AN4071 datasheet(23/27 Pages) STMICROELECTRONICS

部件名	AN4071

功能描述	Introduction to comparators, their parameters and basic

PDF	27 Pages

Scroll/Zoom	100%

制造商	STMICROELECTRONICS [STMicroelectronics]

网页	http://www.st.com

标志

23 / 27 page

AN4071

Relaxation oscillator

Doc ID 022939 Rev 1

23/27

While C1 is discharging: VC1(t) = VHIGH • e

-t/

= 2/3

• VCC • e -t/τ

Capacitor C1 is discharged at voltage VLOW after time t2:

Equation 11

VLOW = 2/3 • VCC • e

-t2/

1/3

• VCC = 2/3 • VCC • e-t2/τ

1 = 2

• e-t2/τ

-t2/τ = ln (1/2)

t2 = τ • ln (2)

Because t1 = t2, the output square signal has 50% duty cycle. The output signal period T is

the sum of the time t1 and the time t2:

T = t1 + t2= τ • ln (4), where τ = R1 • C1

In the configuration described in Figure 11, the output frequency is around 72 kHz.

Output frequency doesn't depend on the power supply voltage. As the TS3021 circuit can

work with a wide power supply voltage range from 1.8 V to 5 V, the output signal amplitude

has the same value as the power supply due to its rail-to-rail output stage. Frequency can be

adjusted simply by changing the value of R1 or C1. In case a different duty cycle is required,

R2, R3 and R4 should not be kept equal.

AN4071 数据表(PDF) 23 Page - STMicroelectronics