PIC18F2221 MICROCHIP [Microchip Technology], PIC18F2221 Datasheet - Page 252

• Manufacturer Part Number: PIC18F2221
• Description: 28/40/44-Pin Enhanced Flash Microcontrollers with 10-Bit A/D and nanoWatt Technology
• Manufacturer: MICROCHIP [Microchip Technology]

PIC18F4321 FAMILY
FIGURE 22-3:
22.5
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 22-4 shows a
possible voltage curve. Over time, the device voltage
decreases. When the device voltage reaches voltage
V
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 T
tion a time window, represented by the difference
between T
DS39689E-page 250
A
, the HLVD logic generates an interrupt at time T
CASE 1:
CASE 2:
Enable HLVD
Enable HLVD
Applications
A
B
. The HLVD, thus, would give the applica-
and T
HLVDIF
HLVDIF
IRVST
IRVST
V
V
B
DD
DD
, to safely exit.
HIGH-VOLTAGE DETECT OPERATION (VDIRMAG =
HLVDIF may not be set
Internal Reference is stable
Internal Reference is stable
Preliminary
T
T
IRVST
IRVST
A
.
HLVDIF cleared in software,
HLVDIF remains set since HLVD condition still exists
FIGURE 22-4:
V
V
A
B
Legend:
HLVDIF cleared in software
V
V
A
B
1
= HLVD trip point
= Minimum valid device
)
TYPICAL LOW-VOLTAGE
DETECT APPLICATION
© 2007 Microchip Technology Inc.
operating voltage
Time
HLVDIF cleared in software
T
A
V
V
LVD
LVD
T
B