The Smart Timing Choice



The Smart Timing Choice



SiT2021B

High Frequency, -55°C to +125°C One-Output Clock Generator

Rev. 1.0

Page 9 of 12

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Pin 3 Configuration Options (OE, ST, or NC)

Pin 3 of the SiT2021 can be factory-programmed to support

three modes: Output Enable (OE), standby (ST) or No

Connect (NC).

Output Enable (OE) Mode

In the OE mode, applying logic Low to the OE pin only disables

the output driver and puts it in Hi-Z mode. The core of the

device continues to operate normally. Power consumption is

reduced due to the inactivity of the output. When the OE pin is

pulled High, the output is typically enabled in <1µs.

Standby (ST) Mode

In the ST mode, a device enters into the standby mode when

Pin 3 pulled Low. All internal circuits of the device are turned

off. The current is reduced to a standby current, typically in the

range of a few µA. When ST is pulled High, the device goes

through the “resume” process, which can take up to 5 ms.

No Connect (NC) Mode

In the NC mode, the device always operates in its normal

mode and outputs the specified frequency regardless of the

logic level on pin 3.

Table 12 below summarizes the key relevant parameters in the

operation of the device in OE, ST, or NC mode.

Output on Startup and Resume

The SiT2021 comes with gated output. Its clock output is

accurate to the rated frequency stability within the first pulse

from initial device startup or resume from the standby mode.

In addition, the SiT2021 has “no runt” pulses, “no glitch” output

during startup or resume as shown in the waveform captures

in Figure 17 and Figure 18.

Figure 17. Startup Waveform vs. Vdd

Figure 18. Startup Waveform vs. Vdd

(Zoomed-in View of Figure 17)

Table 12. OE vs. ST vs. NC

OE

ST

NC

Active current 125 MHz (max, 1.8V)

6 mA

6 mA

6 mA

OE disable current (max. 1.8V)

4.5 mA

N/A

N/A

Standby current (typical 1.8V)

N/A

0.6 uA

N/A

OE enable time at 125 MHz (max)

130 ns

N/A

N/A

Resume time from standby

(max, all frequency)

N/A

5 ms

N/A

Output driver in OE disable/standby mode

High Z

weak

pull-down

N/A

Clock Output

Vdd

Clock Output

Vdd