AN2
Using the Microchip TC54 Voltage Detector
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 V
IN
for an under-voltage condition.
When such a condition occurs, the output is forced to the active
(LOW) state and remains there until V
IN
is once again within
tolerance. As shown in the timing diagram of Figure 1, the output
is forced active when V
IN
< (–V
DET
) (Where (–V
DET
) is the threshold
voltage) and returns HIGH when V
IN
exceeds (–V
DET
) plus 5%
hysteresis (example: if (–V
DET
) = 2.0V, the output will go HIGH
when V
IN
> 2.1V).
TC54VC only
2
V
IN
Input Voltage
Hysteresis
Voltage
Release
Voltage
(+V
DET
)
Detect Voltage (–V
DET
)
Minimum Operating Voltage
Ground Level
–
+
V
OUT
1
Output Voltage
V
REF
V
SS
3
Ground Level
FIGURE 1:
TC54 block diagram and timing.
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).
V
IN
V
IN
V
OUT
R
100
V
SS
MCLR
PIC
Microcontroller
TC54VC
FIGURE 2:
Microcontroller reset circuit using TC54.
© 2001 Microchip Technology, Inc.
DS00779A-page 1
AN2
MFGR
Motorola
Motorola
Motorola
Motorola
Motorola
Motorola
T.I.
T.I.
MICROCHIP
PART#
MC33064P-5
MC34064P-5
MC34164P-3
MC34164P-5
MC33164P-3
MC33164P-5
TL7757ILP
TL7757CLP
MICROCHIP #
TC54VN4502EZB
TC54VN4502EZB
TC54VN2702EZB
TC54VN4302EZB
TC54VN2702EZB
TC54VN4302EZB
TC54VN4502EZB
TC54VN4502EZB
DESCRIPTION
4.5V trip, –40 to +85C, TO-92
4.5V trip, 0 to +70C, TO-92
2.7V trip, 0 to +70C, TO-92
4.3V trip, 0 to +70C, TO-92
2.7V trip, –40 to +85C, TO-92
4.3V trip, –40 to +85C, TO-92
4.5V trip, –40 to +85C, TO-92
4.5V trip, 0 to +70C, TO-92
ATTRIBUTE
500 times less power
500 times less power
10 times less power
10 times less power
10 times less power
10 times less power
2000 times less power
2000 times less power
Table 1:
TC54 cross reference listing.
MODIFYING THE TRIP POINT, –V
DET
Although the TC54 has a pre-programmed –V
DET
, 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 –V
DET
lower than that of V
SOURCE
(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 –V
DET
= 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.
V
SOURCE
V
SOURCE
(
R1
R1 + R2
)
= (–V
DET
)
R2
V
IN
TC54
V
OUT
Where:
V
SOURCE
= Voltage to be monitored
(–V
DET
) = Threshold Voltage Setting of TC54
Note:
In this example, V
SOURCE
must be greater than (–V
DET
)
R1
V
SS
Figure 3:
Modify trip point of TC54 using external resistor divider.
DS00779A-page 2
© 2001 Microchip Technology, Inc.
AN2
4.3V
270
V
IN
TC54VN
V
OUT
V
CC
V
IN
RL
Pwr
Sply
MTP3055EL
V
SS
V
SS
TC54Vx
V
OUT
Power Good
Figure 4:
MOSFET low drive protection.
Figure 6:
Power good monitor.
OTHER APPLICATIONS
V
IN
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.
TC54Vx
V
OUT
V
SS
BATLOW
Figure 5:
Battery voltage monitor.
© 2001 Microchip Technology, Inc.
DS00779A-page 3
AN2
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
use or otherwise. Use of Microchip’s products as critical com-
ponents in life support systems is not authorized except with
express written approval by Microchip. No licenses are con-
veyed, implicitly or otherwise, under any intellectual property
rights.
Trademarks
The Microchip name and logo, the Microchip logo, PIC, PICmicro,
PICMASTER, PICSTART, PRO MATE, K
EE
L
OQ
, SEEVAL,
MPLAB and The Embedded Control Solutions Company are reg-
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U.S.A. and other countries.
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Lab, MXDEV, microID,
FlexROM, fuzzyLAB,
MPASM,
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Migratable Memory, FanSense, ECONOMONITOR, Select
Mode and microPort are trademarks of Microchip Technology
Incorporated in the U.S.A.
Serialized Quick Term Programming (SQTP) is a service mark
of Microchip Technology Incorporated in the U.S.A.
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
certification for its worldwide headquarters,
design and wafer fabrication facilities in
Chandler and Tempe, Arizona in July 1999. The
Company’s quality system processes and
procedures are QS-9000 compliant for its
PICmicro
®
8-bit MCUs, K
EE
L
OQ
®
code hopping
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development systems is ISO 9001 certified.
DS00779A-Page
4
2001 Microchip Technology Inc
AN2
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