PIC18F23K22-ESLASHML datasheet(346/496 Pages) MICROCHIP

346 / 496 page

PIC18(L)F2X/4XK22

DS41412C-page 346

Preliminary

 2010 Microchip Technology Inc.

FIGURE 23-3:

HIGH-VOLTAGE DETECT OPERATION (VDIRMAG = 1)

23.5

Applications

In many applications, it is desirable to detect a drop

below, or rise above, a particular voltage threshold. For

example, the HLVD module could be periodically

enabled to detect 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 23-4 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 a controlled shutdown before the

device voltage exits the valid operating range at TB.

This would give the application a time window,

represented by the difference between TA and TB, to

safely exit.

FIGURE 23-4:

TYPICAL LOW-VOLTAGE

DETECT APPLICATION

VHLVD

VDD

HLVDIF

VHLVD

VDD

Enable HLVD

TIRVST

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

TIRVST

IRVST

Internal Reference is stable

IRVST

Time

VA = HLVD trip point

VB = Minimum valid device

operating voltage

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PIC18F23K22-E/ML Datasheet(PDF) 346 Page - Microchip Technology

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