PIC18F2610ESLASHSOSQTP datasheet(234/376 Pages) MICROCHIP

234 / 376 page

PIC18F2X1X/4X1X

DS39636D-page 236

FIGURE 21-3:

HIGH-VOLTAGE DETECT OPERATION (VDIRMAG = 1)

21.5

Applications

In many applications, the ability to detect a drop below

or rise above a particular threshold is desirable. For

example, the HLVD module could be periodically

enabled to detect a Universal Serial Bus (USB) attach

or detach. This assumes the device is powered by a

lower voltage source than the USB when detached. An

attach would indicate a high-voltage detect from, for

example, 3.3V to 5V (the voltage on USB) and vice

versa for a detach. This feature could save a design a

few extra components and an attach signal (input pin).

For general battery applications, Figure 21-4 shows a

possible voltage curve. Over time, the device voltage

decreases. When the device voltage reaches voltage

VA, the HLVD logic generates an interrupt at time TA.

The interrupt could cause the execution of an ISR,

which would allow the application to perform “house-

keeping tasks” and perform a controlled shutdown

before the device voltage exits the valid operating

range at TB. The HLVD thus would give the application

a time window, represented by the difference between

TA and TB, to safely exit.

FIGURE 21-4:

TYPICAL

HIGH/LOW-VOLTAGE

DETECT APPLICATION

VLVD

VDD

HLVDIF

VLVD

VDD

Enable HLVD

TIVRST

HLVDIF may not be set

Enable HLVD

HLVDIF

HLVDIF cleared in software

HLVDIF cleared in software,

CASE 1:

CASE 2:

HLVDIF remains set since HLVD condition still exists

TIVRST

IRVST

Internal Reference is stable

IRVST

Time

VA = HLVD trip point

VB = Minimum valid device

operating voltage

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