LTC6909 Linear Dimensions Semiconductor, LTC6909 Datasheet - Page 6

• Manufacturer Part Number: LTC6909
• Description: Multiphase Silicon Oscillator
• Manufacturer: Linear Dimensions Semiconductor

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LTC6909
PIN FUNCTIONS
V
This supply should be kept free of noise and ripple. It
should be bypassed directly to GND with a 0.1μF or greater
low ESR capacitor. V
same supply voltage.
GND (Pin 2): Ground Connections. Should be tied to a
ground plane for best performance.
PH0, PH1, PH2 (Pins 3, 4, 15): Output Phasing Selec-
tion Pins. These are standard CMOS logic input pins and
they do not have an internal pull-up or pull-down. These
pins must be connected to a valid logic input 0 or 1 volt-
age. Connect the pins to GND for a logic 0 and to the V
pin for a logic 1. These pins confi gure the output phase
relationships as follows:
The PH0, PH1, PH2 pin connections not only determine
the phase relationship of the output signals but also divide
the master oscillator frequency by the value PH.
OUT1 Through OUT8 (Pins 5 Through 12): Oscillator
Outputs. These are CMOS rail-to-rail logic outputs with
a series resistance of approximately 40Ω, capable of
driving 1k and/or 50pF loads. Larger loads may cause
minor frequency inaccuracies due to supply bounce at high
frequencies. When any output pin is not in use, it is in a
fl oating, high impedance state. The outputs are also held
in a high impedance state during start-up. After the part’s
6
+
A (Pin 1): Analog Voltage Supply (2.7V ≤ V
PH2
0
0
0
0
1
1
1
1
PH1
0
0
1
1
0
0
1
1
PH0
0
1
0
1
0
1
0
1
+
A and V
MODE
All Outputs Are Floating (Hi-Z)
All Outputs Are Held Low
3-Phase Mode (PH = 3)
4-Phase Mode (PH = 4)
5-Phase Mode (PH = 5)
6-Phase Mode (PH = 6)
7-Phase Mode (PH = 7)
8-Phase Mode (PH = 8)
+
D must be connected to the
+
A ≤ 5.5V).
+
D
internal frequency setting loop has settled, the outputs
are active, clean and operating at the set frequency (fi rst
cycle accurate).
V
This pin should be bypassed directly to GND with a 0.1μF
or greater low ESR capacitor. V
nected to the same supply voltage.
MOD (Pin 14): Spread Spectrum Frequency Modulation
Setting Input. This input selects among four modulation
rate settings. The MOD pin should be tied to ground for
an f
an f
to V
active outputs to the MOD pin turns the modulation off.
To detect a fl oating MOD pin, the LTC6909 attempts to
pull the pin to the midsupply point. This is realized with
two internal current sources, one tied to V
and the other one tied to GND and MOD. Therefore, driv-
ing the MOD pin high requires sourcing approximately
2μA. Likewise, driving the MOD pin low requires sinking
approximately 2μA. When the MOD pin is fl oated for the
f
1nF or larger, capacitor to GND. Any AC signal coupling
to the MOD pin could potentially be detected and stop the
frequency modulation.
SET (Pin 16): Frequency Setting Resistor Input. The value
of the resistor connected between this pin and V
mines the frequency of the master oscillator. The output
frequency, f
by PH as set by the PH0, PH1 and PH2 pin connections.
The voltage on this pin is held approximately 1.1V below
V
resistor with a value between 20k and 400k, and limit the
capacitance on the pin to less than 10pF. Resistor values
outside of this range will have some loss of accuracy as
noted in the Electrical Characteristics table.
OUT
+
+
A. For best performance, use a precision metal fi lm
D (Pin 13): Digital Voltage Supply (2.7V ≤ V
OUT
OUT
+
/32 modulation rate, it must be bypassed using a
D for the f
/16 modulation rate. Floating the MOD pin selects
/32 modulation rate. The MOD pin should be tied
OUT
, is the master oscillator frequency divided
OUT
/64 modulation rate. Tying one of the
+
D and V
+
A must be con-
+
D and MOD
+
D ≤ 5.5V).
+
A deter-
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