ST7GEME4 datasheet(18/28 Pages) STMICROELECTRONICS

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Electrical characteristics

ST7GEME4

18/28

4.4.2

Crystal resonator oscillators

The ST7 internal clock is supplied with one Crystal resonator oscillator. All the information

given in this paragraph are based on characterization results with specified typical external

components. In the application, the resonator and the load capacitors have to be placed as

close as possible to the oscillator pins in order to minimize output distortion and start-up

stabilization time. Refer to the crystal resonator manufacturer for more details (frequency,

package, accuracy...).

Table 14.

Crystal resonator oscillator characteristics

Symbol

Parameter

Conditions

Min

Typ

Max

Unit

fOSC

Oscillator Frequency(1)

MP: Medium power oscillator

MHz

Feedback resistor

150

Ω

CL1

CL2

Recommended load

capacitances versus equivalent

serial resistance of the crystal

resonator (RS)

See Table 16

(MP oscillator)

OSCOUT driving current

VDD=5V, VIN=VSS (MP oscillator)

1.5

3.5

The oscillator selection can be optimized in terms of supply current using an high quality resonator with small RS value.

Refer to crystal resonator manufacturer for more details.

Table 15.

Typical crystal resonator characteristics

Oscillator

Reference

Freq.

Characteristic(1)

CL1

[pF]

CL2

[pF]

tSU(osc)

[ms](2)

JAUCH

SS3-400-30-

30/30

4MHz

∆f

OSC=[±30ppm25°C,±30ppm

∆Ta],

Typ. RS=60Ω

7~10

Resonator characteristics given by the crystal resonator manufacturer.

tSU(OSC) is the typical oscillator start-up time measured between VDD=2.8 V and the fetch of the first instruction (with a quick

VDD ramp-up from 0 to 5 V (<50 µs).

Table 16.

Recommended values for 4 MHz crystal resonator

Symbol

Min

Typ

Max

Unit

RSMAX

(1)

Ω

COSCIN

COSCOUT

RSMAX is the equivalent serial resistor of the crystal (see crystal specification).

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