PIC18F2420-I/SOC01 Microchip, PIC18F2420-I/SOC01 Datasheet - Page 248

• Manufacturer Part Number: PIC18F2420-I/SOC01
• Description: 28 pin, 16 kb flash, 3804 ram, 25 i/o...
• Manufacturer: Microchip

PIC18F2420/2520/4420/4520
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 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
DS39631E-page 246
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
Advance Information
Internal Reference is Stable
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
1
A
B
)
= HLVD trip point
= Minimum valid device
TYPICAL LOW-VOLTAGE
DETECT APPLICATION
© 2008 Microchip Technology Inc.
operating voltage
Time
HLVDIF Cleared in Software
T
A
V
V
LVD
LVD
T
B