PRELIMINARY INFORMATION
LINEAR BUILDING BLOCK –
VOLTAGE REFERENCE, DUAL OP AMP,
DUAL COMPARATOR WITH SHUTDOWN MODE
TC43
tor C1 charges through R1 until a voltage equal to
VDD/2 is reached, at which point the WAKE is driven active.
Voltage Reference
A 4% tolerance, internally biased, 1.20V bandgap volt-
age reference is included in the TC43. It has a push-pull
output capable of sourcing 5mA or sinking 200µA. The
voltage reference remains fully enabled during shutdown.
Upon wake-up, the microcontroller resets the timer by
forcing a logic low on a dedicated, open drain I/O port pin.
This discharges C1 through R4 (the value of R4 is chosen to
limit maximum current sunk by the I/O port pin). With a 3V
supply, the circuit as shown consumes typically 8µA and
furnishes a nominal timer duration of 25 seconds.
Shutdown Input
SHDN at VIL disables both op amps and one compara-
tor. The SHDN input cannot be allowed to float; when not
Precision Battery Monitor
Figure 2 is a precision battery low/battery dead monitor-
ing circuit. Typically, the battery low output warns the user
that a battery dead condition is eminent. Battery dead
typically initiates a forced shutdown to prevent operation at
low internal supply voltages (which can cause unstable
system operation).
The circuit of Figure 2 uses a single TC43 (one Op Amp
unused) and only 7 external resistors. AMP 1 is a simple
buffer while CMPTR1 and CMPTR2 provide precision volt-
age detection using Vr as a reference. Resistors R2 and R4
set the detection threshold for BATT LOW while resistors
R1 and R7 set the detection threshold for BATT FAIL. The
component values shown assert BATT LOW at 2.2V (typi-
cal) and BATT FAIL at 2.0V (typical). Total current con-
sumed by this circuit is typically 22µA at 3V.
used, connect to VDD
.
TYPICAL APPLICATIONS
The TC43 lends itself to a wide variety of applications,
particularly in battery-powered systems. It typically finds
application in power management, processor supervisory,
and interface circuitry.
Wake-up Timer
Many microcontrollers have a low power “sleep” mode
that significantly reduces their supply current. Typically, the
microcontrollerisplacedinthismodeviaasoftwareinstruc-
tion, and returns to a fully enabled state upon reception of
an external signal (“wake-up”). The wake-up signal is usu-
allysuppliedbyahardwaretimer. Mostsystemapplications
demand that this timer have a long duration (typically
seconds or minutes), and consume as little supply current
as possible.
DUAL LDO with Shutdown
Figure 3 shows a portion of a TC43 configured as a dual
low drop regulator with shutdown. AMP1 and AMP2 are
independent error amplifiers that use Vr as a reference.
Resistors RA and RB set the feedback around the amplifier
and therefore determine the output voltage setting (please
seeequationinthefigure). RAandRBcanhavelargeohmic
values (i.e. 100’s of KΩ) to minimize supply current.
Using the 2N2222 output transistors as shown, these
regulators exhibit low dropout operation. For example, with
VOUT = 3.0V, the typical drop out voltage is only 50mV at an
output current of 50mA. The unused comparators can be
used in conjunction with this circuit as power-on reset or low
voltage detectors for a complete LDO solution at a very low
installed cost.
The circuit shown in Figure 1 is a wake-up timer made
from comparator CMPTR2. (CMPTR2 is used because the
wake-uptimermustoperatewhenSHDNisactive.)Capaci-
MICROCONTROLLER
R4
I/O*
VDD
R1
5M
CMPTR2
–
C1
WAKE-UP
+
EVALUATION KIT
10µF
TheTC43EVconsistsofafourinchbysixinchpre-wired
application circuit board. Pre-configured circuits include a
pulse width modulator, wake-up timer, function generator,
andothers. On-boardcurrentmeterterminals, voltageregu-
lator and a user-prototyping area speed circuit develop-
ment. Please contact your local TelCom Semiconductor
representative for more information.
R2, 1M
R3, 1M
*OPEN DRAIN PORT PIN
Figure 1. Wake-Up Timer
4
TELCOM [ TELCOM SEMICONDUCTOR, INC ]
