Microchip Technology ARD00385 Data Sheet

DS39957D-page 404

 2009-2011 Microchip Technology Inc.

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, 

 shows a

possible voltage curve. Over time, the device voltage
decreases. When the device voltage reaches voltage,
V

A

, the HLVD logic generates an interrupt at time, T

A

.

The interrupt could cause the execution of an ISR
(Interrupt Service Routine), which would allow the
application to perform “housekeeping tasks” and a
controlled shutdown before the device voltage exits the
valid operating range at T

B

. This would give the appli-

cation a time window, represented by the difference
between T

A

 and T

B

, to safely exit.

V

HLVD

V

DD

HLVDIF

V

HLVD

V

DD

Enable HLVD

T

IRVST

HLVDIF May Not be Set

Enable HLVD

HLVDIF

HLVDIF Cleared in Software

HLVDIF Cleared in Software

HLVDIF Cleared in Software, 

HLVDIF remains Set since HLVD Condition still Exists

T

IRVST

IRVST

Internal Reference is Stable

Internal Reference is Stable

IRVST

V

A

 = HLVD trip point

V

B

 = Minimum valid device

         operating voltage