CDP68HC68A2 View Datasheet(PDF) - Intersil

Part Name

Description

Manufacturer

CDP68HC68A2

CMOS Serial 10-Bit A/D Converter

Intersil 

CDP68HC68A2

The Internal Schmitt Oscillator

Figure 6 shows a simplified model of the Schmitt oscillator

used to help familiarize the user with its operation. Table 2

shows typical internal oscillator frequency versus

capacitance at 5V and 25oC.

TABLE 2. TYPICAL OSCILLATOR FREQUENCY vs

CAPACITANCE AT VDD = 5V, TA = 25oC

C(pF)

f(MHz)

C(pF)

f(MHz)

18

1.0 - 3.0

218

0.148 - 0.40

38

0.65 - 2.0

318

0.111 - 0.25

48

0.54 - 1.6

409

0.107 - 0.23

68

0.38 - 1.1

528

0.072 - 0.17

118

0.26 - 0.75

1018

0.040 - 0.10

When measuring the oscillator, probe capacitance will affect

frequency. An alternative to direct frequency measurement

of the oscillator input is to measure the interval between

successive interrupts in modes 1 and 2.

VDD

D1

OSCILLATOR

INPUT

OSC

D2

EXTERNAL

CAP

330pF

PMOS

Q3

I1

200µA

CONTROL

N1

I2

200µA

HYSTERESIS

COMPARATOR

NMOS

Q4

N2

CONTROL

VSS

FIGURE 6. EQUIVALENT CIRCUIT FOR OSCILLATOR INPUT

13

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