TC1270AMAVRCTR datasheet(23/42 Pages) MICROCHIP

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DS20002035F-page 23

TC1270A/70AN/71A

5.4

Modifying The Trip Point, VTRIP

Although the TC127XA device has a fixed voltage trip

point (VTRIP), it can be necessary to make custom

adjustments. This is accomplished by connecting an

external resistor divider to the TC127XA VDD pin. This

causes the VSOURCE voltage to be higher than it is

when the TC127XA input equals its VTRIP voltage

(Figure 5-5).

To maintain detector accuracy, the bleeder current

through the divider should be significantly higher than

the 15 µA maximum operating current required by the

TC127XA. A reasonable value for this bleeder current

is 1 mA (67 times the 10 µA required by the TC127XA).

For example, if VTRIP = 2V and the desired trip point is

2.5V, the value of R1 + R2 is 2.5 k (2.5V/1 mA). The

value of R1 + R2 can be rounded to the nearest

standard value and plugged into the equation shown in

Figure 5-5 to calculate values for R1 and R2.

1% tolerance resistors are recommended.

FIGURE 5-5:

Modifying Trip-Point using

External Resistor Divider.

5.5

MOSFET Low-Drive Protection

Low operating power and small physical size make the

TC1270AN series ideal for many voltage detector

applications. Figure 5-6 shows a low-voltage gate drive

protection circuit that prevents the logic-level MOSFET

from overheating due to insufficient gate voltage. When

the input signal is below the threshold of the

TC1270AN, its output grounds the gate of the

MOSFET.

FIGURE 5-6:

MOSFET Low-Drive

Protection.

TC127XA

VDD

RST

VSS

VSOURCE

or RST

VSOURCE

R1 R2

--------------------



VTRIP



Where:

Note: In this example, VSOURCE must be greater

than VTRIP.

VSOURCE = Voltage to be monitored

VTRIP = Threshold Voltage setting

VDD

RST

VSS

TC1270AN

270

(1)

MTP3055EL

VDD

VTRIP

Note 1: This resistance should be sized appro-

priately for the selected trip point volt-

age related to the VOL operation.

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