TC1270ASCVRCTR datasheet(24/40 Pages) MICROCHIP

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TC1270A/70AN/71A

DS22035B-page 24

5.4

Modifying The Trip Point, VTRIP

Although the TC127XA device has a fixed voltage trip

point (VTRIP), it is sometimes necessary to make

custom adjustments. This can be accomplished by

connecting an external resistor divider to the TC127XA

VDD pin. This causes the VSOURCE voltage to be at a

higher voltage than when the TC127XA input equals

it’s 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 kΩ (2.5V/1 mA). The

value of R1 + R2 can be rounded to the nearest stan-

dard value and plugged into the equation of Figure 5-5

to calculate values for R1 and R2. 1% tolerance resis-

tors 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

TC1270AN 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

TC1270AN, its output grounds the gate of the

MOSFET.

FIGURE 5-6:

MOSFET Low-Drive

Protection.

TC127XA

VDD

RST

VSS

VSOURCE

or RST

SOURCE

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

TRIP

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

Ω (1)

MTP3055EL

VDD

VTRIP

Note 1:

This resistance needs to be properly

sized for the selected Trip point voltage

related to the VOL operation.

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