LTC6909HMS#TRPBF Linear Technology, LTC6909HMS#TRPBF Datasheet - Page 8

• Manufacturer Part Number: LTC6909HMS#TRPBF
• Description: IC OSCILLATOR SIL 5.5V 16-MSOP
• Manufacturer: Linear Technology
• Type: Oscillator, Siliconr

Specifications of LTC6909HMS#TRPBF

• Frequency: 6.67MHz
• Voltage - Supply: 2.7 V ~ 5.5 V
• Current - Supply: 2.4mA
• Operating Temperature: -40°C ~ 125°C
• Package / Case: 16-MSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Count: -

operAtion
LTC6909
As shown in the Block Diagram, the LTC6909’s master
oscillator is controlled by the ratio of the voltage between
the V
(I
tion (SSFM) is disabled, I
the (V
is enabled, I
dom noise (PRN) signal. Here the I
random value uniformly distributed between (I
and (I
to produce an approximately flat frequency spectrum,
centered about the set frequency with a bandwidth equal
to approximately 20% of the center frequency.
The voltage on the SET pin is forced to approximately 1.1V
below V
age. This voltage is accurate to ±5% at a particular input
current and supply voltage (see Figure 1). The LTC6909
is optimized for use with resistors between 20k and 400k
corresponding to master oscillator frequencies between
500kHz and 10MHz. Accurate master oscillator frequen-
cies up to 20MHz (R
voltage is greater than 4V. The R
between the V
V
to attain excellent frequency accuracy regardless of the
precision of the SET pin. The master oscillation frequency is:
8
SET
MASTER
f
MASTER
) voltage and the current I
+
+
SET
A and SET pins and the current entering the SET pin
A – V
+
). When the spread spectrum frequency modula-
A by the PMOS transistor and its gate bias volt-
+ 10%). In this way, the frequency is modulated
= 20MHz • 10k/R
SET
Figure 1. V
MASTER
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.1
+
) voltage and the R
A and SET pins, locks together the (V
T
A
= 25°C
is modulated by a filtered pseudoran-
SET
+
1
– V
= 10k) are attainable if the supply
MASTER
SET
I
RES
V
SET
+
Variation with I
10
= 3V
(µA)
SET
V
+
SET
is strictly determined by
= 5V
SET
. This allows the parts
resistor. When SSFM
100
MASTER
resistor, connected
6909 F01
RES
1000
current is a
SET
– 10%)
+
A –
When the spread spectrum frequency modulation (SSFM)
is disabled, the master oscillator frequency is stationary.
When SSFM is enabled, the master oscillator frequency
varies from 0.9 • f
Output Frequency and Configurations
The output frequency of the LTC6909 is set by the R
resistor value and the connections of the PH0, PH1 and
PH2 logic input pins. The following formula defines the
relationship:
where PH = 3, 4, 5, 6, 7 or 8 and is defined as follows:
The PH0, PH1 and PH2 pins are standard logic input pins.
These pins do not have any active pull-up or pull-down
circuitry. As such, they cannot be left floating and must be
connected to a valid logic high or low voltage. The PH0,
PH1 and PH2 pin connections not only divide the master
oscillator frequency by the value PH but also determine
the phase relationship between the output signals. Figure
2 shows the output waveforms for each of the eight pos-
sible output configurations.
Note that 2-phase, complementary (180° phase shifted)
outputs are available in the 4-, 6- and 8-phase modes
by choosing the correct pair of signals. For example, in
4-phase mode, OUT1 and OUT3 (or OUT2 and OUT4) are
complementary.
PH2
f
OUT
0
0
0
0
1
1
1
1
= 20MHz • 10k/(R
PH1
0
0
1
1
0
0
1
1
MASTER
PH0
1
0
1
0
1
0
1
0
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)
SET
to 1.1 • f
• PH)
MASTER
.
6909fa
SET