CY28800
Document #: 38-07723 Rev *B
Page 7 of 16
SRC_STP Clarification
The SRC_STP signal is an asynchronous input used for clean
stopping and starting the DIFT/C outputs. This input can be
Active High or Active Low based on the strapped value of the
OE_INV input. The SRC_STP signal is a debounced signal in
that its state must remain unchanged during two consecutive
rising edges of DIFC to be recognized as a valid assertion or
deassertion. (The assertion and deassertion of this signal is
absolutely asynchronous.) In the case where the output is
disabled via OE control, the output will always be tri-stated
regardless of the SRC_STP Drive Mode register bit state.
Notes:
1. Disabling of the SRCT_IN input clock prior to assertion of PWRDWN is an undefined mode and not recommended. Operation in this mode may result in glitches
excessive frequency shifting.
2. The total power-up latency from power on to all outputs active is less than 1 ms (assuming a valid clock is present on SRC_IN input).
3. LOCK output is a latched signal that is reset with the assertion of PWRDWN or when VDD<1.8V.
4. Special care must be taken to ensure that no abnormal clock behavior occurs after the assertion PLL LOCK (i.e., overshoot/undershoot is allowed).
5. In PLL mode, if power is valid and PWRDWN is deasserted but no input clocks are present on the SRC_IN input, DIF clocks will remain disabled. Only after valid
input clocks are detected, valid power, PWRDWN deasserted with the PLL locked and stable, are the DIF outputs enabled.
6. In the case where OE is asserted low, the output will always be three-stated regardless of SRC_STP drive mode register bit state.
DIFC
DIFT
Tstable
<1 ms
PWRDWN
Tdrive_Pwrdwn#
<300
µs, >200 mV
Figure 4. PWRDWN Deassertion Diagram, OE_INV = 1
Table 4. Buffer Power-up State Machine
State
Description
0
3.3V Buffer power off
1
After 3.3V supply is detected to rise above 1.8V–2.0V, the buffer enters state 1 and initiates a 0.2-ms–0.3-ms delay
2[5]
Buffer waits for PWRDWN deassertion (and a valid clock on the SRC_IN input if in PLL mode)
3[2, 3, 4]
Outputs enabled for normal operation (PLL lock to the SRC_IN input is assured in PLL mode)
Figure 5. Buffer Power-up State Diagram[1]
Table 5. SRC_STP Functionality[6]
OE_INV
SRC_STP
DIFT
DIFC
0
1
Normal
Normal
0
0
Iref * 6 or Float
Low
1
1
Iref * 6 or Float
Low
1
0
Normal
Normal
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