MDS 307-01/02 F

5

Revision 121304

ICS307-01/02

Bypass Mode

If R6:0 is programmed to 0000000, the PLL is powered down and bypassed; the reference frequency will

come from both CLK1 and CLK2. It is possible to generate glitches going into and out of this mode.

Configuring the ICS307

The ICS307 can be programmed to set the output functions and frequencies. The three data bytes are

written in DATA pin in this order:

C1 is loaded into the port first and R0 last.

R6:R0

Reference Divder Word (RDW)

V8:V0

VCO Divider Word (VDW)

S2:S0

Output Divider Select (OD)

F1:F0

Function of CLK2 Output

TTL

Duty Cycle Settings

C1:C0

Internal Load Capacitance for Crystal

The ICS307 can be reprogrammed at any time during operation. If R6:0, V8:0, TTL, or C1:0 are changed, the

frequency will transition smoothly to the new value over about 1 ms, without glitches or short cycles. If S2:0 is

changed, it is possible to generate glitches on CLK1 and also on CLK2 for F1:0 = 1 1.

Changing F1:0 will generate glitches on CLK2.

Power up default values for ICS307-02

The input frequency will come from both outputs.

A warning about using the default configuration with input frequencies lower than 13.75 MHz

The VCO will run only as low as its minimum frequency, which is guaranteed to be no more than 55 MHz.

So, in the powerup default condition, the PLL is guaranteed to lock to the input frequency down to 55/4 =

13.75 MHz. However, the part will typically run much slower. The typical minimum VCO frequency is about

30 - 40 MHz, depending on voltage, temperature, and lot variation; so in the powerup default setting, the

CLK2 output will be a minimum of 7.5 - 10 MHz even if the input frequency is lower than that. The output is

not locked to the reference input and so the frequency is not very stable and the phase noise is higher. In

this condition, the CLK2 output will accurately provide the reference frequency down to 0 Hz because this

signal path bypasses the PLL.

C1

C0

TTL

F1

F0

S2

S1

S0

V8

V7

V6

V5

V4

V3

V2

V1

V0

R6

R5

R4

R3

R2

R1

R0

MSB

LSB

MSB

LSB

MSB

LSB

001000

11

0000

0100

000

00110