TC1270A Datasheet, PDF (24/40 Pages) Microchip Technology – Voltage Supervisor with Manual Reset Input

TC1270A/70AN/71A
5.4 Modifying The Trip Point, V_TRIP
Although the TC127XA 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 TC127XA
V_DD pin. This causes the V_SOURCE voltage to be at a
higher voltage than when the TC127XA input equals
it’s V_TRIP 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 V_TRIP = 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.
V_SOURCE
R₂
V_{DD TC127XA RST}
or RST
R₁
V_SS
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.
V_{TRIP 270Ω (1)}
V_DD
RST
TC1270AN
V_DD
R_L
MTP3055EL
V_SS
Note 1: This resistance needs to be properly
sized for the selected Trip point voltage
related to the V_OL operation.
FIGURE 5-6:
Protection.
MOSFET Low-Drive
Where:
× VSOURCE
-------^R----1--------
R₁ + R₂
=
VTRIP
V_SOURCE = Voltage to be monitored
V_TRIP = Threshold Voltage setting
Note: In this example, V_SOURCE must be
greater than (V_TRIP).
FIGURE 5-5:
Modify Trip-Point using
External Resistor Divider.
DS22035B-page 24
© 2007 Microchip Technology Inc.