Datasheet

TLV3491, 3492, 3494
SBOS262D
8
www.ti.com
APPLICATIONS
RELAXATION OSCILLATOR
The TLV349x can be configured as a relaxation oscillator to
provide a simple and inexpensive clock output (see Figure
3.) The capacitor is charged at a rate of 0.69RC. It also
discharges at a rate of 0.69RC. Therefore, the period is
1.38RC. R
1
may be a different value than R
2
.
FIGURE 3. TLV349x Configured as a Relaxation Oscillator.
FIGURE 4. The TLV349x Configured as a Reset Circuit for
the MSP430.
POWER-ON RESET
The reset circuit shown in Figure 4 provides a time delayed
release of reset to the MSP430 microcontroller. Operation of
the circuit is based on a stabilization time constant of the
supply voltage, rather than on a predetermined voltage
value. The negative input is a reference voltage created by
a simple resistor divider. These resistor values should be
relatively high to reduce the current consumption of the
circuit. The positive input is an RC circuit that provides a
power-up delay. When power is applied, the output of the
comparator is low, holding the processor in the reset condi-
tion. Only after allowing time for the supply voltage to
stabilize does the positive input of the comparator become
higher than the negative input, resulting in a high output state
and releasing the processor for operation. The stabilization
time required for the supply voltage is adjustable by the
selection of the RC component values. Use of a lower-valued
resistor in this portion of the circuit will not increase current
consumption because no current flows through the RC circuit
after the supply has stabilized. The reset delay time needed
depends on the power-up characteristics of the system
power supply. R
1
and C
1
are selected to allow enough time
for the power supply to stabilize. D1 provides rapid reset if
power is lost. In this example, the R
1
• C
1
time constant is
10ms.
V+
F
= 724Hz
V+
2/3 (V+)
1/3 (V+)
R
1
1MΩ
R
2
1MΩ
R
2
1MΩ
R
2
1MΩ
V
OUT
V
C
V+
t
C
1000pF
T
1
T
2
t
TLV349x
V+
C
1
10nF
R
1
1MΩ
R
2
2MΩ
R
3
2MΩ
RESET
MSP430