Datasheet

MCP131X/2X
DS21985D-page 36  2005-2012 Microchip Technology Inc.
5.4 Modifying The Trip Point, V
TRIP
Although the MCP131X/2X device has a fixed voltage
trip point (V
TRIP
), it is sometimes necessary to make
custom adjustments. This can be accomplished by
connecting an external resistor divider to the
MCP131X/2X V
DD
pin. This causes the V
SOURCE
voltage to be at a higher voltage than when the
MCP131X/2X input equals its V
TRIP
voltage
(Figure 5-5).
To maintain detector accuracy, the bleeder current
through the divider should be significantly higher than
the 10 µA maximum operating current required by the
MCP131X/2X. A reasonable value for this bleeder
current is 1 mA (100 times the 10 µA required by the
MCP131X/2X). For example, if V
TRIP
= 2V and the
desired trip point is 2.5V, the value of R
1
+ R
2
is 2.5 k
(2.5V/1 mA). The value of R
1
+ R
2
can be rounded to
the nearest standard value and plugged into the
equation of Figure 5-5 to calculate values for R
1
and
R
2
. 1% tolerance resistors are recommended.
FIGURE 5-5: Modify Trip-Point using
External Resistor Divider.
5.5 MOSFET Low-Drive Protection
Low operating power and small physical size make the
MCP131X/2X series ideal for many voltage detector
applications. Figure 5-6 shows a low-voltage gate drive
protection circuit that prevents overheating of the logic-
level MOSFET due to insufficient gate voltage. When
the input signal is below the threshold of the
MCP131X/2X, its output grounds the gate of the
MOSFET.
FIGURE 5-6: MOSFET Low-Drive
Protection.
5.6 Low-Power Applications
In some low-power applications, the longer the micro-
controller (such as a PIC
®
MCU) can be in the “Sleep
mode”, the lower the average system current consump-
tion will be.
The WDT feature can be used to “wake-up” the PIC MCU
at a regular interval to service the required tasks before
returning to sleep. This “wake-up” occurs after the PIC
MCU detects a MCLR
reset during Sleep mode (for mid-
range family; POR
= 1, BOR = 1, TO = 1, and PD = 1).
Note: In this example, V
SOURCE
must be
greater than (V
TRIP
)
MCP131X/2X
V
DD
RST
V
SS
R
1
V
SOURCE
R
2
or RST
V
SOUR CE
R
1
R
1
R
2
+
--------------------
 V
TRIP

Where:
V
SOURCE
= Voltage to be monitored
V
TRIP
= Threshold Voltage setting
V
DD
RST
V
SS
MCP131X/2X
270
MTP3055EL
V
DD
R
L
V
TRIP