TC1027 Datasheet, PDF(6/18 Page) TelCom Semiconductor, Inc – LINEAR BUILDING BLOCK - QUAD LOW POWER COMPARATOR AND VOLTAGE REFERENCE

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TC1027 Datasheet, PDF (6/18 Pages) TelCom Semiconductor, Inc – LINEAR BUILDING BLOCK - QUAD LOW POWER COMPARATOR AND VOLTAGE REFERENCE

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TC1027

Capacitor C1 will charge up through R4. When the

voltage at the comparatorâs inverting input is equal to

VH, the comparator output will switch. With the output

at ground potential, the value at the non-inverting input

terminal (VL) is reduced by the hysteresis network to a

value given by:

EQUATION 4-7:

-V----D---D--

Using the same resistors as before, capacitor C1 must

now discharge through R4 toward ground. The output

will return to a high state when the voltage across the

capacitor has discharged to a value equal to VL. The

period of oscillation will be twice the time it takes for the

RC circuit to charge up to one half its final value. The

period can be calculated from:

EQUATION 4-8:

--------1--------- = 2(0.694 )(R4)(C1)

FREQ

The frequency stability of this circuit should only be a

function of the external component tolerances.

Figure 4-6 shows the circuit for a pulse width modulator

circuit. It is essentially the same as in Figure 4-4, but

with the addition of an input control voltage. When the

input control voltage is equal to one-half VDD, operation

is basically the same as described for the free-running

oscillator. If the input control voltage is moved above or

below one-half VDD, the duty cycle of the output square

wave will be altered. This is because the addition of the

control voltage at the input has now altered the trip

points. The equations for these trip points are shown in

Figure 4-6 (see VH and VL).

Pulse width sensitivity to the input voltage variations

can be increased by reducing the value of R6 from

10kâ¦ and conversely, sensitivity will be reduced by

increasing the value of R6. The values of R1 and C1

can be varied to produce the desired center frequency.

FIGURE 4-1:

TC1027

VSRC

COMPARATOR

EXTERNAL HYSTERESIS

CONFIGURATION

VDD

1/4

VOUT

FIGURE 4-2:

PRECISION BATTERY MONITOR

To System DC/DC

Converter

VDD

+ TC1034

AMP1

R2, 330k, 1%

R4, 470k, 1%

R5, 7.5M

VDD

CMPTR1

1/4

BATTLOW

Alkaline

TC1027

R1, 270k, 1%

VDD

1/4

CMPTR2

BATTFAIL

R6, 7.5M

R3, 470k, 1%

DS21284B-page 6

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