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DS00779A-page 1
© 2001 Microchip Technology, Inc.
Using the Microchip TC54 Voltage Detector
TC54 AS A MICROCONTROLLER
RESET GENERATOR
Reset generators external to the microcontroller are necessary in
systems that have slowly rising power supplies. It is necessary to
hold the microcontroller in its reset state until the power supply has
reached a valid operating level. Commonly used simple Schmitt
trigger/capacitor circuits are inadequate since they do not
accurately monitor the power supply voltage tolerance. The TC54
series overcomes this problem with precise voltage detection.
Figure 2 shows a reset circuit using a TC54 replacing bipolar
integrated voltage detectors (see Table 1).
FIGURE 1: TC54 block diagram and timing.
FIGURE 2: Microcontroller reset circuit using TC54.
INTRODUCTION
Microchip's TC54 series of voltage detectors are designed to
supersede a variety of discrete comparator circuits and bipolar
technology voltage detectors.
These voltage detectors are especially suited for application in
battery powered systems because of their extremely low 1µA
operating current. Each part is laser programmed to the desired trip
point voltage over the range of 1.1V to 6.0V in 100mV steps. For
complete design flexibility, complementary or open-drain output
versions are available. TC54 package options include surface
mount SOT-23A and SOT-89 or through-hole TO-92 types.
OPERATION
The TC54 equivalent circuit is shown in Figure 1. The internal
precision temperature-compensated reference and comparator
circuit consistently monitor VIN for an under-voltage condition.
When such a condition occurs, the output is forced to the active
(LOW) state and remains there until VIN is once again within
tolerance. As shown in the timing diagram of Figure 1, the output
is forced active when VIN < (–VDET) (Where (–VDET) is the threshold
voltage) and returns HIGH when VIN exceeds (–VDET) plus 5%
hysteresis (example: if (–VDET) = 2.0V, the output will go HIGH
when VIN > 2.1V).
VOUT
TC54VC only
1
3
2
VSS
VIN
VREF
+
–
Input Voltage
Detect Voltage (–V
DET
)
Minimum Operating Voltage
Ground Level
Hysteresis
Voltage
Output Voltage
Release
Voltage
(+V
DET
)
Ground Level
TC54VC
V
IN
V
OUT
V
IN
V
SS
PIC
Microcontroller
R
100
MCLR
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© 2001 Microchip Technology, Inc.
DS00779A-page 2
( )
R1
R1 + R2
Figure 3: Modify trip point of TC54 using external resistor divider.
Table 1: TC54 cross reference listing.
MICROCHIP
MFGR PART# MICROCHIP # DESCRIPTION ATTRIBUTE
Motorola MC33064P-5 TC54VN4502EZB 4.5V trip, –40 to +85C, TO-92 500 times less power
Motorola MC34064P-5 TC54VN4502EZB 4.5V trip, 0 to +70C, TO-92 500 times less power
Motorola MC34164P-3 TC54VN2702EZB 2.7V trip, 0 to +70C, TO-92 10 times less power
Motorola MC34164P-5 TC54VN4302EZB 4.3V trip, 0 to +70C, TO-92 10 times less power
Motorola MC33164P-3 TC54VN2702EZB 2.7V trip, –40 to +85C, TO-92 10 times less power
Motorola MC33164P-5 TC54VN4302EZB 4.3V trip, –40 to +85C, TO-92 10 times less power
T.I. TL7757ILP TC54VN4502EZB 4.5V trip, –40 to +85C, TO-92 2000 times less power
T.I. TL7757CLP TC54VN4502EZB 4.5V trip, 0 to +70C, TO-92 2000 times less power
MODIFYING THE TRIP POINT, –VDET
Although the TC54 has a pre-programmed –VDET, it is sometimes
necessary to make adjustments during prototyping. This can be
accomplished by connecting an external resistor divider to a TC54
which has a –VDET lower than that of VSOURCE (Figure 3).
To maintain detector accuracy, the bleeder current through the
divider should be significantly higher than the 1µA operating
current required by the TC54. A reasonable value for this bleeder
current is 100µA (100 times the 1µA required by the TC54). For
example, if –VDET = 2V and the desired trip point is 2.5V, the value
of R1 + R2 is 25kΩ (2.5V/100µA). The value of R1 + R2 can be
rounded to the nearest standard value and plugged into the
equation of Figure 3 to calculate values for R1 and R2. 1%
tolerance resistors are recommended.
TC54
VIN VOUT
VSS
R1
VSOURCE
R2
VSOURCE = (–VDET)
Where:
VSOURCE = Voltage to be monitored
(–VDET) = Threshold Voltage Setting of TC54
Note: In this example, VSOURCE must be greater than (–VDET)
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DS00779A-page 3
© 2001 Microchip Technology, Inc.
Figure 4: MOSFET low drive protection.
Figure 5: Battery voltage monitor.
Figure 6: Power good monitor.
OTHER APPLICATIONS
Low operating power and small physical size make the TC54 series
ideal for many voltage detector applications, such as those shown
in Figures 4, 5 and 6. Figure 4 shows a low-voltage gate drive
protection circuit, which prevents overheating of the logic-level
MOSFET due to insufficient gate voltage. When the input signal is
below the threshold of the TC54VN, its output grounds the gate of
the MOSFET. Figures 5 and 6 show the TC54 in conventional
voltage monitoring applications.
V
IN
V
CC
V
OUT
V
SS
4.3V
270
RL
MTP3055EL
TC54VN
VIN
VOUT
VSS
Pwr
Sply Power Good
TC54Vx
VIN
VOUT
VSS
BATLOW
TC54Vx
DS00779A-Page 4 2001 Microchip Technology Inc
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Information contained in this publication regarding device
applications and the like is intended through suggestion only
and may be superseded by updates. It is your responsibility to
ensure that your application meets with your specifications.
No representation or warranty is given and no liability is
assumed by Microchip Technology Incorporated with respect
to the accuracy or use of such information, or infringement of
patents or other intellectual property rights arising from such
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ponents in life support systems is not authorized except with
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All other trademarks mentioned herein are property of their
respective companies.
© 2001, Microchip Technology Incorporated, Printed in the
U.S.A., All Rights Reserved.
Printed on recycled paper.
Microchip received QS-9000 quality system
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Company’s quality system processes and
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development systems is ISO 9001 certified.
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DS00779A-page 5
© 2001 Microchip Technology, Inc.
06/01/01
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