Datasheet

MCP2122
DS21894C-page 6 Preliminary © 2007 Microchip Technology Inc.
2.3.1 BROWN-OUTS
Some applications may subject the MCP2122 to a
brown-out condition. Good design practice requires
that when a system is in brown-out, the system should
be in reset to ensure that the system is in a known
state when the system exits the brown-out. This
brown-out circuitry is external to the MCP2122.
2.3.1.1 External Brown-Out Reset Circuits
Figure 2-2 shows a circuit for external brown-out
protection using the TCM809 device.
Figure 2-3 and Figure 2-4 illustrate two examples of
external circuitry that may be implemented. Each
option needs to be evaluated to determine if they
satisfy the requirements of the application.
FIGURE 2-2: EXTERNAL BROWN-OUT
PROTECTION USING THE
TCM809
FIGURE 2-3: EXTERNAL BROWN-OUT
PROTECTION CIRCUIT 1
FIGURE 2-4: EXTERNAL BROWN-OUT
PROTECTION CIRCUIT 2
VSS
RST
TCM809
VDD
MCP2122
VDD
RESET
Note 1: Resistors should be adjusted for the
characteristics of the transistor.
2: This circuit will activate reset when
V
DD goes below (Vz + 0.7V),
where Vz = Zener voltage.
VDD
33 kΩ
10 k
Ω
40 kΩ
V
DD
RESET
MCP2122
Q1
R2
40 kΩ
V
DD
RESET
MCP2122
R1
Q1
VDD
Note 1: This circuit is less expensive, but
less accurate. Transistor Q1 turns
off when V
DD is below a certain level
such that:
2: Resistors should be adjusted for the
characteristics of the transistor.
V
DD •
R1
R1 + R2
= 0.7V