Rainbow Electronics MAX3622 - Manual (Page 5)

MAX3622
Pin Description
PIN NAME FUNCTION
1 QAC_OE
LVCMOS/LVTTL Input. Enables/disables QA_C clock output. Connect pin high to enable QA_C.
Connect low to set QA_C to a high-impedance state. Has internal 50k
input impedance.
2 GNDO_A Ground for QA_C Output. Connect to supply ground.
3 QA_C LVCMOS Clock Output
4 V
DDO_A
Power Supply for QA_C Clock Output. Connect to +3.3V.
5, 6 RES1, RES2 Reserved. Do not connect.
7 V CCA
Analog Power Supply for the VCO. Connect to +3.3V. For additional power-supply noise filtering,
this pin can connect to V
CC through 10.5 as shown in Figure 2 (requires V CC = +3.3V ±5%).
8 V CC Core Power Supply. Connect to +3.3V.
9, 15 GND Supply Ground
10 X_OUT Crystal Oscillator Output
11 X_IN Crystal Oscillator Input
12 V CCO_B Power Supply for QB Clock Output. Connect to +3.3V.
13 QB LVPECL, Inverting Clock Output
14 QB LVPECL, Noninverting Clock Output
16 QB_OE
LVCMOS/LVTTL Input. Enables/disables QB clock output. Connect pin high to enable LVPECL clock
output QB. Connect low to set QB to a logic 0. Has internal 50k
input impedance.
Low-Jitter, Precision Clock Generator
with Two Outputs
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Detailed Description
The MAX3622 is a low-jitter clock generator designed
to operate at Ethernet frequencies. It consists of an on-
chip crystal oscillator, PLL, LVCMOS output buffer, and
an LVPECL output buffer. Using a 25MHz crystal as a
reference, the internal PLL generates a high-frequency
output clock with excellent jitter performance.
Crystal Oscillator
An integrated oscillator provides the low-frequency ref-
erence clock for the PLL. This oscillator requires a
25MHz crystal connected between X_IN and X_OUT.
PLL
The PLL takes the signal from the crystal oscillator and
synthesizes a low-jitter, high-frequency clock. The PLL
contains a phase-frequency detector (PFD), a lowpass
filter, and a voltage-controlled oscillator (VCO). The
VCO output is connected to the PFD input through a
feedback divider. The PFD compares the reference fre-
quency to the divided-down VCO output (f
VCO /25) and
generates a control signal that keeps the VCO locked
to the reference clock. The high-frequency VCO output
clock is sent to the output dividers. To minimize noise-
induced jitter, the VCO supply (V
CCA ) is isolated from
the core logic and output buffer supplies.
Output Dividers
The output dividers are set to divide-by-five for the
LVCMOS output QA_C and divide-by-four for the
LVPECL output QB.
LVPECL Driver
The differential PECL buffer (QB) is designed to drive
transmission lines terminated with 50
Ω to V
CC - 2.0V.
The output goes to a logic 0 when disabled.
LVCMOS Driver
QA_C, the LVCMOS output, is designed to drive a sin-
gle-ended high-impedance load. This output goes to a
high-impedance state when disabled.
Reset Logic/POR
During power-on, the power-on reset (POR) signal is
generated to synchronize all dividers.