6.2.2 Square-Wave Oscillator

Square-wave oscillator can be used as low cost timing reference or system supervisory clock source. A push-

pull output (TLV1812-EP) is recommended for best symmetry.

C1

100 pF

+

±

R1

100 kŸ

VCC

R2

100 kŸ

OUT

VA

VC

t1

t2

0

V

+

R3

100 kŸ

R4

100 kŸ

Figure 6-9. Square-Wave Oscillator

6.2.2.1 Design Requirements

The square-wave period is determined by the RC time constant of the capacitor C1 and resistor R4. The

maximum frequency is limited by propagation delay of the device and the capacitance load at the output. The

low input bias current allows a lower capacitor value and larger resistor value combination for a given oscillator

frequency, which may help to reduce BOM cost and board space. TI recommends that R4 be over several

kilo-ohms to minimize loading of the output.

6.2.2.2 Detailed Design Procedure

The oscillation frequency is determined by the resistor and capacitor values. The following calculation provides

details of the steps.

Figure 6-10. Square-Wave Oscillator Timing Thresholds

First consider the output of Figure Figure 6-9 as high, which indicates the inverted input VC is lower than the

noninverting input (VA). This causes the C1 to be charged through R4, and the voltage VC increases until it is

equal to the noninverting input. The value of VA at the point is calculated by Equation 7.

CC

2

A1

2

1

3

V

R

V

R

R I IR

u

(7)

if R1 = R2= R3, then VA1 = 2VCC/ 3

At this time the comparator output trips pulling down the output to the negative rail. The value of VAat this point is

calculated by Equation 8.

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TLV1812-EP, TLV1822-EP

SNOSDJ3 – MAY 2024

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