ST72F521M datasheet(167/199 Pages) STMICROELECTRONICS

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ST72521M/R/AR

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CLOCK CHARACTERISTICS (Cont’d)

12.5.4 RC Oscillators

The ST7 internal clock can be supplied with an RC

oscillator. This oscillator can be used with internal

or external components (selectable by option

byte).

Figure 85. Typical Application with RC oscillator

Notes:

1. Data based on design simulation.

2. REX must have a positive temperature coefficient (ppm/°C), carbon resistors should therefore not be used.

3. iCEX is the current needed to load the CEX capacitor while OSC1 is forced to VSS or 1.5V (RC oscillation voltage range).

Figure 86. Typical fOSC(RCINT) vs VDD

Figure 87. Typical fOSC(RCINT) vs TA

Symbol

Parameter

Conditions

Min

Typ

Max

Unit

fOSC (RCINT)

Internal RC oscillator frequency

See Figure 86 and Figure 87

TA=25°C, VDD=5V

3.5

5.6

MHz

fOSC(RCEXT)

External RC oscillator frequency 1)

5 / (REX.CEX)

REX

Oscillator external resistor 2)

100

Ω

CEX

Oscillator external capacitor

470

|iCEX|

Capacitor load current 3)

OSC1 = VSS or 1.5V

290

350

µA

OSC2

OSC1

fOSC

CEX

REX

EXTERNAL RC

INTERNAL RC

VREF

VDD

Current copy

Voltage generator

CEX discharge

ST72XXX

RIN

CIN

iCEX

0.5

1.5

2.5

3.5

4.5

2.35

5.5

VDD(V)

TA=-45C

TA=25C

TA=130C

3.1

3.2

3.3

3.4

3.5

3.6

3.7

3.8

3.9

-45

130

TA(°C)

Vdd = 2.4V

Vdd = 5V

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