Figure 4.

Nonmaskable Interrupt

The DS1846 generates a nonmaskable interrupt ( NMI ) for early warning of a power failure. A precision

comparator monitors the voltage level at the IN pin relative to an on-chip reference generated by an

internal bandgap. The IN pin is a high-impedance input allowing for a user-defined sense point. An

external resistor voltage-divider network (Figure 4) is used to set a trip point. This sense point may be

derived from a regulated supply or from a higher DC voltage level closer to the main system power input.

With the IN trip point, VTP, the proper values for R1 and R2 can be determined by the equation as shown

in Figure 4. Proper operation of the DS1846 requires that the voltage at the IN pin be limited to VCC.

Therefore, the maximum allowable voltage at the supply being monitored (VMAX) can also be derived as

shown in Figure 4. A simple approach to solving the equation is to select a value for R2 high enough to

keep power consumption low, and solve for R1. The flexibility of the IN input pin allows for detection of

power loss at the earliest point in a power-supply system, maximizing the amount of time for system

shut-down between NMI and RST/ RST .

When the supply being monitored decays to the voltage sense point, the DS1846 pulses the NMI output

to the active state for a minimum tNMI. During a power-up, any detected IN pin levels below VTP by the

comparator are disabled from generating an interrupt until VCC rises to VCCTP. As a result, any potential

NMI pulse is not initiated until VCC reaches VCCTP.

Connecting NMI to PBRST allows the nonmaskable interrupt to generate an automatic reset when an out-

of-tolerance condition occurred in a monitored supply. An example is shown in Figure 4.

10 of 18

Share Link: