SL811HS

Document 38-08008 Rev. *F

Page 4 of 32

PLL Clock Generator

Either a 12 MHz or a 48 MHz external crystal is used with the

SL811HS[1]. Two pins, X1 and X2, are provided to connect a low

cost crystal circuit to the device as shown in Figure 2 and

Figure 2. Use an external clock source if available in the appli-

cation instead of the crystal circuit by connecting the source

directly to the X1 input pin. When a clock is used, the X2 pin is

not connected.

When the CM pin is tied to a logic 0, the internal PLL is bypassed

so the clock source must meet the timing requirements specified

by the USB specification.

Figure 2. Full Speed 48 MHz Crystal Circuit

Figure 3. Optional 12 MHz Crystal Circuit

Typical Crystal Requirements

The following are examples of ‘typical requirements.’ Note that

these specifications are generally found as standard crystal

values and are less expensive than custom values. If crystals are

used in series circuits, load capacitance is not applicable. Load

capacitance of parallel circuits is a requirement. 48 MHz third

overtone crystals require the Cin/Lin filter to guarantee 48 MHz

operation.

Note

1. CM (Clock Multiply) pin of the SL811HS must be tied to GND when 48 MHz crystal circuit or 48 MHz clock source is used.

Cbk

0.01

μF

Rs

100

X1

48 MHz, series, 20-pF load

Cout

22 pF

Rf

1M

X2

Cin

22 pF

Lin

2.2

μH

X1

12 MHz Crystals:

Frequency Tolerance:

±100 ppm or better

Operating Temperature Range:

0

°C to 70°C

Frequency:

12 MHz

Frequency Drift over Temperature:

± 50 ppm

ESR (Series Resistance):

60

Ω

Load Capacitance:

10 pF min.

Shunt Capacitance:

7 pF max.

Drive Level:

0.1–0.5 mW

Operating Mode:

fundamental

48 MHz Crystals:

Frequency Tolerance:

±100 ppm or better

Operating Temperature Range:

0

°C to 70°C

Frequency:

48 MHz

Frequency Drift over Temperature:

± 50 ppm

ESR (Series Resistance):

40

Ω

Load Capacitance:

10 pF min.

Shunt Capacitance:

7 pF max.

Drive Level:

0.1–0.5 mW

Operating Mode:

third overtone

X1

12 MHz , series, 20-pF load

Rf

1M

Cin

22 pF

Cout

22 pF

Rs

100

X2

X1

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