Datasheet
2016-2017 Microchip Technology Inc. DS00002117F-page 66
KSZ9031RNX
10.0 REFERENCE CLOCK - CONNECTION AND SELECTION
A crystal or external clock source, such as an oscillator, is used to provide the reference clock for the KSZ9031RNX.
The reference clock is 25 MHz for all operating modes of the KSZ9031RNX.
The KSZ9031RNX uses the AVDDH supply, analog 3.3V (or analog 2.5V option for commercial temperature only), for
the crystal/clock pins (XI, XO). If the 25 MHz reference clock is provided externally, the XI input pin should have a min-
imum clock voltage peak-to-peak (V
PP
) swing of 2.5V reference to ground. If V
PP
is less than 2.5V, series capacitive
coupling is recommended. With capacitive coupling, the V
PP
swing can be down to 1.5V. Maximum V
PP
swing is 3.3V
+5%.
Figure 10-1 and Table 10-1 show the reference clock connection to XI and XO of the KSZ9031RNX, and the reference
clock selection criteria.
FIGURE 10-1: 25 MHZ CRYSTAL/OSCILLATOR REFERENCE CLOCK CONNECTION
11.0 ON-CHIP LDO CONTROLLER - MOSFET SELECTION
If the optional LDO controller is used to generate 1.2V for the core voltage, the selected MOSFET should exceed the
following minimum requirements:
• P-channel
• 500 mA (continuous current)
• 3.3V or 2.5V (source – input voltage)
• 1.2V (drain – output voltage)
•V
GS
in the range of:
- (–1.2V to –1.5V) @ 500 mA for 3.3V source voltage
- (–1.0V to –1.1V) @ 500 mA for 2.5V source voltage
The V
GS
for the MOSFET needs to be operating in the constant current saturated region, and not towards the V
GS(th)
,
the threshold voltage for the cut-off region of the MOSFET.
See Table 6-11 for LDO controller output driving range to the gate input of the MOSFET.
Refer to application note ANLAN206 – KSZ9031 Gigabit PHY Optimized Power Scheme for High Efficiency, Low-Power
Consumption and Dissipation as a design reference.
TABLE 10-1: 25 MHZ CRYSTAL/REFERENCE CLOCK SELECTION CRITERIA
Characteristics Value
Frequency 25 MHz
Frequency Tolerance (max.) ±50 ppm
Crystal Series Resistance (typ.) 40
Total Period Jitter (peak-to-peak) <100 ps
22pF
22pF
NC
XI
XO
XI
XO
25 MHz XTAL
±50PPM
25 MHz OSC
±50PPM