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RELAXATION OSCILLATOR

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

POWER-ON RESET

TLV3492

V+

C

1

10nF

R

1

1MΩ

R

2

2MΩ

R

3

2MΩ

RESET

MSP430

TLV3491A-EP, TLV3492A-EP, TLV3494A-EP

SGDS035 – DECEMBER 2007

The TLV3492 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 0.69 RC. It also discharges at a rate of 0.69 RC. Therefore, the

Figure 3. TLV3492 Configured as a Relaxation Oscillator

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 condition. 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

to allow enough time for the power supply to stabilize. D1 provides rapid reset if power is lost. In this example,

Figure 4. The TLV349x Configured as a Reset Circuit for the MSP430.

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