MCP2155 datasheet(6/34 Pages) MICROCHIP

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MCP2122

DS21894B-page 6

Preliminary

 2004 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

VDD goes below (Vz + 0.7V),

where Vz = Zener voltage.

VDD

33 k

Ω

10 k

Ω

40 k

Ω

VDD

RESET

MCP2122

40 k

Ω

VDD

RESET

MCP2122

VDD

Note 1: This circuit is less expensive, but

less accurate. Transistor Q1 turns

off when VDD is below a certain level

such that:

2: Resistors should be adjusted for the

characteristics of the transistor.

VDD •

R1 + R2

= 0.7V

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