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15
About NS9750
USB clock

USB is clocked by a separate PLL driven by an external 48 MHz crystal, or it can be

driven directly by an external 48 MHz oscillator.

Figure 5: USB clock
Y1_PWR
**
**
Y1_OUT
**
TANK_LC
3R3V
C17
10pF
**
3
41
2
X1
48.0000MHz
C16
100pF_5%

NS9750

L4
1uH_5%
TANK_RC
X2_USB_OSC
Y1
EC2600_TTS_48M
4
2
1 3
VCC
GND
TEST OUT
R7
68R1
NOTE: ** = OPTIONAL Crystal circuit
C15
10pF
X1_IN
X1_USB_OSC
R8 1.5M
Tank Circuit
X1_USB
**
**
C9
100nF
R9
100 OHM
**
X2_USB
R6
100
TB1
BEAD_0805_601
** X1 is a 48-MHz 3rd harmonic crystal. It has
the same physical characteristics as a 16MHz crystal. The circuit may have a tendencyto oscillate at 16 MHz unless precautions aretaken. A LC-tank circuit is added to provide a“low impedance” for the 16 MHz oscillation toground.