Datasheet

1.0 Signal/Pin Connection and Description (Continued)
7
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USBN9603/USBN9604
1.2 DETAILED SIGNAL/PIN DESCRIPTIONS
1.2.1 Power Supply
1.2.2 Oscillator, Clock and Reset
Oscillator Circuit
The XIN and XOUT pins may be connected to make a 24 MHz closed-loop, crystal-controlled oscillator. Alternately, an ex-
ternal 24 MHz clock source may be used as the input clock for the device. The internal crystal oscillator uses a 24 MHz
fundamental crystal. See Table 1 for typical component values and Figure 1 for the crystal circuit. For a specific crystal,
please consult the manufacturer for recommended component values.
If an external clock source is used, it is connected to XIN. XOUT should remain unconnected. Stray capacitance and induc-
tance should be kept as low as possible in the oscillator circuit. Trace lengths should be minimized by positioning the crystal
and external components as close as possible to the XIN and XOUT pins.
Table 1. Approximate Component Values
I/O Name Description
NA Vcc Digital Power Supply (V
CC
). Power-on reset is detected when the input voltage is at the same
level as GND and then raised to the required V
cc
level. The power-on reset causes all registers
to be set to their reset values, the clock generator to be reset and stalls the CLKOUT output for
2
14
XIN clock cycles. During this time, no internal register is accessible.
NA GND Digital Power Supply (GND)
NA AGND Analog Power Supply (AGND)
NA V3.3 Transceiver 3.3V Voltage Supply. This pin can be used as the internal 3.3V voltage regulator
output. The regulator is intended to power only the internal transceiver and one external pull-up.
An external 1 µF de-coupling capacitor is required on this pin. The voltage regulator output is dis-
abled upon reset. When the internal voltage regulator is left disabled, this pin must be used as a
3.3V supply input for the internal transceiver. This is the case during 3.3V operation.
I/O Name Description
NA XIN Crystal Oscillator Input. Input for internal 24 MHz crystal oscillator circuit. A 24 MHz funda-
mental crystal may be used.
NA XOUT Crystal Oscillator Output
O CLKOUT Clock Output. This programmable clock output may be disabled and configured for different
speeds via the Clock Configuration register. After a power-on reset and hardware reset (as-
sertion of
RESET), a 4 MHz clock signal is output (there may be an initial phase discontinuity).
In the USBN9604, a hardware reset causes CLKOUT to stall for 2
14
XIN clock cycles while the
internal DLL is synchronized to the external reference clock.
I RESET Reset. Active low, assertion of RESET indicates a hardware reset, which causes all registers
in the device to revert to their reset values.
In the USBN9604, the hardware reset action is identical to a power-on reset. Signal condition-
ing is provided on this input to allow use of a simple, RC power-on reset circuit.
Component Parameters Values Tolerance
Crystal Resonator Resonance Frequency 24 MHz 2500 ppm
(max)
Type AT-Cut
Maximum Serial Resistance 50 Ω
Maximum Shunt Capacitance 10 pF
Load Capacitance 20 pF
Resistor R1
1MΩ±5%
Obsolete